Research Article, Issue 1
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
------------------------
Shahnaz Teimoori
a
, Amir Hessam Hassani
b,*
, Mostafaa Panaahie
b
a
PhD student of environmental engineering, Faculty of Natural Resources and Environment, Science and Research Branch, Islamic Azad University, Tehran, Iran
b
Department of environmental engineering, Faculty of Natural Resources and Environment, Science and Research Branch, Islamic Azad University, Tehran, Iran
Agency (EPA), benzene is one of the primary
pollutants that adversely affects human health [6] .It
is a serious health problem, causing several human
diseases such as cancer, central nervous system
disorders, leukemia, respiratory problems, skin
and eye diseases [7-9]. Considering these health
concerns and based on U.S.EPA announcement,
the standard level of benzene in drinking water
should not exceed 5 μg
-l
[6]. Therefore, it is crucial
to remove this pollutant from water supplies,
especially surface water, and ground waters. Since
their discovery by Iijima et al in 1991 [10], Carbon
nanotubes (CNTs) have been in a major area of
Extraction and determination of benzene from waters and
wastewater samples based on functionalized carbon nanotubes
by static head space gas chromatography mass spectrometry
1. Introduction
Benzene is a chemical aromatic and flammable
compound which is a natural component of
petroleum-derived products. It is one of the most
highly used groups of raw materials and solvents
in numerous chemical synthesis processes, and
manufacturing industries [1-3] .The presence
of benzene in groundwater is due to petroleum
product’s leakage into water sources and leaking
underground storage tanks and pipelines [4, 5].
According to the US Environmental Protection
* Corresponding Author: Amir Hessam Hassani
Email: ahh1346@gmail.com
DOI: https://doi.org/10.24200/amecj
A R T I C L E I N F O:
Received 30 Nov 2019
Revised form 10 Jan 2020
Accepted 11 Feb 2020
Available online 26 Mar 2020
Keywords:
Benzene,
Water,
Dispersive micro solid phase extraction,
Phenyl sulfonic acid,
Carbon nanotubes,
Static head space gas chromatography
mass spectrometry
A B S T R A C T
Removal of benzene, as hazardous pollutants from waters and
wastewater is a main problem of environment contamination due to
high risk factor in human health. In this study, the phenyl sulfonic acid
(PhSA) modified carbon nanotubes (CNTs) were used for benzene
removal from waters by dispersive micro solid phase extraction method
(D- μSPE). Due to adsorption mechanism, the polar–π and π–π electron
donor–acceptor interactions was provided between the aromatic ring
of benzene with the surface sulfonic acid groups (SO
3
H) and phenyl
ring (-C6H5) of CNTs, respectively. Therefore, 20-100 mg of sorbent,
concentration of benzene (0.1–10 mg L
-1
), pH (1-12) and contact time
(5–120 min) were investigated and optimized for benzene removal
from water samples in static system. The concentration of benzene
in water was determined by static head space gas chromatography
mass spectrometry (SHS-GC-MS). The results showed, the Langmuir-
Freundlich (LF) isotherm provided the best fit for benzene sorption.
By using the Langmuir model, the maximum adsorption capacity of
157.34 mg g
-1
and 22.86 mg g
-1
was achieved for benzene removal
from waters with CNTs@PhSA and CNTs, respectively. The method
was validated by certified reference material in waters.
Benzene extraction from waters by CNTs@PhSA Shahnaz Teimoori et al
Anal. Method Environ. Chem. J. 3 (1) (2020) 17-26
18
Anal. Method Environ. Chem. J. 3 (1) (2020) 17-26
interest within many contexts, especially in water
treatment. CNTs are graphitic carbon sheets folded
into hollow cylinders with diameters and lengths
in nanometer and micrometer scales, respectively
[11-13]. Unique properties of CNTs including
hydrophobicity, high specific surface area, hollow
and layered structure and existence of π-electrons
on their surface make them superior adsorbents for
removal of contaminants [14-16]. Some studies put
further steps and investigated the effect of CNT’s
modification on their adsorption performance. Lu
et al. showed that NaOCl-oxidized CNTs have
significant adsorption capacity in comparison
to other types of carbon adsorbents [17]. Su et al
conducted a research in which multiwalled carbon
nanotubes were oxidized by sodium hypochlorite
solution and turned to a new adsorbent with
enhanced adsorption performance [18]. These
studies show high affinity of CNTs toward organic
compounds, and open new avenue for developing
carbon nanotube technologies to treat benzene and
other organic chemicals in water. However, there is
a high number of CNTs that can be used to remove
benzene from water supplies and which subtype of
CNTs family can have the most effective adsorption
capacity, is still unknown. To our knowledge, so
far, there is no data about the adsorption capacity
of phenyl sulfonic acid (PhSA) modified hybrid
carbon nanotubes (CNTs). Therefore, the main
objective of this study is using phenyl sulfonic
acid (PhSA) modified hybrid carbon nanotubes
(CNTs) to remove benzene from water sources by
dispersive solid phase extraction method.
