Analytical Methods in Environmental Chemistry Journal Vol 1(2018) 47-56
Research Article, Issue 1
Analytical Methods in Environmental Chemistry Journal
AMECJ
A magnetic graphitic carbon nitride as a new adsorbent for simple
separation of Ni (II) ion from foodstuff by ultrasound-assisted
magnetic dispersive-micro solid phase extraction method
Bahareh Fahimirada and Alireza Asgharia*
a Department of Chemistry, Semnan University, Semnan, Iran
A R T I C L E I N F O:
A B S T R A C T
In this research, a magnetic graphitic carbon nitride (g-C3N4-SnFe2O4) was
Received 18 Sep 2018
successfully synthesized and utilized as an efficient adsorbent for nickel (Ni2+)
Revised form 16 Nov 2018
separation/extraction from vegetable samples by ultrasound-assisted magnetic
Accepted 25 Nov 2018
dispersive micro solid-phase extraction (UA-M-D-μSPE). After separation
Available online 28 Dec 2018
and preconcentration step, Ni ions were determined via micro-sampling flame
atomic absorption spectrometry (MS-FAAS). A successful synthesis of g-C3N4-
SnFe2O4 was investigated by Fourier transform infrared spectroscopy (FT-
------------------------
IR), X-ray diffraction (XRD), field emission scanning electron microscopy
(FE-SEM), and vibrating sample magnetometer (VSM). The optimization of
Keywords:
adsorption and desorption steps was effectively studied by the on-at-a time
g-C3N4
method. In addition, under the optimum experimental conditions, the limits
of detection (LODs), the linear ranges (LR) and relative standard deviations
Ni (II)
(RSDs%, for n = 5) were obtained 1.0 μgL−1, 4.0 ─ 500.0 μgL−1, and 1.4
Vegetables
respectively.
SPE
SnFe2O4
1. Introduction
electrothermal atomic adsorption spectrometry
One of the important category of foodstuff is
(ETAAS), inductively coupled plasma-optical
Vegetables. This category of foodstuff contain
emission spectrometry (ICP-OES), and inductively
vitamins, anti-oxidants, minerals, and diverse
coupled plasma-mass spectrometry (ICP-MS)[7].
beneficial phytochemicals[1,
2]. In presence of
But micro-sampling-FAAs (µ-FAAs) due to low
heavy metals in vegetables, even at trace levels, is
cost which requires a low operational facility, and
one of health concern from industrial wastewater
uses a small volume of the eluent, has recently been
[3]. Among a variety of metal ions, nickel is toxic,
very much considered [7].
even at trace levels
[4-6]. Different methods
In any case, the use of these methods to measure low-
use for determination of this metal ion such as
nickel amounts is not suitable because of their low
flame atomic adsorption spectrometry
(FAAS),
sensitivity. Therefore, the sample preparation step
is required before the measurement by the µ-FAAs
aasghari@semnan.ac.ir
* E-mail:
[8]. Among the various types of sample preparation
48
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
methods, solid phase extraction (SPE) is very much
FeCl3.6H2O, HCl (37%), HNO3, NaOH, H2SO4,
appreciated due to its simplicity, low cost, high speed;
and ethanol were of the highest available purity,
moreover, the solid phase extraction requires low
supplied from Merck Company. Standard solution
amounts of reagents, a high recovery, environmentally
was prepared by dissolving appropriate amounts
friendly, and a low organic solvent consumption [9,
of Ni (NO3)2. In addition, 3H2O in doubly distilled
10]. The ultrasound-assisted dispersive magnetic
water at a concentration of 1000 mg L−1. Working
solid-phase extraction
(UA-DM-SPE) is a new
standard solutions with intermediate concentrations
form of SPE which leads to more rapidity and ease
were prepared daily by dilution of the stock
of operation compared with the conventional SPE.
solutions.
