- Email: [email protected]
Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes
MOLLIQ-05081; No of Pages 6 Journal of Molecular Liquids xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes Behzad Heibati a,b,⁎, Mahboobeh Ghoochani b,⁎⁎, Ahmad B. Albadarin c, Alireza Mesdaghinia d, Abdel Salam Hamdy Makhlouf e, Mohammad Asif f, Arjun Maity g,j, Inderjeet Tyagi h, Shilpi Agarwal h,j, Vinod Kumar Gupta h,i,j,⁎⁎⁎ a
Department of Occupational Health Engineering, Faculty of Health and Health Sciences Research Center, Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran Department of Environmental Health Engineering, Faculty of Public Health, Tehran University of Medical Sciences Tehran, Iran c Department of Chemical and Environmental Sciences, University of Limerick, Ireland d Center for Water Quality Research (CWQR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran e Department of Manufacturing Engineering, College of Engineering and Computer Science, University of Texas Pan-American, USA f Department of Chemical Engineering, King Saud University Riyadh, Saudi Arabia g National Centre for Nanostructured Materials, CSIR Material Science and Manufacturing, Pretoria 0001, South Africa h Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India i Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia j Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa b
a r t i c l e
i n f o
Article history: Received 22 May 2015 Received in revised form 16 August 2015 Accepted 18 August 2015 Available online xxxx Keywords: Multiwalled carbon nanotubes Linear alkyl benzene sulfonates Wastewater treatment Adsorption Surface modification
a b s t r a c t This paper explores the possibility of employing Oxidized Multiwalled Carbon Nanotubes (MWCNT-COOH) for the removal of toxic Linear Alkyl benzene Sulfonate (LAS). LAS is among the most toxic industrial and house hold waste surfactants. This study discusses the feasibility of removing LAS from aqueous solutions using MWCNT-COOH. The effects of operational parameters such as solution pH, LAS concentration and contact time on the removal of LAS were studied. The four linear forms of Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin models were applied to determine the best fit of equilibrium expressions. Our results showed that the experimental adsorption isotherm complies with Freundlich model. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Fitting of the experimental results to kinetic models showed the relevance of the pseudo second-order (R2 N 0.99) model for LAS. Our results confirmed that MWCNT-COOH would be promising adsorbents for LAS removal in aqueous solution. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Surfactants are used widely in household, personal care products, agriculture and industry [1,2]. Surfactants are a diverse group of chemicals with cleaning properties and consist of two heads with a different polarity or solubility in water: a polar head group, which is well solvated in water, and a non-polar hydrocarbon tail, which is not easy to dissolve in water [3,4]. Surfactants are classified by their ionic activity in water into four types: anionic, cationic, non-anionic and
⁎ Correspondence to: B. Heibati, Department of Occupational Health Engineering, Faculty of Health and Health Sciences Research Center, Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran. ⁎⁎ Corresponding author. ⁎⁎⁎ Correspondence to: V. K. Gupta, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247667, India. E-mail addresses: [email protected] (B. Heibati), [email protected] (M. Ghoochani), [email protected], [email protected] (V.K. Gupta).
amphoteric [5]. LAS is the largest group of anionic surfactants (Fig. 1). Synthetic surfactants are formed of LAS and its isomers with other additives [6,7]. Anionic surfactants (AS), especially LAS, are used extensively due to their impacts on ecosystems and are usually disposed after their use into the environment [8,9]. Therefore, they represent one of the main causes of water pollution. A recent study reported the presence of LAS in different water channels in Iran [5]. The concentrations of surfactants in natural water vary from area to area and ranged from 3.780 to 1456 mg/L. This high percentage of waste chemical components should be removed from water. The conventional treatment methods such as combination of biodegradation and sorption/settling processes and Oxidative treatments and cannot remove them [10–12]. Other methods have been proposed to remove surfactants such as: (i) adsorption [13]and (ii) coagulation using polyelectrolytes with powdered activated carbon (PAC) and powdered clinoptilolite simultaneously [14].Several researchers have shown that the adsorption is an efficient process for the removal of LAS from aqueous solutions [13,16]. For this purpose, a
http://dx.doi.org/10.1016/j.molliq.2015.08.046 0167-7322/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
2
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Fig. 1. Formulation of Linear Alkyl benzene Sulfonate.
