Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Determination of pollutions in the surface of water samples

from Ogbajarajara river, Nigeria by spectrophotometer and

atomic absorption spectrometry before evaluation of health

risk assessment

Stanley Chukwuemeka Ihenetu a,*, Victor Obinna Njokua, Francis Chizoruo Ibea, Gang Lib,

Arinze Chinweubac and Christian Ebere Enyoha,d

a Department of Chemistry, Faculty of Physical Sciences, Imo State University, P.M.B 2000 Owerri, Nigeria

b CAS Key Laboratory of Urban Environmental and Health, Institute of Urban Environment, Chinese Academy of Science,

1799 Jimei Road, Xiamen 361021, China

c Chemistry Department, Chukwuemeka odimegwu Ojukwu University Uli, Anambra Nigeria

d Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 8570-338, Japan

ABSTRACT

Determination of environmental pollution in the surface water is very

important. So, in this study, determination, and health risk assessment

were evaluated. The pollutions such as anions, cations, and heavy

metals were analyzed in surface water by photometer spectrometry

and atomic absorption spectrometry (AAS). Other parameters such as

pH and TDS were determined. The results showed us, the electrical

conductivity (EC) in this study falls between 100.68 ± 1.0 - 194.74

±1.4 μs cm-1 in the dry and wet season. The pH value in this study for

the two seasons varied from 5.57±0.22 to 5.73±0.28 which shows a

little acidity. In the current study, TDS for wet and dry seasons goes

from 122.17±1.74 mg L-1 to 63.80±0.86 mg L-1. This may conceivably

be a sign of typical pollution from the runoff of soils in the study area.

The high phosphate levels in both wet and dry seasons are recorded

from 60.74±0.61 to 60.27±0.38 mg L-1 in both seasons. Iron values

observed range from 8.42±0.06 to 6.28±0.11 mg L-1 in the wet and dry

season, Cu was recorded between 0.08±0.01 - 0.07±0.01 mg L-1, Mn

recorded from 0.07±0.01 to 0.06±0.01 mg L-1, Zn recorded between

2.29±0.09 - 1.15±0.09 mg L-1, and Pb recorded from 0.69±0.09 to

0.40±0.18 mg L-1 while Cd and Ni were not detected in the study.

Water quality index (WQI) values were determined as 549 for wet and

328 for the dry season, the hazard indices for both seasons are below

one. The outcomes in this present study showed that the level of Pb in

the surface water could present a carcinogenic risk to both adults and

children. All heavy metals results were validated by electrothermal

atomic absorption spectrometry (ET-AAS).

Keywords:

Heavy metal,

Environment,

Pollution,

Surface water,

Spectrophotometer,

Atomic absorption spectrometry

ARTICLE INFO:

Received 19 Nov 2021

Revised form 21 Jan 2022

Accepted 15 Feb 2022

Available online 30 Mar 2022

*Corresponding Author: Stanley Chukwuemeka Ihenetu

Email: ihenetustanley@yahoo.com

https://doi.org/10.24200/amecj.v5.i01.162

------------------------

1. Introduction

As a universal solvent, water exists as a solid,

liquid, and gaseous state. Water is mostly used in

a liquid state. Since water is crucial for all known

types of life, ensuring our water is clean and

preserved should be the most signicant and head

for this present generation and the next generation

to come [1]. Water can be viewed as a chemical

substance that is fundamental for all known types

of life. So, the pollution in water must be analyzed

6Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

by analytical methods [2]. For the most part,

surface waters comprise streams, rivers, reservoirs,

lakes, and wetlands. Stream is applied to epitomize

other streaming surface waters, beginning from

c/reeks to the huge rivers [3]. Water pollution is

a serious biological and chemical hazard. At the

point when water is polluted, it then represents an

unsafe impact on all creatures and the wellbeing of

humans. At the point when poisonous constituents

break down in waterways of each kind like oceans,

lakes, and rivers, the water becomes polluted.

Poisons consistently defame the surface water,

which stands a genuine risk to families that use the

polluted water.

Recently. The researchers used supported liquid

extraction (SLE), the micro solid-phase extraction

(MSPE), liquid-liquid microextraction (LLME),

(liquid-liquid extraction) LLE, Liquid-phase

membrane extraction (LPME) for metal, pesticides,

carboxylic acids, and phenol in water matrixes. Also,

many metals and VOCs were determined by different

ionic liquids and adsorbents. Cloud point extraction

(CPE) has been utilized for the preconcentration

of cobalt, mercury, and nickel, after the

arrangement of a complex with 1-(2-thiazolylazo)-

2-naphthol (TAN), and later examination by

ame atomic absorption spectrometry utilizing

octylphenoxypolyethoxyethanol (Triton X-114)

as surfactant [3,4]. The inhabitants of this area

depend on the Ogbajarajara River [Og] for their

domestic and recreational purposes without

proper knowledge of the river water quality and

possible health implications. The introduction

of surface water pollution in rural areas is due to

different anthropogenic activities villagers do on

the surface water and the washing away of surface

soil directly to the surface water after manures are

applied straightforwardly on the farmland. Quick

urbanization leads to rigorous anthropogenic

activities and the consumption of resources and

energy in urban areas [4]. Individuals from these

communities in Nwangele Local Government

rely upon the surface water for their homegrown

exercises with not much pipe-borne water around the

communities which is situated in a further place for

the residents to get to. This fact, therefore, propelled

the necessity of this study to nd out the quality

of surface water from the Ogbajarajara river in the

Nwangele local government area. It is therefore

accepted that in the consumption of surface water,

certain tests should have been completed before

consumption in guidelines with the standards of

the World Health Organization (WHO) and Federal

Ministry of Environment (FMEv). [5], evaluated

the water quality of the Nwangele River located in

the Southeast area of Nigeria and concluded that

the river is slightly polluted with heavy metals and

the present river studied has a ow with Nwangele

River. [6], researched the effectiveness of the water

quality index in Izombe in the Imo state of Nigeria.

The scientic research was done in areas where gas

aming is unremitting to build up pollution levels

in rainwater and boreholes as they are viewed as

the two signicant establishments of water supply

in the area. The grouping of pollution among

the examined water assets was accomplished by

contrasting the result of physicochemical tracers

and that of WHO norms for drinking water.

The Ogbajarajara is a well-known river in the

Nwangele local government area of the Imo State

Nigeria. The major occupation in this area includes

farming with few traders. The farming activities

have an important bearing on the ecology of the

area. Daily activities in this river include; washing

and fermentation of cassava. Other activities are

washing clothes, motorcycles, and cars, kitchen

utensils, bathing, shing, and road construction

near the rivers. Recently many technologies such

as the spectrophotometer [7], atomic absorption

spectrometry [8], HPLC [9], gas chromatography

[10], and electrochemistry were used for the

determining of pollutions. The sole aim of this work

is the determination of pollution in surface waters

and the evaluation of human risk assessment due

to the presence of heavy metals in surface water

sources in this area.

2. Experimental

2.1. Study Area

The research area is the Ogbajarajara River located

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

in the Nwangele local government area of Imo

state. The Nwangele is in the tropical rainforest

region and it has two different seasons which are

the dry and wet seasons. The wet season changes

from April completely through October with top

occurrence in June and September through the dry

season starts in November entirely through March

yearly. Nwangele has its headquarter in Amaigbo

and an area of 63 km2 (24 sq mi) and a populace of

128,472 as of the 2006 census (Fig.1). The geology

of the Nwangele area includes plain soil which is

about 0.05-2.0 mm in size and it is to some degree

permeable, deep, and profoundly leached. Nwangele

Local Government has numerous networks

including Abba community, Isu Community,

Umuozu community, Abajah community, and

Amaigbo community. Topographically, the area

falls between directions of latitude 5.7045779011-

5.7111225452 and longitude of 7.13319502340-

7.4222545475. The occupants of these areas are

dominatingly Igbos and they are Christians with not

very many conservatives and other religions. Their

signicant occupation is farming with not many

traders. The farming exercises have a signicant

bearing on the ecology of the area. Daily exercises

in this river incorporate; washing and aging of

cassava. Different exercises are washing clothes,

bikes, cars, cooking wares, bathing, and shing.

2.2. Sample Collection

Ten surface water samples were collected randomly

within the dry and wet seasons during the research

period. Sampling was carried out for both dry and

wet seasons and specied as Ogw and Ogd, where

Fig. 1. Map of the Nwangele L.G.A. and its environs showing the Ogbajarajara River

Ogw will be for wet and Ogd will be for dry season

respectively. The samples were collected using a

clean plastic bottle from the surface waters. Five

[5] samples were collected from the river to make

up a composite sampling technique. The plastic

bottles used for the collection of the surface water

samples were appropriately marked and cleaned

before sample collection by soaking it in 10% HCl

for 48 hours, washed and cleaned with deionized

water, and dried up [11,12].

2.3. Laboratory Analysis

The surface water samples were analyzed for

the following: Electrical conductivity (EC), pH,

Dissolved Oxygen (DO), Total dissolved solids

(TDS), Temperature, and color. Also anions and

cations such as, Calcium (Ca), Sodium (Na),

Potassium (K), Phosphate (PO4

3-), Nitrate (NO3

), Sulphate (SO4

2-), Lead (Pb), Copper (Cu), Iron

(Fe), Nickel (Ni), Manganese (Mn), Zinc (Zn) and

Cadmium (Cd) were determined

2.4. Instrumentation and reagents

The heavy metals concentrations were determined

by a double beam ame atomic absorption

spectrometer (FAAS, GBC 906, Aus.). The Air or

N2O-acetylene (C2H2), the deuterium lampas was

used by FAAS. The Avanta system was used for

calculating data. In addition, the electrothermal

atomic absorption spectrophotometer ET-

AAS, GBC, Aus.) was used for the validation

of heavy metals in surface water samples. The

current and wavelength of the HCL lamp were

adjusted for each element. Chemical modiers

such as Pd(NO3)2 and Mg (NO3)2 were used

for increasing the ashing point. The electrical

conductivity was assessed using the HANNA

HI8733 EC METER in µS cm-1 and the pH was

assessed using JENWAY 3510 pH METER. The

DO centralization of the surface water tests was

set up using a JENWAY 9071 digital oxygen

analyzer. The anion examination was done using

multi-parameter bench photometer HI 82300

by HANNA instruments. TDS were done using

Groline TDS meter by HANNA instruments.

Also, many anions and cations such as calcium,

sodium, potassium, iron, copper, cadmium, nickel,

manganese, zinc, and lead, in the surface water

during the dry and wet seasons were analyzed

using atomic absorption spectrophotometer [13].

All reagents with AAS grade such as; metal solution,

inorganic solutions (HNO3, NaOH) were purchased

from Sigma Aldrich (Germany). Metal standard solution

(M) was diluted from the stock of 1000 mg L-1 solution in

2 % nitric acid for further studies. The standard solutions

were diluted by distilled water (DW) from Millipore

(USA). Reagents utilized all through the research were

of high-quality analytical grade, which was bought from

BDH Chemical Ltd, UK, and Sigma-Aldrich Chemie

GmbH, Germany. Detergents and deionized water were

utilized to wash the dish sets and sample bottles. They

were splashed for the time being with a solution of 10%

HNO3 in a 1% HCl solution, trailed by washing with

deionized water. Additionally, the reagents that were

utilized for the assurance of anion focuses with the

Hanna Hi 83,200 Instrument were gotten from Hanna

Instruments. The instrument (GBC 903) utilized for the

assurance of the groupings of metallic elements in the

samples has high sensitivity—commonly (more than

0.9 absorbances) with an exactness (less than 0.5%

RSD) from ten-second integrations for 5 mg L-1 metal

standard.

2.5. Data Analysis

The data were evaluated for their mean and

standard deviation by SPSS software. The data

obtained was subjected to pollution index models

and contamination. Also, Spear-manʼs correlation

coefcient, degree of contamination, Hierarchical

Cluster Analysis (HCA), water quality index

(WQI) analysis and, health risk assessment was

carried out.

3. Results and Discussion

3.1. Physicochemical parameters of surface

water

The physicochemical analysis of the surface water

collected in the dry and rainy seasons is presented

in Table 1. The obtained results were compared

with WHO permissible limits.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

The temperature of water centers on its proposed

usage. The temperature of surface water,

conferring to the standards used falls within 20-

300C. From this study and displayed in Table 1

above, the temperature of the assessed river was

higher during the dry season and this could be

attributed to the hot weather during the dry season.

It can be seen that the season has an effect on the

temperature of the river body. Nevertheless, the

dry season in the study revealed a minor upsurge

in temperature which possibly will be due to the

current weather condition of the environment

at the location of study. Decline and expansion

in temperature level are some of the prominent

signicant highlights of seasonal variation and

weather change. The slight increase in dissolved

oxygen [DO] and pH during the wet season can be

concentrated in accordance with the affectation by

comparative anthropogenic exercises. Interrelated

outcomes were seen for Nworie river [14]. The EC

can critically affect the taste of water. The EC in

this study falls between 100.68±1.0 - 194.74±1.37

μS cm-1 in the dry and wet seasons. The values

obtained were contained by the WHO standard

for risk-free drinking water. The pH value in this

study for the two seasons varied from 5.57±0.22

to 5.73±0.28 μS cm-1 which shows a little acidity

that was not in agreement with the standard pH

(6.50-8.50) recorded by [11] guidelines for safe

drinking water. The lower pH might be a result

of daily anthropogenic activities on this river on

daily basis by the community inhabitants. In the

current study, TDS for wet and dry seasons goes

from 122.17±1.74 mg L-1 and 63.80±0.86 mg L-1.

This may conceivably be a sign of typical pollution

from the runoff of soils in the study area. Color

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

Table 1. The mean levels of studied parameters linked with WHO in wet and dry season

Parameters

wet dry

W.H.O

Ogw1Ogw2Ogw3Ogw4Ogw5Mean±Std Ogd1Ogd2Ogd3Ogd4Ogd5Mean±Std

Temp. (OC) 24.32 25.43 25.48 25.71 25.53 25.29±0.55 28.37 27.99 29.01 28.36 28.31 28.40±0.38 20-30

DO (mg-1) 8.87 8.92 8.65 9.02 8.9 8.87±0.13 5.49 5.29 5.36 5.41 5.59 5.42±0.12 10.0

EC 197.55 200.21 199.11 199.36 196.85 194.74±1.37 99.02 100.57 101.61 100.96 101.24 100.68±1.0 2500

pH 5.24 5.57 5.82 5.49 5.74 5.57±0.22 5.33 5.02 5.29 5.79 5.44 5.37±0.28 6.50-8.50

TDS 122.07 123.03 123.34 119.36 123.07 122.17±1.74 64.32 63.47 62.63 63.71 64.91 63.80±0.86 500

Color 11.00 12.00 11.00 13 12 11.8±0.83 12.00 13.00 13.00 14.00 13.00 13±0.00 15

NO3

- (mg L-1) 22.4 21.32 22.94 21.32 21.54 21.9±0.73 21.33 21.41 22.31 20.59 21.32 21.39±0.61 50

PO4

2-(mg L-1) 59.93 60.24 61.32 60.97 61.23 60.74±0.61 59.97 60.39 60.12 59.99 60.89 60.27±0.38 1.0

SO4

2- (mg L-1) 0.57 0.52 0.51 0.58 0.52 0.54±0.03 0.42 0.47 0.44 0.41 0.45 0.43±0.02 250

Ca(mg L-1) 3.67 4.02 4.13 3.99 4.17 4.0±0.19 3..40 3.44 3.60 3.41 3.52 3.49±0.08 75

Na (mg L-1) 7.05 7.63 7.04 7.14 7.11 7.19±0.24 6.20 5.98 6.02 6.07 6.13 6.08±0.08 200

K(mg L-1) 5.88 5.39 5.47 5.71 5.69 5.63±0.19 5.09 5.12 5.42 5.15 5.17 5.19±0.13 20

Fe (mg L-1) 8.42 8.36 8.52 8.39 8.42 8.42±0.06 6.31 6.32 6.42 6.11 6.28 6.28±0.11 0.3

Cu(mg L-1) 0.06 0.07 0.07 0.06 0.07 0.07±0.01 0.08 0.09 0.08 0.07 0.09 0.08±0.01 2.00

Cd (mg L-1) 0.00 0.00 0.00 0..00 0.00 0.00±0.00 0.00 0..00 0.00 0.00 0.00 0.0±0.0 0.003

Ni (mg L-1) 0.00 0.00 0.00 0.00 0.00 0.00±0.00 0.00 0.00 0.00 0.00 0.00 0.0±0.0 0.02

Mn(mg L-1) 0.05 0.06 0.05 0.07 0.07 0.06±0.01 0.07 0.08 0.07 0.08 0.08 0.07±0.01 0.4

Zn(mg L-1) 2.22 2.16 2.39 2.35 2.33 2.29±0.09 1.11 1.31 1.09 1.13 1.13 1.15±0.09 3.00

Pb ( mg L-1) 0.63 0.71 0.59 0.82 0.74 0.69±0.09 0.47 0.09 0.50 0.49 0.48 0.40±0.18 0.01

10 Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

in essence corresponds to the appearance, taste,

and also general drinkability of water. The color

of the water samples at all the sampling locations

was lower than the permissible limit which has

13.00±0.00 – 11.0.38 PCU in the wet and dry

season against 15 PCU used as the W.H.O standard.

The nitrate in this present study for the wet season

was all found to be below the standard of WHO

standard for safe drinking water both for wet and

dry seasons and they range from 8.72-2154 mg L-1

to 1.20-21.32 mg L-1. Sulfate values observed in the

current study 0.54±0.03 mg L-1 in the wet season and

0.43±0.02 mg L-1 in the dry season were all below

WHO standard for good drinking water and for

domestic water use. Similar ndings were observed

in sulfate values obtained from the study carried

out in the Okumpi river [11]. One of the huge and

crucial nutrients responsible for the richness and

strength of sh ponds is phosphorous. Phosphate

at a sensible sum is tting for the development of

plankton [16]. The phosphate level in both wet and

dry seasons goes from 60.74±0.61 to 60.27±0.38

mg L-1 in both seasons. The high phosphate levels

obtained from this current study; likely could be as

a result of the existence of blue-green growth on

the water surface in the study area in both seasons.

This research perhaps will conclude that phosphate

grounded fertilizer may possibly have been applied

on farmlands near the rivers. Nitrate in all the points

is below the WHO standards. Calcium, potassium,

and sodium as found from the current study in the

wet and dry seasons are below the standard used

for this current study. This result is in agreement

with the outcome of the result obtained from the

Obiaraedu River [17] and the Okumpi River in

Imo State [11].

Fig. 2. Clustered column plots for the distribution of the heavy metal

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

Cadmium and nickel were not detected in the

surface water from the Ogbajarajara River in both

seasons, the plotted distribution of heavy metals

are presented in Figures 2. Iron values observed

in this current study ranges from 8.42±0.06 to

6.28±0.11 mg L-1 in wet and dry season are higher

than WHO standards of 0.3 mg L-1. Iron detected in

every one of the samples in the wet season may be

as a result of the utilization of iron coagulants [18].

This higher concentration of Fe observed during

the wet than the dry season might be because most

mineral residues on the soil may have a high level

of iron, subsequently runoff from residue may taint

the water, particularly during the rainy season.

Copper is an imperative supplement, also drinking

water impurity [19]. Cu amount for both wet and

dry seasons in this current study was all underneath

WHO standard for drinking water and domestic

uses and they went from 0.08±0.01 to 0.07±0.01

mg L-1. Running river is probably going to display

a low level of copper [19]. The low level of copper

in this current study is in line with the result

observed in the Nwangele River [5] and in River

Nworie [14]. Equivalent discoveries were likewise

seen in a study done on River Uramurukwa in Imo

State [20] and Obiaredu River [17]. Manganese

goes from 0.07±0.01 to 0.06±0.01 mg/L through

the wet and dry season. With respect to WHO

standard and NSDWQ for household and drinking

water value for Mn, all points for the wet season

showed a low level of Mn. At high concentrations,

Mn can comprise an aggravation with a particular

metallic taste and staining properties [16]. Zinc

observed both in wet and dry season between

2.29±0.09‒1.15±0.09 mg L-1; were observed to be

below the WHO standard for water quality against

the scheduled level of 3.0 mg L-1. Zinc uncovered

an unwanted harsh taste to water [15]. Pollution

of lead in a river may conceivably be an outcome

of the disbanding of lead from the soil and earth’s

external layer. Lead is in participation a harmful and

superuous metal that has no healthful signicance

to living creatures. Lead levels in every one of

the samples are observed to be high, going from

0.69±0.09 to 0.40±0.18 mg L-1 in the wet and dry

season which are higher than the WHO standard at

0.01 mg L-1. No amount of Pb is viewed as protected

in drinking water. A related study was observed in

a study of the river Uramurukwa in Imo State [20].

3.2. Correlation coefcient matrix

A substantial positive correlation (r > 0.5) was

observed between some of the metals, and anions

parameters. Table 2 shows the coefcient of

relationship for all the metals and anions. The

metals showed a negative association/relationship

with copper and cadmium. Nevertheless,

signicant positive relations during the wet season

were exhibited between NO3

-/Fe (0. 0.888), PO4

2-/

Ca (0.847), PO4

2-/Fe (0.544), PO4

2-/Zn (0.894), Ca/

Cu (0.769) and Mn/Pb (0.934). Signicant positive

associations through the dry season were exhibited

between NO3

-/Fe (0. 888), PO4

2-/Ca (0.847), PO4

2-/

Fe (0.544), PO4

2-/Zn (0.894), SO4

2-/K (0.746), Ca/

Cu (0.769), Ca/Zn (0.524), Fe/Zn (0.691) and Mn/

Pb (0.934). Once the correlation is seen positive,

the establishment of tainting of the positively

connected metals is indistinguishable while

negative correlation suggests disparate/various

bases of contamination. Notable pollution can be

through the washing of engine cars, tricycles and,

motorcycles at the river. Some of the relationship

shown by the metals has been examined by [21].

3.3. Hierarchical Cluster Analysis (HCA)

Additionally, we performed Hierarchical Cluster

Analysis (HCA) to identify groupings of

physicochemical characteristics based on their

Square Euclidian Distance (SED) [21]. The cluster

plots for physicochemical parameters in the water in

dry and wet seasons are presented in Figure 3. In the

dry season, three groups were identied. In group 1,

the combination included all parameters except for

pH, Phosphate, and, EC in another group and then

TDS in the third group. Similarly, in the wet season,

the combination includes all parameters except for

DO and temperature in group 2 while TDS and EC

in group 3. The clustering of all metals in similar

indicates that their source(s) are common. The HCA

results agree with correlation analysis.

12 Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

Table 2. Correlation coefcient matrix heavy metals and anions from surface water samples in wet/dry season (mg L-1)

NO3

- PO4

2- SO4

2- Ca Na K Fe Cu Cd Ni Mn Zn Pb

Wet

NO3

- 1

PO4

2- 0.098 1

SO4

2- -0.217 -0.402 1

Ca -0.168 0.847 -0.702 1

Na -0.586 -0.398 -0.277 0.115 1

K 0.051 -0.260 0.746 -0.635 -0.642 1

Fe 0.888 0.544 -0.384 0.256 -0.671 -0.083 1

Cu 0.054 0.424 -0.986 0.769 0.365 -0.772 0.257 1

Cd 000000001

Ni 0 0 0 0 0 0 0 0 0 1

Mn -0.848 0.383 0.154 0.457 0.161 0.063 -0.540 -9.312 0 0 1

Zn 0.338 0.894 -0.072 0.524 -0.721 0.064 0.691 0.047 0 0 0.181 1

Pb -0.900 0.155 0.424 0.203 0.235 0.134 -0.693 -0.271 0 0 0.934 0.040 1

Dry

NO3- 1

PO4

2- 0.098 1

SO4

2- -0.217 -0.402 1

Ca -0.168 0.847 -0.705 1

Na -0.586 -0.398 -0.277 0.115 1

K 0.051 -0.260 0.746 -0.635 -0.642 1

Fe 0.888 0.544 -0.384 0.256 -0.671 -0.083 1

Cu 0.054 0.424 -0.986 0.769 0.365 -0.772 0.257 1

Cd 000000001

Ni 0 000000001

Mn -0.844 0.383 0.154 0.457 0.161 0.063 -0.540 -9.344 0 0 1

Zn 0.338 0.894 -0.072 0.524 -0.721 0.064 0.691 0.047 0 0 0.181 1

Pb -0.900 0.155 0.424 0.203 0.239 0.134 -0.693 -0.271 0 0 0.934 0.040 1

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

3.4. Chemometric Analysis

3.4.1.Contamination factor

The contamination factor was employed to check

the rate of individual metal contamination in

the water samples. Contamination factors were

calculated with equation I.