2. Experimental
2.1. Material and methods
Gas chromatography based on mass detector
(GC-MS) and air sample loop injection (ASL)
was used for benzene determination by static
head space accessory (SHS-GC-MS, Netherland).
The headspace may be sampled using a gas tight
syringe of appropriate volume. Gas-tight syringe
(GTS) was used for determination VOCs
1
from
water samples by shaking and heating samples.
1- Volatile organic compound
The auto-sampling of GTS units can retrofit to a
standard GC with a split/split less injector. The
GTS auto-sampler is beneficial for use with diverse
samples. The Agilent 7890A GC can accommodate
up to three detectors identified as front detector,
back detector, and auxiliary detector. This model
of GC design with three detectors in front, back,
and auxiliary (FID, TCD, MS) and equipped
with a split injector with poly di-methyl siloxane
column (Table 1). The mass detector chosen was
selected for benzene analysis in gas/liquid. Before
injection, Slide the plunger carrier down until it is
completely over the syringe plunger, and tighten
the plunger thumb screw until finger- tight. The
injector temperature was adjusted to 190°C and
the detector temperature at 240°C. The GC oven
temperature was programmed from 25°C to 250°C
which was held for 12 min. Hydrogen(Cas number:
1333-74-0) as the carrier gas was used at a flow rate
of 1.0 mL min
–1
. The scanning electron microscopy
(SEM) and Raman spectra were recorded by
electron microscopy and spectrometer of CNTs@
PhSA (Bruker). Fourier transformed infrared
spectroscopy (FTIR, IR-200 Thermo-Nicolet 2.2)
in KBr in the range 400–4000 cm
–1
was used to
confirm the covalently bound benzenesulfonic
acid (CAS N: 98-11-3) group on the CNT surface.
Transmission electron microscopy (TEM, Philips)
with a conventional 15 kV electron microscope was
used to analyze the surface morphology of CNTs@
PhSA. X-ray diffraction (XRD; Panalytical) was
used for XED patterns with wavelength 0.15405
nm for CNTs@PhSA. The intensity was measured
by step scanning in a 2θ range of 5–80°. Benzene
(CAS N: 71-43-2; C
6
H
6
) purchased from Sigma
Aldrich. Five calibration solutions of benzene were
prepared and the approximate concentrations of
benzene were 0.1, 0.2, 0.5, 1.0, 5,0 and 10 mg L
-1
.
The other chemicals with high purity (99%) were
purchased from Sigma (Germany). The analytical
grade solvents such as benzene, chloroform, (CAS
N: 67-66-3), 4-benzenediazoniumsulfonate (CAS:
305-80-6), acetone (CAS N: 67-64-1),, HNO
3
(CAS N:7697-37-2), HCl (CAS N: 7647-01-0),
H
2
SO
4
(CAS N: 7664-93-9), acetic acid (CAS N:
19
Benzene extraction from waters by CNTs@PhSA Shahnaz Teimoori et al
64-19-7) and NaOH (CAS N:1310-73-2) were
also from Merck.CNTs@PhSA was synthesized in
RIPI laboratory, Iran. Ultrapure water (18 MΩ·cm)
was obtained from Millipore continental water
system (Millipore, USA). Samples of water and
wastewater collected in polyethylene bottles were
filtered through Millipore cellulose membrane
filter (0.45 µm porosity) to remove suspended
particulate matter.
2.2. Synthesis of phenyl sulfonic acid modied
hybrid carbon nanotubes
High-purity CNTs were synthesized by use of
camphor, an environmentally friendly hydrocarbon
as a carbon source using chemical vapor deposition
method on Co‒Mo/MgO nanocatalysts. The
nanocatalyst was synthesized by sol-gel method.