variety of natural and synthetic materials have been tested as LAS, including activated carbon [17], mineral clay [17], soils [13] and others. Advanced membrane filtration techniques (e.g. microfiltration, ultrafiltration, nanofiltration and reverse osmosis) exhibited superior performance in treatment and removal of chemical and biological contaminants over conventional systems [18]. Hybrid methods can also be more effective than any of the previous process alone. The combination of ion exchange and ultrafiltration was more effective in surfactant removal than ultrafiltration process alone [19]. In recent years, nanotechnology has introduced different types of nanomaterials for water treatment. Nanosorbents such as carbon nanotube (CNTs) [15] and zeolites [20] proved to exhibit special adsorption properties. CNTs, in particular, received special attention for potential application in environmental protection and to work effectively against chemical and biological contaminants [15,18,21]. Single and multiwalled carbon nanotubes (MWCNTs) have been used in water and wastewater treatment [15]. The objective of this study is to investigate the adsorption mechanism of LAS using MWCNTs and to determine the optimum parameters for the maximum/efficient adsorption capacity. 2. Experimental 2.1. Materials Multi-walled CNTs (MWCNTs) were synthesized by catalytic chemical vapor deposition (CVD) method at the Research Institute of Petroleum Industry (RIPI), Tehran, Iran. MWCNTs were used as adsorbents to study the adsorption characteristic of LAS detergent from water. The size of the outer diameter of MWCNTs was more than 10 nm while the length ranged from 5 to 15 μm. In addition, the mass ratio of the amorphous carbon of MWCNTs was less than 5%, and specific surface area was 280 m2/g. Because of the presence of amorphous carbon in carbon nanotubes, the adsorption rate is very low. Therefore, carbon nanotubes must be purified before the adsorption process. The stock solution was stored in the refrigerator to minimize biodegradation. 10 mL of stock LAS solution was diluted to 1000 mL with distilled water; 1 mL = 10 μg LAS. Dilute solutions of concentrations 1.5, 2 and 4 mg/L LAS were prepared. The stock solution of LAS was prepared using standard methods for the examination of water & wastewater book No. 5540C [22].
Fig. 2. Schematic diagram of adsorbent preparation.
Fig. 3 shows the probable synthesis reaction of carboxyl and amino functionalized CNTs. This figure illustrates that carboxyl group could be formed first and may have higher number of reactive sites that could lead to better interaction with polymers. 2.3. Adsorption experiments Batch adsorption experiments were performed in glass bottles with LAS solution (250 mL) of the mentioned concentration (i.e. 4 mg/L) and 25 mg of MWCNT-COOH was added to each bottle. The amount of MWCNT-COOH was kept constant in all experimental steps. According to a previous study [5], the concentration of detergent in Tehran surface water was 0.14–3.78 mg/L. Based on LAS concentration ranging from 1.5 to 4 mg/L was selected for this study [5]. The bottles were shaken using a magnetic shaker (IKA® RCT basic) at 25 °C until equilibrium. The pH of the solutions was adjusted by adding HCl or NaOH solutions. The solution pH ranges from 3 to 9. After achieving equilibrium (corresponding to the saturation of the adsorbent), the suspension was filtered through a 0.2 μm filter and the filtrate was analyzed using NO. 5540C standard method and spectrophotometer (Perkins-Elmer Lambeda 25-UV/Vis and 652 nm wavelengths with the thickness of cell 1 cm). 2.4. Surface characterization The morphology of the adsorbents was investigated using scanning electron microscopy (SEM, KYKY-EM3200) and X-ray diffraction (XRD, Quantachrome, NOVA2000).
2.2. Functionalization of MWCNTs Schematic diagram of adsorbents preparation is shown in Fig. 2. In order to functionalize MWCNTs, 0.3 g of MWCNTs were scattered in 25 mL of nitric acid (65 wt.%) in a 100 mL flask equipped with a condenser and scattering was refluxed under magnetic stirring for 48 h [23]. Then, the resulting scattering was diluted in water and filtered. The filtrate was rinsed to neutral pH and the sample was dried in vacuum at 40 °C overnight to obtain MWCNT-COOH.
Fig. 3. Schematic diagram for chemical fictionalization of MWCNTs.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
3
3. Results and discussion 3.1. Characterization of MWCNT-COOH SEM images and XRD spectra of MWCNT-COOH are shown in Fig. 4. As shown in Fig. 4(a), the peaks at 2θ = 20, 24, and 43° are related to graphite structure of CNTs that were sharper in functionalized nanotubes. According to the SEM images of the functionalized MWCNTs, the adsorbents have no porous structure. 3.2. Effect of contact time Fig. 5 shows the effect of the contact time on the removal efficiency of LAS using MWCNT-COOH. The removal efficiency increased with time until it reaches an equilibrium constant value after 45 min, corresponding to the saturation of the adsorbent. The removal of LAS was found to be rapid at the initial period of contact time, then, slow down with the increase of contact time. This is probably due to the initially abundant number of active sites on the sorbents, whereas, with the gradual increased occupancy of these sites, the sorption process becomes less efficient with increasing time [24,25].