(Eq. I)

Where Cf connote contamination factor, C metal

address the grouping of heavy metal and C background

means the foundation worth of metal. WHO

suggestions for safe drinking water are taken

as the foundation esteems for a water sample.

Contamination factor ranking followed by Table 3.

3.4.2.Pollution load index (PLI)

The proposed pollution load record through

Tomlinson for distinguishing pollution levels in

soil was applied to the water tests to recognize the

convergence of contamination of heavy metal in the

different areas. The PLI appraises the metal xation

status and gives a thought of the different moves that

can be made to control the issue [22]. Scientists have

assessed the pollution load index utilizing equation II.

(Eq. II)

A PLI value > 1 point toward an instantaneous

intervention to ameliorate pollution; a PLI value <

1 species that extreme rectication procedures are

not needed.

High contamination factor was recorded for lead

Fig. 3. Hierarchical cluster analysis for physicochemical properties in the dry and wet season

Table 3. Contamination factor ranking

Cf values Contamination factor level

Cf < 1 Low contamination

1 ≤ Cf < 3 Moderate contamination

3 ≤ Cf < 6 Considerable contamination

6 ≤ CfVery high contamination

14 Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

Fig. 4. Contamination factor and PLI for heavy metals and anions in the wet season

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

and iron in this present study both in wet and dry

seasons. The contamination was higher during

the wet seasons and this may be due to runoff

during the wet season which comes directly

from the farmlands surrounding the river. The

contamination factor was recorded accordingly

Pb>Fe>n>Mn>Cu>Cd and Ni in both wet and dry

seasons. The river has shown a high pollution load

index of 1.192 in wet and 1.8 in the dry season

as shown in Figure 4 above. However, there is a

need to constantly evaluate the water source in this

location.

3.4.3.Water quality index (WQI)

WQI is a number-arithmetic articulation used to

change the enormous number of adjustable data into

a solitary number, which implies the water quality

level. The WQI is created from the accompanying

formula presented to equation III [23].

(Eq. III)

Where: Wi is equal to the comparative weight, wi is

equal to the mass of every single parameter and n is

confer to the parameters. Water quality evaluation

may be developed conferring to equation VI [24, 25].

(Eq. IV)

Where qi is the quality positioning, Ci is the

concentration of every chemical boundary in each

and every water sample in mg L-1, and Si is the

WHO drinking water quality standard. To work

out the WQI, the SI was set up for every chemical

boundary, which is then used to decide the WQI

utilizing Equation V and VI.

(Eq. V)

(Eq.VI)

SIi is the sub-index of ith (mathematics Occurring

at position [i] in the sequence) parameter, qi is

the rating dependent on the concentration of ith

parameter and n is the number of parameters.

The benchmark esteems were procured from

World Health Organization (WHO) standard for

drinking water, 2007. The accompanying point of

arrangement of (WQI) and the nature of water WQI

showed in Table 4 [27].

The examined samples from this study are severely

polluted with physicochemical tracers given the

value of 549 for wet and 328 for a dry season as

reported in Figure 5 below, which makes the water

unsuitable for drinking. Various activities around the

sampling point might have contaminated the rivers

in an intense way, while the wet season recorded

more concentration from this present study.

Table 4. Water Quality Index Values

Cf Value Water Quality

WQI < 50 Excellent water quality

50 < WQI ≤ 100 Good water quality

100 < WQI ≤ 200 Poor water quality

200 < WQI ≤ 300 Very poor water quality

WQI > 300 Unsuitable for drinking

16 Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

Fig. 5. WQI values of the sampling points in the wet

season

3.5. Assessment of health risk after

determination

3.5.1.Dermal and ingestion exposure, Hazard

quotient (HQ), Hazard Indices (HI)

Health risk through human exposure to these metals

contamination can be either by means of dermal

ingestion, inhalation, or absorption, which are the

normal contact passageways to the water. Thusly

all the rivers studied in this research are constantly

utilized by individuals generally for their domestic

exercises and sporting exercises. The calculation

of health risk was calculated using equations VII

and VIII according to the USEPA risk estimation

method [30-32].

(Eq. VII)

(Eq. VIII)

Exp ing denotes the exposure dose through ingestion

of water (mg kg-1 per day); Expderm addresses the

exposure dose by means of dermal absorption

(mg kg-1 per day); Cwater: show the normal level

of the assessed metals in water (μg L-1); IR shows

the ingestion level in this study (2.2 L per day for

adults; 1.8 L per day for children); EF shows the

exposure equation frequency (365 days/year); ED

shows the exposure duration (70 years for adults;

and 6 years for children); BW show the normal

body weight (70 kg for adults; 15 kg for children);

AT shows the averaging time (365 days/year × 70

years for a grown-up; 365 days per year × 6 years

for a children); SA shows the uncovered skin area

(18,000 cm2 for adults; 6600 cm2 for children);

Kp shows the dermal permeability coefcient in

water, (cm/h), 0.001 for Cu, Mn, Fe and Cd, though

0.0006 for Zn; 0.0001 for Ni; and 0.004 for Pb; ET

shows the exposure time (0.58 h per day for adults;

1 h per day for children) and CF shows the unit

conversion factor (0.001 L cm-3) [29]. Potential

non-cancer-causing chances in line for exposure

of heavy metals were set up by assessing the

determined toxin exposures from every exposure

path (ingestion and dermal) with the proposal dose

[29] utilizing equation IX.

(Eq. IX)

Where RfDing/derm addresses the ingestion and

dermal toxicity suggestion dose (mg kg-1 day-1).

The RfDderm and RfDing esteem were gotten from the

literature [30, 31]. An HQ under 1 is presumed to

be safe and taken as substantial non-carcinogenic

as equation X [29].

(Eq. X)

Where HI ing/derm is hazard index through dermal

contact or ingestion.

The dermal and ingestion exposure determined

in Table 5 were utilized to decide the hazard

quotient in Table 6. The hazard quotient (HQ)

was resolved and both HQderm and HQing in the

two seasons for all the trace metals checked in

the examination were lower one (1) as seen in

Table 6 for adults and children. This shows there

is basically no adversative health sway expected

to be ordered by any of these metals when the

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

surface water is used. The HQ ing and HQ derm

decreased in the request for lead > iron > zinc

> manganese > copper > nickel > and cadmium,

lead > manganese> iron > copper > zinc > nickel

and cadmium, for the two children and adults

in wet season, individually. HQing and HQderm

decreased in the request for nickel > lead > man-

ganese > copper > zinc > iron and lead >zinc >

nickel > copper > manganese > iron > for the both

children and adults in dry season, individually. It

has been suggested that the calculated HQ results

for metals > 1 for children ought not to be ignored

[32], presumably in light of the fact that, children

are limitlessly disposed to pollutants [33]. The

signicant source of non-cancer-causing health

risk in the two ways were Pb and Ni. The assessed

absolute HQ esteems were less than one as found

in Table 6.

Table 5. Dermal and ingestion exposure (mg kg-1 per day) for adults and children both in wet and dry season

Wet Dry

Metals RfDderm RfDing

EXPderm

(Adult)

EXPderm

(Children)

Ding

(Adult)

Ding

(Children)

EXPderm

(Adult)

EXPderm

(Children)

Ding

(Adult)

Ding

(Children)

Fe 140 700 1.25E-2 3.7E-3 2.26E0 `1.01E0 9.36E-3 2.76E-3 1.97E0 7.53E-1

Cu 8 40 1.04E-4 3.08E-5 2.2E-2 8.0E-3 1.19E-4 3.52E-5 2.5E-2 9.0E-3

Cd 0.5 0.025 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Ni 5.4 20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Mn 0.96 24 8.94E-5 2.64E-5 1.8E-2 7.0E-3 1.04E-4 3.08E-5 2.22E-2 8.0E-3

Zn 120 300 2.04E-3 6.04E-4 7.19E-1 2.74E-1 1.02E-3 3.03E-4 3.61E-1 1.38E-1

Pb 0.42 1.4 4.11E-3 1.21E-3 2.16E-1 8.2E-2 2.38E-3 7.04E-4 1.25E-1 4.8E-2

Table 6. Hazard quotient for potential non-carcinogenic risk (HQ) and cumulative hazard indices (HI)

for each heavy metal present in wet and dry season for Adult and Children

Wet Dry

Metals HQderm

(Adult)

HQderm

(children)

HQing

(Adult)

HQing

(children)

HQderm

(Adult)

HQderm

(children)

HQing

(Adult)

HQing

(children)

Fe 1.78E-4 2.64E-5 3.22E-3 1.44E-3 6.68E-5 1.79E-5 2.71E-3 1.07E-3

Cu 1.3E-5 3.85E-6 5.5E-4 2.0E-4 1.48E-5 4.4E-6 6.25E-4 2.25E-4

Cd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Ni 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Mn 1.02E-4 275E-5 7.5E-4 2.91E-4 1.08E-4 3.2E-5 9.25E-4 3.33E-4

Zn 1.7E-5 5.03E-6 2.39E-3 9.0E-4 8.5E-6 2.52E-6 1.2E-3 4.6E-4

Pb 9.78E-3 2.88E-3 1.52E-1 5.85E-2 5.66E-3 1.67E-3 8.92E-2 3.42E-2

HI 1.01E-2 2.94E3 1.61E-1 6.13E-2 5.85E-3 1.73E-3 9.46E-2 3.63EE-2

18 Anal. Methods Environ. Chem. J. 5 (1) (2022) 5-21

3.5.2.Chronic daily intake (CDI) and

Carcinogenic risk (CR)

The carcinogenic risk (CRing) shows a gradual

possibility that an individual will foster cancer

during his lifetime inferable from disclosure

under portrayed conditions were registered for

the selected metals in this current study [30]. The

chronic daily consumption of heavy metals through

ingestion was computed using equation XI.

(Eq. XI)

Where C water addresses the centralization of trace

metal in water in (mg L-1), DI infer the; normal

everyday admission of water which is referred to

as daily intake (2.2 L each day for adults; 1.8 L

each day for children) and BW shows the entire

body weight (70 kg for adults; 15 kg for children),

correspondingly [34]. The cancer risk (CR) was

calculated using the formula in equation XII.

(Eq. XII)

whereas SFing represent the cancer slop factor. The

SFing for Pb is 8.5 mg kg-1 per day [26].

The CDI indices for heavy metals during the

experimental time frame for the two ages were

discovered to be in the request for Fe > Pb > Zn

> Cu > Mn > Ni > Cd in wet season; and Fe > Zn

> Pb > Mn > Cu > Ni > Cd in dry season as seen

in Table 7. This proposes that the surface water

expects less health dangers to the two adults and

children by means of the pathways, except for Fe

during the wet season for children which appears to

be more than one. Table 8 present the carcinogenic

risk of Pb for this present study for both adults and

children in wet and dry season, for the reason that

the value of carcinogenic slope factor for different

metals couldn’t be followed in literature, only

lead was determined. Under extreme regulatory

program the carcinogenic risk esteems within the

range of 10−6 and 10−4 could present possible risk

to an individual, subsequently, the outcomes in this

present study showed that the level of Pb in the

surface water could present a carcinogenic risk to

both adults and children.

Table 7. Chronic risk assessment (CDI ing) of heavy metals in adults and children

wet dry

Metals CDI (Adult) CDI

(children) CDI (Adult) CDI

(children)

Fe 2.64E-1 1.01E-0 1.97E-1 7.53E-1

Cu 2.19E-3 8.4E-2 2.51E-3 9.6E-3

Cd 0.00 0.00 0.00 0.00

Ni 0.00 0.00 0.00 0.00

Mn 1.88E-3 5.0E-1 219E-3 8.E-3

Zn 7.19E-2 2.74E-1 3.6E-1 1.38E-1

Pb 2.16E-2 8.28E2 1.25E-2 4.8E-2

Table 8. Carcinogenic risk assessment (CRing) of Pb for wet and dry season for both adults and children

Metal Wet Dry

Adult Children Adult Children

Pb 2.54E-3 9.74E-3 1.47E-3 5.64E-3

Determination of pollutions in surface of water samples Stanley Chukwuemeka Ihenetu et al

4. Conclusion

The current study has shown that some actual

appearances of pollution from surface water from

the study area during the wet and dry seasons are not

in line with WHO guidelines. The heavy metals; and

cations were analyzed in surface water by photometer

spectrometry and ame atomic absorption

spectrometry (F-AAS). The results for metal

analysis were validated by electrothermal atomic

absorption spectrometry (ET-AAS). The study has

shown additionally that the pH of all the sampling

points is acidic. Phosphate apparently is high in all

the sampling points at the various season and this can

be related to the high utilization of more phosphate

grounded fertilizer on farmlands surrounding the

Rivers. The current study has uncovered also that the

surface waters are profoundly contaminated with Fe,

Zn and Pb, also this current study has shown that the

surface water isn’t appropriate for drinking purposes

as shown by the high water quality index (> 300).

5. Recommendation

With regard to the results of the present study, the

succeeding references are made after pollution

analysis.

• The water resources observed in the Nwangele

Local Government area should be done routinely

to survey pollution levels (instrumental analysis)

to check the spread of water-related complexities,

particularly in the study area.

• In a circumstance of uncertain water quality,

treatment is recommended through ltration,

boiling, and the utilization of added substances

(alum, liming, chlorine), accordingly lessening the

danger of water-related issues.

6. Acknowledgments

The authors sincerely appreciate the efforts of the

laboratory attendants of the chemistry department

of Imo State University and Anambra state

university Uli.

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Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

A new analytical method based on Co-Mo nanoparticles

supported by carbon nanotubes for removal of mercury vapor

from the air by the amalgamation of solid-phase air removal

Danial Soleymani-ghoozhdi a, Rouhollah Parvari a, Yunes Jahani b, Morteza Mehdipour-Raboury a

and Ali Faghihi-Zarandi a, *

a Department of Occupational Health and Safety at Work, Kerman University of Medical Sciences, Kerman, Iran

b Department of Biostatistics and Epidemiology, School of Public Health, Kerman University of Medical Sciences, Kerman, Iran

ABSTRACT

Heavy metals are a major cause of environmental pollution, and

mercury is a well-known toxicant that is extremely harmful to the

environment and human health. In this study, new carbon nanotubes

coated with cobalt and molybdenum nanoparticles (Co-Mo/MWCNT)

were used for Hg0 removal from the air by the amalgamation of solid-

phase air removal method (ASPAR). In the bench-scale setup, the

mercury vapor in air composition was produced by the mercury vapor

generation system (HgGS) and restored in a polyethylene airbag (5

Li). In optimized conditions, the mercury vapor in the airbag passed

through Co-Mo/MWCNT and was absorbed on it. Then, the mercury

was completely desorbed from Co-Mo/MWCNT by increasing

temperature up to 220 °C and online determined by cold vapor atomic

absorption spectrometry (CV-AAS). The recovery and capacity of Co-

Mo/MWCNT were obtained at 98% and 191.3 mg g-1, respectively.

The Repeatability of the method was 32 times. The mercury vapors

absorbed on Co-Mo/MWCNT adsorbent could be maintained at

7 days at the refrigerator temperature. The Co-Mo/MWCNT as a

sorbent has many advantages such as; high capacity, renewable, good

repeatability and chemical adsorption (amalgamation) of mercury

removal from the air. The method was successfully validated by a

mercury preconcentrator analyzer (MCA) and spiking of real samples.

Keywords:

Mercury removal,

Air,

Adsorption,

Cobalt and molybdenum nanoparticles,

Multiwalled Carbon nanotube,

Amalgamation solid-phase air removal

ARTICLE INFO:

Received 5 Dec 2021

Revised form 10 Feb 2022

Accepted 26 Feb 2022

Available online 28 Mar 2022

*Corresponding Author: Ali Faghihi-Zarandi

Email: Alifaghihi60@yahoo.com

https://doi.org/10.24200/amecj.v5.i01.163

------------------------

1. Introduction

Heavy metals are a major cause of environmental

pollution, and mercury (Hg) is a well-known

toxicant that is extremely harmful to the

environment and human health because of its

persistence, bioaccumulation, and neurological

toxicity [1, 2]. Hg can affect many organs and

cause a variety of symptoms in the body, although it

targets the nervous system, it may also have serious

toxicological effects on the kidney. In addition to the

nervous and kidney system, other systems such as

the cardiovascular system can also be damaged by

exposure to mercury [3, 4]. Mercury has been used

in various products and processes due to its unique

properties. It is utilized in industrial processes that

produce chlorine, sodium hydroxide (Chlor-alkali

plants), the vinyl chloride monomer for polyvinyl

chloride (PVC) production, and polyurethane

elastomers. Mercury is also released from coal-

red power plants and cement production [5, 6].

Therefore, Hg emissions have attracted worldwide

attention. Minamata Convention on mercury, which

Co-Mo@MWCNTs for removal of mercury from air Danial Soleymani-ghoozhdi et al

aims is to protect human health and the environment

from anthropogenic emissions and releases of

mercury and mercury compounds, entered into

force on 16 August 2017 [7, 8]. Recently, the

different methods have been introduced for the

sampling and analysis of mercury. NIOSH 6009

and OSHA 140 are the recommended methods

for the sampling of mercury. In these methods,

sample preparation depends on the applied nitric

acid and hydrochloric acid which can be hazardous

to the environment and human health [9, 10].

Emissions from different sources, mercury release

in different forms, including elemental mercury

(Hg0), oxidized mercury (Hg2+), and particulate

bond mercury (Hgp) [11, 12]. Among of various

states of mercury, Hg0 is difcult to remove due to

its stability, long persistence time, high volatility

and insolubility in water [13, 14]. Therefore,

effective Hg0 control technologies are immediately

needed. Several control technologies for Hg0,

including catalytic oxidation [15], photocatalytic

oxidation [16], photochemical removal [17], wet

oxidation [18], and adsorption method [19] have

been developed. Among the various Hg0 removal

methods, the adsorption technique has been widely

studied because of its simplicity, economical,

and good removing efciency [20, 21]. In recent

years, novel carbon-based materials, such as

graphene and graphene oxide, carbon nanotubes

and nanobers, carbon spheres, and metal-organic

frameworks, have been applied for Hg0 removal.

Carbon nanotubes (CNTs) are one type of one-

dimensional nanomaterials, which have been used

for Hg0 removal from water and air due to their

unique physicochemical properties. Carbon-based

materials Because of their large surface area,

exible surface chemistry, and variety diversity, are

the most widely studied adsorbents for Hg0 removal

from ue gases and air [21–23]. Because of its high

removal efciency, the activated carbon (AC) based

adsorption process is considered one of the most

effective technologies for mercury removal, but high

operation costs and adsorbent loss have impeded its

further development [22, 23]. Therefore, developing

more cost-effective carbon-based sorbents for Hg0

removal has signicance [21]. In recent years,

novel carbon-based materials, such as bio-chars

[24], graphene and graphene oxide [25, 26], carbon

nanotubes and nanobers [27, 28], metal-organic

frameworks [29], have been applied for Hg0 removal

by analytical methods. Carbon nanotubes (CNTs) are

one type of one-dimensional nanomaterials which

have been used for Hg0 removal from water and

air due to their unique physicochemical properties

[30-32]. Also, to improve the performance of Hg0

adsorption, some modication methods have been

studied which mainly improve the surface pore

structure of adsorbents and/or increase the active

sites on the surface of adsorbents [33]. Metal or

metal oxide loaded on the surface of CNTs and

other carbon-based materials were a type of catalyst

with both high adsorption and catalytic capability.

Consequently, these types of catalysts can be an

effective material for Hg0 removal from the air.

Shen et al. reported that the surface area (BET) of

activated carbon (AC) was decreased after loading of

Mn or Co on AC, but the on the other hand, the metal

oxide functionalized on the AC surface can promote

Hg0 catalytic oxidation [34]. Ma et al used the

analytical method based on Fe-Ce decorated multi-

walled carbon nanotube (MWCNT) for removal of

Hg0 from ue gas. The results showed that Fe-Ce/

MWCNT had good Hg0 removal performance [32].

Liu et al Suggested the adsorption of Co/TiO2 for

Hg0. The results showed that the high oxidation

activities for Hg0 was obtained by this catalyst [35].

Molybdenum (Mo) is commonly added as a promoter

to vanadium-based catalysts in Hg0 oxidation, but its

catalytic oxidation activity is poor [36].

In this work, Hg0 was removed from the air by using

Co-Mo/MWCNTs. Brunauer−Emmett−Teller (BET)

analysis, X-ray diffraction (XRD), scanning electron

microscopy (SEM) and transmission electron

microscopy (TEM) were employed to analyze

the characteristics of the samples. Experimental

parameters affecting the Hg0 removal process from

the air such as temperature and ow rate were

investigated and optimized. Also, comparisons

between the proposed method and previous methods

were obtained.

24 Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

2. Experimental

2.1. Materials and Chemical reagents

Mercury standard was used in the mercury vapor

generation system (HgGS). It was prepared by

dilution of 1 ppm (1000 mg L-1) Hg (II) standard

solution (CAS Number.: 7487-94-7) which was

purchased from Fluka, Germany. Deionized water

(DW) was prepared by water purication system

from RIPI. The stannous chloride (SnCl2, CAS

Number: 7772-99-8) and the NaBH4 (CAs Number:

6940-66-2) analytical grade were purchased from

Merck and Sigma (Germany) which was diluted

with DW. The SnCl2 or the NaBH4 as reducing

agents was used by dissolving in HCl and NaOH/

DW, respectively. The reducing agents was added

to 100 mL deionized water (DW) and mixed well.

All the laboratory glassware (Sigma) and PVC

plastics were cleaned by nitric acid (10% ,v/v)

for at least 2 days and then washed for many

times with DW. Cobalt (II) nitrate hexahydrate

(Co (NO3)2.6 H2O; CAS Number: 10026-22-

9) and Molybdenum powder (10 μm, ≥99.95%,

CAS Number: 7439-98-7) were purchased from

Sigma Aldrich (Germany). The MWCNTs and Co/

Mo-MWCNTs adsorbents was synthesized and

prepared from nano center of RIPI. In this study,

the Co-Mo/MWCNTs adsorbent was used for

mercury removal from air.

2.2. Apparatus

The mercury standard (Hg0) was generated by

the mercury vapor generation system (HgGS) in

chamber. The bench scale included of HgGS for

HgH2, chamber, PVC bags, the quartz tubes as a

column, the heater accessory (220 AC Voltage, 35-

450 °C), the digital ow meter control (50-500 ml

min Ar/air), Pure air accessory, O2 and water digital

detectors, the digital temperature control, the

MC-3000 as trace mercury analyser (Germany),

and the CV-AAS for determining the mercury

concentration. The pure air pushed with owrate

of 50-250 ml min-1 to chamber and mixed with

mercury vapour at 100 °C. The air lines (tubes)

and PVC bags were covered with heating jackets.

The quartz tubes with outer diameter of 0.35 inch,

inner diameter of 0.2 inch and length of 4.0 inch

was used as a column for the Co-Mo/MWCNTs

adsorbent. The Hg0 determined by a cold vapor

atomic absorption spectrometer (CV-AAS, GBC

Plus 932, AUS). A mercury hollow-cathode lamp

with a current of 8 mA, the wavelength of 253.7

nm based on a spectral band width (0.5 nm) was

used. Argon (99.99%) was used as a carrier gas for

mixer of CV-AAS and glass separator. The SKC air

sampling pump (USA), 50 to 2000 ml min-1 was

used.