HCNTs were grown at temperatures of about
900‒1000
o
C in 45‒60 min. Concentration of active
metals was 5‒10%. The nanocatalyst (Co‒Mo/
MgO) was prepared by our special sol-gel method
[19]. For functionalization of CNTs with phenyl-
SO
3
H (CAS N: 98-11-3) group, CNTs surface
was activated by 50% HNO
3
(CAS N: 7697-37-
2) for 1 h and washed with ultrapure water many
times. The diazotization reaction was used for
functionalization as follows; 0.03 mol of sulfanilic
acid CAS N: 121-57-3) was dispersed in 300 mL
of 1 M HCl (7647-01-0) in a three-necked ground
flask [20]. The flask was kept in an ice water bath
and the temperature controlled around 3ºC under
stirring. Then, 33 mL of 1 M NaNO
2
(CAS N:
7632-00-0) was added dropwise into the mixture
and stirred for 1 h at the same temperature. The
resulting precipitate was filtered and washed
with deionized water. In the following step, 5 g
of 4-benzenediazonium sulfonate and 180 mg of
activated CNTs were added into 120 mL of mixture
of water and ethanol (1:1, v/v) at 3°C. Subsequently,
60 mL of H
3
PO
2
aqueous solution (50 wt.%) was
added to the mixture and stirred for 30 min. After
this time, another 60 mL of H
3
PO
2
(CAS N: 6303-
21-5) was added and stirred for 1 h. The resulting
mixture was washed with deionized water and
dried overnight in an oven at 80°C (Fig. 1).
2.3 Extraction Procedure
The CNTs@PhSA nanostructures based on D-μSPE
method was used for extraction of benzene from
waters (Fig. 2). First, 10 mg of CNTs@PhSA or
Table 1. The conditions of GC-MS for determination
benzene
ConditionsGC-MS
Agilent, 7890A
0.1-20 ng
Model
Sensitivity
1-5 μL; 10:1 splitInjection Volume
2:1Split ratio
30 meter, 0.32mm x 0.25μmColumn
220 °CTemperature Injector
230 °CDetector FID
25 to 100 °C at 25 °C per minProgram , time= 5.0 min
N
2
, 1 mL min
-1
Carrier Gas
60°C
Column Oven Pressure
Pulse
6 ml min
-1
Column Flow
8.153 (min)Retention Time
19.125 (min)Run Time (Min)
30 (mL min
-1
)Flow Rate N
2
34(mL min
-1
)Flow Rate H
2
1-5μLInjection size
200-400(mL min
-1
)Flow Rate air
2:1
Split ratio
30 meter, 0.32mm x 0.25μm
Column
220 °C
Temperature Injector
230 °C
Detector FID
25 to 100 °C at 25 °C per min
Program , time = 5.0 min
N2, 1 mL min
-1
Carrier Gas
60°C
Column Oven Pressure Pulse
6 ml min
-1
Column Flow
8.153 (min)
Retention Time
19.125 (min)
Run Time (Min)
30 (mL min
-1
)
Flow Rate N2
34(mL min
-1
)
Flow Rate H2
1-5 μL
Injection size
200-400(mL min
-1
)
Flow Rate air
2.2. Synthesis of phenyl sulfonic acid modified hybrid carbon nanotubes
High-purity CNTs were synthesized by use of camphor, an environmentally friendly hydrocarbon as a
carbon source using chemical vapor deposition method on Co‒Mo/MgO nanocatalysts. The nanocatalyst
was synthesized by sol-gel method. HCNTs were grown at temperatures of about 900‒1000
o
C in 45‒60
min. Concentration of active metals was 5‒10%. The nanocatalyst (Co‒Mo/MgO) was prepared by our
special sol-gel method [19]. For functionalization of CNTs with phenyl-SO
3
H (CAS N: 98-11-3) group,
CNTs surface was activated by 50% HNO
3
(CAS N: 7697-37-2)
for 1 h and washed with ultrapure water
many times. The diazotization reaction was used for functionalization as follows; 0.03 mol of sulfanilic
acid CAS N: 121-57-3) was dispersed in 300 mL of 1 M HCl (7647-01-0) in a three-necked ground flask
[20]. The flask was kept in an ice water bath and the temperature controlled around 3ºC under stirring.
Then, 33 mL of 1 M NaNO
2
(CAS N: 7632-00-0) was added dropwise into the mixture and stirred for 1 h
at the same temperature. The resulting precipitate was filtered and washed with deionized water. In the
following step, 5 g of 4-benzenediazonium sulfonate and 180 mg of activated CNTs were added into 120
mL of mixture of water and ethanol (1 : 1, v/v) at 3C. Subsequently, 60 mL of H
3
PO
2
aqueous solution
(50 wt.%) was added to the mixture and stirred for 30 min. After this time, another 60 mL of H
3
PO
2
(CAS
N: 6303-21-5) was added and stirred for 1 h. The resulting mixture was washed with deionized water and
dried overnight in an oven at 80°C (Fig.1).