In this method, using ultrasonic waves, the contact
surface of the adsorbent with the analyte is increased
2.2. Instrumentation
in a very short time, as well as due to the adsorbent
For determination of Ni(II) in the samples, an
magnetic property, the centrifuge step is removed
Agilent model 240 AA Shimadzu (USA) flame
and the process of separation and preconcentration is
atomic adsorption spectrometer was used with the
performed in short time [8]. As a result, in this method
Ni hollow cathode lamps as the radiation sources.
use a novel nanoadsorbents with a high adsorption
The pH values of the solutions were adjusted by a
efficiency and the easy separation is an important
pH meter, PHS-3BWModel (Bell, Italy) with a glass
step. A graphitic carbon nitride (g-C3N4) is a new form
combination electrode. An ultrasonic bath (SW3,
of organic polymer-like material, and due to its quick
Switzerland) was used at a frequency of 50/60 kHz
and facile synthesis, special structure, and low cost has
to dissipate adsorbent in a sample solution.
been a lot touched recently [11]. The g-C3N4 sheets
Fourier transform-infrared
(FT-IR) spectra
can be used as SPE sorbents, but they have several
using a Shimadzu
8400s spectrometer were
problems, such as Re-aggregation of the nanosheets,
determined in the range of
400-4000 cm-1.
and also their low surface area [12]. Therefore, to raise
Scanning electronmicroscopy (FE-SEM) analysis
any of the characteristics of this compound and rapid
was carried out using a Tescanvega II XMU
separation of it from sample solution, nanomagnetic
Digital Scanning Microscope. Energy-dispersive
of SnFe2O4 was used for increasing of surface area
X-ray spectroscopy elemental analysis
(EDX)
and separation of g-C3N4 of the solution.
of the samples was obtained using a Philips XL-
Therefore, in this work, the nanoadsorbent g-C3N4-
30 energy-dispersiveX-ray spectroscope. X-ray
SnFe2O4 with a very high absorption power as an
diffraction
(XRD) patterns were obtained on a
efficient nanoadsorbent for ultrasound-assisted
Burker AXS (Model B8-Advance). The magnetic
magnetic dispersive micro solid-phase extraction
properties were analyzed using a vibrating sample
(UA-M-D-μSPE) was synthesized and applied
magnetometer
(VSM, Lakeshore7407) at room
for the separation and preconcentration of the Ni
temperature.
(II) ion and toxic metal ion was measured using
the micro-sampling flame atomic adsorption
2.3. Synthesis of g-C3N4-SnFe2O4
spectrometry (µS-FAAS) technique.
3 g of melamine was placed in a crucible and hated
in 520 0C with a rate of 10 0C/min for 4 hours.
2. Experimental Procedure
Finally, yellow g-C3N4 precipitate was formed. In
2.1. Materials
the next step, to synthesis of SnFe2O4 nanostructure,
All the reagents used in this work including
SnCl2.2H2O and FeCl3.6H2O with a stoichiometric
melamine, Ni
(NO3)2.3H2O, SnCl2.2H2O,
ratio of 1:2 were mixed in 100 mL of distilled water
Separation of nickel from foodstuff by MGCN Bahareh Fahimirad, et al
49
and was heated at 80 0C. Then pH of the solution
for 4 min. Then, HNO3 solution as the eluent was
was adjusted using NaOH solution in 10. After
collected and then injected into FFAS by means of
3hours, a black precipitate of SnFe2O4 was formed.
a micro-sampler for determining the metal ions.
A black precipitate was collected by an external
The extraction recovery (ER), and relative recovery
magnetic field, and repeatedly washed with ethanol
(RR) for each metal ion were calculated as:
and distilled water. Finally, the black precipitate was
dried at 120 ° C for 24 h. To synthesis of the g-C3N4-
(1)
SnFe2O4 nanoadsorbent, 0.13 g of g-C3N4 whit 0.2 g
of the SnFe2O4 nanostructure was homogeneously
where Cinj is the concentration of the metal ions in
mixed by grinding in an agate mortar for 30 min
200 μl eluent (in the desorption step), and c0 is the
and then the powder was calcined in a furnace at
initial concentration of the metal ions.
400 0C for 4 hours [13].
(2)
2.4. Preparation of real samples
The vegetable were provided from Tehran markets
where cfound, creal, and cadded are the concentration
in Iran. The vegetables were cut into small pieces,
of the analyte after adding the standard to the
washed with deionized water. Then, the samples
real sample, concentration of the real sample, and
were dried in an oven for 24 hours. 25 mL of HNO3
concentration of the standard solution which was
(65%) was added to 1.2 gr of each sample and
injected to the real sample, respectively[14].