2.3. Co and Mo Catalyst preparation

The sol-gel method has been extensively used in the

preparation of supported metal catalysts because it

typically results in highly homogeneous materials

with high degree of metal dispersion. In this sense,

catalysts were supported on silica sol-gel with the

metal to 50 percent based on silica added. To obtain

metallic catalyst supported on high-surface area

silica by the sol-gel method, the polymerization of

an alkoxy-silane such as tetrathoxysilane (TEOS),

also known as tetraethyl orthosilicate, is carried out

in the presence of the appropriate metal precursors.

In our case, catalyst nanoparticles were prepared

from high purity salts of the transition metals:

Co (NO3)2.6H2O and (NH4)6Mo7O4. 4H2O, from

Baker Co. To accelerate the polymerization, an

increase in pH can be brought about by addition of

a base, which causes a rapid hydrolysis followed

by polymerization. Simultaneously with this

polymerization process, the metallic ions (Co and

Mo) precipitate, thus forming a homogeneous and

well-dispersed mixture (Fig.1).

2.4. Co-Mo/MWCNTs synthesis

As Figure 1, After placing the catalyst inside a

quartz tube, a continuous nitrogen ow rate of 1 L

min-1 was passed through the reactor for removing

the oxygen. Subsequently, the reduction process

was accomplished within at 600 °C. The reduction

process was kept for 30 minutes in an atmosphere

of 90 % v/v of N2 and 10 % v/v of H2. Next, the

temperature was increased up to 700 °C for the

nucleation and growing of CNTs [37-39].

Co-Mo@MWCNTs for removal of mercury from air Danial Soleymani-ghoozhdi

2.5. Characterization

The high-resolution images were obtained using

a high-resolution transmission electron microscope

JEOL JEM-2010, operated at 200 kV and a

scanning electron microscopy (SEM) JEOL JSM

5300 operated at 5 kV. Complementary RAMAN

spectroscopy was performed. The Co-Mo/

MWCNTs samples were deposited onto a sample

holder with an adhesive carbon foil and sputtered

with Au before imaging. The morphology of Co-Mo/

MWCNTs was obtained by a transmission electron

microscopy (TEM, Zeiss, Germany). For the TEM

analysis, the samples were dispersed in C2H5OH

and a drop was used. The chemical analysis for

the determination of Co and Mo concentration in

synthesized samples was performed using F-AAS.

2.6. General Procedure

The mercury vapor removal was performed using

a bench-scale setup (Fig. 2). First, 40 mg of Co-

Mo/MWCNTs nanoadsorbent was put onto the the

quartz tubes. Then, the end of the adsorbent were

tied by re-proof linen. The pure air was mixed

with mercury vapor in chamber containing 0.1-10

μg Hg0 per liter air (21% O2, 0.2% H2O) at 25 °C.

By the procedure, 0.1─10 μg of Hg0 was generated

by the mercury vapor generation system (HgGS)

and restored in a PVC bag. The value of mercury

in PVC bag was validated using MC analyzer. Due

to procedure, the mercury standard solution (1-2

mL min-1), HCl (5% v/v, 5 mL min-1), and SnCl2

as reducing agent (2.5 mL min-1) were mixed with

pure air in mixer and pass through a peristaltic

pumps. Elemental mercury vapor was generated

in the reaction loop, and pumped into a 5 L

polyethylene (PE) bag, as a bulk container. Finaly,

the the mercury concentration was obtained 0.1-10

μg Hg0 per liter air in the polyethylene bag (5 L)

was mixed with 21 % O2 and 0.2 % H2O vapor

at 25 °C (10─100×TLV OSHA). Then The mixure

Hg0 and pure air passed through 40 mg of the Co-

Mo/MWCNTs adsorbents, at optimized air ow

rate 250 ml min. After amalgamation/adsorption

process, the elemental mercury was released from

the Co-Mo/MWCNTs adsorbents by a thermal

desorption accessory at 220 °C, under Ar ow rate

and transffered to the absorption cell of CV-AAS

(Fig.2). Finally, Hg0 concentration was determined

by CV-AAS. The conditions were presented in

Table 1.

Fig.1. Synthesis of Co-Mo/MWCNTs by Sol gel method and CVD procedure

3. Results and Discussion

3.1. Co-Mo/MWCNTs Raman Spectra

Figure 3a shows the Raman spectra for CNTs-

Co, in which the ratio ID/IG is 0. 26, relating a

high purity material. On the other hand, with Mo

the quality is decreased in a high level (Figure

3b), mainly with Mo (ID/IG ~ 0.59). This is due

to the solubility of C in Mo. In order to obtain

a better quality, in this case the CVD process

must performed to high temperatures (~900°C).

In our experiments, for comparison purposes,

the temperature was always the same for the

different metal-catalyst (~700°C). According

to previous reports, the increase of the D band

intensity (characteristic peak at ~1350 cm-1)

with decreasing multiwalled carbon nanotubes

(MWCNT) content, is a direct result of the addition

of carbonaceous by-products. In the same sense,

a decrease in the G’ band intensity (characteristic

peak at ~2700 cm-1) is observed as the MWCNT

mass fraction decreases. The G’ band on Figures

a reects the well-structured carbon walls in the

samples with Co catalyst, while the Figure 3b

(CNTs-Mo), indicate a less ordered structures,

due to the carbonaceous byproducts.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

Fig.2. The procedure for removal mercury vapor from air based on Co-Mo/MWCNTs by the ASPAR procedure

Table1. Method conditions for mercury vapor removal with the Co-Mo/MWCNTs

Chamber Conditions Value

Hg0 values 0.1─10 μg per liter

O2 (g) 21%

H2O (g) 0.2%

PVC bag 5 L

Ar ow rate 0.2 L min-1

Air owrate 0.25 L min-1

Heat 220 °C

Removal efciency with air More than 95%

Absorption capacity 191.3 mg g-1 (2% Co and 2% Mo)

Adsorbent amount 40 mg

3.2. SEM imaging

The morphology and structural features of Co-

Mo/MWCNTs and MWCNTs were shown by the

SEM images. As shown in Figures 4a and 4b, the

morphology of MWCNTs and the Co-Mo/MWCNTs

were shown in the nanoscale range between 30-

80 nm. Co and Mo were seen in MWCNTs as the

brilliant spots. The elemental analysis (EDX) of Co-

Mo/MWCNTs was shown in Table 2.

Co-Mo@MWCNTs for removal of mercury from air Danial Soleymani-ghoozhdi

Table 2. EDX analysis for elemental values for the Co-Mo/MWCNTs

Elements %Values

Carbon 67.5

N 17.2

Co 2.6

Mo 2.8

H 4.3

O 5.6

Fig.3. Raman spectra of CNTs samples using a) Co-MWCNTs and b) Mo-MWCNTs

Fig.4b. SEM image of Co-Mo/MWCNTsFig.4a. SEM image of MWCNTs

3.3. TEM imaging

The TEM of MWCNTs showed in Figure 5a. Also.

The TEM of Co-Mo/MWCNTs adsorbent can be

seen that Co and Mo nanoparticles (brilliant points)

were incorporated into the MWCNTs, both on the

external and internal surface of MWCNTs, with no

effect on the porous structure of MWCNTs (Fig. 5b).

The Co and Mo particles in MWCNTs distributed

with the average size of 35 nm (20-50 nm).

3.4. XRD analysis

The immobilized Co and Mo on MWCNTs were

characterized by XRD spectroscopy. In Figure

6. A many peaks can be observed from Co-Mo/

MWCNTs, which was ascribed to the highly

crystalline structure of carbon nanotubes. The

diffraction peaks at 26° and 41° are related to

(002) and (100) planes of hexagonal graphite.

There are, however, no characteristic peaks of Co

and Mo in the XRD pattern of Co/Mo-MWCNTs.

This indicates that Co and Mo are uniform

dispersed on the MWCNTs, and no effect on

XRD spectrum of MWCNTs. The Textural

properties of samples for Co-Mo/MWCNTs and

MWCNTs adsorbents synthesized with the CO-

MO/MWCNTs (Table 3)

Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

Fig. 5b. TEM image of Co-Mo/MWCNTs Fig. 5a. TEM image of MWCNTs

Fig. 6. The XRD analysis for CO/MO-MWCNTs

3.5. Optimization of parameters for removal

mercury

In this work, a novel method was used for the

removal of mercury vapor (Hg0) from air by using

of the Co-Mo/MWCNTs adsorbent. The chamber

was designed to generate a gas containing amounts

of mercury vapor based on O2, and H2O vapor.

For efcient removal of Hg0, the conditions of

proposed method were optimized.

3.5.1.Effect of O2 and H2O

The general procedure was performed with O2 and

H2O vapor for Hg0 removal by Co-Mo/MWCNTs

adsorbent. In presence of O2 and H2O vapor, the

percentages of mercury removal decreased about

4-8%. Due to oxidation of the Co-Mo/MWCNTs,

the surface activity of the adsorbent decreased.

The results showed, the quantitative recoveries

of Hg0 were obtained at the moisture contents

of 0.05-0.22%. By increasing of water vapor

content, slightly decreased the recovery values. By

increasing the O2, the surface morphology of the

Co-Mo/MWCNTs adsorbent was changed due to

the oxidation of Co and Mo nanoparticles. So, the

removal efciency of adsorbent a slightly decreased

at 25oC (5%). On the other hand, the oxidation

process accelerates in high temperature and reduce

the surface area (BET) and the adsorption capacity.

At 35-55 °C, the removal efciency was decreased

from 5% to 25% in present of O2 value.

3.5.2.Effects of Co-Mo/MWCNTs amount and

ow rate

The effect of the Co-Mo/MWCNTs amount on

the mercury removal from air was evaluated

(Fig. 7). It was evaluated with different

amounts of Co-Mo/MWCNTs adsorbent in

the range of 1 to 50 mg. Due to results, the

adsorption of Hg0 was increased more than

25 mg of adsorbent. So, the high recovery for

removal of mercury vapor in air were achieved

more than 95% by 40 mg of Co-Mo/MWCNTs

adsorbent. Also, the MWCNTs adsorbent

had low recovery about 10-14%. Due to high

surface area and metal sites of Co and Mo, the

high absorption capacity was achieved for the

Co-Mo/MWCNTs adsorbent by amalgamation

process (Co-Hg; Mo-Hg).

The mercury vapor was generated in chamber and

mixed with pure air (21% O2; 0.2% of H2O, 0.1-10

μg L-1). The ow rate is a critical role in removal

recovery of mercury, which was directly affected

on interaction and adsorption process. The ow rate

must be tuned to enable a high recovery for mercury

removal from air. So, the effect of ow rates was

evaluated in ranges of 50-500 mL min−1 (25°C). The

results showed us, the best removal efciency was

occurred at ow rates of 50-300 mL min−1 (25°C).

However, it was observed that the absorption

process started to decrease at more than 300 mL

Co-Mo@MWCNTs for removal of mercury from air Danial Soleymani-ghoozhdi

Table 3. Textural properties of samples synthesized with the Co-Mo/MWCNTs

Material SBET (m2 g-1) aV (cm3 g-1) ba(nm)cd (nm)dW (nm)e

MWCNTs 288.84 0.52 5.1 3.85 1.55

CO-MO/MWCNTs 145.16 0.34 4.9 3.8 1.62

a BET specic surface area, b the pore volume, c Unit cell parameter obtained from XRD diffractograms,

d the pore diameter (nm), e Wall thickness(nm)

Fig. 7. The effect of sorbent mass for Hg0 removal

min−1. Therefore, the owrate of 250 mL min-1 was

selected as optimum owrate for mercury removal

by the Co-Mo/MWCNTs adsorbent (Fig. 8).

3.5.3.Effect of temperature

The main role for the adsorption and desorption

of Hg0 by the Co-Mo/MWCNTs and MWCNTs

adsorbents is temperature. So, the effect of

temperature for the adsorption and desorption of

mercury from Co-Mo/MWCNTs adsorbents were

examined in the range of 25–60°C and 50-400°C,

respectively (21% O2, 0.2% H2O; 0.1-10 μg L-1

Hg0).

As Figure 9, the mercury vapor removed from air

at temperatures up to 30 °C. In higher temperatures

the Hg0 adsorption was decreased. Moreover, the

desorption of Hg0 from the Co-Mo/MWCNTs

and MWCNTs adsorbents were obtained at 190-

250 °C. Therefore, the Co-Mo/MWCNTs can be

removed the mercury from air by the amalgamation

interactions at 220 °C (Fig.10).

3.5.4. Adsorption capacity

In-addition the adsorption capacities of mercury

vapor by the Co/Mo-MWCNTs and MWCNTs

adsorbents were evaluated (21% O2, 0.2% H2O; 0.1-

10 μg L-1

Hg0). The mercury vapor was generated

and passed through the Co-Mo/MWCNTs and

MWCNTs adsorbents (40 mg) at the optimized

conditions. The maximum adsorption capacities of

the Co-Mo/MWCNTs and MWCNTs adsorbents for

mercury removal from air were obtained 191.3 mg

g-1 and 22.4 mg g-1, respectively. This mechanism

was related to the interaction of mercury with Mo

and Co which was supported on MWCNTs due to

amalgamation process. The physical adsorption of

MWCNTs (about 20%) and chemical adsorption

by the amalgamation processes (more than 80%)

caused to increase the removal efciency of

mercury from air. In chamber, 40 mg of the Co-Mo/

MWCNTs and MWCNTs adsorbents were placed

on PVC bag and mercury vapor generated/ owed

in column by 250 mL min-1. Then the mercury

concentration in stock PVC bag was determined

by MC-3000. In dynamic system, the adsorption

Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

Fig. 8. The effect of owrate for Hg0 removal

Fig. 10. Effect of temperature on desorption mercury

Fig. 9. Effect of temperature on absortion mercury

capacities of the Co-Mo/MWCNTs and MWCNTs

for mercury removal were found 132.7 mg g-1 and

8.4 mg g-1, respectively which was lower than static

system. The reusability of the Co-Mo/MWCNTs

adsorbent for mercury removal was decreased after

32 times absorption/desorption process.

3.5.5.Method Validation

The ASPAR method was used for the removal

of Hg0 from the air. The method was validated

based on the Co-Mo/MWCNTs and MWCNTs

adsorbent by spiking real samples in present

of air (21% O2, 0.2% H2O; 0.1-10 μg L-1

Hg0).

Due to absorption and desorption process the

concentration of mercury was determined by CV-

AAS at optimized conditions. Also, the validation

of the methodology was followed by MC3000

analyzer. There is no standard reference material

(SRM) for mercury vapor from air, So, the method

validation for Hg0 removal found by spiking of the

standard mercury solutions which was conrmed

the accuracy and precision of the ASPAR method.

The mixture of mercury in pure air (21% O2,

0.2% H2O, 0.1-10 μg), was moved from chamber

to the PVC bags and then moved into the Co-

Mo/MWCNTs and MWCNTs adsorbents. Many

spiked samples based on various concentration of

Hg0 were used in presence of air (Table 4). The

procedure was found for real samples in presence

of air composition which was validated based

on spiking samples and compared to MC3000

analyzer (Table 5). The results showed a simple,

low cost, high recovery and favorite repeatability

for mercury removal from air.

Co-Mo@MWCNTs for removal of mercury from air Danial Soleymani-ghoozhdi

Table 4. Validation of the ASPAR method based on Co-Mo/MWCNTs by spiking of mercury vapour (µg L-1 air)

Sample **HgGS Added *Found Recovery (%)

Air 1 0.102± 0.005 ----- 0.108± 0.006 -----

0.1 0.210± 0.011 102

Air 2 0.532± 0.026 ----- 0.528± 0.025 -----

0.5 1.021± 0.044 98.6

Air 3 1.076± 0.062 ----- 1.009± 0.066 -----

1.0 1.984± 0.096 97.5

Air 4 3.035± 0.145 ----- 2.965± 0.152 -----

3.0 5.882± 0.274 97.2

Air 5 5.578± 0.238 ----- 5.397± 0.255 -----

5.0 10.226± 0.513 96.6

Air 6 10.124± 0.453 ----- 9.965± 0.493 -----

10 20.051± 0.937 100.9

*Mean of three determinations ± condence interval (P = 0.95, n = 3)

** Mercury in HgGS determined by CV-AAS (n=10)

Table 5. Validation of the ASPAR method based on Co-Mo/MWCNTs by spiking of real sample

and compared to MCA (µg L-1 air)

Sample **MCA(µg) Added (µg) *Found (µg) Recovery (%)

Air I 0.402± 0.018 ----- 0.392± 0.022 97.5

0.5 0.882± 0.042 98.0

Air II 0.957± 0.053 ----- 0.962± 0.063 100.5

1.0 1.938± 0.096 97.6

Air III 2.882± 0.144 ----- 2.756± 0.154 95.6

2.5 5.198± 0.268 97.7

Air VI 5.264± 0.246 ----- 5.361± 0.253 101.8

5.0 10.188± 0.483 96.5

Air V 8.016± 0.412 ----- 7.914± 0.388 98.7

10 17.865± 0.832 99.5

*Mean of three determinations ± condence interval (P = 0.95, n = 3)

**Mercury determined by MC3000

3.5.6.Discussion

By the ASPAR method, the mercury removal

from air was achieved based on Co-Mo/MWCNTs

adsorbent and compared to other published

methods (Table 6). Ma et al were investigated on

Hg0 removal by multi-walled carbon nanotubes

supported Fe-Ce mixed oxides nanoparticles (Fe-

CeOx/MWCNTs). The Fe(2) Ce (0.5) Ox/MWCNTs

catalyst showed the best catalytic activity, its

Hg0 removal efciency reached as high as 88.9%

at 240 °C [32]. Also, the removal of Hg0 was

studied based on Mn–Mo/CNT by Zhao et al.

The optimum temperature and MnO2 content for

removal of Hg0 was 250 °C and 5 wt%. Also,

experimental of mercury oxidized by Mn–Mo/

CNT indicated that SO2 could increase mercury

oxidation by this catalyst and that the optimum

temperature for mercury oxidized by Mn–Mo/CNT

decreased to 150 °C [27]. According to the study

of Wu et al, the removal efciency of Hg0 based

on Ce−Mn/TiO2 was investigated by N2, 6% O2

and 500−2000 ppm of SO2. The average removal

efciency of Ce−Mn/TiO2 was obtained about

80% which was lower than Co-Mo/MWCNTs

(more than 95%). Furthermore, the results showed

the reusability of Ce−Mn/TiO2 was achieved for

10 times (adsorption/desorption cycles)which was

lower than the Co-Mo/MWCNTs adsorbent with

32 times [2]. Ma et al showed the Hg0 removal

from ue gas with Ag-Fe3O4@rGO composite. The

Hg0 was efciently removed higher than 92% at

100 °C, which was lower than Co-Mo/MWCNTs

[26]. Yang et al was studied on Hg0 removal from

air based on Fe3-xMnxO4/CNF. The results showed

that at the optimal temperature (150–200 °C), the

removal efciency for Hg0 was attained above 90

% [28]. Xu et al showed that ultrasound-assisted

impregnation promoted Hg0 removal with Cu-Ce/

RSU. the optimal Cu/Ce molar ratio, loading value

and reaction temperature were 1/5, 0.18 mol L-1 and

150 °C, respectively. Also, the highest Hg0 removal

efciency obtained was 95.26%. As compared to

Co-Mo/MWCNTs, the removal efciency of Cu-

Ce/RSU was lower value [24]. In another study,

Xu et al synthesized MnOx/graphene composites

for the removal of Hg0 in ue gas. MnOx/graphene

sorbents with 30% graphene showed that the Hg0

removal efciency was achieved more than 90%

at 150 °C (4% O2). Furthermore, MnOx/ graphene

showed an good regenerative ability [25]. Liu et al.

prepared Co/TiO2 catalysts for Hg0 removal. results

showed that the optimal loading of Co was 7.5%.

The Hg0 removal efciency was reached more than

90% at the temperature range 120–330 °C [35].

Anal. Methods Environ. Chem. J. 5 (1) (2022) 22-35

Table 6. Comparing of ASPAR method for the mercury removal from air based on Co-Mo/MWCNTs

with other published methods

Adsorbent Mechanism/method Sample Adsorption

capacity

Removal

Efciency

Ref.

Mn–Mo/CNT chemisorption Flue gas -- 80% [27]

Ag-CNT Amalgamation Flue gases 9.3 mg g-1 --- [40]

Silver nano particles/

MGBs Amalgamation/SPGE Air/Articial Air 91.8 mg g-1 98% [41]

NPd@MSN amalgamation/adsorption Air 149.4 mg g-1 95% [42]

Mn/MCM-22 catalytic oxidation and

chemisorption Flue gas 300 mg g-1 92% [43]

Cu-Zn/SBA-15 Adsorption Natural Gas 12.75 mg g-1 100% [44]

Co-Mo/MWCNTs Amalgamation Air 191.3 mg g-1 98% This study

4. Conclusions

In this research, a novel Co-Mo/MWCNTs adsorbent

was used for mercury removal from air by the ASPAR

method and nally mercury was measured by CV-

AAS. First the mercury vapor generated by HgGS

(0.1-10 μgL-1 air), mixed with pure air (21% of O2 and

0.2% of H2O) and moved to column which was lled

with the Co-Mo/MWCNTs adsorbent. The mechanism

of absorption was obtained by amalgamation Co and

Mo. The best thermal desorption was occurred at 220

°C. Due to results, the mean recovery, the reusing

and adsorption capacity were obtained 98.8%, 32,

191.3 mg g-1, respectively. The range of adsorption

efciencies for ten air samples with 40 mg of the Co-

Mo/MWCNTs adsorbent was achieved between 94.6-

102.4 in optimized conditions. The O2 content may be

affected by oxidation of Co or Mo and can reduce the

mercury adsorption by the adsorbent by about 5-10%.

The ASPAR method was validated by spiking samples

and MC3000 analyzer.

5. Acknowledgements

The authors thanks from department of occupational

health and safety at work and department of

biostatistics and epidemiology, Kerman University

of Medical Sciences (KUMS), Kerman, Iran.

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Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Management and removal of nitrate contamination of water

samples based on modied natural nanozeolite before

determination by the UV-Vis spectrophotometry

Bahareh Azemi Motlagha, Ali Mohammadia,* and Mehdi Ardjmand b,c

a Department of Natural Resource and Environment, Science and Research Branch, Islamic Azad University, Tehran, Iran

b Chemical Engineering Department, South Tehran Branch, Islamic Azad University, Tehran, Iran

c Nanotechnology Research Center, South Tehran Branch, Islamic Azad University, Tehran, Iran

ABSTRACT

Nitrate is a hazardous substance for human health, the removal of

which is an important environmental priority. Therefore, in this study,

rst, the sources of nitrate pollution of water were investigated, then

the structure, role, and application of nanozeolites for the removal

of nitrate ions were studied by the analytical method. Also, the

presentation of management solutions, identication of polluting

industrial sectors, different methods of removal and fabrication

of ZSM-5/Fe/Ni nanosorbents, and the determination of optimal

conditions for nitrate removal were investigated by experimental

design software and graphical analysis of effective parameters.

The results of graphical analysis of laboratory method showed us,

the highest nitrate removal efciency at a residence time of 150

minutes, pH 3, 4 g L-1 adsorbent, and 40 mg L-1 nitrate were achieved

(%RE:91.5-97.4). Experimental results indicate the high efciency,

absorption capacity, and effectiveness of ZSM-5/Fe/Ni adsorbents for

nitrate removal in waters. Finally, the absorbance values or nitrate

concentrations between 20-120 mg L-1 were measured by the UV-Vis

spectrophotometry. The maximum absorption capacity of ZSM-5/Fe/

Ni adsorbents for nitrate was obtained 136.7 mg g-1. The developed

method based on a novel ZSM-5/Fe/Ni adsorbents has many

advantages such as simple, low cost, high efciency, and favorite

recovery of more than 90% for removal nitrate in water samples by

nanotechnologies as compared to other reported methods.