Fig.1. Synthesis of composite with resonance structure
2.3 Extraction Procedure
Fig. 1. Synthesis of composite with resonance structure
20
Anal. Method Environ. Chem. J. 3 (1) (2020) 17-26
CNTs nanostructures was put on 5 mL of water
samples with different benzene standard solution
(0.1--10 mg L
-1
) in GC vial. The mixture shacked
for 10 min by magnetic shaker accessory (MSA)
and after centrifuging for 3 min (3500rpm), the
solid phase separated from liquid phase and finally
the benzene concentration in water sample was
determined by static head space gas chromatography
mass spectrometry (SHS-GC-MS). After
extraction, the recoveries were calculated with
the ratio of initial/final concentration of benzene
in vial GC by SHS-GC-MS (Eq. A). In addition,
adsorption capacity and removal efficiency (RE)
was calculated by equation Eq. B and Eq. C. X
is the initial concentration of benzene in solution
and Y is final concentration of benzene which
determinate by SHS-GC-MS in water samples. The
adsorption capacity (AC) of benzene (mg g
-1
) and,
the removal efficiency of benzene (%) was shown
in Eq. B and Eq. C. The C
i
(mg L
-1
) and C
f
(mg L
-1
)
are the concentration of benzene before and after
extraction procedure, Vs (L) is the sample volume,
and mass (g) is the amount of CNTs@PhSA.
The CNTs@PhSA nanostructures based on D-μSPE method was used for extraction of benzene from
waters (Fig.2). First, 10 mg of CNTs@PhSA or CNTs nanostructures was put on 5 mL of water samples
with different benzene standard solution (0.1--10 mg L
-1
) in GC vial. The mixture shacked for 10 min by
magnetic shaker accessory (MSA) and after centrifuging for 3 min (3500rpm), the solid phase separated
from liquid phase and finally the benzene concentration in water sample was determined by static head
space gas chromatography mass spectrometry (SHS-GC-MS). After extraction, the recoveries were
calculated with the ratio of initial/final concentration of benzene in vial GC by SHS-GC-MS (Eq. A). In
addition, adsorption capacity and removal efficiency (RE) was calculated by equation Eq. B and Eq. C. X
is the initial concentration of benzene in solution and Y is final concentration of benzene which
determinate by SHS-GC-MS in water samples. The adsorption capacity (AC) of benzene (mg g
-1
) and, the
removal efficiency of benzene (%) was shown in Eq. B and Eq. C. The C
i
(mg L
-1
) and C
f
(mg L
-1
) are the
concentration of benzene before and after extraction procedure, Vs (L) is the sample volume, and mass
(g) is the amount of CNTs@PhSA.
(Eq. A)
(Eq. B)
(Eq. C)
Fig. 2. Benzene extraction from waters based on CNTs@PhSA by D-μ-SPE method
3. Results and discussion
Mechanism of extraction of benzene with CNTs@PhSO
3
H was achieved based on π–π stacking between
aromatic chain and S=O bond of CNTs@PhSO
3
H and SO b and molecular of benzene in waters by
sandwich or T shaped π–π bonding (Fig. 3).
(Eq. A)
(Eq. B)
(Eq. C)
3. Results and discussion
Mechanism of extraction of benzene with CNTs@
PhSO
3
H was achieved based on π–π stacking
between aromatic chain and S=O bond of CNTs@
PhSO
3
H and SO b and molecular of benzene in
waters by sandwich or T shaped π–π bonding (Fig.
3).
3.1. Characterization
Figure 4 (a, b) showed the SEM and TEM images
revealed the CNTs@PhSO
3
H consist of randomly
aggregated and crumpled thin tubes which are
closely associated with each other forming a
disordered solid, and it can be inferred that the
functionalization process does not change the
general structure of HCNTs. The FTIR spectrum of
the CNTs@PhSO
3
H sample showed the O=S=O,
OH as a broad peak, C=C and C-S bond which
was confirmed the SO
3
bond in CNTs (Fig. 5).
Raman spectroscopy is a useful technique for
the characterization of carbon nanotubes quality.
Raman patterns of CNTs@PhSO
3
H confirm the
presence of CNTs (Fig. 6) and XRD image showed
the hexagonal structures in CNTs@PhSO
3
H. After
the attachment of SO
3
H groups on the carbon
wall of CNTs the three peaks which confirms the
functionalization of SO
3
H on CNTs@Ph have not
any changes on the structure of CNTs (Fig. 7).