placed in acid overnight. Then the samples were
heated at 250 oC, until their liquid contents were
3. Results and discussions
evaporated, and they became almost dried. In order
3.1. Characterization of synthesized nanoadsorbent
to complete the digestive process, 5 mL of H2O2
The crystalline structures of g-C3N4, SnFe2O4,
(30%) was added to the samples and then heated
and g-C3N4-SnFe2O4 were determined by XRD.
to vaporize their liquid contents. Afterwards, the
In Fig.1a, two typical diffraction peaks can be
samples were washed with deionized water and
observed at 2ϴ= 27.47 and 13.510 for pure g-C3N4,
heated to boil the solutions. Then the contents were
which represent the inter-planar graphitic stacking;
cooled and transferred to sample flask of 25 mL,
these peaks well-agreed with the values in the
and diluted with deionized water to 25 mL. Finally,
standard card (JCPDF 87-1526). Also, in Fig 1b,
the pH values for the solutions were adjusted, and
the peaks at 2ϴ=20.18, 23.31, 33.23, 37.26, 39.2,
certain amounts of the metal ions were spiked.
40.98, 47.71, 53.75, and 59.38 confirm SnFe2O4.
Also Fig. 1c confirms the formation of the g-C3N4-
2.5. Procedure for magnetic dispersive micro
SnFe2O4 composite according to reference[8].
solid-phase extraction
The FT-IR spectra in Fig 2a shows the peaks for
10.0 mg nanoadsorbent was added to 10.0 mL
pure g-C3N4 at 1241,1319, and 1409 cm-1 can be
of sample solution in a glass vial containing
attributed to aromatic C-N stretching and the
containing 50.0 μgL-1 of Ni (II) at a pH value of
peak at 810 cm−1 can be attributed to triazine units
6.0. The solution was sonicated for 5 min at 25±3
and also, the peaks at 1568 and 1650 cm-1 can be
oC, and then the nanoadsorbent was separated from
related to C=N stretching [15, 16]. The adsorption
the solution by a magnetic field within 2 min. In
peak in Fig. 2 b at 570 cm-1 can be attributed to the
the desorption step, 250 μL of HNO3 (3 molL-1)
stretching vibrations of the Sn-O and Fe-O bonds
was added to the sample solution, and sonicated
[17]. Finally, the index peaks in Fig. 2c confirm
50
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
Fig. 1. FT-IR spectra of (a) g-C3N4 , (b) SnFe2O4, and (c) g-C3N4- SnFe2O4.
the formation of the g-C3N4-SnFe2O4 compound.
at room temperature. Fig. 4 show the magnetic
The FE-SEM micrographs for the nanostructures
hysteresis curve for SnFe2O4 and g-C3N4-SnFe2O4 in
g-C3N4 and g-C3N4-SnFe2O4 are shown in Figs.
an applied magnetic field. The maximum saturation
3a and b. According to these figures, the SnFe2O4
magnetization (Ms) values of SnFe2O4 and g-C3N4-
nanostructure is cubic with a quite uniform size of
SnFe2O4 were found to be 4.87 and 3.14 emu g-1
about 60-120 nm. The Fig 3b shows that the cubic
respectively. The results of this analysis show that
particles of SnFe2O4 are uniformly distributed on
synthesized nanoadsorbent has a good magnetic
the g-C3N4 surface. The magnetic properties of
strength, and that it can be separated easily from
the synthesized nanoadsorbent was investigated
the aqueous solution with the help of an applied
through a vibrating sample magnetometer (VSM)
magnetic field.
Fig. 2. XRD pattern of (a) g-C3N4 (b) SnFe2O4 and (c) g-C3N4- SnFe2O4.
Separation of nickel from foodstuff by MGCN Bahareh Fahimirad, et al
51
Fig. 3. SEM image of (a), g-C3N4 and (b) g-C3N4- SnFe2O4.
3.2 Optimization of experimental conditions
adsorbent, and the solution was ultrasound for
To investigation of effective parameters,
a specific time. In this step, Ni (II) was desorb
in adsorption step, first
10 mL of solutions
in to eluent, and finally was injected to FAAs
containing metal ions with concentration of
by using micro-sampling device.
10 µgL-1 were prepared and a certain amount
of adsorbent was added to it. Then, pH of
3.2.1 Effect of solution pH, adsorbent amounts,
solutions was set using HCl or NaOH solutions
and ultrasonic time in adsorption step
(0.1 molL-1) and the solution was ultrasound for
The solution pH was investigated in the range
a specific time. Then adsorbent was separated
of 3 to 8. The results in Fig. 5a show that in
by using magnetic field. In desorption step,
pH 6, the most recovery is achieved. In acidic
the certain volume of eluent was added to
pH values, there is a strong competition
Fig. 4. Magnetization curves of (a), SnFe2O4 and (b) g-C3N4- SnFe2O4.