Keywords:

Removal,

Nitrate,

Adsorption,

Water samples,

Nanozeolite,

UV-Vis spectrophotometry

ARTICLE INFO:

Received 20 Nov 2021

Revised form 17 Jan 2022

Accepted 23 Feb 2022

Available online 28 Mar 2022

*Corresponding Author: Ali Mohammadi

Email: ali.mohammadi@srbiau.ac.ir

https://doi.org/10.24200/amecj.v5.i01.165

------------------------

1. Introduction

Nitrate and nitrite compounds are important factors

in groundwater pollution. Due to the lack of

nitrication of municipal, industrial and agricultural

wastewater, its average amount is increasing.

Therefore, various methods such as adsorption,

ion exchange, reverse osmosis, chemical, and

biological methods are used [1-3]. Banu et al Have

identied the chitosan beads (CS) technique as an

efcient biosorbent for the removal of toxic anions

from aqueous solutions. In this study, zirconium

encapsulated quaternary chitosan beads (Zr@CSQ)

were prepared and used to remove nitrate and

phosphate ions from the prepared water. Zr@CSQ

beads were identied by a sequence of analytical

techniques, including XRD, SEM, EDAX, BET,

FTIR, and TGA-DSC analysis. Various kinetic

models and known Langmuir, Freundlich, and

Dubinin-Radushkovich (D-R) isotherm models

have been used to dene the isotherm [4]. Revilla

et al Studied the removal of nitrate from aqueous

solutions using adsorption-activated biochar

from municipal solid waste (MSWAB). Initially,

municipal solid waste (MSW), another important

source of environmental pollution, was used as a

raw material for biochar production, which was

activated using potassium hydroxide to produce

MSWAB. MSWAB activation increased the level

from 2.5 to 6.5 m2/g. Then, the effect of initial

nitrate concentration (A), pH (B), and adsorbent

dose (C) on nitrate removal was evaluated using

a 2K factorial experimental design. The results

showed that the initial nitrate concentration, pH,

and bilateral interactions of AB and AC have a

signicant effect on nitrate removal [5]. Liyun Yang

et al reported a new modied steel slag for nitrate

removal from water. Steel slag (SS) has been used

to remove nitrate pollution from the liquid phase.

They prepared and activated SS by mixing steel

with aluminum hydroxide and deionized water at

800 ° C. The physicochemical properties of steel

scrap before and after modication were also

investigated to compare the effect of their surface

properties on nitrate adsorption behavior, contact

time, adsorbent dose effects, and pH effects on

it. The results showed that nitrate uptake was

signicantly increased due to the increase in

the specic surface area of the modied waste

compared to the unmodied type. They reported

the optimal parameters for nitrate removal with

this adsorbent: 20 mg L-1 nitrate concentration, 1 g

per 100 mL adsorbent, and 180 min residence time

in Freundlich adsorption isotherm [6]. In another

study, Caterji et al Investigated the uptake of nitrate

on bisulfate-modied chitosan seeds. The results

showed that cross-link and capacity modication

increased uptake compared to conventional

chitosan seeds. The maximum absorption capacity

relative to the crosslink is 0.4. The maximum

modied NaHSO4 concentration capacity was

reported to be 0.1 mM. The maximum nitrate

uptake was 104 mg g-1 at pH 5. It also corresponds

to the Freundlich isotherm model [7]. Betangar et

al used nano-alumina to remove nitrate from water.

Their study studied the parameters of contact

time, pH, and nitrate concentration with a pseudo-

second-order kinetic model. The highest nitrate

removal was observed at a concentration of 4 mg/g,

a temperature of 23-27°C, and a pH of 4.4. The

Langmuir isotherm model was used to study nitrate

uptake. This study showed that nano-adsorbent

nanoalumina is useful and effective for the removal

of nitrate from aqueous solutions [8]. Morado

et al removed nitrate in water with zero-capacity

iron and copper/iron nanoparticles. Zero-capacity

iron and copper/iron particles in this study were

fabricated by reducing sodium bromide at room

temperature and atmospheric pressure. The results

showed an increase in the rate of nitrate reduction

by copper/iron particles so that the residence time

of nitrate removal was reduced from 150 minutes

to 60 minutes [9]. Hanache et al Developed an

anion exchange ZSM-5 nanocatalyst modied with

a cationic surfactant. This study showed that the

larger the surface area of this nanocatalyst and the

smaller the particle size, the higher its adsorption

and properties. This modied nanocatalyst has

been shown to have a high adsorption capacity and

is modied by surfactants. The adsorption kinetics

of this system is consistent with the Pseudo-Second

isotherm model [10]. Due to the effectiveness of

the adsorption method to remove nitrate and the

existence of many sources of zeolites in our country,

which can act as a suitable substrate for adsorption

due to their high porosity and high specic surface

area. In this study, the management strategies of

nitrate ion removal by interviewing several experts

and also the removal of this ion through adsorption

by ZSM-5 nano zeolite functionalized with iron

and nickel metals will be investigated. Also, in this

study, the management methods of ion removal

were reviewed and discussed through interviews

with active experts in the water and wastewater

industry. Several analytical methods such as high-

performance liquid chromatography [11] and

spectrophotometric [12] have been used for nitrate

analysis in waters. The Association of analytical

chemists announced that the spectrophotometric

method is the favorite determination of Nitrite and

Nitrate in waters [13]. The 3D image of nitrate ion

Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents Bahareh Azemi Motlagh et al

38 Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

was shown in Figure 1.

Moreover, the metals such as Al, Sn, Zn, Fe,

and Ni are effective agents for remediation of

contaminated groundwater. Hence the present study

was tested based on iron functionalized on ZSM-

5 nanozeolite for removal nitrate in waters due to

its availability, inexpensiveness, non-toxicity, high

efciency, and rapid reaction in the decomposition

of contaminants. In addition, nitrate concentration

was determined by the UV-Vis spectrophotometry

and the optimal conditions based on effective

factors for nitrate removal, including pH, contact

time, and adsorbent dosage were evaluated.

Fig.1. The 3D image of nitrate ion

2. Experimental

2.1. Material

The ZSM-5 nanozeolite powder (from the Zeolites

family) was purchased from Sigma Aldrich with

a crystal size of 0.5 μm and a pore size of 5.5A0.

Ferric chloride (FeCl3), sodium hydroxide (NaOH),

potassium nitrate(KNO3), hydrochloric acid (HCl),

and %98 sulfuric acids (H2SO4) were also obtained

from Merck Germany.

2.2. Characterization

X-ray diffraction (XRD, STADI-P, the USA) was used

to investigate ferrous (Fe) metals in the nanozeolite

structure functionalized with these metals. Brunauer-

Emmett-Teller (BET) surface area analysis (Belsorb

apparatus, Japan) was used to determine the SSA of

nanozeolite particles. The concentration of nitrate

was measured with Spectrophotometer UV-Vis Hach

model Dr2800 was used.

2.3. Preparation of ZSM-5/Fe/Ni nanosorbent

To Preparation the functionalized ZSM-5

nanozeolite, the rst 2.5 g of ZSM-5 nanozeolite

powder was placed in the furnace at a temperature

of 500°C for 4 hours and calcined. Then, 0.5 g of

ferric chloride (FeCl3) powder was dissolved in

distilled water twice for one hour, added to the

calcined ZSM-5 nanozeolite powder and mixed

for another 30 minutes, and ltered with a lter

paper. The resulting powder was rinsed three times

with distilled water and placed in an oven at a

temperature of 80°C for 2 hours. Next, the powder

was separated from the lter paper and re-calcined

at a temperature of 500°C for 4 hours. To produce

ZSM-5/Fe/Ni nanozeolite powder, ZSM-5 was

rst doped with Fe as previously mentioned, and

then 0.5 g of nickel sulfate (Ni2SO4) powder was

dissolved in deionized water for one hour. Next, the

calcined ZSM-5/Fe nanozeolite powder was added

and stirred for 30 minutes. Afterward, the solution

was ltered and the powder was washed three

times with distilled water and placed in an oven at

a temperature of 80°C for 2 hours. The resulting

powder was re-ltered and placed in the furnace at

a temperature of 500°C for 4 hours [14].

2.4. Preparation of solutions and procedure

To prepare a standard concentrated potassium

nitrate solution, 7 g of anhydrous KNO3 was dried at

100°C for an hour. After cooling, 1.805 g of KNO3

was dissolved in a volumetric ask and diluted to

250 ml, thus preparing a standard solution of 1000

mg L-1 or 1 mg mL-1. HCl and NaOH solutions

were prepared to set the pH values. Then, nitrate

solutions with concentrations of 20, 40, 60, 80,

100, and 120 mg per liter were prepared from the

standard solution of potassium nitrate 1000 mg L-1

[15]. In this research, the experimental design table

was rst provided using the effective variables of

pH, contact time, and stirring speed in the intervals

dened to RSM and the central composite design

(CCD) by Design Expert.7 software. Then, the

value of each parameter was provided according

to the experimental design table and nally, the

absorbance values or nitrate concentrations in

Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents Bahareh Azemi Motlagh et al

water samples were measured by the UV-Vis

spectrophotometry. A UV-Vis spectrophotometer

(Thermo Fisher, GENESYS, 140/150 Vis/UV-

Vis Spectrophotometers) was used to collect

absorbance data from 190 to 1100 nm. Due to the

comparatively low concentrations and absorbance

of NO2 −, all the samples were measured in a 2-4

cm quartz cuvette. DW was used as the reference.

The spectral resolution was set as 1-2 nm. A higher

resolution (0.3–1 nm) yields similar results. The

results were analyzed by experimental design

software, and the optimal values of pH, contact

time, and stirring speed were determined.

3. Results and Discussion

3.1. XRD characterization

The XRD spectrum for the ZSM-5/Fe/Ni nanozeolite

conrms the presence of iron and nickel particles

doped with silicate particles (Fig.2a-2c). The XRD

spectrum for the ZSM-5 nanozeolite conrms the

silicate particles (Fig.2a) and iron in ZSM-5/Fe

(Fig.2b) and iron and nickel in ZSM-5/Fe/Ni (Fig.2c)

Fig.2a. The XRD spectrum for ZSM-5

Fig. 2b. The XRD spectrum for ZSM-5/Fe

3.2. BET characterization

By comparing the BET parameter as in Figure 3

and Table 1. In each of the four BET analysis

curves of the nanozeolite, the highest SSA was

related to the zeolite functionalized with Fe and Ni

metal (ZSM-5/Fe/Ni, which was determined to be

418.76 m2 g-1).

Fig. 2c. The XRD spectrum for ZSM-5/Fe/Ni

Fig. 3. BET curves of the prepared nanosorbent.

ZSM-5 ZSM-5/Fe/Ni

Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

3.3. Optimization and experimental design

In this research, the experimental design using

RSM in combination with the CCD method was

performed to investigate the effects of inuential

variables of pH (range: 2-8) (A), contact time

(30-180 minutes) (B), and adsorbent dosage (1-5

g L-1) (C) on nitrate removal efciency. Due to

the extensive use of research on (A), (B), and

these parameters as effective factors were used

for optimizing nitrate removal [16-17]. The RSM

method is a mathematical and statistical method

used for the analysis and empirical modeling of

problems where a given answer is inuenced by

several variables and the RSM can be calculated to

determine the optimal conditions. One advantage

of this method is to reduce the number of empirical

tests which was performed to obtain statistically

valid results. In addition, the RSM method can

also analyze the interactions between variables. By

optimizing parameters, the result can report more

comprehensive and accurate data by performing

the least number of experiments [18-19]. In this

study, Table 2 showed the range of independent

variables and design levels of the experiments

examined. The results of the complete design of

the test and the exact responses of the tests used

are also listed in Table 3.

According to the results of the data analysis in

Table 4, a quadratic function model can t well

to the empirical results. The t of this model was

evaluated by Analysis of Variance (ANOVA),

normal probability plot, and residual analysis. The

quadratic function for nitrate removal efciency is

expressed as follows:

% Removal Nitrate = 51.29-(10.17× A)+(4.13×

B)-(3.51 × C)+(11.69 × D)+(5.16 × A × B)+(3.69×

A × C)-(0.056 × A ×D)+(2.84× B × C)+5.59× B ×

D)- (2.43 ×C × D)+(0.47 × A2)+(0.83 × B2)+(2.81

× C2)- (1.28 × D2)

In Table 4, the ANOVA analysis showed the

importance of each parameter in response to nitrate

removal by P and F values. The smaller the P-value,

the higher its impact factor and its contribution to

the response variable. The P values less than 0.05

indicate that the model expressions are signicant.

The P values of more than 0.1 indicate that the

model terms are insignicant. Accordingly, the

seven terms of (AC), (BD), and (C2) are signicant

parameters of the model and have the greatest

effect on nitrate removal efciency. The P values

of the other terms were greater than 0.05, which

means that their effect on the response model was

not statistically signicant.

Figure 4 shows the residual curve in terms of

the predicted response for the response of nitrate

removal efciency. This Figure shows that all

empirical data are uniformly distributed around

the mean response variable. This indicates that

the proposed model is sufcient and there has

Table 2. Factors and levels for CCD study

Level pH Temperature Time

-α

-1

+α

-22.4874

472.487

-4.31981

59.3198

-13.7046

86.7046

Table1. The specic surface area of the prepared nanozeolite

Unit

BETNanocatalystsRow

m2 g-1

m2g-1

374/66

418/76

ZSM-5

ZSM-5/Fe/Ni

Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents Bahareh Azemi Motlagh et al

Desi g n-Expert® Software

%R emoval Nitrate

Color points by value of

%R emoval Nitrate:

93.51

21.13

Predicted

Internally Studentized Residuals

Residuals vs. Predicted

-3.00

-1.50

0.00

1.50

3.00

22.33 40.12 57.90 75.68 93.47

Table 3. Experimental range and values of different variables studied.

standard Run Block pH Time

(Min)

Nitrate

(mg L-1)

Absorbent

(g L-1)

%Removal

Nitrate(mg L-1)

5 1 Block 1 7 60 40 4 46.62

7 2 Block 1 3 150 100 4 78.11

11 3 Block 1 5 105 70 3 51.42

8 4 Block 1 3 60 40 2 68.27

12 5 Block 1 5 105 70 3 51.19

1 6 Block 1 7 150 100 2 43.28

10 7 Block 1 5 105 70 3 49.41

3 8 Block 1 7 60 100 4 39.56

9 9 Block 1 5 105 70 3 54.12

6 10 Block 1 3 60 100 2 58.34

211 Block 1 7 150 40 2 30.47

4 12 Block 1 3 150 40 4 91.51

14 13 Block 2 8 105 70 3 29.19

17 14 Block 2 5 105 20 3 60.73

20 15 Block 2 5 105 70 5 57.16

22 16 Block 2 5 105 70 3 50.92

21 17 Block 2 5 105 70 3 51.69

15 18 Block 2 5 30 70 3 37.48

18 19 Block 2 5 105 120 3 45.33

13 20 Block 2 2 105 70 3 67.11

19 21 Block 2 5 105 70 1 18.81

16 22 Block 2 5 180 70 3 58.25

Fig. 4. The residual value curve in terms of the predicted response

Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

Table 4. Experimental design and actual results of nitrate removal efciency.

Sum of Mean F p-value

Source Squares dF Square Value Prob > F

Block 346.13 1 369.12

Model 5119.11 13 331.08 18.81 0.0007 significant

A-pH 714.14 1 713.46 35.61 0.0007

B-Time 121.42 1 121.29 6.59 0.0354

C-gr nitrate 176.02 1 176.14 11.41 0.0181

D-gr absorbent 809.74 1 783.41 42.12 0.0005

AB 94.18 1 95.13 4.26 0.0576

AC 105.00 1 106.63 5.09 0.0413

AD 0.011 1 0.011 6.417E-004 0.9563

BC 73.61 1 66.57 3.94 0.0791

BD 107.46 1 103.34 7.16 0.0465

CD 62.52 1 58.49 2.83 0.1017

A2 3.93 1 3.83 0.62 0.6173

B2 13.17 1 13.41 0.51 0.4019

C2 157.63 1 162.83 7.68 0.0238

D2 43.08 1 47.19 2.36 0.1609

Residual 105.38 5 19.04

Lack of Fit 83.59 3 40.56 8.17 0.0381 significant

Pure Error 18.53 3 4.69

Cor Total 5568.06 23

been no deviation from the hypotheses made. As

can be seen in Table 5, the difference between the

adjusted R2 and the predicted R2 is less than 0.2

and the precision of the model is 19.461 (which

is greater than 4), indicating the used model is

accurate.

Figure 5 shows a comparison between the actual

response values obtained from the empirical

results and the predicted response values obtained

from the quadratic function model equation. It is

observed that the model describes the empirical

results and data fairly accurately, meaning that it

has been successful in comparing the correlations

between the three variables. In addition, there is

a sufcient correlation with the linear regression

coinciding with the R-value of about 0.94612.

Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents Bahareh Azemi Motlagh et al

Figure 6 shows the three-dimensional interaction

curves of contact time, pH, adsorbent dosage, and

initial nitrate concentration for nitrate removal

efciency. The highest nitrate removal efciency

was reported at the contact time of 150 min, pH

value of 3, an adsorbent dosage of 4 g L-1 and an

initial concentration of 40 mg L-1. Analysis of

the diagrams in Figure 6 revealed higher nitrate

removal efciency at lower pH values and longer

contact times.

Table 5. Model equation statistical parameters for ANOVA model for nitrate removal efciency

ValueType of variables

3.79Std. Dev.

0.94612R-Squared

51.14Mean

0.9056Adj R-Square

7.18C.V. %

-3.0346Pred R-Squared

25147.62PRESS

19.461Adeq Precision

Desig n-Expert® Software

%Removal Nitrate

Color points by value of

%Removal Nitrate:

93.51

21.13

Actual

Predicted

Predicted vs. Actual

21.00

39.25

57.50

75.75

94.00

21.13 39.23 57.32 75.42 93.51

Fig. 5. Comparison between predicted and actual empirical values of nitrate removal efciency.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48



Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents



*Corresponding Author: Ali Mohammadi

Email: ali.mohammadi@srbiau.ac.ir

https://doi.org/10.24200/amecj.v5.i01.165

16



AD

BE

CF

100

39.5

62.5

%Removal Nitrate

A: pH C: gr nitrate

105

127

150

37.75

47.5

57.25

%Removal Nitrate

A: pH B: Time

34.25

47.5

60.75

%Removal Nitrate

A: pH D: gr absorbent

105

127

150

100

%Removal Nitrate

B: Time C: gr nitrate

100

33.75

46.5

59.25

%Removal Nitrate

C: gr nitrate D: gr absorbent

105

127

150

%Removal Nitrate

B: Time D: gr absorbent

Fig. 6. 3D response surface method curves of nitrate removal efciency

Removal of nitrate in water by ZSM-5/Fe/Ni adsorbents Bahareh Azemi Motlagh et al

4. Management

According to the interviews conducted with active

experts in the water and wastewater industry, the

following items can be suggested as management

strategies to remove and monitor nitrate ions

from the source. According to the survey and

statistical analysis of the interviewees, the highest

amount of suggestions was related to the use of

new technologies and nanosorbents (%85). Also,

this procedure can be suggested as a management

strategy to remove and monitor nitrate ions from

the source. According to the survey and statistical

analysis (Fig. 7 and Table 6), the highest number of

suggestions was related to using new technologies

and nanosorbents (%85).

*Identication of nitrate pollution-producing

industries through sampling and testing

*Continuous instantaneous monitoring of efuents

of different industries

*Establishment of nitrication unit in the efuent

reservoirs of petrochemical industries and use of

expert experts to manage it

*Transfer of efuent to the central treatment plant

of industrial sites for re-treatment

*Designing the capacity of the central treatment

plant in proportion to the amount of input and

pollution of petrochemical units in the region to

apply the conditions of complete nitrication

*Perform frequent inspections of various industries

*Prevent the activity of polluting industries

Table 6. Percentage of the importance of the proposed solutions

of the interviewees to remove nitrate

PercentageCases

71Pre-purication

71Nitrication unit

85New technologies and nanosorbent materials

42Online monitoring

42Experienced experts

14Renery capacity

57Frequent inspections

Fig.7. The percentage of importance of the proposed solutions of the interviewees to remove nitrate

Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

5. Conclusions

This study showed that the use of chemical

fertilizers, lack of control of wastewater, including

municipal, industrial, especially wastewater

from food production plants and animal waste,

and the entry of treatment plant efuents without

applying the nitrication process are important

sources of mixing nitrate with groundwater. It

can be controlled by the following management

methods. It can be eliminated by various executive

methods such as adsorption, ion exchange, reverse

osmosis, chemical and biological methods such

as thermal hydrolysis, solar photocatalysis, and

microbial fuel cells. According to the results of

the analysis of three-dimensional diagrams, the

highest nitrate removal efciency (91.51%) was

reported at a residence time of 150 minutes, pH 3

and 4 g L-1 of sorbent, and 40 mg L-1 nitrate which

indicates the high efciency and effectiveness of

this nanosorbent in nitrate removal. Therefore,

nanosorbent (ZSM-5 /Fe/ Ni) can be introduced

as a promising adsorbent to remove nitrate from

efuents. As compared to other studies, this

nanosorbent is cheaper due to its abundance in

the soils of our country, and in most cases, has a

higher efciency than others in removing nitrate.

Another advantage of the proposed method is to

use of the experimental design method with Design

Expert.7 software, which will reduce the number of

experiments performed by statistical and software

methods. By procedure, the use of materials and

nanosorbents was greatly reduced. The main

difference and advantage of ZSM-5 /Fe/ Ni

nanosorbents with other adsorbents is completely

green and environmentally friendly. Another

advantage of the present study is the management

methods for removing this ion through interviews

and the presentation of management solutions.

6. Suggestions

Due to the widespread use of nanozeolites as

adsorbents for nitrate, nitrite, and heavy metals

from aqueous media in various articles, it can be

used in future research for the removal of heavy

metals in waters.

7. Acknowledgments

The authors would like to thank and appreciate Dr.

Mostafa Hassani.

8. References

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Anal. Methods Environ. Chem. J. 5 (1) (2022) 36-48

Anal. Method Environ. Chem. J. 5 (1) (2022) 49-60

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Measurement of heavy metals in soil, plants and water

samples based on multi-walled carbon nanotube modied

with Bis(triethoxysilylpropyl)tetrasulde by ame atomic

absorption spectrophotometry

Mohammad Reza Rezaei Kahkhaa, Ahmad Salarifarb,*, Batool Rezaei Kahkhaa

a Department of Health Engineering, Zabol University of Medical Sciences, Zabol, Iran.

b Environmental Engineering Department, Faculty of Natural Resources, Islamic Azad University, Bandar Abbas Branch, Iran

ABSTRACT

Heavy metals (HMs) are considered as the major environmental

pollutants that accumulated in soil and plant. Consumption of such

contaminated plants by humans and animals would ultimately harm

the health of communities. This study aims to evaluate the amount

of copper(Co), cadmium(Cd), and lead(Pb) in soil and cultivated

plants that are irrigated by the city of Zabol’s wastewater. Also,

the heavy metals determined in 20 mL of Zabol’s water based on

Bis(triethoxysilylpropyl)tetrasulde (S4[C3H6Si(OEt)3]2, TEOSiP-

TS) modied on MWCNTs as an adsorbent by the uniform dispersive

-micro-solid phase extraction (UD-µ-SPE) at optimized pH. In this

study, 52 samples including wheat, corn grain, and wild spinach, as

well as agricultural soil were selected randomly from three village

stations. The concentrations of heavy metals in plants, soils, and water

samples were measured using a ame atomic absorption spectrometer

(F-AAS). The one-way ANOVA test was applied to compare the mean

value of heavy metals at the three mentioned stations. The results

indicate that the amount of lead at all three stations and in all types

of plants exceeds the permissible range. The amount of copper in

plant species and water is lower than the permitted range, while it is

higher in agricultural soil. By optimizing parameters, the linear range

(LR) and the detection limit (LOD) of Cu, Cd, and Pb were obtained

1.5-1000 μg L-1, 1-200 μg L-1, 5-1500 μg L-1 and 0.5 μg L-1, 0.25 μg

L-1, 1.5 μg L-1, respectively in water samples (RSD%<2). This study

indicates that irrigation of agricultural elds using wastewater causes

the accumulation of heavy metals in soil and plants.