Fig. 5. Effect of the contact time on LAS removal (adsorbent dosage 1 g/L, pH 3 and temperature = 24 °C).
The equation of Langmuir [26,27] can be expressed as: qe ¼
3.3. Effect of the initial solution pH on LAS removal The pH of the solution is an important factor controlling the surface charge of the adsorbent and the degree of ionization of the materials in the solution. To determine the optimum solution pH for maximum LAS removal, the equilibrium adsorption of LAS (for an initial concentration of 4 mg/L) was investigated for a solution pH ranging from 3 to 9 while the other parameters such as adsorbent dose (1 g/L) and contact time (45 min) were maintained constant. According to Fig. 6, the removal efficiency of LAS decreased with increasing solution pH. Therefore, we suggest that acidic medium favors the adsorption process of LAS by MWCNT-COOH. High adsorption of LAS at low pH indicates that due to the weak basicity of LAS, its acidic form (R–C6H4–CO3H) is predominant in acidic solutions and better adsorbed by MWCNTs. The percentage removal efficiency for LAS increased with increasing LAS concentration. These results indicate that energetically high favorable sites became involved in increasing LAS concentrations in the aqueous solution.
Equilibrium data, commonly known as adsorption isotherms, describe how the adsorbate interacts with adsorbents and gives a comprehensive understanding of the nature of interaction. Several isotherm equations have been developed and employed for such analysis, and the four important isotherms including Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin isotherms were applied in this study.
ð1Þ
It can conveniently be written in a linearized form as: Ce 1 1 þ ¼ Ce qe qm b qm
ð2Þ
where: qe is the adsorbed amount at equilibrium (mg/g), Ce is the adsorbate concentration at equilibrium (mg/L), qm is the maximum adsorption capacity and b is the Langmuir constant related to the energy of adsorption [28–30]; qm and b can be deduced from the slope and intercept, by plotting Ce/qe versus Ce. The influence of the adsorption isotherm shape can be discussed to examine whether adsorption is favorable in terms of RL, a dimensionless constant referred to as separation factor or equilibrium parameter. RL is defined by the following relationship: RL ¼
3.4. Adsorption isotherms
qm bC e 1 þ bC e
1 1 þ bC o
ð3Þ
RL values between 0 and 1 indicates favorable adsorption, while RL N 1, RL = 1, and RL = 0 indicate unfavorable, linear, and irreversible adsorption isotherms, respectively [31,32]. The Freundlich isotherm [33] can be expressed as: qe ¼ K f C 1=n e
ð4Þ
Fig. 4. XRD (a) and SEM (b) of MWCNT-COOH.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
4
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
adsorption capacity, Ce is the equilibrium concentration of LAS, K is the constant related to mean free energy, R is universal gas constant and T is the absolute temperature (K). The mean free energy of adsorption (E) was calculated from the constant “K” using the relation [36,37]: E ¼ ð2K Þ‐0:5
ð7Þ
It is defined as the free energy change when 1 mol of ion is transferred to the surface of the solid from infinity in solution. The Temkin isotherm [38,39] has been used for heterogeneous adsorption of adsorbate on a surface. The following is the linear form of the Temkin model: qe ¼ β ln K T þ βlnCe
Fig. 6. Effect of solution pH on the adsorption of LAS by MWCNT-COOH (adsorbent mass = 1 g/L, and temperature = 24 °C).