The CNTs@PhSA nanostructures based on D-μSPE method was used for extraction of benzene from
waters (Fig.2). First, 10 mg of CNTs@PhSA or CNTs nanostructures was put on 5 mL of water samples
with different benzene standard solution (0.1--10 mg L
-1
) in GC vial. The mixture shacked for 10 min by
magnetic shaker accessory (MSA) and after centrifuging for 3 min (3500rpm), the solid phase separated
from liquid phase and finally the benzene concentration in water sample was determined by static head
space gas chromatography mass spectrometry (SHS-GC-MS). After extraction, the recoveries were
calculated with the ratio of initial/final concentration of benzene in vial GC by SHS-GC-MS (Eq. A). In
addition, adsorption capacity and removal efficiency (RE) was calculated by equation Eq. B and Eq. C. X
is the initial concentration of benzene in solution and Y is final concentration of benzene which
determinate by SHS-GC-MS in water samples. The adsorption capacity (AC) of benzene (mg g
-1
) and, the
removal efficiency of benzene (%) was shown in Eq. B and Eq. C. The C
i
(mg L
-1
) and C
f
(mg L
-1
) are the
concentration of benzene before and after extraction procedure, Vs (L) is the sample volume, and mass
(g) is the amount of CNTs@PhSA.
(Eq. A)
(Eq. B)
(Eq. C)
Fig. 2. Benzene extraction from waters based on CNTs@PhSA by D-μ-SPE method
3. Results and discussion
Mechanism of extraction of benzene with CNTs@PhSO
3
H was achieved based on π–π stacking between
aromatic chain and S=O bond of CNTs@PhSO
3
H and SO b and molecular of benzene in waters by
sandwich or T shaped π–π bonding (Fig. 3).
Fig. 2. Benzene extraction from waters based on CNTs@PhSA by D-μ-SPE method
21
Benzene extraction from waters by CNTs@PhSA Shahnaz Teimoori et al
Fig.3. Mechanism of extraction of benzene with CNTs@PhSO
3
H
3.1. Characterization
Figure 4(a, b) showed the SEM and TEM images revealed the CNTs@PhSO
3
H consist of randomly
aggregated and crumpled thin tubes which are closely associated with each other forming a disordered
solid, and it can be inferred that the functionalization process does not change the general structure of
HCNTs. The FTIR spectrum of the CNTs@PhSO
3
H sample showed the O=S=O, OH as a broad peak,
C=C and C-S bond which was confirmed the SO
3
bond in CNTs (Fig.5). Raman spectroscopy is a useful
technique for the characterization of carbon nanotubes quality. Raman patterns of CNTs@PhSO
3
H
confirm the presence of CNTs (Fig.6) and XRD image showed the hexagonal structures in
CNTs@PhSO
3
H. After the attachment of SO
3
H groups on the carbon wall of CNTs the three peaks which
confirms the functionalization of SO
3
H on CNTs@Ph have not any changes on the structure of CNTs
(Fig. 7).
Fig.3. Mechanism of extraction of benzene with CNTs@PhSO
3
H
3.1. Characterization
Figure 4(a, b) showed the SEM and TEM images revealed the CNTs@PhSO
3
H consist of randomly
aggregated and crumpled thin tubes which are closely associated with each other forming a disordered
solid, and it can be inferred that the functionalization process does not change the general structure of
HCNTs. The FTIR spectrum of the CNTs@PhSO
3
H sample showed the O=S=O, OH as a broad peak,
C=C and C-S bond which was confirmed the SO
3
bond in CNTs (Fig.5). Raman spectroscopy is a useful
technique for the characterization of carbon nanotubes quality. Raman patterns of CNTs@PhSO
3
H
confirm the presence of CNTs (Fig.6) and XRD image showed the hexagonal structures in
CNTs@PhSO
3
H. After the attachment of SO
3
H groups on the carbon wall of CNTs the three peaks which
confirms the functionalization of SO
3
H on CNTs@Ph have not any changes on the structure of CNTs
(Fig. 7).
Fig.3. Mechanism of extraction of benzene with CNTs@PhSO
3
H
3.1. Characterization
Figure 4(a, b) showed the SEM and TEM images revealed the CNTs@PhSO
3
H consist of randomly
aggregated and crumpled thin tubes which are closely associated with each other forming a disordered
solid, and it can be inferred that the functionalization process does not change the general structure of
HCNTs. The FTIR spectrum of the CNTs@PhSO
3
H sample showed the O=S=O, OH as a broad peak,
C=C and C-S bond which was confirmed the SO
3
bond in CNTs (Fig.5). Raman spectroscopy is a useful
technique for the characterization of carbon nanotubes quality. Raman patterns of CNTs@PhSO
3
H
confirm the presence of CNTs (Fig.6) and XRD image showed the hexagonal structures in
CNTs@PhSO
3
H. After the attachment of SO
3
H groups on the carbon wall of CNTs the three peaks which
confirms the functionalization of SO
3
H on CNTs@Ph have not any changes on the structure of CNTs
(Fig. 7).