Keywords:

Heavy Metals,

Environment sample,

Bis(triethoxysilylpropyl)tetrasulde,

Uniform dispersive -micro-solid phase

extraction,

Flame atomic absorption spectrophotometer

ARTICLE INFO:

Received 17 Nov 2021

Revised form 23 Jan 2022

Accepted 12 Feb 2022

Available online 28 Mar 2022

*Corresponding Author: Ahmad Salarifar

Email: salarifar562@gmail.com

https://doi.org/10.24200/amecj.v5.i01.167

------------------------

1. Introduction

Heavy metals(HMs) as hazardous elements,

caused by human activities in different sections

of industry, agriculture, and business. It has been

discharged for years into the ecosystem and has

polluted water, soil, and agricultural farms. Also,

heavy metals have endangered the health of

humans and other creatures [1]. Heavy metals enter

the environment on a large scale through natural

and human-made resources. The releasing amount

of heavy metals to the environment is considerable

[2]. The rst inuencing element of metal pollution

in an ecosystem is the existence of heavy metals

in the biomass of polluted areas which endangers

human health. One of the most fundamental issues,

50 Anal. Methods Environ. Chem. J. 5 (1) (2022) 49-60

in terms of heavy metals, is that body does not

metabolize them [3]. This would cause several

diseases and complications in the body. In general,

neurological disorders (Parkinson’s, Alzheimer’s,

depression, schizophrenia), various cancers,

nutrient deciency, and hormones imbalance are

the results of heavy metals amass in the human

body [4]. Some analytical techniques were used for

the measurement of HMs in environmental samples

such as atomic absorption spectrophotometry [5,6],

laser-induced breakdown spectroscopy [7], X-ray

uorescence spectroscopy [8], and electrochemical

methods [9]. Among these techniques, atomic

absorption spectrophotometry has a very advantages

such as simplicity, effectiveness, reliability, and low

detection limit[10]. Zabol’s urban wastewater is

used in some villages to irrigate agricultural farms

at the time of drought. In this study, to evaluate the

amount of heavy metals lead, copper, and cadmium

in agricultural soil and cultivated plants, such as

wheat, corn, and a species of wild spinach, which

are irrigated with wastewater, three stations were

selected in which the irrigation of agricultural

elds with wastewater is common. After wheat

sampling and given that most of the planted wheat

used to feed livestock in late winter or early spring

is immature, the root of the plant was separated

and all methods of sample preparation were

applied to analyze the plant, without considering

other parts of it. A similar approach was applied

to grain corn. Wild spinach is a volunteer plant in

wheat elds, and as it is used widely in the Sistan

region for the purpose of cooking a type of local

food during fall and winter, it was sampled from

mentioned stations in order to evaluate the heavy

metals accumulation. Recently, many adsorbents

such as graphene/graphene oxide [11], CNT [12],

activated carbon [13 ], and silica pours [14] were

used for extraction HMs in water samples. Also

functionalized nanocarbon structures were also

reported for extraction heavy metals in water, plant

and soil samples [15]. In addition, the different

technology such as, liquid-liquid extraction [16],

dispersive ionic liquid –liquid extraction [17],

dispersive micro solid-phase extraction [18], and

magnetic solid phase extraction were presented for

water samples. In this study, the plants and soil

samples were analyzed with F-AAS after sample

digestion procedure and water samples determined

after sample preparation method based on TEOSiP-

TS@MWCNTs adsorbent by the UD-µ-SPE

procedure.

2. Materials and Methods

2.1. Sampling and reagents

This research is conducted to evaluate the number

of heavy metals such as lead, copper, and cadmium

in three different types of plants, i.e. wheat, corn,

and spinach, as well as in agricultural soil of

selected elds. Given that use of wastewater in

irrigation is performed in only three stations of

Zabol in the east of Iran, and taking the extent

of farmland areas, in total 52 samples were

selected from all stations. Samples were randomly

collected in June 2020 and February 2021. The

water sample was prepared from Zabol by a

clean glassy tube (100 mL) which was acidied

with HNO3 (2%) and ltered by Whatman lter

Sigma, Germany (200 nm) by ASTM method for

sampling of waters. The calibration of copper(Co),

cadmium(Cd), and lead(Pb) in soil, cultivated

plants, and water solution was prepared daily

by appropriate Co(II), Cd(II), and Pb(II) stock

solution (1000 mg L-1) in Deionized water (DW,

Millipore, USA) which was purchased from

Sigma, Germany. The acid solutions such as HCl,

H2SO4, and HNO3 were purchased from Sigma,

Germany. The bis(triethoxysilylpropyl)tetrasulde

(S4[C3H6Si(OEt)3]2, TEOSiP-TS, CAS N:40372-

72-3) was purchased from Merck, Germany.

2.2. Synthesis of Adsorbent

The modication of the Bis(triethoxysilylpropyl)

tetrasulde (S4[C3H6Si(OEt)3]2, TEOSiP-TS) on

the surface of MWCNTs nanostructure has shown

in Figure 1. By the acid treatment methods (HNO3

& H2SO4), the carboxylic acid-functionalized

MWCNTs (MWCNTs-COOH) were synthesized

based on previously reported papers [19]. By

reducing the COOH to the OH groups, MWCNTs@

Measurement of heavy metals by Nanotechnology Mohammad Reza Rezaei Kahkha et al

OH created. By stirring, 5 g of MWCNTs-COOH

mixed with 0.5 g of NaBH4 and CH3OH in a

100 mL ask condenser. Then, the mixture was

reuxed for 3 h and then it was cooled in room

temperature after 2 h. Finally, the MWCNTs-OH

nanomaterials were ltered with a Whatman lter

and washed many times with the methanol/DW.

For the synthesis of the EOSiP-TS@MWCNTs

adsorbent, 2 g of MWCNTs-OH were added to a

solution of Bis(triethoxysilylpropyl)tetrasulde

(TEOSiP-TS) in presence of toluene in a 100

ml round-bottom ask equipped with magnetic

stirring, and then the mixture was heated at 80 °C

for 3.5 h by Ar gas. Finally, the TEOSiP-TS @

MWCNTs product was ltered with a Whatman

lter.

2.3. Sample preparation

Soil samples were collected from the depth of

2 cm. Polyethylene sampling containers were

initially washed with detergent powder and then

kept in a container containing 5% nitric acid for a

certain period (acid washing). Then, it was rinsed

with ionized water. Plant samples were collected

inside polyethylene bags, then transferred to the

laboratory, and after that completely washed with

three-time distilled water to eliminate potential

pollutions.

Afterward, the samples were dried up at room

temperature. Dried samples were milled and

completely crushed and then passed through a

sieve with a pore diameter of approximately 0.5

mm. The milled plant samples were placed inside

clean glass containers and were dried again at 65°C

for 24 hours. For digestion of plant sample, 2g of

milled dried samples were placed inside a round-

bottom ask, and then concentrated perchloric

acid (4ml), concentrated sulphuric acid (2ml),

and concentrated nitric acid (20ml) were added,

respectively. The above solution was heated to

boil carefully under a hood and over a heater to

reduce its volume. In the next step, 20ml water

was added to dissolve the sediments, and heated

up again to reduce their volume. Afterward, the

solution was ltered and its volume was reduced

to 250ml. Soil samples were completely oven-

dried for 24 hours in the laboratory at 70°C. In

the next stage, they were sieved and milled to

obtain a completely smooth powder. 0.5 g of the

above sample was prepared to be injected into the

device, using the complete digestion method [20-

22]. After digestion, all samples were analyzed

with F-AAS.

2.4. Analytical measurement

Flame atomic absorption spectroscopy (F-AAS,

Agilent 55B-AA) was used to measure all elements

in the sample. To obtain the required sensitivity in

measurements, air/acetylene ame was applied. In

order to ensure the accuracy of evaluation, each

measurement was performed three times on each

sample, and standard deviation and mean of data

were obtained. One-way analysis of variance

was used to compare the average heavy metals

content in various types of selected plants at those

three stations. The instrumental conditions for the

determination of Cu, Pb, and Cd by F-AAS have

explained in Table 1.

Fig. 1. Synthesis of EOSiP-TS@MWCNTs adsorbent by the Bis(triethoxysilylpropyl)tetrasulde

2.5. General Procedure

The plant and soil samples were digested with acid

solutions and after dilution with DW, the Cu, Pb,

and Cd ions were determined with F-AAS. On the

other hand, by the UD-µ-SPE method, 20 mL of

water samples were used for the separation and

extraction of the Cu, Pb, and Cd ions at pH 6-6.5.

In this procedure, 20 mg of EOSiP-TS@MWCNTs

adsorbent dispersed to a mixture of ionic liquid

([HMIM][PF6], 50 mg) and acetone (250μL). The

mixture was rapidly injected into 20 mL of water

and standard solution (5-200 μg L−1) at pH≈6. After

ultrasonic for 5.0 min, the Cu, Pb, and Cd ions

were chemically adsorbed by four sulfur groups of

EOSiP-TS@MWCNTs ([Cu, Cd, Pb]+2→[: S-S─

EOSiP]). By procedure, the Cu+2, Cd2+, Pb+2 ions

were extracted by coordination of dative bond

of sulfur at pH= 6.5. At high pH of more than

7.5, Cu+2, Cd2+, Pb+2 ions converted to Cu(OH)2,

Pb(OH)2, Cd(OH)2 and precipitated (Recovery of

extraction: 65%, 57%, 36%). Finally, the Cu+2,

Cd2+, Pb+2 ions were extracted from waters by a

dative bond of S-S and trapped on the IL phase.

Then, the IL/ EOSiP-TS@MWCNTs phase was

collected by centrifuging for 5 min at 3500 rpm

and settled down in the bottom of the conical tube.

After back extraction of Cu+2, Cd2+, Pb+2 ions, the

resulting solution was determined by FAAS after

dilution up to 1 mL with DW (Fig. 2).

Table1. The instrument conditions for determination Cu, Pb, and Cd ions by F-AAS

Metal Lamp current Fuel Wavelength

(nm)

Slit Width

(nm)

Working

Range (μg/mL)

Copper 4.0 Air- acetylene 324.7 0.5 0.03-10

327.4 0.2 0.1-24

217.9 0.2 0.2-60

Lead 5.0 Air- acetylene 217.0 1.0 0.1–30

283.3 0.5 0.5–50

261.4 0.5 5–800

Cadmium 4.0 Air- acetylene 228.8 0.5 0.02–3

326.1 0.5 20-1000

Fig. 2. General procedure for determination Ions in the plant, soil, and, water sample

Anal. Methods Environ. Chem. J. 5 (1) (2022) 49-60

3. Results and Discussion

3.1. Evaluation of Lead in plant and soil

Figure 3 represents that the amount of lead

in wild spinach in three stations is above the

permissible level for human consumption (2

mg kg-1 ). While; it is within the normal range

for plants (0.1-10 mg kg-1). In addition, the

concentration of this metal in agricultural soil

of all areas is above its permissible range (10

mg kg-1). The statistical analysis was done using

SPSS 19 and ANOVA. The findings showed that

there is a significant difference between lead

concentration in selected areas (P 7.13>4.1),

where the confidence level is 95% and the

significance level is less than 0.05.

3.2. Evaluation of Cadmium in plant and soil

Figure 4 indicates that the concentration of

cadmium in wild spinach at all three stations is

close to the borderline of the permissible range. By

increasing in irrigation of wastewater, the cadmium

concentration in the plant increased a little. The

level of cadmium in wheat and grain corn is lower

than the detection limit of the atomic absorption

spectrophotometer and therefore not mentioned

in Figure 4. The agricultural soil has high level of

cadmium. The ANOVA analysis of results indicated

that at a condence level of 95% and a signicance

level of lower than 0.05, (P 2.26>4.1), there is a

signicant difference between mean concentrations

of cadmium in the selected regions.

Fig. 3. The concentration of lead in plants and soil in selected stations.

Fig. 4. The amount of cadmium in plant and soil in selected stations

Measurement of heavy metals by Nanotechnology Mohammad Reza Rezaei Kahkha et al

3.3. Evaluation of copper in plant and soil

Figure 5 showed that the amount of copper in plant

samples is lower than its permissible level (20

mg Kg-1) but, in soil samples at all three stations

is higher than its permissible range. The ndings

of ANOVA, at condence level of 95% and

signicance level of lower than 0.05 (P 12.43>4.1),

indicate that the difference of means in copper

measured at mentioned stations is signicant.

3.4. Optimization process

3.4.1. Digestion reagent and time

1.0 g of plants and soil samples put on the beaker

and digested with 10 mL of HNO3/H2SO4 solutions

and 2 mL of H2O2. The mixture is placed on a

heater magnet for 60 min under the hood condition,

then 12 mL of extra reagents HNO3/H2SO4/H2O2

solutions are added to samples and heated for 60

min at 90oc. The results showed us the favorite

time for digestion process is 2 h. The solutions of

digested samples (plants and soil) were determined

by F-AAS after dilution with DW.

3.4.2. The effect of the amount of adsorbent

The favorite extraction of Cu, Cd, and Pb ions

based on the EOSiP-TS@MWCNTs adsorbent

was obtained in water samples. By the UD-µ-

SPE procedure, the amount of the EOSiP-TS@

MWCNTs was studied for 1.5-1000 μg L-1, 1-200

μg L-1, 5-1500 μg L-1 concentrations of Cu, Cd, and

Pb ions, respectively. Therefore, the amount of the

EOSiP-TS@MWCNTs adsorbent between 5-50

mg was evaluated for the Cu, Cd, and Pb extraction

in 20 mL of water samples before being determined

by the F-AAS. The high extraction for the Cu, Cd,

and Pb ions was achieved at 20 mg, 18 mg and

15 mg of the EOSiP-TS@MWCNTs adsorbent in

standard and water samples. Therefore, 20 mg of

the EOSiP-TS@MWCNTs adsorbent was used at

pH 6-6.5 (Fig. 6).

3.4.3.The effect of pH

For extraction of Cu, Cd, and Pb ions in water

samples, the pH samples were studied from 2 to 11 for

20 mg of adsorbent. So, the different pH sample was

evaluated for ions extraction in water and standard

samples. The results showed, the high recovery based

on the EOSiP-TS@MWCNTs adsorbent for the Cu,

Cd, and Pb ions was obtained at pH of 5.5-6.5, 6-7,

and 6-6.5, respectively. So, pH 6 was selected for the

Cu, Cd, and Pb extraction in water samples (Fig. 7).

Also, the recoveries were decreased at less than pH

5.5 and more than pH 7. So, the pH of 6.0 was used

as optimum pH for the Cu, Cd, and Pb extraction in

water samples (Fig.7). The mechanism for the Cu,

Cd, and Pb extraction based on the EOSiP-TS@

MWCNTs adsorbent was obtained by the dative

bond of sulfur groups (MWCNTs-S:-S:) at pH 6.0.

Also, the Cu, Cd, and Pb ions participated at a pH of

more than 8 (M(OH)2).

Fig. 5. The amount of copper in plants and soil in selected stations

Anal. Methods Environ. Chem. J. 5 (1) (2022) 49-60

3.4.4. The effect of sample volume

Due to the Figure, the extraction of the Cu, Cd, and

Pb ions was studied for various volumes of water

samples. So, the different volumes between 5-50

mL were evaluated for a concentration of 1.5-1000

μg L-1, 1-200 μg L-1, 5-1500 μg L-1, respectively.

The efcient recovery was observed at less than 25

mL, 30 mL and 20 mL for extraction of the Cu,

Cd, and Pb ions in water samples, respectively at

pH 6.0. So, 20 mL of water samples were used as

optimum sample volume for extraction of the Cu,

Cd, and Pb ions in water samples by the EOSiP-

TS@MWCNTs adsorbent (Fig. 8).

3.4.5. Interference of ions and absorption

capacity

The effect of some ions such as Co2+, Ni2+, Zn2+,

V3+, Ag+, Mn2+, Na+, Li+, K+, Mg2+, Ca2+, S2 , CO3

 , NO3

, F , Cl  and I  for extraction of the Cu, Cd,

and Pb ions in water samples were evaluated by the

UD-µ-SPE procedure. For evaluating, the different

interfering ions with various concentrations (2-10

Measurement of heavy metals by Nanotechnology Mohammad Reza Rezaei Kahkha et al

Fig.6. Effect of EOSiP-TS@MWCNTs adsorbent for extraction of Cu, Cd,

and Pb ions in water samples by the UD-µ-SPE procedure

Fig.7. Effect of pH on extraction of Cu, Cd, and Pb ions in water samples

by the UD-µ-SPE procedure

mg L-1) were examined for 20 mL of water samples.

The main concomitant ions in water samples were

used and the Cu, Cd, and Pb ions concentrations in

the liquid phase were determined by the F-AAS.

The results showed that the interference ions

cannot decrease the extraction recovery of the Cu,

Cd, and Pb ions in water samples by the EOSiP-

TS@MWCNTs adsorbent (Table 2).

The absorption capacities of the EOSiP-TS@

MWCNTs adsorbent are related to the size,

chemical adsorption, and surface area for the

Cu, Cd, and Pb ions extraction in water samples.

In a closed tube, 20 mg of the EOSiP-TS@

MWCNTs adsorbent were mixed to 100 mg

L-1 of the standard solution of the Cu, Cd, and

Pb ions in 100 mL of water sample at pH 6.0.

After 40 minutes, the Cu, Cd, and Pb ions were

chemically adsorbed by the sulfur group of the

Table 2. The effect of the interference of ions for extraction of the Cu, Cd, and Pb ions in water

and digested plant/soil samples by the UD-µ-SPE procedure

Interference of

Elements

Mean ratio

(CIE /CPb,Cd,Cu)Recovery Pb (%) Recovery Cd (%) Recovery Cu (%)

Zn2+ 600, 650,750 97.3 98.4 96.8

V3+ 600, 650, 800 97.2 97.9 98.5

Co2+ 400, 400, 600 98.3 97.5 98.6

Na+, K+, Li+, Mg2+, Ca2+ 800, 850,1000 98.7 99.2 98.1

F , Cl  , I  900, 1000, 1200 98.2 98.6 97.9

Ni2+ 400, 500, 500 97.1 98.4 96.9

Mn2+ 500, 600,700 97.9 99.3 96.5

Ag+200, 200, 250 97.8 98.5 97.1

CO3

2  , NO3

, S2  700, 900, 900 98.0 97.5 97.8

Anal. Methods Environ. Chem. J. 5 (1) (2022) 49-60

Fig.8. Effect of sample volume on extraction of Cu, Cd, and Pb ions

in water samples by the UD-µ-SPE procedure

EOSiP-TS@MWCNTs adsorbent. Finally, the

final concentration of mercury in the liquid phase

was determined by F-AAS. Due to the results,

the mean of adsorption capacities (AC) of the

EOSiP-TS@MWCNTs adsorbent for the Cu, Cd,

and Pb ions was achieved at 135.6 mg g-1.

3.4.6. Validation in real samples

By the UD-µ-SPE procedure, the Cu, Cd, and Pb

ions were extracted based on the EOSiP-TS@

MWCNTs adsorbent in water samples at a pH of

6.0. The results were validated by spiking to the

water samples by the UD-µ-SPE procedure. So,

the different concentrations of the Cu, Cd, and

Pb ions were spiked by standard solutions (Table

3-5). Also, the Cu, Cd, and Pb ions in plant and

soil samples were simply measured by F-AAS

after acid digested samples and validated by a

microwave digestion system (Table 6).

Table 3. Determination of lead (Pb2+) in water samples based on the EOSiP-TS@MWCNTs adsorbent

by the UD-µ-SPE procedure

Sample Added (μg L-1)*Found (μg L-1) Recovery (%)

a Drinking water ------- ND -------

5.0 4.91 ± 0.15 98.2

b Well water ------- 15.75 ± 0.54 -------

15 29.94 ± 0.15 94.6

c Wastewater ------- 765.76 ± 28.4 -------

750 1496.32 ± 56.33 97.4

d River water ------- 9.54 ± 0.43 -------

10 19.85 ± 0.88 103.1

 Mean of three determinations ± condence interval (P= 0.95, n=5)

ND: Not Detected

a drinking water prepared from Zabol city

b well water prepared from agricultural water of Zabol

c Wastewater prepared from an industrial chemical in Zabol city

d River water prepared from Helmand river of Zabol

Table 4. Determination of cadmium (Cd2+) in water samples based on the EOSiP-TS@MWCNTs adsorbent

by the UD-µ-SPE procedure

Sample Added (μg L-1)*Found (μg L-1)Recovery (%)

a Drinking water ------- ND -------

1.0 0.95 ± 0.15 95.0

b Well water ------- 6.34 ± 0.22 -------

5.0 11.46± 0.46 102.4

c Wastewater ------- 87.26 ± 3.72 -------

100 185.82 ± 8.34 98.6

d River water ------- 2.54 ± 0.11 -------

2.0 4.47 ± 0.88 96.5

 Mean of three determinations ± condence interval (P= 0.95, n=5)

ND: Not Detected

a drinking water prepared from Zabol city

b well water prepared from agricultural water of Zabol

c Wastewater prepared from an industrial chemical in Zabol city

d River water prepared from Helmand river of Zabol

Measurement of heavy metals by Nanotechnology Mohammad Reza Rezaei Kahkha et al

4. Conclusions

Today, due to potential adverse ecological effects,

soil contamination with heavy metals has become

a critical concern for the environment. Results

obtained in this research showed that amount

of heavy metals is accumulated in soil and some

plants. Although, the mentioned plants in this

study are used to feed livestock and only in a few

cases the wheat is used to prepare our, but lack

of suitable grasslands and pastures in Sistan and

water shortage would stimulate ranchers to use

wastewater increasingly for farmlands. Also, the

Cd, Pb, and Cu were determined in digested plant

and soil samples by F-AAS. Moreover, the Cd,

Pb, and Cu ions in water and wastewater samples

based on EOSiP-TS@MWCNTs adsorbent

were determined by F-AAS after the UD-µ-SPE

procedure at pH 6-6.5. The RSD% of results was

obtained between 1.23-3.11. The mean absorption

capacity (AC) of EOSiP-TS@MWCNTs adsorbent

for Cd, Pb, and Cu ions was achieved at 144.8 mg

g-1, 127.4 mg g-1, and 134.6 mg g-1, respectively in

a static system.

5. Acknowledgments

The authors sincerely appreciate the efforts of the

chemistry laboratory of Zabol and the department

of health engineering, Zabol University of medical

sciences, Zabol, Iran.

