Extraction and determination of benzene from waters and wastewater samples based on functionalized carbon nanotubes by static head space gas chromatography mass spectrometry

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 VOCs1 from water samples by shaking and heating samples. 1Volatile 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 fingertight. 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; C6H6) 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),, HNO3 (CAS N:7697-37-2), HCl (CAS N: 7647-01-0), H2SO4(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 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 900‒1000oC 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 phenylSO3H (CAS N: 98-11-3) group, CNTs surface was activated by 50% HNO3 (CAS N: 7697-372) 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 NaNO2 (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 H3PO2 aqueous solution (50 wt.%) was added to the mixture and stirred for 30 min. After this time, another 60 mL of H3PO2 (CAS N: 630321-5) 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 Conditions GC-MS Agilent, 7890A 0.1-20 ng Model Sensitivity 1-5 μL; 10:1 split Injection Volume


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][2][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 18 Anal. Method Environ. Chem. J. 3 (1) (2020) [17][18][19][20][21][22][23][24][25][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][12][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][15][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.

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: 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.

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 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).

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

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 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). 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.
he CNTs@PhSA nanostructures based on D-μSPE method was used for extraction of benzene from aters (Fig.2). First, 10 mg of CNTs@PhSA or CNTs nanostructures was put on 5 mL of water samples ith different benzene standard solution (0.1--10 mg L -1 ) in GC vial. The mixture shacked for 10 min by agnetic shaker accessory (MSA) and after centrifuging for 3 min (3500rpm), the solid phase separated rom liquid phase and finally the benzene concentration in water sample was determined by static head pace gas chromatography mass spectrometry (SHS-GC-MS). After extraction, the recoveries were alculated with the ratio of initial/final concentration of benzene in vial GC by SHS-GC-MS (Eq. A). In ddition, adsorption capacity and removal efficiency (RE) was calculated by equation Eq. B and Eq. C. X s the initial concentration of benzene in solution and Y is final concentration of benzene which eterminate by SHS-GC-MS in water samples. The adsorption capacity (AC) of benzene (mg g -1 ) and, the emoval 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 oncentration of benzene before and after extraction procedure, Vs (L) is the sample volume, and mass g) is the amount of CNTs@PhSA.

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). 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).

Characterization
The CNTs@PhSA nanostructures based on D-μSPE method was used for extraction of benzene from waters (Fig.2).

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).   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).  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). 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).  J. 3 (1) (2020) 17-26

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

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). 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)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(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). 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). 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). 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).  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).

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][22][23][24][25][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][28][29][30]. Osanloo at el was used graphene modified by ionic liquid (NG-IL) for toluene removal [31].  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].

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.