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
23
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 difcult 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 efciency [20, 21]. In recent
years, novel carbon-based materials, such as
graphene and graphene oxide, carbon nanotubes
and nanobers, 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 efciency, 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 signicance [21]. In recent years,
novel carbon-based materials, such as bio-chars
[24], graphene and graphene oxide [25, 26], carbon
nanotubes and nanobers [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 modication 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 purication 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].
25
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
26
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 reects 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 efciency with air More than 95%
Absorption capacity 191.3 mg g-1 (2% Co and 2% Mo)
Adsorbent amount 40 mg
27
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
28
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
29
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 efcient 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 efciency 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 efciency 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 efciency 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 specic 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
30
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 efciency 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
31
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 conrmed
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 ± condence 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 ± condence interval (P = 0.95, n = 3)
**Mercury determined by MC3000
32
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 efciency 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 efciency of Hg0 based
on Ce−Mn/TiO2 was investigated by N2, 6% O2
and 500−2000 ppm of SO2. The average removal
efciency 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 efciently 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 efciency 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
efciency obtained was 95.26%. As compared to
Co-Mo/MWCNTs, the removal efciency 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 efciency 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 efciency 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
Efciency
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/Articial 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
33
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
efciencies 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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