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Table 5. Determination of copper (Cu2+) in water samples based on the EOSiP-TS@MWCNTs adsorbent by the

UD-µ-SPE procedure

Sample Added (μg L-1)*Found (μg L-1) Recovery (%)

a Drinking water ------- 4.65 ± 0.23 -------

5.0 9.61 ± 0.39 99.2

b Well water ------- 44.94 ± 2.13 -------

50 93.96± 4.32 98.1

c Wastewater ------- 523.94 ± 20.73 -------

500 999.87 ± 43.62 95.2

d River water ------- 13.65 ± 0.47 -------

10 23.41 ± 1.08 97.6

 Mean of three determinations ± condence interval (P= 0.95, n=5)

a drinking water prepared from Zabol city

b well water prepared from agricultural water of Zabol

c Wastewater prepared from an industrial chemical in Zabol city

d River water prepared from Helmand river of Zabol

Table 6. Validation of acid digested procedure for determination of the Cu, Cd, and Pb ions in plant

and soil samples by F-AAS and compared to microwave digestion system coupled to F-AAS

Sample *Microwave/F-AAS (mg L-1) *Acid digestion/F-AAS (mg L-1) A Recovery MW (%)

Plant 1.77 ± 0.11 1.82 ± 0.12 102.8

Soil 11.56 ± 0.42 10.96 ± 0.38 94.8

Plant 2.01 ± 0.09 1.93 ± 0.12 96.1

Soil 8.85 ± 0.28 8.66 ± 0.25 97.8

 Mean of three determinations ± condence interval (P= 0.95, n=5, RSD< 2%)

A Recovery MW: Recovery Acid digestion/microwave digestion

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Anal. Methods Environ. Chem. J. 5 (1) (2022) 49-60

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Application of experimental design methodology to

optimize acetaminophen removal from aqueous environment

by magnetic chitosan@multi-walled carbon nanotube

composite: Isotherm, kinetic, and regeneration studies

Ebrahim Nabatian a, b, Maryam Dolatabadi c, Saeid Ahmadzadeh d, e*

a Student Research Committee, Kerman University of Medical Sciences, Kerman, Iran.

b Department of Chemistry, Faculty of Sciences, Shahid Bahonar University of Kerman, Kerman, Iran.

c Environmental Science and Technology Research Center, Department of Environmental Health Engineering, School of Public

Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.

d Pharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran.

e Pharmaceutical Sciences and Cosmetic Products Research Center, Kerman University of Medical Sciences, Kerman, Iran

ABSTRACT

Acetaminophen is a widely used drug worldwide and is frequently

detected in water and wastewater as a high-priority trace pollutant.

This study investigated the applicability of the adsorption processes

using a composite of magnetic chitosan and multi-walled carbon

nanotubes (MCS@MWCNTs) as an adsorbent in the treatment of

acetaminophen. The model was well tted to the actual data, and the

correlation coefcients of R2 were 0.9270 and 0.8885, respectively.

The maximum ACT removal efciency of 98.1% was achieved at

ACT concentration of 45 mg L-1, pH of 6.5, MCS@MWCNTs dosage

of 400 mg L-1, and the reaction time of 23 min. The result shows that

BET specic surface area of 640 m2 g-1. The adsorption isotherms

were well tted with the Langmuir Model (R2 =0.9961), depicting

the formation of monolayer adsorbate onto the surface of MCS@

MWCNTs. The maximum monolayer adsorption capacity of 256.4

mg g-1 was observed for MCS@MWCNTs. The pseudo-second-

order kinetic model well depicted the kinetics of ACT adsorption on

MCS@MWCNTs (R2=0.9972). Desorption studies showed that the

desorption process is favored at high pH under Alkaline conditions.

The results demonstrate that the MCS@MWCNTs is an efcient,

durable, and sustainable adsorbent in water purication treatment.

Keywords:

Adsorption,

Acetaminophen,

Experimental design,

Isotherm, Kinetic,

Regeneration

ARTICLE INFO:

Received 23 Dec 2021

Revised form 20 Feb 2022

Accepted 2 Mar 2022

Available online 29 Mar 2022

*Corresponding Author: Saeid Ahmadzadeh

Email: chem_ahmadzadeh@yahoo.com

https://doi.org/10.24200/amecj.v5.i01.168

------------------------

1. Introduction

Pharmaceutical pollutants (PPs) are a group of

emerging anthropogenic hazard contaminants that

contain different groups of human and veterinary

medicinal compounds that are used widely all over

the globe [1, 2]. Acetaminophen (ACT) is one of

the most frequently used drugs worldwide. ACT is

a type of analgesic and antipyretic drug commonly

used as a fever reducer and pain reliever. Because

of high consumption worldwide, it is one of the

most frequently detected drugs in bodies of water

and wastewater [3-5]. Overdoses of ACT produce

the accumulation of toxic metabolites, which may

cause severe and sometimes fatal hepatoxicity,

and nephrotoxicity; generally, due to their bio-

accumulation, they pose a potential long-term risk

for aquatic and terrestrial organisms. To improve

the water quality and protect human health, the

water contaminated with emerging contaminants,

including pharmaceuticals, must be efciently

treated using an appropriate technique before being

supplied for consumption [6, 7]. Various physical,

chemical, and biological technologies can be

employed to treat ATC from water and wastewater.

Among the different treatments, adsorption

technology is attractive due to its effectiveness,

efciency, and economy. The common adsorbents

primarily include activated carbons, zeolites, clays,

industrial by-products, agricultural wastes, biomass,

and polymeric materials. AC is characterized

by high porosity and an extensive surface area,

enabling it to adsorb many kinds of pollutants

efciently. Despite its high adsorption capacity, the

use of AC on a large scale is limited by process

engineering difculties such as the dispersion of

the AC powder and the cost of its regeneration.

However, these adsorbents described above suffer

from low adsorption capacities and separation

inconvenience. Therefore, efforts are still needed to

investigate new promising adsorbents [8]. Chitosan

(CS) has gained considerable attention as a non-

conventional adsorbent in water decontamination

research due to its favorable properties such as

non-toxicity, eco-friendliness, high availability,

biodegradability, good biocompatibility, low cost,

and good adsorption properties. However, the high

solubility of CS at lower pH (i.e., below 4) and

poor mechanic properties are the limiting problems

for taking advantage of the interaction ability of

CS with Pollutant molecules. Thus, it might be

not advisable to use untreated CS as an adsorbent

in aqueous media [9-12]. One good strategy is to

immobilize CS on solid matrixes that can stabilize

CS in acid solutions and improve its mechanical

strength to overcome these problems. Different

kinds of solid organic or inorganic matrixes have

been used to form composites with CS, such as

glass plates, activated clay, silica, and polymer

spheres.

Recently, carbon nanotubes (CNTs) have also been

used as a matrix to prepare CS/CNTs composites.

CNTs, a fascinating new member of the carbon

family, have attracted strong research interest

since their discovery because of their unique

morphologies and various potential applications,

as well as their remarkable mechanical properties

[13]. CNTs have been proven to possess excellent

adsorption capacity in removing organic and

inorganic pollutants because of their hollow and

layered nanosized structures with a large specic

surface area. Also, CNTs can provide improved

mechanical strength and better structural integrity

conditions. However, the difculty in collecting

these adsorbents from treated efuents can cause

inconveniences in their practical application.

As an efcient, fast, and economical method for

separating magnetic materials, Magnetic separation

technology has received considerable attention

in recent years. Imparting magnetic properties to

adsorbents can isolate them from the medium using

an external magnetic eld without the need for

complicated centrifugation or ltration steps [11,

14].

The current work aimed to investigate the

efcacy of magnetic CS and multi-walled carbon

nanotubes (MCS@MWCNTs) as the adsorbent in

ACT removal under various operating conditions.

Effective parameters on ACT removal such as

solution pH, reaction time, ACT concentration, and

adsorbent dosage were optimized with response

surface method (RSM) using central composite

design (CCD). In addition, some extra experiments

were performed to study adsorption kinetics and

isotherms, and adsorbent reusability.

2. Experimental

2.1. Chemicals

Chitosan (Merck), Multi-walled carbon nanotubes

(Sigma-Aldrich), Acetaminophen (C8H9NO2,

Merck), Ferric chloride (FeCl3.6H2O, Merck),

Sodium acetate (C2H3NaO2 Merck), Ethylene

glycol (C2H6O2, Merck), Acetone (C3H6O, Merck),

Parafn (CnH2n+2, Merck), Sodium hydroxide

(NaOH, Merck), Hydrochloric acid (HCl, Merck),

were of analytical grade. All solutions used in the

experiments were prepared with distilled water.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

2.2. Preparation of Fe3O4 nanoparticles

Typically, 1.35 g of FeCl3.6H2O and 3.6 g of

sodium acetate were dissolved in 40 mL ethylene

glycol with stirring and heating simultaneously.

The temperature has risen to 80-100 °C. After

stirring for 30 min, the yellow-brown color

solution was transferred to a Teon-lined stainless-

steel autoclave and heated in the oven at 180°C

for 12 h. Then, the autoclave was allowed to cool

down to room temperature naturally. The black

magnetite particles were washed with acetone and

water several times and dried in the oven at 60°C

overnight [15].

2.3. Preparation of MCS@MWCNTs

The composites of MCS@MWCNTs were

synthesized by a suspension cross-linking approach

with some modication. Typically, 0.1 g of

chitosan was dissolved in 20 mL of 2% (v/v) acetic

acid solution under ultrasonication. Subsequently,

0.2 g of Fe3O4 and 0.2 g of MWCNTs were added

into the chitosan solution, and the reaction system

was further ultrasonicated for 20 min. Then, the

above mixture was slowly dispersed in 40 mL of

parafn containing 2 mL of span-80 under stirring.

After 30 min of emulsication, 1 mL of 25% (v/v)

glutaraldehyde was introduced into the system for

the cross-linking of chitosan. Then the mixture was

stirred continuously for 1 h at 70 °C. Afterward,

the pH value of the reaction solution was adjusted

to 9–10 with 1 mol L-1 NaOH and the reaction

system was allowed to stir for another 1 h at 80

°C. The particles were washed with petroleum

ether, ethanol, and ultrapure water three times,

respectively. Finally, MCS@MWCNTs were

obtained by magnetic separation and freeze-dried

for 12 h [16].

2.4. Characterization of MCS@MWCNTs

The standard BET equation was employed to

calculate the Brunauer-Emmert-Teller (BET)

surface area from the desorption isotherms. The pore

size distribution was determined from desorption

isotherms using the Barrett, Joyner, and Halenda

(BJH) method. All calculations were performed

automatically by an Accelerated Surface Area and

Porosimeter system (ASAP 2010, Micromeritics,

U.S.A.). The pH of zero point charge (pHzpc)

describes the condition when the charge density

on the surface is zero. It is usually determined

concerning the pH of the mixtures. Researchers

proposed a mass titration method to determine the

values of pHzpc: portions of 20 mL NaCl (0.01 M)

solution were added into different asks. The initial

pH was adjusted with NaOH or HCl to the desired

values between 2 and 12 (metrohm 827 pH/mV lab

pH meter). Then, 20 mg of the MCS@MWCNTs

sample was suspended into each ask. The asks

with caps were placed in a shaker. After shaking

for 24 h, the pH of the solutions was measured and

designated as pHnal. The pHzpc value is the point

where the pHinitial = pHnal [17].

2.5. Experimental design and statistical analysis

The response surface methodology (RSM) is a

set of statistical and mathematical methods used

to analyze experimental results. RSM is used in

conditions that many input variables affect the

performance and response characteristics of the

process. A complete description of a process

requires that it be modeled as a polynomial function

generally of degree 2 or higher. Since operational

conditions may be associated with changes, the

nonlinear second-order model can describe it. The

quadratic regression model was considered in the

form of Equation 1[18-20]:

(Eq. 1)

where Y represents the response of process, i and j

index numbers for factors, Xi and Xj are the design

variables, βi and βj represents the coefcient of rst-

order effect, βij is the coefcient of interaction,β0 is

constant-coefcient, k is the number of factors

and ε is the model error. In this study, CCD is

based on a four-factor design, including ACT

concentration (X1), pH (X2), adsorbent dosage

(X3), and reaction time (X4) were discussed. In the

Acetaminophen removal from aqueous environment by MCS@MWCNTs Ebrahim Nabatian et al

design of the experiments, each variable with ve

levels was considered, in accordance with Table

1. The statistical signicance of CCD modeling

parameters and their combined interactions at

certain levels were examined based on their p

values. Analysis of variance (ANOVA) was used

to check the experimental data and accuracy of

the response surface model. The coefcient of

variation (C.V. %) and R2 values was calculated

to evaluate the goodness of t of the regression

model. The model precision associated with the

range of predicted values at the given points was

also elucidated.

2.6. Adsorption experiments

All adsorption experiments were carried out in

100 mL of pyrex reactor by mixing a given dose of

MCS@MWCNTs with a certain concentration of

ATC solution in a thermostatic shaker. The initial

pH of the ACT solution was adjusted to a certain

value using NaOH and HCl solution by pH meter.

After adsorption, the mixture was immediately

centrifuged, and the supernatant was analyzed for

the concentration of ATC was measured using a UV/

Vis spectrophotometer (Optizen). The wavelength

corresponding to the maximum absorbance of

ATC was 242 nm. Each experiment was repeated

at least three times, and the average value was

recorded. The ACT removal (qe) and adsorption

capacity were calculated by Equations (2) and (3),

respectively [15, 21]:

(Eq. 2)

(Eq. 3)

Where C0 is the initial ACT concentration (mg L-1),

Ce is the ACT concentration (mg L-1) after the batch

adsorption procedure, m is the adsorbent dosage (g

L-1), and qe is the amount of ACT adsorbed by the

adsorbent (mg g-1).

2.7. Kinetic and isotherm models

Two widely used kinetics models, pseudo-rst-

order and pseudo-second-order models were

examined to t the experimental data. The linear

expression of pseudo-rst-order and pseudo-

second-order models are expressed as Equation 4

and 5 [15, 22].

(Eq. 4)

(Eq. 5)

where k1 (min-1) is the rate constant of the pseudo-

rst-order, k2 (g mg-1 min-1) is the second-order

rate constant. qe and qt (mg g-1) are the adsorption

capacities at equilibrium and time t (min),

respectively.

Three commonly used isotherm models, the

Langmuir and Freundlich isotherms, are selected

to analyze the equilibrium experimental data for

the adsorption of ACT onto MCS@MWCNTs. The

two models are given as Equation 6 and 7 [23].

(Eq. 6)

(Eq. 7)

where Ce (mg L-1) is the equilibrium concentration

of the ACT, qe (mg g-1) is the amount of ACT

Table 1. Coded and actual values of independent process variables used in the design

of an experimental matrix using the RSM-CCD framework.

Coded Variables (Xi) Factors

Coded Level

-α -1 0 +1 +α

X1A= ACT Concentration (mg L-1) 20.0 40.0 60.0 80.0 100.0

X2B= pH 4.00 5.50 7.00 8.50 10.00

X3C= Adsorbent dosage (mg L-1)100 200 300 400 500

X4D= Reaction time (min) 5.00 11.25 17.50 23.75 30.00

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

adsorbed under equilibrium, b (L mg-1) is the

Langmuir adsorption constant, and qm (mg g-1) is

the maximum adsorption amount. KF and n are

Freundlich constants. n presents the adsorption

intensity, assessing the unfavorable adsorption

(n<1) or preferential adsorption (n > 1), and KF

((mg g-1 (L mg-1)1/n) is the adsorption capacity of

the adsorbent.

The isotherm can predict if an adsorption system

is favorable or unfavorable. Researchers pointed

out that the essential characteristics of the

Langmuir isotherm can be expressed in terms

of a dimensionless constant, RL, as presented in

Equation 8.

(Eq. 8)

where, RL is the separation factor or equilibrium

parameter, which is a direct function of the

Langmuir constant b. The values of RL indicate

the shape of the isotherm: RL>1 (unfavorable),

RL =1 (linear), 1 > RL > 0 (favorable) and RL = 0

(irreversible).

3. Results and discussions

3.1. Characterization of adsorbent

Figure 1 shows the N2 adsorption-desorption isotherms

of MCS@MWCNTs. According to Figure 1, the N2

adsorption nearly completed at a lower relative pressure

of P/P0 < 0.1, suggesting that the sample has the

micropore size distribution. In addition, the N2 hysteresis

loop at P/P0 > 0.5 was observed, indicating the presence

of mesopores structure. Accordingly, the micropore

volume fraction is higher than 79%, conrming the

majority of micropores. The MCS@MWCNTs had a

high BET-specic surface area of 640 m2 g-1.

The adsorbent’s pHzpc value was determined to

explain the adsorption behavior. This parameter

reveals the characteristics of the surface’s active

sites in a linear range of solution pH. The pHzpc

of MCS@MWCNTs was found to be around 6.8,

implying that the surface of the adsorbent would

be positively charged at solution pH below 6.8

and negatively charged at solution pH above 6.8.

Hence, one can conclude that adsorption of cationic

molecules is favored at pH>6.8, while anionic

molecules adsorption is favored at pH < 6.8.

Acetaminophen removal from aqueous environment by MCS@MWCNTs Ebrahim Nabatian et al

Fig. 1. N2 adsorption–desorption isotherms of MCS@MWCNTs.

3.2. Development and analysis of regression

model equation

CCD is considered a reliable method to analyze

diagnostic plots, such as the normal probability

plot of residuals and to predict versus actual values,

to validate the adequacy of the model. The normal

probability plot of the studentized residuals is an

excellent graphical representation for the diagnosis

of data normality (Fig. 2). The data were well tted

with the line. In addition, the residuals followed a

random distribution around zero with a variation of

±3.0 (Fig. 3).

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

Normal % Probability

-3.0 -1.5 0.0 1.5 3.0

Externally Studentize d Re siduals

Design- Expert® Software

removal

Color points by value of

removal:

60.3096

Run Number

Internally Studentized Residuals

Residuals vs. Run

-3.00

-1.50

0.00

1.50

3.00

1 5 9 13 17 21 25 29

Run Number

3.0

1.5

0.0

-1.5

-3.0

Internally Studentize d Re siduals

Fig. 2. Normal probability plot of the internally studentized

residuals for ACT removal.

Fig. 3. Run number versus residual data for ACT removal.

The result indicates that the data were normally

distributed in the model response. In addition, the

corresponding relationship between the residual

and the predicted value of the equation also could

reect the reliability of the model. When the points

are distributed discretely in the Figure, it could

represent the higher reliability of the model.

ANOVA carried out the analysis of obtained

experimental data. Table 2 shows ANOVA data

for the removal efciency (Y). F-value in ANOVA

implies that the model is signicant for the

dependent variable. As shown in Table 2, F-value

is 87.47 for removal efciency, which indicates

the model is signicant. Prob>F or p-value less

than 0.05 demonstrates that these model terms

are important. The lack of t F-value of 4.13 with

the associated p-value of 0.0612 for the response

was insignicant due to relative pure error. The

validity of the model is checked by some statistical

parameters, including the determination coefcient

(R2), adjusted R2, predicted R2, adequate precision

(AP), and coefcient of variation (CV). R2 is

dened as a measure of the degree of t. As R2

approaches unity, the degree of t increases.

The similarity between R2 and adjusted R2 shows

the model’s compatibility to predict the dependent

variable. The difference between predicted R2 and

adjusted R2 must be less than 0.2. It is indicated

that predicted R2 is in acceptable agreement with

adjusted R2. AP is dened as a measure of the

ratio of the signal to noise. A ratio greater than 4

is desirable. In our current study, all ndings in

Table 2 were acceptable, which conrmed the

model’s tness with the experimental results.

Overall, the ANOVA analysis was reliable to

optimize and determine the level of each factor for

removal ACT. Therefore, it is pretty satisfactory

to predict the ACT removal efciency by the

second-order polynomial model. In the present

study, ve model terms (X1(ACT concentration),

X2(pH), X3(Adsorbent dosage), X4(Reaction time),

2(quadratic effect of pH)) was most important

because of their p-values less than 0.05. These

model terms are shown in the model equation.

Based on ANOVA results, the empirical model

equation in terms of coded variables was developed

for the removal efciency as Equation 9.

(Eq. 9)

The positive sign in the equation indicates the

synergistic effect of the corresponding factor on

the response, and the negative sign represents

Acetaminophen removal from aqueous environment by MCS@MWCNTs Ebrahim Nabatian et al

Table 2. Analysis of variance (ANOVA) for regression model.

Source Sum of Squares Degree of

freedom (df)

Mean

Squares F-Value Probability

P-value > F

Model 2775.21 5 555.04 87.47 < 0.0001

561.89 1 561.89 88.55 < 0.0001

256.30 1 256.30 40.39 < 0.0001

781.29 1 781.29 123.12 < 0.0001

744.41 1 744.41 117.31 < 0.0001

431.33 1 431.33 67.97 < 0.0001

Residual 152.30 24 6.35 - -

Lack of Fit 143.18 19 7.54 4.13 0.0612

Pure Error 9.12 5 1.82 - -

Cor Total 2927.51 29 - - -

Fit Statistics

R20.9480 SD 2.52

Adjusted R20.9371 CV 3.16

Predicted R20.9140 AP 34.40

the antagonistic effect. The effect of the initial

concentration (20-100 mg L-1) was investigated.

The removal efciency for ACT is highly

dependent on the initial ACT concentration. Figure.

4 illustrated that removal efciency decreases from

92.3 to 72.6%, increasing ACT concentration

from 20 to 100 mg L-1. The effect of initial ACT

concentration depends on the immediate relation

between the concentration of the ACT and

the available sites on an adsorbent surface. In

general, the removal efciency decreases with an

increase in the initial ACT concentration due to

the saturation of adsorption sites on the adsorbent

surface. On the other hand, the increase in initial

ACT concentration will cause an increase in the

capacity of the adsorbent, which may be due to the

high driving force for mass transfer at a high initial

ACT concentration.

Figure 4 shows the effect of solution pH ranging

from 4 to 10 on the adsorption of ACT onto MCS@

MWCNTs. Figure 4 implies that the adsorption of

ACT onto MCS@MWCNTs at pH solution between

4 and 7.0 is a pH-dependent phenomenon, so the

adsorption performance was around 85% in all pH

ranges. The increase of solution pH to 7.0 caused

improvement of the adsorption. A decreasing trend

in adsorption of ACT was observed for the solution

pH over 7.0. Accordingly, the optimum solution

pH at which the maximum adsorption of the

ACT under the selected experimental conditions

was obtained was found to be 6.5. The effect of

solution pH on the adsorption of ACT onto MCS@

MWCNTs can be justied considering the pHzpc

of MCS@MWCNTs (6.8) and pKa of ACT (9.4).

According to Figure 4, the adsorption of ACT

onto MCS@MWCNTs is almost independent of

solution pH over the solution pHs between 4.0

and 7.0. At this pH range, the ACT molecules

remain mostly neutral and nonionic and thus

unfavorable for electrostatic and π-π interactions

with the functional groups on the surface of

MCS@MWCNTs. Therefore, the hydrophobic

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

X1: ACT Concentration (mg L

-1

)

20 40 60 80 100

10.0

8.0

6.0

4.0

X2: pH

Fig. 4. Contour plot of ACT removal showing the effect of variables of ACT concentration

and pH (MCS@MWCNTs dosage of 300 mg L-1 and reaction time of 17.5 min).

interactions might be the primary mechanism

anticipated in the ACT adsorption under these

conditions. Considering that the pKa of ACT is

9.4, the main fraction of ACT molecules was in

anionic form at solution pHs above this value. In

contrast, the surface of MCS@MWCNTs (pHzpc

= 6.8) is negatively charged at alkaline solution

pH. Therefore, the reduction of ACT adsorption at

the pH over 7.0 can be related to the electrostatic

repulsion that occurred between anionic ACT

molecules and the negatively charged functional

groups on the surface of MCS@MWCNTs. This

effect tends to enhance the adsorption of ACT

onto MCS@MWCNTs. The greater the solution

pH over 7.0, the more negative the surface of

MCS@MWCNTs and the more ionized the ACT

molecules. Therefore, the greater the repulsive

force leads to reduced adsorption. The MCS@

MWCNTs dosage as adsorbent was one of the

dominant parameters controlling the adsorption of

ACT. The relation of MCS@MWCNTs dosage and

pH on removal efciency of ACT is illustrated in

Figure 5. Increasing MCS@MWCNTs dosage from

100 to 500 mg L-1 leads to an improvement in ACT

removal efciency from 71.4% to 94.2% at ACT

concentration of 60 mg L-1, pH of 7, and reaction

time 17.5 min. The increase in removal efciency

with increasing adsorbent dose is probably due to

the greater adsorbent surface area and pore volume

available at higher adsorbent dose providing more

functional groups and active adsorption sites that

result in higher removal efciency.