Fig. 3. Mechanism of extraction of benzene with CNTs@PhSO
3
H
Fig. 4(a). SEM of CNTs@PhSO
3
H Fig. 4(b). TEM of CNTs@PhSO
3
H
Fig. 5. FTIR spectrum of the CNTs@PhSO
3
H
Fig. 4(a). SEM of CNTs@PhSO
3
H Fig. 4(b). TEM of CNTs@PhSO
3
H
Fig. 5. FTIR spectrum of the CNTs@PhSO
3
H
Fig. 6. Raman patterns of CNTs@PhSO
3
H
22
Anal. Method Environ. Chem. J. 3 (1) (2020) 17-26
3.2. Optimization parameters
The D-μ-SPE procedure based on CNTs@PhSO
3
H
nanocomposite was used for extraction of benzene
from well water and wastewater samples. The main
effectiveness parameters such as, pH, amount of
CNTs@PhSO
3
H, volume of waters, adsorption
capacity of sorbent were evaluated and studied.
The pH sample is critical parameters and must be
optimized. High adsorption of benzene from water
samples based on CNTs@PhSO
3
H nanocomposite
depended on pH solution which was extracted
by D-μ-SPE methods. The pH range (1-12) was
adjusted with buffer solution and the extraction
efficiency of benzene in water samples was
evaluated by benzene concentration (0.1-10 mg
L
-1
) and 10 mg of CNTs@PhSO
3
H. The results
showed, the recovery of extraction for benzene was
decreased at acidic and basic pH ranges. Therefore,
pH of 5.5-7.5 was selected as optimized pH for
benzene extraction in waters (Fig. 8).
By D-μ-SPE method, the amount of on CNTs@
PhSO
3
H nanocomposite
was studied for 5 mL
of water and wastewater samples. So, 1-20 mg
of CNTs@PhSO
3
H and CNTs was examined by
proposed procedure. The results showed us, benzene
in water samples can be efficiently extracted with
8 mg CNTs@PhSO
3
H in optimized pH=7. So, 10
mg of CNTs@PhSO
3
H nanocomposite
was used
as optimum mass for benzene extraction in waters
(Fig. 9).
The sample volume (SV) in important factor
and must be studied. So, the effect of sample
Fig. 4(a). SEM of CNTs@PhSO
3
H Fig. 4(b). TEM of CNTs@PhSO
3
H
Fig. 5. FTIR spectrum of the CNTs@PhSO
3
H
Fig. 6. Raman patterns of CNTs@PhSO
3
H
Fig. 7. XRD image of hexagonal structures in CNTs@PhSO
3
H
3.2. Optimization parameters
The D- μ-SPE procedure based on CNTs@PhSO
3
H nanocomposite was used for extraction of benzene
from well water and wastewater samples. The main effectiveness parameters such as, pH, amount of
CNTs@PhSO
3
H, volume of waters, adsorption capacity of sorbent were evaluated and studied. The pH
sample is critical parameters and must be optimized. High adsorption of benzene from water samples
based on CNTs@PhSO
3
H nanocomposite depended on pH solution which was extracted by D-μ-SPE
methods. The pH range (1-12) was adjusted with buffer solution and the extraction efficiency of benzene
in water samples was evaluated by benzene concentration (0.1-10 mg L
-1
) and 10 mg of CNTs@PhSO
3
H.
The results showed, the recovery of extraction for benzene was decreased at acidic and basic pH ranges.
Therefore, pH of 5.5-7.5 was selected as optimized pH for benzene extraction in waters (Fig. 8).
Fig. 8. The effect of pH on benzene extraction from water samples
By D-μ-SPE method, the amount of on CNTs@PhSO
3
H nanocomposite
was studied for 5 mL of water
and wastewater samples. So, 1-20 mg of CNTs@PhSO
3
H and CNTs was examined by proposed
procedure. The results showed us, benzene in water samples can be efficiently extracted with 8 mg
CNTs@PhSO
3
H in optimized pH=7. So, 10 mg of CNTs@PhSO
3
H nanocomposite
was used as optimum
mass for benzene extraction in waters (Fig. 9).
0
20
40
60
80
100
120
2 3 4 5 6 7 8 9 10
Recovery (%)
pH
CNTs@PhSO3H
CNTs
Fig. 6. Raman patterns of CNTs@PhSO
3
H
Fig. 7. XRD image of hexagonal structures in CNTs@PhSO
3
H
23
Benzene extraction from waters by CNTs@PhSA Shahnaz Teimoori et al
Fig. 7. XRD image of hexagonal structures in CNTs@PhSO
3
H
3.2. Optimization parameters
The D- μ-SPE procedure based on CNTs@PhSO
3
H nanocomposite was used for extraction of benzene
from well water and wastewater samples. The main effectiveness parameters such as, pH, amount of
CNTs@PhSO
3
H, volume of waters, adsorption capacity of sorbent were evaluated and studied. The pH
sample is critical parameters and must be optimized. High adsorption of benzene from water samples
based on CNTs@PhSO
3
H nanocomposite depended on pH solution which was extracted by D-μ-SPE
methods. The pH range (1-12) was adjusted with buffer solution and the extraction efficiency of benzene
in water samples was evaluated by benzene concentration (0.1-10 mg L
-1
) and 10 mg of CNTs@PhSO
3
H.