The equation is conveniently used in its linear form by taking the logarithm of both sides as: logqe ¼ logK f þ
1 logce n
ð5Þ
where: Kf and n are the Freundlich constants. For favorable adsorption, the value of n should be in the range from 1 to 10 [34,35]. In order to understand the adsorption type, equilibrium data were tested with D-R isotherm [36]. The linearised D-R equation can be written as: ln qe ¼ ln qs −Kε 2
ð6Þ
where: ε is polanyi potential, and is equal to RT ln(1 + 1/Ce), qe is the amount of LASadsorbed per unit mass of adsorbents, qs is the theoretical
ð8Þ
where KT is the equilibrium binding constant (L/mg) corresponding to the maximum binding energy and constant b = RT/β (KJ/mol) is related to the heat of adsorption. Isothermal studies of LAS removal are shown in Fig. (7). In this paper, the fit of experimental values by using the four isotherm models were patterned and the results are presented in Table 1. As can be seen from the correlation coefficients (R2), the Freundlich model fits the experimental values better than the other models. Conformation of the data into the Freundlich isotherm model demonstrated the formation of multilayer coverage of LAS at the outer surface of adsorbents and showed the heterogeneous nature of LAS adsorption onto adsorbents which suggests that adsorption sites are identical and energetically equivalent [33]. The values of KF and 1/n were calculated from the slope and intercept of the plot in Fig. (7B) and reported in Table 1. Kf is a constant indicates the adsorption capacity of the adsorbent; while n is an empirical constant related to the magnitude of the adsorption driving force [33,40]. Table 1 and Fig. (7B) show that the theoretical value of the adsorption capacity is 0.001. However, the Langmuir constant b, connected to the adsorption free energy and specifying the adsorbents affinity for LAS binding, is 0.016, indicating a favorable capability of LAS molecules to form a stable complex with MWCNTs. Furthermore, when the values of n are within 1 b n b 10 it means
Fig. 7. (A) Langmuir; (B) Freundlich; (C) Dubinin Radushkevich and (D) Temkin adsorption isotherms of LAS.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx Table 1 Isotherm constants for the adsorption of LAS on MWCNT-COOH for different initial LAS concentrations at pH 3, adsorbent dose 1 g/L and contact time 45 min. Model
Parameter
Parameter
Freundlich MWCNTs Langmuir MWCNTs D-R MWCNTs Temkin MWCNTs
Kf(mg/g) 0.001 qm(mg/g) 62.5 qm(mg/g) 262.8 KT (L/g) 1189
n 0.632 b(L/mg) 0.016 E (kJ/mol) 2.67 β(mg/L) 0.016
Parameter
Parameter
RL(L/mg) 0.94 K (mol2 k/J) 7 × 10−8 b(KJ/mol) 154.84
R2 0.967 R2 0.679 R2 0.920 R2 0.920
favorable adsorption [24]. The value of constant RL is 0.86 and 0.94 l/mg indicating favorable adsorption. The monolayer adsorption capacity was 62.5 mg/g. The plot of ln(qe) against ε2 was almost linear with correlation coefficients R2 = 0.929 (Fig. 7). D-R isotherm constants K and qs were calculated from the slope and intercept of the plot, respectively. The value of K was found to be 7 × 10−8 mol2 k/J2 and that of qs was 262.8 mg/g. The value of E was found to be 2.67 kJ/mol. Table 1 depicts further that the experimental data had a relatively lower correlation with the Temkin isotherm (R2 = 0.92). 3.5. Adsorption kinetics studies The kinetic of adsorption describes the rate of LAS adsorption on adsorbent, which controls the equilibrium time and influences the adsorption mechanism. For an adsorption process, there are typically three major steps that take place at the solid–liquid interface: external diffusion, intra-particle diffusion and surface reaction. The “external diffusion” is not often decisive, especially when the experimental system is well agitated. In order to adequately correlate the experimental data, the pseudo-first order equation, pseudo-second order equation and intra-particle diffusion were used to investigate the kinetics of adsorption. The most accurate model was considered based on the regression coefficient (R2) and the comparison of the qe values to the experimental ones. Kinetics of LAS removal is shown in Fig. 8. The corresponding
5
parameters are collected in Table 2. By contrast, the experimental data of kinetic model were well-fitted by the pseudo-second-order model for all studied LAS concentrations. In addition, Fig. 8B and Table 2, show that the q values (qe,cal) determined from the pseudo secondorder model were closer to the experimental q values (qe,exp) than other models. This indicates that chemisorption was the ratecontrolling step. Fig. 8 showed that the adsorption of LAS was very fast in the first few minutes (0–5 min). Sharp slope curves of LAS adsorption onto MWCNT-COOH reveals an immediate adsorption which could be attributed to the effect of surface functional groups. Consequently, the adsorption behavior and mechanism of LAS was believed to happen via surface adsorption till the surface functional active sites were entirely occupied. Subsequently, LAS molecules diffused into the pores of the MWCNT-COOH for further adsorption [41]. The plot of qt versus t1/2 may present multi linearity [42], which indicates that two or more steps occur in the adsorption process. The first sharper stage is the external surface adsorption or instantaneous adsorption stage and the second portion is the gradual adsorption stage, where the intra-particle diffusion is rate-controlled. In Fig. 8C, the plot of qt versus t1/2 is depicted. The slope of the line in each stage is written as the rate parameter kip. The value of the rate constant for intra-particle transport increased with the increase in the initial LAS concentration (Table 2). Fig. 8C shows that the first stage has a quick diffusion rate at the highest studied concentration (i.e. 4 mg/L). The plots are linear but did not pass through the origin (Fig. 8C), indicating that external mass transfer is the main rate controlling step at the initial stages. 4. Conclusions Functionalized MWCNTs (MWCNT-COOH) have been employed as adsorbents for the removal of the LAS from aqueous solutions. Freundlich model for adsorption isotherms appeared to fit more accurately the experimental data. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Adsorption kinetics was successfully fitted to the pseudo-second-order kinetics model. Therefore, the results obtained point out MWCNT-COOH as a promising adsorbent for LAS removal.