The dependence of the removal efciency of ACT

on reaction time is shown in Figure 6. This Figure

shows that removal efciency increases with

time, and adsorption reaches equilibrium in about

25 minutes. It indicates that the rapid increase in

removal efciency is achieved during the rst 20

min. The fast adsorption at the initial stage may

be due to the higher driving force making an

immediate transfer of adsorbate ions to the surface

of MCS@MWCNTs particles and the availability

of the uncovered surface area and the remaining

active sites on the adsorbent. According to the

results, an equilibrium time was set to 25 min for

adsorption of ACT onto MCS@MWCNTs.

Acetaminophen removal from aqueous environment by MCS@MWCNTs Ebrahim Nabatian et al

Removal Efficiency (%)

Fig. 5. Response surface plot of ACT removal showing the effect of variables of MCS@MWCNTs dosage

and pH (ACT concentration of 60 mg L-1 and reaction time of 17.5 min).

Removal Efficiency (%)

3.3. Optimization and validation test

The optimization of operating conditions was

conducted to determine the optimum values

of these parameters required to achieve the

highest ACT removal efficiency. Optimization

was performed by numerical technique built

in the Design-Expert software. The desired

goal for the variables was chosen as “in

range”, while removal efficiency (response)

was chosen as “maximize”. According to the

output results, the removal efficiency of ACT

could reach a maximum value of 98.1% with

the ACT concentration of 45 mg L-1, pH of

6.5, MCS@MWCNTs dosage of 400 mg L-1,

and the reaction time of 23 min. An additional

experiment was conducted to validate the model

prediction (the optimal conditions) in this study.

It was found that the results were greatly agreed

with the predicted value through the quadratic

model (Table 3). The experimental data were

close to predicted data, indicating the accurate

prediction ability of the model.

3.4. Adsorption kinetics and isotherms studies

The calculated kinetic parameters for pseudo-rst-

order and pseudo-second-order models are listed

in Table 4. The pseudo-second-order model’s

correlative coefcient (R2) was better than that

of the pseudo-rst-order model. These results

indicated that the kinetic data tted well with

pseudo-second-order models. The pseudo-second-

order model assumes that the rate-limiting step

might be chemical adsorption in the adsorption

process.

The adsorption isotherm is critically important

in designing an adsorption system. The sorption

data were tted by the Langmuir and Freundlich

equations, and the calculated parameters are

Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

Fig. 6. Response surface plot of ACT removal showing the variables effect of reaction time

and ACT concentration (MCS@MWCNTs dosage of 300 mg L-1, and pH of 7).

summarized in Table 5. It was found that the

Langmuir model provided a better t to the observed

data for the ACT, with high correlation coefcients

(R2=0.996). The maximum ACT sorption capacity

(qm) was 256.4 mg g-1. The values of n and RL were

obtained at 3.52 and 0.026, respectively, suggesting

that the adsorbent was favorable for removing ACT

from the aqueous solution.

3.5. Regeneration studies

Desorption studies are necessary to complete the

investigation of the mechanism involved in the

adsorption of an adsorbate by an adsorbent and to

regenerate the adsorbent for economic success. In

the present study, desorption was explored, varying

the pH from 4.0 to 10.0 and keeping the adsorbent

dosage constant at 300 mg L-1. An increase in pH

favored ACT desorption from MCS@MWCNTs

because of electrostatic repulsion between

negatively charged sites on the adsorbent surface

and ACT molecules. The feasibility of using MCS@

MWCNTs in successive adsorption-desorption

cycles was examined by contacting 45 mg L-1 ACT

solution with 400 mg L-1 recycled adsorbent at pH

10.0. Under these conditions, ACT removal by

MCS@MWCNTs and recycled MCS@MWCNTs

was 98.1% and 86.7%, respectively. Such a marked

loss of sorption capacity suggests that the reuse

of desorbed MCS@MWCNTs would need some

regeneration before recycling.

Acetaminophen removal from aqueous environment by MCS@MWCNTs Ebrahim Nabatian et al

Table 3. Optimization and validation tests for ACT removal efciency.

NO ACT concentration

(mg L-1)pH MCS@MWCNTs

dosage (mg L-1)

Reaction

time (min)

Experimental removal

efciency (%)

Predicted removal

efciency (%)

I 45 6.5 400 23 98.7 98.1

II 60 7.0 300 18 84.5 85.3

III 40 8.5 400 12 79.4 80.0

IV 80 8.5 200 25 71.0 69.4

Table 4. Parameters of kinetic equations for the adsorption of ACT.

Pseudo-First-Order model Pseudo-Second-Order model

qe(mg g-1) k1(min-1) R2qe(mg g-1) k2 (g mg-1 min-1) R2

121.47 0.0689 0.9452 217.4 0.0008 0.9972

Table 5. Langmuir and Freundlich constants for the adsorption of ACT.

Langmuir Freundlich

qm (mg g-1) b (L mg-1) RLR2Kf (L g-1) n R2

256.4 0.658 0.026 0.9961 103.1 3.52 0.9542

72 Anal. Methods Environ. Chem. J. 5 (1) (2022) 61-74

4. Conclusions

The process was optimized using central

composite design (CCD), a statistical tool used to

optimize response surface methodology (RSM).

A second-order polynomial model adequately

t the experimental data with an adjusted R2 of

0.9270, showing that the model could efciently

predict the ACT removal. It was found that all

selected variables signicantly affect ACT removal

efciency. Under these conditions, the maximum

adsorption capacity for MCS@MWCNTs was

found to be 256.4 mg g-1. The results showed that

the Langmuir and the pseudo-second-order kinetic

models presented better ttings for the adsorption

equilibrium and kinetics data. This study showed

that MCS@MWCNTs are a useful adsorbent for

the removal of ACT from aqueous solutions.

5. Acknowledgements

The authors would like to express their appreciation

to the student research committee of Kerman

University of Medical Sciences [Grant number

400000753] for supporting the current work.

Funding: This work received a grant from the

Kerman University of Medical Sciences [Grant

number 400000753].

Conict of interest: The authors declare that they

have no conict of interest regarding the publication

of the current paper.

Ethical approval: The Ethics Committee of

Kerman University of Medical Sciences approved

the study (IR.KMU.REC.1400.503).

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Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Rapid analysis of chromium (III, VI) in water and

wastewater samples based on Task-specic ionic

liquid by the ultra-assisted dispersive ionic liquid-liquid

microextraction

Vahid Saheba and Tayebeh Shamspur b,*

a Department of Chemistry, College of Science, Shahid Bahonar University of Kerman, Postal code:7616914111, Kerman, Iran

bDepartment of Chemistry, College of Science, Shahid Bahonar University of Kerman, 7616914111, Iran

ABSTRACT

Exposure to hexavalent chromium (Cr VI) causes cancer in cells of the

human body. So, the speciation and determination of the Cr (VI) and

Cr (III) in water and human samples based on sensitive techniques are

necessary. In this research, 2-mercapto-1-methylimidazole a novel

Task-specic ionic liquid (C4H6N2S; HS-CH3-IM) was used with a new

approach for speciation of Cr (III, VI) from water samples by ultra-

assisted dispersive ionic liquid-liquid microextraction procedure

(USA-D-ILLME). Due to the procedure, 100 mg of HS-CH3-IM and

0.2 mL of acetone were mixed and injected into 10 mL of water or

standard Cr (III) and Cr (VI) solution in the conical tube. After stirring

for 5 min, the Cr (VI) and Cr (III) were extracted with a positive and

negative charge of the thiol group (HS2+, HS-) in pH 2 or 8 and pH

5, respectively. The mixture of the HS-CH3-IM was collected at the

bottom of the conical tube by centrifuging. The upper liquid phase

was vacuumed with a peristaltic pump and the Cr (III, VI) loaded

on the HS-CH3-IM was back-extracted in a liquid solution. Finally,

the concentration of the Cr (III, VI) ions in a remained solution were

measured with ET-AAS after dilution up to 0.5 mL with DW. The

total chromium was determined in water samples by summarizing

the Cr (VI) and Cr (III) contents. All parameters such as the amount

of HS-CH3-IM, the sample volume, pH, and the shaking/centrifuging

time were optimized. Under the optimal conditions, good linear

range (LR), LOD, and enrichment factor (EF) were obtained 0.05–

1.7 μg L−1, 15 ng L−1, and 19.82 respectively (RSD% < 1.45). The

procedure was validated by spiking samples and good accuracy and

precision results were achieved.

Keywords:

Chromium III, VI;

Water samples;

2-Mercapto-1-methylimidazole;

Dispersive ionic liquid-liquid

microextraction,

Electrothermal atomic absorption

spectrometry

ARTICLE INFO:

Received 28 Oct 2021

Revised form 10 Jan 2022

Accepted 4 Feb 2022

Available online 27 Mar 2022

*Corresponding Author: Tayebeh Shamspur

Email: tsh@uk.ac.ir

https://doi.org/10.24200/amecj.v5.i01.170

------------------------

1. Introduction

Heavy metals have a toxic effect on environmental

matrixes (air, soil, water). they can enter from

waters, food, or vegetables and accumulate in brain,

liver, or renal tissues. A trace amount of heavy

metals can cause cellular damage in the human

body. Chromium(VI) is a major pollutant for the

environment and enters from many sources such as

chemical industries, steelworks, and electroplating.

The chromium cause diseases such as gene mutations,

carcinogen effect, and DNA lesions in human [1,2].

Two different oxidation forms of chromium exist

in the environment (Cr III and Cr VI). Cr (III)

compounds have an important role in the metabolism

of glucose and protein in humans[3]. Moreover, the

Cr (VI) has carcinogenic effects in cell tissues with a

strong oxidation potential in the human body which

enables to provide damage to DNA. Also, Cr (VI) is

harmful to the lungs and kidneys [4,5]. Chromium

values in drinking water are lower than 2 µg L-1

[6]. The World Health Organization (WHO) was

reported that the genotoxicity of Cr (VI) in humans is

50 µg L-1. The ACGIH announced the normal range

for chromium levels in human blood and urine were

achieved at 1.8 µg L-1 and 2.0 µg L-1, respectively

[7,8]. The Federal Committee on drinking water

(FCDW) has reported new information on Cr(III,

VI) and guideline technical documents on Cr(III,

VI) in drinking water. The FCDW showed a

maximum acceptable concentration (MAC) of 50 µg

L-1 to Cr(VI). This document focuses on the health

effects of Cr(VI) and total chromium considered

about 100 µg L-1. Some of the analytical methods

measure the total chromium Cr(III, VI) in drinking

water at the lower limit of the reported MAC[9].

Many sample preparations based on adsorbents or

ligands were was used for extraction chromium

from water samples. In addition, Cr(III) is likely to

be converted to oxidized form [Cr(VI)] after sample

preparation. Therefore, it is important to analyze

chromium species and total chromium(TCr) in

waters. In conventional studies, the best method for

the treatment TCr is coagulation based on ltration

and ion exchange [10]. Coagulation-based ltration

and ion exchange are favorite methodologies for

extracting Cr(VI) from drinking water. The drinking

water treatment technologies able to be certied to

international standards for reduction of TCr, Cr(VI),

and Cr(III) individually, include adsorption, reverse

osmosis, and distillation [11]. Recently, the different

techniques, include, ion chromatography(IC),

inductively coupled plasma mass spectrometry

(ICP-MS) [12], stripping voltammetry (SV) [13],

co-precipitation [14], ame atomic absorption

spectrometry (F-AAS) [15], , inductively coupled

plasma optical emission spectrometry (ICP-OES)

[16], ion chromatography inductively coupled

plasma-mass spectrometry (IC-ICP-MS) [17] and

electrothermal atomic absorption spectrometry

(ETAAS) [18] were used for determination of

chromium species in water samples. Due to

difculty matrixes and low detection for chromium

in water samples, treatment process such as liquid-

liquid extraction (LLE) [19], dispersive liquid-

liquid microextraction (DLLME) [20], magnetic

solid-phase extraction (SPE) [21], dithiocarbamate-

modied magnetite nanoparticles (DC-MNPs) [22]

and cloud point extraction (CPE) [23] are developed.

Dispersive liquid-liquid microextraction (DLLME)

is a conventional technique, where the extraction

phase (a microliter of hydrophobic solvent) was

dispersed in the water sample. Many organic

solvents (ethanol, methanol, toluene) were used in

the extraction phase. Recently, ionic liquids (IL) as

green solvent, low vapor pressure, high stability, and

large viscosity have been used in LLE [24,25].

The aim of this study is the speciation of Cr (III)

and Cr (VI) in water samples based on HS-CH3-IM

by the USA-D-ILLME procedure. The important

parameters for the extraction of chromium were

optimized and the concentration of chromium was

determined by ET-AAS.

2. Experimental

2.1. Instrumental

Chromium was determined with an atomic absorption

spectrometer (AAS, GBC Plus 932, Australia) using

a graphite furnace accessory (GF3000, ET-AAS).

The main parameters such as temperature (ash,

atomized, drying), auto-sampler into graphite tube,

owrate Ar gas, and temperature programming for the

chromium were adjusted by the book manufacturer.

A hollow cathode lamp of chromium (HCLcr) tuned

at a current (6 mA) and a wavelength of 357.9 nm

with a slit of 0.2 nm was used. The linear range (1.5-

33 µg L-1) and sample injection of 20 μL was used

(Peak Area). The pH of samples was controlled by

a digital pH meter (Metrohm 744). A centrifuge and

shaker (Germany, Product N: SIAL311GZ2F) was

used for dispersing and separating IL from samples.

For validation results, ICP-MS (Perkin Elmer) was

used for ultra-trace determination of chromium in

standard and water samples.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85

2.2. Reagents and materials

Ultra-trace reagents with HPLC or AAS analytical

grade purchased from Merck or Sigma Co.

(Germany). The modier for chromium [Mg(NO3)2]

for increasing ashing temperature, hexane, ethanol,

acetone, HNO3, H2SO4, and HCl were prepared

from Merck, Germany. The standard solution of

Cr (III) was prepared from an appropriate amount

of Cr(NO3)3 in 0.01 mol L-1 HNO3 (1000 mg L-1

Cr III, 1.0 g L-1). The standard solution of Cr (VI)

was purchased from Merck which was prepared by

1.0 g of K2CrO4 in 1 % HCl (1000 mg L-1 CrVI).

The standard solutions fthe or calibration curve of

chromium (0.1, 0.2, 0.4, 0.5, 1.0, 1.5 µg L-1) were

prepared daily by dilution of the stock solution. The

pH adjustments were made using appropriate buffer

solutions including sodium phosphate for pH 2.0-2.5,

ammonium acetate for pH 4.0-5.5 and ammonium

chloride for pH 8-10 (Merck). 2-Mercapto-1-

methylimidazole as Task-specic ionic liquid was

purchased from Sigma, Germany (HS-CH3-IM,

CAS N: 60-56-0, 25 g). Ultra-pure water (DW) was

obtained from a pure Water System (RIPI).

2.3. Water Sampling

The glass tubes were washed with HNO3 solution

(1 M) for two days and rinsed 10 times with DW.

Due to low concentrations of chromium in water

samples, even trace contamination, and sample

storage caused to affect the accuracy of the results.

The acidied water sample was put into the conical

tube (10-20 mL) and kept at -20OC. After ltering,

water samples were prepared from river water from

Karaj, well water from Varamin city, drinking water

from Tehran city, industrial wastewater, Tehran, Iran

prepared by ASTM procedure for waters.

2.4. Extraction Procedure

A pre-concentration procedure based on HS-CH3-

IM by the USA-D-ILLME was performed as

follows: rst, 100 mg of HS-CH3-IM as a TSIL, 0.2

mL of acetone were mixed and injected into 10 mL

of water and chromium standard samples (Fig.1).

After shaking for 5 min, the Cr VI and Cr III were

extracted by thiol group of HS-CH3-IM at pH 2 and

5, respectively. For optimizing, 10 mL of 0.1 - 1.5

μg L-1 Cr (III) and Cr (VI) standard solutions as the

lower and upper limit of quantication was used

instead of water samples in a conical centrifuge

tube. First, 100 mg of HS-CH3-IM dispersed in 0.2

mL of acetone in a I mL syringe and injected to 10

mL of chromium standard in a conical tube. The

pH was adjusted at 2 and 5 by the buffer solutions,

then the mixture solution was shaken for 5 min, and

chromium extracted by TSIL at 25 OC. To separation

phase, the turbid solution was centrifuged for 5 min

at 4000 rpm and the liquid phase was vacuumed

with an autosampler. Then, Cr (III) and Cr (VI)

were back-extracted from TSIL in acidic and basic

by adding 0.25 mL of 1.2 mol L-1 HNO3 and 0.2

mL of 1.0 mol L-1 NaOH, respectively. Finally,

the remained aqueous phase was determined by

ET-AAS after dilution with DW up to 0.5 mL. In

the optimum pH conditions, total chromium was

calculated by summarizing Cr (VI) to Cr (III)

contents. The blank solutions proceeded in the same

way and were used for the calibration ET-AAS. The

extraction conditions based on the HS-CH3-IM (IL)

for chromium speciation were shown in Table 1.

Fig.1. The extraction and speciation chromium based on HS-CH3-IM by the USA ─D-ILLME procedure

Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al

3. Results and discussion

The TSIL (HS-CH3-IM) with the USA-D-ILLME

procedure was used for chromium speciation in the

standard solution and water samples. The results

showed us, the mean concentrations of Cr (III

and VI) in wastewater samples were signicantly

higher than water samples [(5.13 ± 0.22 μg L-1,

3.92 ± 0.18 μg L-1) and (0.19 ± 0.02μg L-1, 0.12 ±

0.01 μg L-1)], respectively.

The extraction recovery (Equation 1) was obtained

as the percentage of the ratio of the extraction

chromium (Cex) into the IL phase vs total chromium

in water(Ctotal).

Extraction Recovery =

(Eq. 1)

3.1. FTIR spectrum

The FT-IR spectra of HS-CH3-IM are presented in

Figure 2. The peak of FT-IR spectra at 1600 cm-1

is related to C=O bond vibration of the carboxylic

acid groups. The spectrum shows a band around

3100 cm-1 which can be attributed to the hydroxyl

groups. In addition, bands around 2900 cm-1 are

due to regular C-H stretching of the CH2 groups of

HS-CH3-IM.

3.2. PH effect

The effect of pH on extraction of Cr (III) and Cr(VI)

ions on the HS-CH3-IM as a TSILwas investigated

using different pH from 2 to 12 for 0.1 μg L-1 Cr (III)

and Cr(VI) ions as a lower LOQ and 1.5 μg L-1 Cr

(III) and Cr(VI) ions as upper LOQ. The extraction

was strongly dependent on the pH of solutions and

subsequently affected recovery. The results show

that the highest extraction efciency for Cr (III) was

achieved at pH 4 to 6 by the thiol group of the HS-

CH3-IM and the Cr (VI) extracted at pH 2-3. Thus,

the procedure was applied to speciation of two

forms of chromium at pH 5 and 2 for the Cr (III)

Table 1. Extraction conditions for chromium (III, VI) based on HS-CH3-IM by the USA ─D-ILLME method

ValueParameters

4 for Cr(III) and 2 for Cr(VI)

10 mL

0.2 mL for KOH/0.25 mL for HNO3

1 mL

1.0 mol L-1 for KOH/1.2 mol L-1 for HNO3

100 mg

200 mL

5 min

Sample volume

Volume of back-extraction reagents

Volume of Buffer (0.1-0.2 mol L-1)

Concentration of back-extraction

Amount of IL

Volume of Acetone

Shaking time

Centrifugation time

Fig.2. FTIR spectra for HS-CH3-IM

Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85

and Cr(VI), respectively (Fig. 3). The mechanisms

of Cr (III) and Cr(VI) ions on the HS-CH3-IM were

obtained by complex formation between Cr (III)

and Cr(VI) ions and HS groups of the HS-CH3-IM

at optimized pH. The HS can be deprotonated (SH-

) at a wide range of pH from 4 to 9. The extraction

efciency of Cr (III) can be attributed to the afnities

of HS of the HS-CH3-IM as a TSIL for the Cr 3+

cations existing at pH from 4 to 6. The different

anionic species of Cr (VI) exist at low and high

pH (pH=2 and pH > 8), namely HCrO4

-, CrO4

2- and

Cr2O7

2- and negatively charged of anionic species

can be extracted by positive charges of SH2+ group.

3.3. Sample volume

Sample volume is the main parameter for the

extraction of chromium in the water sample. So, the

effect of sample volume was studied in a range of

2- 25 mL for 0.1 - 1.5 μg L-1 of Cr (III) and Cr(VI),

respectively. High extraction was obtained between

2 mL and 12 mL of the water sample. At more

volumes, the extraction efciency was decreased.

On the other hand, TSIL can be soluble partially

in water at higher sample volumes and cause non-

reproducible results. Therefore, a sample volume

of 10 mL was used for this study with HS-CH3-IM

by the USA-D-ILLME method (Fig. 4).

Fig.3. Effect of pH on extraction and speciation of Cr (III) and Cr(VI) ions based

on HS-CH3-IM by the USA ─D-ILLME procedure

Fig. 4. Effect of sample volume on extraction and speciation of

Cr (III) and Cr(VI) ions based on HS-CH3-IM by the USA ─D-ILLME procedure

Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al

3.4. Amount of HS-CH3-IM

The results showed us that the extraction efciency

of Cr (III) and Cr(VI) ions was remarkably affected

by the amount of TSIL. Therefore, the amount of

TSIL was evaluated within the range of 50–250

mg. The extraction recovery was observed at more

than 80 mg TSIL. So, 100 mg of TSIL (HS-CH3-

IM) was chosen as optimum IL for extraction of

Cr (III) and Cr(VI) ions in water samples at pH 2

and 5 by the HS group (Fig. 5). For salty water

such as seawater, 120 mg of TSIL for 10 mL of

seawater must be used at optimized pH.

3.5. Centrifuge and sonication time

The sonication and centrifuge time are crucial to

achieving an efcient extraction based on HS-

CH3-IM by the USA-D-ILLME procedure. In this

research, the various sonication and centrifuge

times between 1-10 min was evaluated for

chromium extraction in water samples. The result

showed us, by increasing the sonication time

the relative response for extraction of chromium

increased and reached the maximum value at

4.5 seconds for HS-CH3-IM, and then remained

constant. Therefore, the ultrasonic times of 5.0

minutes for the Cr (III) and Cr(VI) extraction was

used. Also, the centrifuge time of 5.0 minutes

was selected for Cr (III) and Cr(VI) extraction in

water.

3.6. Effect of reagents on back-extraction

Due to the viscosity and organic structure of ionic

liquids, injection of IL into the graphite tube of the

furnace of ETAAS was not possible. So, based on

the USA-D-ILLME procedure, Cr (III) and Cr(VI)

were back-extracted from the HS-CH3-IM with

acid and base reagents. Due to previous research,

decreasing pH leads to dissociation and releasing

of chromium ions released into the aqueous phase

by decreasing or increasing pH. So, the different

concentrations of reagents such as HCl, HNO3,

H2SO4, KOH (0.5 -2.0 mol L-1) were used for

chromium back-extraction from the TSIL (Fig.

9). The research showed that 1.2 mol L-1 of HNO3

Fig. 5. Effect of HS-CH3-IM on extraction and speciation of Cr (III)

and Cr(VI) ions by the USA ─D-ILLME procedure

Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85

(0.25 mL) can be back-extracted Cr (III) from the

HS-CH3-IM to the liquid phase. Also, 1.0 mol

L-1 of KOH (0.2 mL) can be back-extracted Cr

(VI) from the HS-CH3-IM phase. After back-

extraction, the resultant solution was adjusted

to 0.5 mL with DW in a centrifuge conical tube

before determining by ET-AAS (Fig. 6).

3.7. Validation of methodology

The USA ─D-ILLME method was applied to

determine Cr (VI) and Cr (III) found in 10 mL

of water samples. The Cr (VI) and Cr (III) in

wastewater and water samples were evaluated (20

n). The mean concentration of Cr (VI) and Cr (III)

in wastewater was higher than in water samples.