The results showed, the recovery of extraction for benzene was decreased at acidic and basic pH ranges.
Therefore, pH of 5.5-7.5 was selected as optimized pH for benzene extraction in waters (Fig. 8).
Fig. 8. The effect of pH on benzene extraction from water samples
By D-μ-SPE method, the amount of on CNTs@PhSO
3
H nanocomposite
was studied for 5 mL of water
and wastewater samples. So, 1-20 mg of CNTs@PhSO
3
H and CNTs was examined by proposed
procedure. The results showed us, benzene in water samples can be efficiently extracted with 8 mg
CNTs@PhSO
3
H in optimized pH=7. So, 10 mg of CNTs@PhSO
3
H nanocomposite
was used as optimum
mass for benzene extraction in waters (Fig. 9).
0
20
40
60
80
100
120
2 3 4 5 6 7 8 9 10
Recovery (%)
pH
CNTs@PhSO3H
CNTs
Fig. 8. The effect of pH on benzene extraction from water samples
Fig. 9. The effect of amount of CNTs@PhSO
3
H on benzene extraction by D-μ-SPE method
Fig. 9. The effect of amount of CNTs@PhSO
3
H on benzene extraction by D-μ-SPE method
The sample volume (SV) in important factor and must be studied. So, the effect of sample volume on
benzene extraction in waters examined at optimized conditions. Due to procedure, the different water
volumes between 1-10 mL with 10 mgL
-1
of standard benzene solution were selected for benzene
extraction by D-μ-SPE methodology. As magnetic shaking for 10 min, high recovery obtained for 10 mL
of waters. Therefore, 5 mL of sample volume selected for further work (Fig. 10).
Fig 10. The effect of sample volume on benzene extraction by D-μ-SPE method
The validation methodology based on spiking well water and wastewater samples was achieved by
concentration of standard benzene solution from LLOQ as 0.1 mgL
-1
and ULOQ as 10 mgL
-1
by
optimized conditions (Table 2). All samples analyzed by static head space gas chromatography mass
spectrometry (SHS-GC-MS).
Table 2. The validation methodology based on CNTs@PhSO
3
H by SHS-GC-MS
0
20
40
60
80
100
2
5
6
8
10
15
20
Recovery (%)
Amount of CNTs@PhSO
3
H ( mg)
CNTs@PhSO3H CNTs
0
20
40
60
80
100
120
1 2 5 8 10 15 20
Recovery (%)
Sample Volume (mL)
CNTs@PhSO3H
CNTs
Fig 10. The effect of sample volume on benzene extraction by D-μ-SPE method
Fig. 9. The effect of amount of CNTs@PhSO
3
H on benzene extraction by D-μ-SPE method
The sample volume (SV) in important factor and must be studied. So, the effect of sample volume on
benzene extraction in waters examined at optimized conditions. Due to procedure, the different water
volumes between 1-10 mL with 10 mgL
-1
of standard benzene solution were selected for benzene
extraction by D-μ-SPE methodology. As magnetic shaking for 10 min, high recovery obtained for 10 mL
of waters. Therefore, 5 mL of sample volume selected for further work (Fig. 10).
Fig 10. The effect of sample volume on benzene extraction by D-μ-SPE method
The validation methodology based on spiking well water and wastewater samples was achieved by
concentration of standard benzene solution from LLOQ as 0.1 mgL
-1
and ULOQ as 10 mgL
-1
by
optimized conditions (Table 2). All samples analyzed by static head space gas chromatography mass
spectrometry (SHS-GC-MS).
Table 2. The validation methodology based on CNTs@PhSO
3
H by SHS-GC-MS
0
20
40
60
80
100
2
5
6
8
10
15
20
Recovery (%)
Amount of CNTs@PhSO
3
H ( mg)
CNTs@PhSO3H CNTs
0
20
40
60
80
100
120
1 2 5 8 10 15 20
Recovery (%)
Sample Volume (mL)
CNTs@PhSO3H
CNTs
24
Anal. Method Environ. Chem. J. 3 (1) (2020) 17-26
volume on benzene extraction in waters examined
at optimized conditions. Due to procedure, the
different water volumes between 1-10 mL with 10
mgL
-1
of standard benzene solution were selected
for benzene extraction by D-μ-SPE methodology.