Fig. 8. (A) Pseudo-first order; (B) Pseudo-second order and (C) Intra-particle diffusion for LAS adsorption.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
6
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Table 2 Parameters of kinetic equations. LAS(mg/L)
1.5 4.0
Pseudo-first-order model
Pseudo-second-order model
Intra particle diffusion model
qe,exp. (mg/g)
qe,cal (mg/g)
k
R2
qe,cal (mg/g)
k
R2
kip (g/mg mind/2)
R2
14.31 39.18
14.09 38.37
0.287 0.325
0.999 0.998
14.55 39.59
0.043 0.018
0.999 0.999
0.992 2.604
0.923 0.885
Acknowledgments The authors thank Sakine Shekoohiyan, Mika Sillanpää, Shila Jafari and Chungsying Lu for their helpful suggestions in the modification methods. Also, AM, IT, SA and VKG, are thankful to the Department of Science and Technology, New Delhi, India, for the financial support under project grant DST/INT/South Africa/P-03/2014. Support of the Deanship of Scientific Research grant for the Research Group RGPVPP-292 at King Saud University is appreciated by M. Asif. References [1] M. Garcia, E. Campos, J. Sánchez-Leal, I. Ribosa, Effect of linear alkylbenzene sulphonates (LAS) on the anaerobic digestion of sewage sludge, Water Res. 40 (2006) 2958–2964. [2] M. Mösche, U. Meyer, Toxicity of linear alkylbenzene sulfonate in anaerobic digestion: influence of exposure time, Water Res. 36 (2002) 3253–3260. [3] G.-G. Ying, Fate, behavior and effects of surfactants and their degradation products in the environment, Environ. Int. 32 (2006) 417–431. [4] A.K. Mungray, P. Kumar, Fate of linear alkylbenzene sulfonates in the environment: a review, Int. Biodeterior. Biodegrad. 63 (2009) 981–987. [5] M. Ghoochani, S. Shekoohiyan, A. Mahvi, B. Haibati, M. Norouzi, Determination of detergent in Tehran ground and surface water, Am. Eurasian J. Agric. Environ. Sci. 10 (2011) 464–469. [6] A.K. Mungray, P. Kumar, Occurrence of anionic surfactants in treated sewage: risk assessment to aquatic environment, J. Hazard. Mater. 160 (2008) 362–370. [7] A. Bordoloi, B.M. Devassy, P. Niphadkar, P. Joshi, S. Halligudi, Shape selective synthesis of long-chain linear alkyl benzene (LAB) with AlMCM-41/beta zeolite composite catalyst, J. Mol. Catal. A Chem. 253 (2006) 239–244. [8] C. Verge, A. Moreno, J. Bravo, J.L. Berna, Influence of water hardness on the bioavailability and toxicity of linear alkylbenzene sulphonate (LAS), Chemosphere 44 (2001) 1749–1757. [9] K.K. Brandt, M. Hesselso, P. Roslev, K. Henriksen, J. So, Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation ofNitrosomonas and nitrosospira strains, Appl. Environ. Microbiol. 67 (2001) 2489–2498. [10] D. McAvoy, W. Eckhoff, R. Rapaport, Fate of linear alkylbenzene sulfonate in the environment, Environ. Toxicol. Chem. 12 (1993) 977–987. [11] R. Rapaport, W. Eckhoff, Monitoring linear alkyl benzene sulfonate in the environment: 1973–1986, Environ. Toxicol. Chem. 9 (1990) 1245–1257. [12] M. Carballa, G. Manterola, L. Larrea, T. Ternes, F. Omil, J.M. Lema, Influence of ozone pre-treatment on sludge anaerobic digestion: removal of pharmaceutical and personal care products, Chemosphere 67 (2007) 1444–1452. [13] Z. Ou, A. Yediler, Y. He, L. Jia, A. Kettrup, T. Sun, Adsorption of linear alkylbenzene sulfonate (LAS) on soils, Chemosphere 32 (1996) 827–839. [14] J. Kaleta, M. Elektorowicz, The removal of anionic surfactants from water in coagulation process, Environ. Technol. 34 (2013) 999–1005. [15] M.H. Dehghani, M.M. Taher, A.K. Bajpai, B. Heibati, I. Tyagi, M. Asif, S. Agarwal, V.K. Gupta, Removal of noxious Cr (VI) ions using single-walled carbon nanotubes and multi-walled carbon nanotubes, Chem. Eng. J. (2015) (DOI). [16] W. de Wolf, T. Feijtel, Terrestrial risk assessment for linear alkyl benzene sulfonate (LAS) in sludge-amended soils, Chemosphere 36 (1998) 1319–1343. [17] N. Narkis, B. Ben-David, Adsorption of non-ionic surfactants on activated carbon and mineral clay, Water Res. 19 (1985) 815–824. [18] V.K. Upadhyayula, S. Deng, M.C. Mitchell, G.B. Smith, Application of carbon nanotube technology for removal of contaminants in drinking water: a review, Sci. Total Environ. 408 (2009) 1–13. [19] I. Kowalska, Ion-exchange–ultrafiltration system for surfactants removal from water solutions, Desalin. Water Treat. 25 (2011) 47–53. [20] K. Hui, C. Chao, Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents, J. Hazard. Mater. 137 (2006) 401–409.