Also, the mean concentration of Cr (VI) in well

water was lower than Cr (III) concentration. The

coloration analysis was achieved between Cr

(III) and Cr (VI) in industrial water and drinking

waters and there was a high correlation (r > 0.66).

In addition, in drinking waters, no correlation and

regression were shown between Cr (III) and Cr

(VI) (r > 0.12). The spiked water and wastewater

samples were used to demonstrate the reliability

and validation of the method for speciation and

determination of Cr (III) and Cr (VI) (Table 2). By

back-extraction process, the remaining solution

was spiked with standard solutions of Cr (VI) and

Cr (III) and analyzed with ET-AAS after extraction

based on the HS-CH3-IM by the USA-D-ILLME

method (Table 3). The recovery of spiked samples

is satisfactorily results, which shows the ability of

the procedure for determination and speciation of

the Cr (VI) and Cr (III)

in water samples. For validation of the proposed

method, certied reference materials in waters

(CRM) were obtained by ICP-MS. The spiking

CRM with the chromium standard solution showed

us the validation of methodology for speciation

and determination of Cr (VI) and Cr (III) in water

samples (Table 4). Due to results, high efciency

and accuracy were achieved for the determination

and speciation of Cr (VI) and Cr (III) in water

samples.

Fig. 6. Effect of reagents (acid and base) on back-extraction of Cr (III) and Cr(VI) ions

by the USA ─D-ILLME procedure

Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al

Table 2. The coloration analysis for chromium determination of wastewater and water samples

in different cities, Iran (n=20, μg L-1)

City *Wastewater (n=20) water (n=20) Wastewater

Cr III Cr VI Cr III Cr VI r P-value

Tehran 1.07 ± 0.77 4.28 ± 0.04 0.09 ± 0.22 0.11 ± 0.02 0.098 <0.002

Karaj 2.51 ± 0.03 2.03 ± 0.69 0.14 ± 0.02 0.07 ± 0.04 0.331 <0.001

Kerman 0.75 ± 0.13 1.94 ± 0.81 0.10 ± 0.11 0.06 ± 0.05 0.113 <0.005

*Wastewater diluted with DW up to 50 mL (1:5)

Table 3. Validation of chromium speciation based on the HS-CH3-IM with spiking water samples

by the USA-D-ILLME method

Sample* Added (μg L-1)*Found (μg L-1) Total Recovery (%)

Cr (III) Cr (VI) Cr (III) Cr (VI) Cr (III) Cr (V)

Water 1

--- --- 1.235 ± 0.034 1.028 ± 0.037 2.263 ± 0.088 --- ---

1.0 --- 2.205 ± 0.104 1.055 ± 0.032 3.260 ± 0.126 97.0 ---

--- 1.0 1.229 ± 0.029 1.996 ± 0.097 3.225 ± 0.127 --- 96.8

Water 2

--- --- 0.224 ± 0.012 0.188 ± 0.013 0.412 ± 0.022 --- ---

0.2 --- 0.419 ± 0.019 0.191 ± 0.012 0.610 ± 0.028 97.5 ---

--- 0.2 0.226 ± 0.011 0.393± 0.021 0.619 ± 0.031 --- 102.5

**Wastewater 1

--- --- 4.213 ± 0.186 2.450 ± 0.105 6.663 ± 0.298 --- ---

2.0 --- 6.197 ± 0.304 2.447 ± 0.094 8.644 ± 0.386 99.2 ---

--- 2.0 4.198 ± 0.191 4.406 ± 0.178 8.604 ± 0.411 --- 97.8

**Wastewater 2

--- --- 2.155 ± 0.086 3.175 ± 0.128 5.330 ± 0.237 --- ---

2.0 --- 4.163 ± 0.204 3.179 ± 0.132 7.342 ± 0.335 100.4 ---

--- 3.0 2.162 ± 0.094 6.104 ± 0.275 8.266 ± 0.403 --- 97.6

Water 5

--- --- 0.532 ± 0.025 0.082± 0.004 0.614 ± 0.031 --- ---

0.5 --- 1.026 ± 0.045 0.079 ± 0.003 1.105 ± 0.048 98.8 ---

--- 0.1 0.528 ± 0.024 0.177 ± 0.005 0.705 ± 0.032 -- 95.0

*Mean of three determinations ± condence interval (P = 0.95, n =5)

**wastewater diluted with DW (1:5), so the result calculated after dilution factor (DF× 5)

Water 1: River water from Karaj

Water 2: Drinking water from Tehran city

Water 5: Well water from Varamin city

Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85

4. Conclusions

In this study, a novel method based on HS-CH3-IM as

TSIL was used for the speciation and determination

of the Cr (III) and Cr (VI) in water samples by the

USA-D-ILLME procedure. The important factors

for high extraction were optimized. By procedure,

a sensitive, efcient, low cost, and simple method

for speciation and preconcentration of the Cr (III)

and Cr (VI) in water samples were achieved. Under

optimized conditions, the working range (WR),

LOQ, and RSD% were obtained 0.05–3.6 μg L−1, 50

ng L−1, and 1.45, respectively. The performance of

the method for quantication analysis of chromium

in water samples was obtained. The analytical

performances of detection of Cr (III) and Cr (VI)

in water samples are comparable to previously

reported methods. Finally, the speciation chromium

based on HS-CH3-IM was revealed that most of Cr

(VI) and Cr (III) exist in industrial wastewaters.

5. Acknowledgments

The authors thank from Department of Chemistry,

College of Science, Shahid Bahonar University of

Kerman, Iran

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Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

Sensitive voltammetry method for analysis of the antioxidant

pyrogallol using a carbon paste electrode with CdS

nanoparticle

Hamideh Asadollahzadeha,* and Mahdieh Ghazizadeha

a Department of Chemistry, Faculty of Science, Kerman branch, Islamic Azad University, Kerman, Iran,

P. O. Box 7635131167, Kerman, Iran

ABSTRACT

A voltammetry method for the determination of pyrogallol (PY) was

developed employing a carbon paste electrode (CPE) modied with

CdS nanoparticle that was synthesized by microwave. The effect of

different parameters i.e. time and irradiation power on the morphology

and the sample’s particle size have been investigated. The synthesized

nanostructures were characterized by X-ray diffraction and scanning

electron microscopy. The optimized condition for time and power

consumption to prepare CdS nanoparticles was obtained 4 min and

360 W. Cyclic voltammetry study of the modied electrode indicated

that the oxidation potential shifted towards a lower potential by

approximately 106 mV and the peak current was enhanced by 2 fold

in comparison to the bare CPE. The effect of pH and interferences

from some inorganic salts and organic compounds were studied.

The usability of this method for the quantication of pyrogallol was

investigated with differential pulse voltammetry (DPV). Under the

optimal conditions, the peak current was proportional to pyrogallol

concentration in the range of 7.0 ×10-7 to 3.0 × 10-4 mol L-1 with a

detection limit of 4.8 × 10-7 mol L-1. These values are satisfactory

for application to real samples. Finally, the developed method was

successfully used for the analysis of real samples.

Keywords:

Pyrogallol,

Analysis,

Carbon paste electrode,

Differential pulse voltammetry (DPV),

Cyclic voltammetry(CV),

CdS nanoparticles

ARTICLE INFO:

Received 12 Dec 2021

Revised form 7 Feb 2022

Accepted 28 Feb 2022

Available online 29 Mar 2022

*Corresponding Author: Hamideh Asadollahzadeh

Email: asadollahzadeh90@yahoo.com

https://doi.org/10.24200/amecj.v5.i01.171

------------------------

1. Introduction

Pyrogallol is an important kind of polyphenol with a

strong reduction property and has been widely used

as a useful antioxidant and scavenger free radicals.

Free radicals are chemical species possessing

an unpaired electron that can be considered as

fragments of molecules that are generally very

reactive [1]. Oxidative stress is a phenomenon

caused by an imbalance between the production

and accumulation of oxygen reactive species (ROS)

in cells and tissues and the ability of a biological

system to detoxify these reactive products. Oxidative

stress is the cause of many human diseases like

diabetes, thyroid disorders, hypertension, arthritis,

etc [2, 3]. Antioxidants are compounds that act

as inhibitors of oxidative damage [1]. Therefore,

the determination of pyrogallol is very important

in chemistry, environment, clinic, and biological

system. There are several methods have been

developed for the determination of pyrogallol, such

as UV spectrophotometry [4], chromatography

[5], electrochemiluminescence [6]. However,

these instrumental methods have suffered some

disadvantages such as being time-consuming, solvent

usage intensive, and requiring expensive devices

and maintenance [1]. Electroanalytical methods

represent a cheaper alternative with the possibility of

eld analysis. Modied electrodes have been widely

used in sensitive and selective analytical methods

for the detection of trace amounts of antioxidants

[7-10]. These modied electrodes have shown good

electrocatalytic properties, high surface-to-volume

ratios, high stabilities, and fast electron transfer rates

[8]. Nanomaterials may be mixed with electrode

materials or may be attached to the electrode surface

[11]. Carbon paste electrode has been extensively

modied with nanomaterials and has been used to

measure a wide range of compounds .This is due

to modied electrodes with nanoparticles that can

enhance the electrocatalytic property, stability, fast

reaction rate, and reproducibility in the results.

Various types of nanoparticles such as metal

nanoparticles [12], metal oxides [13], and even

composite nanoparticles [14-16] have been used

to modify the electrodes. Several strategies based

totally on bodily and chemical methods have been

advanced for the synthesis of controlled size and form

nanoparticles [17]. Examples of these procedures

involve solvothermal techniques, template-assisted,

kinetic increase management; sonochemical

reactions, and thermolysis of unmarried-supply

precursors in ligating solvents [17]. Microwave

Irradiation (MWI) methods provide simple and

speedy routes to the synthesis of nanoparticles on

account that no excessive temperature or excessive

strain is needed. The heating effect is generated by

the interaction of the dipole moment of the

molecules with electromagnetic radiation at high

frequency. Moreover, MWI is specically benecial

for a managed huge-scale synthesis that minimizes

the thermal gradient consequences [18-20]. To our

knowledge, no study has reported the electrocatalytic

oxidation of pyrogallol by using CdS modied

carbon paste electrode.

Thus, in the present work, CdS nanoparticles have

been synthesized using a microwave irradiation

process. In this process, changes in power and time

of microwave irradiation caused different CdS

morphologies. A modied carbon paste electrode

is fabricated by using CdS nanoparticles for the

determination of pyrogallol.

2. Experimental

2.1. Chemicals and Reagents

Pure pyrogallol, thioacetamide (TAA), sodium

dihydrogen orthophosphate (NaH2PO4), disodium

hydrogen phosphate (Na2HPO4), sodium phosphate

(Na3PO4), orthophosphoric acid (H3PO4), sodium

hydroxide (NaOH), hydrochloric acid (HCl),

Cd(NO3)2.4H2O and graphite powder were obtained

from Merck. The buffer solutions were prepared

from orthophosphoric acid and its salts in the pH

range of 1 to 7. All the aqueous solutions were

prepared by using double distilled water. High

viscosity parafn (d =0.88 kg L−1) from Merck

was used as the pasting liquid for the preparation of

the carbon paste electrodes.

2.2. Apparatus

Electrochemical studies were performed using a

Metrohm polarograph potentiostat-galvanostat

(Metrohm Computrace 797-VA). Three-electrode

system consisted of a bare CP and CdS/CP

electrode as the working electrode, Ag/AgCl (3

M KCl) as the reference electrode, and a platinum

wire as the auxiliary electrode. A Metrohm 691

pH/Ion meter was used for pH measurements.

Solutions were degassed with nitrogen for 10

min prior to the recording of the voltammogram.

X-ray diffraction (XRD) patterns were recorded

by a Philips, X-ray diffractometer using Ni

ltered Cu Ka radiation. Scanning electron

microscopy (SEM) images were obtained from

LEO instrument model 1455VP.

2.3. Synthesis of CdS Nanoparticles

To synthesize CdS nanoparticles, 1mmol of

Cd(NO3)2 was solubilized in 10 mL of water and

stirred for 10 min. Subsequently, 0.1 mmol of

thioacetamide has added to the solution and stirred

for 15 min. Then the mixture was left for the

reaction to proceed by cyclic microwave radiation

at 360 W power for 4 min. Each cycle was 90 s

long, and composed of 30 and 60 s for the on and

off periods, respectively. The nal precipitate was

washed with water and ethanol, dried at 80 ºC for

24 h.

Analysis of Pyrogallol by carbon paste electrode with CdS Hamideh Asadollahzadeh et al

2.4. Preparation of bare carbon paste electrode

and modied carbon paste electrode

The modied carbon paste electrode was prepared

by hand mixing 0.2 g of CdS nanoparticles with

0.9 g graphite powder with a mortar and pestle.

Then parafn was added to the above mixture and

mixed for 30 min until a uniformly wetted paste was

obtained. This paste was then packed into the end

of a glass tube (ca. 3.35 mm i.d. and 10 cm long).

Electrical connection implemented by a copper wire

leads tted into the tube. A fresh electrode surface

was obtained by squeezing out a small portion of

paste and polishing it with lter paper until a smooth

surface was obtained. Unmodied CPE was prepared

in the same way without adding CdS nanoparticles.

2.5. General procedure for the determination of

pyrogallol

A 25 ml aqueous solution of analyte-containing

5 ml of 0.1 M phosphate buffer at pH 6 and a

specic amount of sample solution was added

to the cell and purged with puried nitrogen

for 5 min to remove oxygen (Fig 1) and CV

and DPV voltammograms were recorded. The

scanning potential was varied from 0 to 0.8

V. Cyclic voltammogram was recorded by the

anodic potential scanning at scan rate 50 mVs-1.

A renewed surface electrode was used for each

measurement.

3. Results and discussion

3.1. XRD analysis

The XRD pattern of the as-obtained CdS

nanoparticles was shown in Figure 2. The

diffraction peaks observed can be indexed to

pure cubic phase CdS with cell constants a =

b = c = 5.3580 A ° (JCPDS No. 05-0731). The

XRD results proved the high crystallinity and

purity of the products synthesized by this method.

According to XRD data, the crystallite size

Anal. Methods Environ. Chem. J. 5 (1) (2022) 86-96

Fig 1. The procedure of voltammetry for determination of pyrogallol

(Dc) of CdS nanoparticles can be determined by

using the Debye-Scherrer formula. The obtained

average particle size was found to be 45 nm.

The dependence of morphology and the average

particle sizes of the products on the irradiation

power was also investigated.

3.2. Scanning electron microscopy

SEM images of the CdS obtained with

thioacetamide in different powers of 180, 360,

and 540 W are shown in Figure 3a–d respectively.

As can be seen from SEM images, at 180 W

power, due to the insufcient heat of the reaction,

cohesive particles are formed. At 540 W, due

to the very high energy produced in this power,

the nucleation of the particles is increased, and

since the particles have a very active surface,

large and cohesive masses are obtained in all

test conditions. However, at 360 power, the

reaction is faster due to the generation of more

free radicals in solution and increased heat

production due to the rotation of these active

species. The formed nanoparticles have relatively

smaller sizes and better distribution. Therefore,

the sample prepared in 360 W power and 4

min time due to the creation of nanoparticles in

nanometer size according to the scale of images

and homogeneous distribution is an optimized

condition for time and power consumption to

prepare of CdS nanoparticles.

Analysis of Pyrogallol by carbon paste electrode with CdS Hamideh Asadollahzadeh et al

Fig. 2. XRD patterns of the synthesized CdS prepared by microwave irradiation

3.3. Electrochemical behavior of pyrogallol at

the CdS/CPE

The electrochemical behavior of pyrogallol has been

studied in two electrodes. Cyclic voltammetry (CV)

was applied to investigate the electrochemical behavior

of 0.4 mM pyrogallol in 0.1 M phosphate buffer at pH

6 with a bare CPE and a CdS/CPE (Fig. 4).

As shown in this Fig 3, in the presence of

pyrogallol, an irreversible oxidation peak at 0.520

V on the bare CPE attributed to the electrochemical

oxidation of pyrogallol. In the case of the CdS /

CPE, the oxidation peak of pyrogallol decreased

to 0.355 V and the peak current increased by 2.0

times compared with that for the bare CPE. These

results suggested that CdS obviously accelerate

the electron transfer at the electrode surface

and improve the electrochemical performance

accordingly.

Anal. Methods Environ. Chem. J. 5 (1) (2022) 86-96

Fig. 3. SEM images of the CdS nanoparticles at (a) 180 W, (b) 360 W and (c, d) 540W

3.4. Effect of pH

The effect of the pH of the solution on the

electrochemical response of pyrogallol was

investigated from pH 1.0 to 7. Due to Figure 5,

the anodic peak current of pyrogallol increased

with increasing pH and the highest peak current

was obtained at a pH of 6.0. Additionally, anodic

potential peaks shifted by 165 mV to a more negative

potential upon increasing pH, which is better for

pyrogallol oxidation. Thus, a buffer solution with

a pH of 6.0 was selected for further studies. In

addition, the relationship between oxidation peak

potential (Ера) and pH value was also investigated

and the results are shown in Figure 5. As pH value

increases from 1.0 to 7.0, the Ера shifts linearly to

a more negative potential, obeying the following

equation: Eра= 631.3–55.4 pH, R2 = 0.9979. (1)

The slope of Ера/pH is –55.4 mV, suggesting that

the number of electrons and protons involved in the

oxidation of pyrogallol is equal.

3.5. Effect of scan rate

The effect of scan rate on the electrocatalytic

oxidation of pyrogallol at the CdS/CPE was

investigated by cyclic voltammetry. As can be seen

in Figure 6a, the scanning potential increases the

peak pyrogallol oxidation shifts to more positive

potentials, which imposes a kinetic constraint on the

electrochemical reaction. Figure 6b illustrates that

a linear relationship existed between the oxidation

peak currents of pyrogallol and the square root

(v1/2) of the scan rate in the range from 10 to 150

mVs-1, indicating a diffusion-controlled process.

The linear regression equation was expressed as

I(µA)= 4.178v1/2 +10.657 (R2 =0.9925).

3.6. Calibration curve

In order to develop a voltammetric method for

the determination of the drug, the DPV mode is

selected, because the peaks are sharper and better

dened at lower concentrations of pyrogallol

Analysis of Pyrogallol by carbon paste electrode with CdS Hamideh Asadollahzadeh et al

Fig. 4. Cyclic voltammograms of CPE and CdS/CPE at the presence of 0.4 mM

pyrogallol in 0.1 phosphate buffer solution (pH 6) at scan rate 50 mVs-1

92 Anal. Methods Environ. Chem. J. 5 (1) (2022) 86-96

Fig. 6. (a) Cyclic voltammograms of CdS/CPE in the presence of 0.4 mM of pyrogallol in 0.1 phosphate buffer

solution (pH 6) at different scan rates (from inner to outer): 10, 30, 50, 70, 100, 130 and 150 mV s-1.

(b) peak current vs. square root of scan rate (v ½).

Fig.5. a) Cyclic voltammogram of pyrogallol at different pH

b) Relationship between the peak potential of pyrogallol and pH

than those obtained by cyclic voltammetry, with a

lower background current, resulting in improved

resolution. According to the obtained results, it was

possible to apply this technique to the quantitative

analysis of pyrogallol. The phosphate buffer

solution of pH 6 was selected as the supporting

electrolyte for the quantication of pyrogallol as it

gave maximum peak current at pH 6. DPV obtained

with increasing amounts of pyrogallol showed that

the peak current increased linearly with increasing

concentration, as shown in Figure 7. Using the

optimum conditions described previously, linear

calibration curves were obtained for pyrogallol in

the range of 7×10 -8 to 3×10-4 M. (Fig. 7 Inset). The

linear equation I= 222.9 x+3.068 (R2=0.9969). The

limit of detection (LOD), dened as DL = 3Sb/m

(where DL, Sb, and m are the limits of detection,

the standard deviation of the blank and slope of the

calibration graph, respectively) was found to be

0.48 μM of pyrogallol.

3.7. Interference study

To assess the prospects of the electroanalytical

assays, several possible interferences of organic

and inorganic chemicals were added into the 100

μM pyrogallol solutions to evaluate their effects on

the current responses. The results were shows no

signicant signal change (below 5%) when 1000-

fold phenol and hydroquinone Ca2+, urea, Mg2+,

and 500 fold of glucose, caffeine, Na+, K+, Cl–, and

100 fold of Zn2+, Fe2+, 10-fold folic acid, ascorbic

acid were added.

3.8. The repeatability and stability

The repeatability of the CdS/CPE was examined

by the determination of 0.8 mM of pyrogallol in

0.1 M phosphate buffer solution at pH=6 with

the same electrode 5 times. A relative standard

deviation (RSD) value of 3.92% was observed,

indicating good reproducibility of CdS/CPE

for pyrogallol determination. Furthermore, the

Analysis of Pyrogallol by carbon paste electrode with CdS Hamideh Asadollahzadeh et al

Fig. 7. (a) DPV obtained at a CdS/CPE for different concentrations of pyrogallol (0.7 to 300 µM). Inset:

(b) linear relationship between the peak current and concentration of pyrogallol, scan rate: 50 mV s-1

94 Anal. Methods Environ. Chem. J. 5 (1) (2022) 86-96

operational stability of CdS/CPE was investigated

by the CV method every 2 days in 23 weeks. Only a

small decrease of current (about 4.0%) for 0.1 mM

pyrogallol was observed, which can be attributed

to the good stability of the modied electrode.

3.9. Analysis of real samples

In order to evaluate the applicability of the proposed

method in the real sample analysis, it was used to

detect pyrogallol in tap water and green tea. The

concentration of pyrogallol in these samples was

obtained according to the calibration curve, and

the results are listed in Table 1. In addition, the

accuracy was evaluated by performing a recovery

test after spiking the samples. The recovery is

between 96.0 and 103.7 %, indicating that the

determination of pyrogallol CdS/CPE is accurate

and feasible. Analytical parameters obtained here

were compared with results obtained by other

methods which show that they are comparable or

better than the values reported by other groups

(Table 2).

4. Conclusion

The CdS nanoparticles were synthesized via the

microwave method. This method is rapid, simple, and

can be easily controlled. The inuence of different

power on the morphology of the products was

investigated. Cyclic voltammetry and differential

pulse voltammetry determination of pyrogallol

was successfully performed using CPE modied

with CdS, which has shown an electrocatalytic

effect on the oxidation of pyrogallol. The proposed

electrode exhibited good sensitivity and stability

for the determination of pyrogallol, with reduced

overpotential. The pyrogallol peak current is linear

Table 1. Results of the recovery tests for pyrogallol using the CdS

Row Sample Spiked (µM) Found(µM) Recovery(%)

1Tap water 0 Not detected -

40 38.4 96

150 155.6 103.7

2Green Tea 0 Not detected -

40 41.3 103.25

150 153.1 102

Table 2. Comparison of detection limits and linear ranges obtained with the proposed electrode for determination

of pyrogallol with those obtained by others

Working system Linear range (µM) Detection limit (µM) Ref.

Pretreated Pt electrode 1-100 0.6 21

Au/CNT/PPY/HRP 1.6-22.4 1.24 22

GCE/poly(PPY-CD) 1 - 10 1.8 23

SPCE 10-1000 0.33 24

SiO2-CPE 2-300 0.7 25

CdS-CPE 0.7-300 0.485 This work

Analysis of Pyrogallol by carbon paste electrode with CdS Hamideh Asadollahzadeh et al

from a concentration range of 0.7 µM to 300 µM

with an excellent R2 value of 0.9969. The detection

limit of this modied electrode was found to be

0.48 µM and good reproducibility, high stability

was obtained for the determination of pyrogallol

using this electrode. The content of pyrogallol

in tap water and green tea was successfully

determined with CdS/CPE, which indicated the

modied electrode is useable for the determination

of pyrogallol concentration in real samples.

5. Acknowledgment

The author is grateful to Islamic Azad University,

Kerman Branch, for nancial assistance of this work.

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