As magnetic shaking for 10 min, high recovery
obtained for 10 mL of waters. Therefore, 5 mL of
sample volume selected for further work (Fig. 10).
The validation methodology based on spiking
well water and wastewater samples was achieved
by concentration of standard benzene solution
from LLOQ as 0.1 mgL
-1
and ULOQ as 10 mgL
-
1
by optimized conditions (Table 2). All samples
analyzed by static head space gas chromatography
mass spectrometry (SHS-GC-MS).
3.3. Discussion
This study set out with the aim of assessing the
modification of CNTs with phenyl sulfonic acid
group and its effect on the extraction efficiency of
benzene in water samples. According to our results,
it is revealed that compared to CNTs, CNTs@PhSA
significantly adsorbs benzene in water. As table 3,
the results showed us the proposed method based
on CNTs@PhSA had more efficient extraction of
benzene from waters than CNTs sorbents which
was presented by different authors [21-26]. Also
the comparing of adsorption capacity(AC) of
CNTs@PhSA (157.34 mg g
-1
)
with other sorbents
such as CNTs (22.86 mg g
-1
), CuO-NPs (100.24
mg g
-1
), GO/MOF-5 (77 mg g
-1
) , ZIF-8/GO(123
mg g
-1
) and GO (158 mg g
-1
) showed, the value of
AC was near or more than others [27-30]. Osanloo
at el was used graphene modified by ionic liquid
(NG-IL) for toluene removal [31].
Table 2. The validation methodology based on CNTs@PhSO
3
H by SHS-GC-MS
samples Added (mgL
-1
) *Found (mgL
-1
) Recovery (%)
Well Water -------
0.43 ± 0.02 -------
0.5
0.94 ± 0.03 102
Paint Wastewater -------
14.16± 0.68 -------
15
28.87± 1.26 98.1
Oil-Factory Wastewater -------
38.12± 2.15 -------
40
76.82± 3.75 96.8
*
Mean of three determinations ± confidence interval (P = 0.95, n = 10)
Table 3. Comparing of dispersive micro solid phase extraction method based on CNTs@PhSA for benzene extraction
from water samples with other published methods
This Study Relevant Studies
In this study, phenyl sulfonic acid group was
used for modification of CNTs in order to extract
benzene from water samples.
CNTs have the capacity to be attached by functional groups. These
functional groups can change physical and chemical properties of
carbon nanotubes [21].
We prepared a range of benzene concentration
including 0.1, 0.2, 0.5, 1.0, 5.0, 10 mg/L
Optimum benzene concentration for the investigation of CNTs
adsorption efficiency in benzene removal procedure is 10 mg/L [22].
Contact time performed in this study was 10 min.
The mixture of CNTs and sample have been shaked for 10 minutes
[22].
Extraction of benzene in waters by sandwich or T
shaped π–π bonding.
Molecular torsion balance, developed by Wilcox et al. representing
a closed model with a T-shaped π–π interaction [23, 24].
SEM and TEM images revealed that the CNTs@
PhSO
3
H consists of randomly aggregated and
crumpled thin tubes.
CNTs accumulation leads to pores formation which can create a
bunch of adsorption sites on them [25].
Addition of SO
3
H on CNTs@Ph had no change
on the structure of CNTs.
According to SEM images of H
2
SO
4
-treated CNTs, there is no
change in the morphology and structure of CNTs [21].
pH optimization in the range of 5.5-7.5 benzene
extraction from water samples
When pH exceeds 6.2, the adsorption efficiency increases
significantly [26].
25
Benzene extraction from waters by CNTs@PhSA Shahnaz Teimoori et al
4. Conclusions
The main goal of the current study was to
determine the effect of phenyl sulfonic acid group
functionalization on the adsorption efficiency of
CNTs for benzene removal in water samples. The
adsorption mechanism is referred to the polar-π and
π-π interaction between aromatic ring of benzene
and surface sulfonic acid group as well as phenyl
ring. Surprisingly, hexagonal structure of CNTs@
PhSA indicated no change in the basic structure
of CNTs, after functionalization with SO
3
H.
However, the adsorption capacity of CNTs@
PhSA for benzene removal was significant. These
findings suggest that in general, CNTs are capable
of being modified and therefore, they represent a
critical role in the adsorption of benzene and other
pollutants. All concentration benzene in waters
determined based on D- μ-SPE procedure by SHS-
GC-MS. Under optimal conditions, adsorption
efficiency of CNTs@PhSA and CNTs was obtained
97.7% and 20.6 % for benzene removal from water
samples, respectively.
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