[21] A. Mittal, J. Mittal, Hen feather: a remarkable adsorbent for dye removal, green chemistry for dyes removal from wastewater: research trends and applications(DOI) 2015 409–457. [22] A. APHA, WEF. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA/AWWA/WEF, Washington, DC, 1998 (DOI). [23] A. Naghizadeh, S. Nasseri, S. Nazmara, Removal of Trichloroethylene from water by adsorption on to multiwall carbon nanotubes, Iran. J. Environ. Health Sci. Eng. 8 (2011). [24] B. Heibati, S. Rodriguez-Couto, A. Amrane, M. Rafatullah, A. Hawari, M.A. Al-Ghouti, Uptake of Reactive Black 5 by pumice and walnut activated carbon: chemistry and adsorption mechanisms, J. Ind. Eng. Chem. (2013) (DOI). [25] H. Daraei, A. Mittal, M. Noorisepehr, J. Mittal, Separation of chromium from water samples using eggshell powder as a low-cost sorbent: kinetic and thermodynamic studies, Desalin. Water Treat. 53 (2015) 214–220. [26] A.B. Albadarin, C. Mangwandi, A.A.H. Al-muhtaseb, G.M. Walker, S.J. Allen, M.N. Ahmad, kinetic and thermodynamics of chromium ions adsorption onto low-cost dolomite adsorbent, Chem. Eng. J. 179 (2012) 193–202. [27] J. Mittal, D. Jhare, H. Vardhan, A. Mittal, Utilization of bottom ash as a low-cost sorbent for the removal and recovery of a toxic halogen containing dye eosin yellow, Desalin. Water Treat. 52 (2014) 4508–4519. [28] A. Bhatnagar, E. Kumar, M. Sillanpää, Nitrate removal from water by Nano-alumina: characterization and sorption studies, Chem. Eng. J. 163 (2010) 317–323. [29] Ş.S. Bayazit, Ö. Kerkez, Hexavalent chromium adsorption on superparamagnetic multi-wall carbon nanotubes and activated carbon composites, Chem. Eng. Res. Des. (2014) (DOI). [30] G. Sharma, M. Naushad, D. Pathania, A. Mittal, G. El-desoky, Modification of hibiscus cannabinus fiber by graft copolymerization: application for dye removal, desalination and water treatment(DOI) 2014 1–8. [31] M.L. Paul, J. Samuel, S.B. Das, S. Swaroop, N. Chandrasekaran, A. Mukherjee, Studies on Cr (VI) removal from aqueous solutions by nanoalumina, Ind. Eng. Chem. Res. 51 (2012) 15242–15250. [32] H. Daraei, A. Mittal, J. Mittal, H. Kamali, Optimization of Cr (VI) removal onto biosorbent eggshell membrane: experimental & theoretical approaches, Desalin. Water Treat. 52 (2014) 1307–1315. [33] A.B. Albadarin, Z. Yang, C. Mangwandi, Y. Glocheux, G. Walker, M. Ahmad, experimental design and batch experiments for optimization of cr (vi) removal from aqueous solutions by hydrous cerium oxide nanoparticles, Chem. Eng. Res. Des. (2013) (DOI). [34] M. Naushad, A. Mittal, M. Rathore, V. Gupta, Ion-exchange kinetic studies for Cd (II), Co (II), Cu (II), and Pb (II) metal ions over a composite cation exchanger, desalination and water treatment(DOI) 2014 1–8. [35] A. Mital, L. Kurup, Column operations for the removal and recovery of a hazardous DyeAcid red-27'from aqueous solutions, using waste materials-bottom ash and De-oiled soya, Ecol. Environ. Conserv. 12 (2006) 181. [36] M. Islam, P.C. Mishra, R. Patel, Fluoride adsorption from aqueous solution by a hybrid thorium phosphate composite, Chem. Eng. J. 166 (2011) 978–985. [37] B. Heibati, S. Rodriguez-Couto, M.A. Al-Ghouti, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, Kinetics and thermodynamics of enhanced adsorption of the dye AR 18 using activated carbons prepared from walnut and poplar woods, J. Mol. Liq. 208 (2015) 99–105. [38] M.I. Tempkin, V. Pyzhev, Kinetics of ammonia synthesis on promoted iron catalyst, J. Phys. Chem. (USSR) 13 (1939) 851–867. [39] B. Heibati, S. Rodriguez-Couto, O. Ozgonenel, N.G. Turan, A. Aluigi, M.A. Zazouli, M.G. Ghozikali, M. Mohammadyan, A.B. Albadarin, A modeling study by artificial neural network on ethidium bromide adsorption optimization using natural pumice and iron-coated pumice, desalination and water treatment(DOI) 2015 1–12. [40] B. Heibati, S. Rodriguez-Couto, N.G. Turan, O. Ozgonenel, A.B. Albadarin, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, Removal of noxious dye—acid orange 7 from aqueous solution using natural pumice and fe-coated pumice stone, J. Ind. Eng. Chem. (2015) (DOI). [41] M.A. Al-Ghouti, M.A. Khraisheh, M.N. Ahmad, S. Allen, Adsorption behaviour of methylene blue onto Jordanian diatomite: a kinetic study, J. Hazard. Mater. 