52
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
Fig. 5. The effect of effective parameters on the recovery percentage of Ni(II) ion in adsorption step.
between H+ ions and metal ion, as the result
3.2.2 Effects of type, concentration, and volume of
in pH less than pH of 6, the recovery of metal
eluent, and ultrasonic time at the desorption step
ion adsorption decrease. On the other hand,
The eluents including HCl, HNO3 and H2SO4 were
in basic pH values, by increasing of OH
investigated on the recovery. The results in Fig 6a
concentration in sample solution, 1) the active
show that HNO3 for metal ion has as better eluent.
sits on the adsorbent surface ( OH and NH
The concentration of eluent and the volume of
groups), due to the formation of the hydrogen
eluent were investigated in rang 1 to 4 mol.L-1 and
bond, deactivated and as a result the recovery
in rang of 100 to 300 µL, respectively. According
reduce; 2) the reduction in recovery can be
to figure 6b and 6c the optimum concentration and
attributed to the formation of the precipitation
volume of eluent were obtained 3 mol.L-1 and 250
of some ion in the form of hydroxides [8]. The
µL of the eluent. The effect of ultrasonic time was
adsorbent amounts was investigated in range of
investigated in rang 2 to 5 min. The results in Fig
3 to 15 mg. The results in Fig 5b shows that an
6d show that by increasing of ultrasonic time to 4
absorbent amount of 10 mg of nano adsorbent
min the recovery of metal ion increase and then the
for the metal ion lead to most recovery. The
recovery is stationary. The result indicates that the
effect of ultrasonic time was investigated on
best time for this step was 4 minutes.
the recovery of metal ions in rang 2 to 6 min.
According to the results shown in figure 5c, the
3.3. Analytical validation
time of 5 min was selected as optimum time.
Under the optimized experimental conditions, the
linear ranges with determination coefficient (r2) of
Separation of nickel from foodstuff by MGCN Bahareh Fahimirad, et al
53
Fig. 6. The effect of effective parameters on the recovery percentage of Ni(II) ion in desorption step.
calibration 0.996 were obtained between 4.0-500.0
metals such as Ni(II) ion in vegetables, hence in
μg L-1. Limit of detection (LOD) for five replicates
the present work, the proposed method was used
were calculated 1.0 μg L-1.
to determination and extraction of Ni ion in the
Also, the relative standard deviations
(RSDs)
samples of Leek, Lettuce, Parsley, and Radish. For
were obtained for 5 repetitions, and were 1.4%.
this purpose, in the obtained optimum condition,
Finally, the results indicate that the proposed
the method was done in real samples, and relative
method has a good precision for the separation and
recovery
(RR) was calculated for Ni
(II) ions
preconcentration of trace amounts of Ni (II) ions.
according to the equation (2). The results in Table 1
show that measured amounts are in good agreement
3.4. Application of method in real samples
with added amounts of Ni (II) ions. Finally, the
Considering the importance of measuring of heavy
obtained results confirm the good high ability of
Table 1. Levels of metal ions in real samples.
aNi (II)
Sample
Added (μg L-1)
(found-real) (μg L-1)
bRR (%)
Leek
BDL
50
49.0±1.5
98.0
Parsley
BDL
50
49.5±1.3
99.0
Radish
BDL
50
50.0±1.5
100.0
Lettuce
BDL
50
48.8±4.0
97.6
a Mean of three determinations ± confidence interval (P = 0.95, n =5)
b Relative Recovery
54
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
Table 2. Effect of potentially interfering ions on recovery of metal ions.
Recovery%
Potentially interfering ions
Tolerance limita (Ci/Ca)
Ni(II)
Na+
1000
99.00
Mg2+
1000
100.00
NO3-
1000
99.00
Cl-
1000
99.40
Zn2+
600
98.83
Al3+
500
98.50
a Concentration ratio of potentially interfering and analyte ions. Adsorption conditions: 10 mg of
adsorbent, pH=6. Desorption conditions: 250 μL of HNO3 with concentration of 3 mol L-1.
the method for determination trace concentration
the proposed method and the other methods.
of Ni ion in real samples.