165 (2009) 589–598. [42] S. Allen, G. McKay, K. Khader, Intraparticle diffusion of a basic dye during adsorption onto sphagnum peat, Environ. Pollut. 56 (1989) 39–50.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes Behzad Heibati a,b,⁎, Mahboobeh Ghoochani b,⁎⁎, Ahmad B. Albadarin c, Alireza Mesdaghinia d, Abdel Salam Hamdy Makhlouf e, Mohammad Asif f, Arjun Maity g,j, Inderjeet Tyagi h, Shilpi Agarwal h,j, Vinod Kumar Gupta h,i,j,⁎⁎⁎ a
Department of Occupational Health Engineering, Faculty of Health and Health Sciences Research Center, Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran Department of Environmental Health Engineering, Faculty of Public Health, Tehran University of Medical Sciences Tehran, Iran c Department of Chemical and Environmental Sciences, University of Limerick, Ireland d Center for Water Quality Research (CWQR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran e Department of Manufacturing Engineering, College of Engineering and Computer Science, University of Texas Pan-American, USA f Department of Chemical Engineering, King Saud University Riyadh, Saudi Arabia g National Centre for Nanostructured Materials, CSIR Material Science and Manufacturing, Pretoria 0001, South Africa h Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India i Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia j Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa b
a r t i c l e
i n f o
Article history: Received 22 May 2015 Received in revised form 16 August 2015 Accepted 18 August 2015 Available online xxxx Keywords: Multiwalled carbon nanotubes Linear alkyl benzene sulfonates Wastewater treatment Adsorption Surface modification
a b s t r a c t This paper explores the possibility of employing Oxidized Multiwalled Carbon Nanotubes (MWCNT-COOH) for the removal of toxic Linear Alkyl benzene Sulfonate (LAS). LAS is among the most toxic industrial and house hold waste surfactants. This study discusses the feasibility of removing LAS from aqueous solutions using MWCNT-COOH. The effects of operational parameters such as solution pH, LAS concentration and contact time on the removal of LAS were studied. The four linear forms of Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin models were applied to determine the best fit of equilibrium expressions. Our results showed that the experimental adsorption isotherm complies with Freundlich model. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Fitting of the experimental results to kinetic models showed the relevance of the pseudo second-order (R2 N 0.99) model for LAS. Our results confirmed that MWCNT-COOH would be promising adsorbents for LAS removal in aqueous solution. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Surfactants are used widely in household, personal care products, agriculture and industry [1,2]. Surfactants are a diverse group of chemicals with cleaning properties and consist of two heads with a different polarity or solubility in water: a polar head group, which is well solvated in water, and a non-polar hydrocarbon tail, which is not easy to dissolve in water [3,4]. Surfactants are classified by their ionic activity in water into four types: anionic, cationic, non-anionic and
⁎ Correspondence to: B. Heibati, Department of Occupational Health Engineering, Faculty of Health and Health Sciences Research Center, Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran. ⁎⁎ Corresponding author. ⁎⁎⁎ Correspondence to: V. K. Gupta, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247667, India. E-mail addresses: [email protected] (B. Heibati), [email protected] (M. Ghoochani), [email protected], [email protected] (V.K. Gupta).