Table
3 shows the type of nanoadsorbent,
method, amount of nanoadsorbent, LOD,
3.5. Effect of foreign species on the recovery
RSD, and volume of eluent for the extraction
In the optimum condition, the effects of the
and preconcentration of the Ni (II) ions. The
foreign ions was investigated on the UA-M-D-
results in Table 3 show that maximum recovery
µSPE method. The tolerance limit is defined
in proposed method in compared with the
as the concentration that results in a change of
other method was obtained with the least
±5% in the recoveries. Accordingly, the results
amount of nanoadsorbent. Also, this method
in Table 2 indicate that the common ions with
is environmentally friendly due to the low
high concentrations in real samples do not have a
use of an elution solvent. This method is also
considerable interference effect on the recovery,
simple and fast. In addition to, compared with
and the adsorbent can be used for this method
the same methods, our method has a low RSD
without significant matrix effects.
and also the limit of detection this method is
comparable to the other methods presented in
3.6. Comparison methods with other methods of
Table3 .
SPE for separation Ni(II).
In order to demonstrate the efficiency of the
4. Conclusions
method, a comparison was done between
In this work, g-C3N4-SnFe2O4 adsorbent with a
Table 3. Comparison between EA-DM-µSPE and other published methods.
Amount of
Final
LOD
RSD
Adsorbent
Metal
Method
adsorbent
volume
Ref.
(ng.mL-1)
(ng.mL-1)
(mg)
of eluent
GO-H2NP1
Ni(II))
SPE column /FAAS
40
5.4 ×10-3
-
5.0 mL
[18]
Ion-imprinted polymers Ni(II)
SPE column /FAAS
200
0.2
2.5
5.0 mL
[19]
DMG/SDS-ACMNPs2
Ni(II)
SPE /FAAS
200
4.6
1.9
2.0 mL
[20]
Molecularly imprinted
Ni(II)
SPE column /FAAS
575
0.3
5.0
5.0 mL
[21]
polymers
This
g-C3N4-SnFe2O4
Ni(II) UA-M-D-µSPE /MS-FAAS
10
1.0
1.4
250 µL
work
1 Graphene oxide with covalently linked porphyrin
2 Dimethylglyoxim/sodium dodecyl sulfate-immobilized on alumina-coated magnetite nanoparticles
Separation of nickel from foodstuff by MGCN Bahareh Fahimirad, et al
55
good activity was successfully synthesized, and
extraction exploiting graphene oxide nanosheets,
its application was investigated for extraction and
Anal. chim. acta, 902 (2016) 33-42.
[5] L. Zhang, V. Hessel, J. Peng, Q. Wang, L. Zhang,
preconcentration of the Ni (II) ion using ultrasound-
Co and Ni extraction and separation in segmented
assisted magnetic dispersive micro solid-phase
micro-flow using a coiled flow inverter, Chem.
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Eng. J, 307 (2017) 1-8.
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[6] A.A. Gouda, S.M. Al Ghannam, Impregnated
adsorption spectroscopy.
multiwalled carbon nanotubes as efficient sorbent
The most important benefits of this method are:
for the solid phase extraction of trace amounts of
low time (9 min), low volume of eluent (250 µL),
heavy metal ions in food and water samples, Food.
Chem, 202 (2016) 409-416.
and low amount of adsorbent (10 mg). Finally,
[7] B. Barfi, A. Asghari, M. Rajabi, S. Sabzalian, F.
the results obtained showed that the method had
Khanalipoor, M. Behzad, Optimized syringe-
low LODs, a high recovery in a short time, and
assisted dispersive micro solid phase extraction
a good preconcentration factor due to the use of
coupled with microsampling flame atomic
a low amount of eluent for trace amounts of the
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understudied ions.
determination of potentially toxic metals in fruit
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5. Acknowledgment
[8] B. Fahimirad, A. Asghari, M. Rajabi, A novel
The authors would like to thank the Semnan
nanoadsorbent
consisting
of
covalently
University Research Council for the financial
functionalized melamine onto MWCNT/Fe3O4
support of this work.
nanoparticles for efficient microextraction of highly
adverse metal ions from organic and inorganic
6. Nomenclature
vegetables: Optimization by multivariate analysis,
FAAS: flame atomic adsorption spectrometry
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