amphoteric [5]. LAS is the largest group of anionic surfactants (Fig. 1). Synthetic surfactants are formed of LAS and its isomers with other additives [6,7]. Anionic surfactants (AS), especially LAS, are used extensively due to their impacts on ecosystems and are usually disposed after their use into the environment [8,9]. Therefore, they represent one of the main causes of water pollution. A recent study reported the presence of LAS in different water channels in Iran [5]. The concentrations of surfactants in natural water vary from area to area and ranged from 3.780 to 1456 mg/L. This high percentage of waste chemical components should be removed from water. The conventional treatment methods such as combination of biodegradation and sorption/settling processes and Oxidative treatments and cannot remove them [10–12]. Other methods have been proposed to remove surfactants such as: (i) adsorption [13]and (ii) coagulation using polyelectrolytes with powdered activated carbon (PAC) and powdered clinoptilolite simultaneously [14].Several researchers have shown that the adsorption is an efficient process for the removal of LAS from aqueous solutions [13,16]. For this purpose, a
http://dx.doi.org/10.1016/j.molliq.2015.08.046 0167-7322/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
2
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Fig. 1. Formulation of Linear Alkyl benzene Sulfonate.
variety of natural and synthetic materials have been tested as LAS, including activated carbon [17], mineral clay [17], soils [13] and others. Advanced membrane filtration techniques (e.g. microfiltration, ultrafiltration, nanofiltration and reverse osmosis) exhibited superior performance in treatment and removal of chemical and biological contaminants over conventional systems [18]. Hybrid methods can also be more effective than any of the previous process alone. The combination of ion exchange and ultrafiltration was more effective in surfactant removal than ultrafiltration process alone [19]. In recent years, nanotechnology has introduced different types of nanomaterials for water treatment. Nanosorbents such as carbon nanotube (CNTs) [15] and zeolites [20] proved to exhibit special adsorption properties. CNTs, in particular, received special attention for potential application in environmental protection and to work effectively against chemical and biological contaminants [15,18,21]. Single and multiwalled carbon nanotubes (MWCNTs) have been used in water and wastewater treatment [15]. The objective of this study is to investigate the adsorption mechanism of LAS using MWCNTs and to determine the optimum parameters for the maximum/efficient adsorption capacity. 2. Experimental 2.1. Materials Multi-walled CNTs (MWCNTs) were synthesized by catalytic chemical vapor deposition (CVD) method at the Research Institute of Petroleum Industry (RIPI), Tehran, Iran. MWCNTs were used as adsorbents to study the adsorption characteristic of LAS detergent from water. The size of the outer diameter of MWCNTs was more than 10 nm while the length ranged from 5 to 15 μm. In addition, the mass ratio of the amorphous carbon of MWCNTs was less than 5%, and specific surface area was 280 m2/g. Because of the presence of amorphous carbon in carbon nanotubes, the adsorption rate is very low. Therefore, carbon nanotubes must be purified before the adsorption process. The stock solution was stored in the refrigerator to minimize biodegradation. 10 mL of stock LAS solution was diluted to 1000 mL with distilled water; 1 mL = 10 μg LAS. Dilute solutions of concentrations 1.5, 2 and 4 mg/L LAS were prepared. The stock solution of LAS was prepared using standard methods for the examination of water & wastewater book No. 5540C [22].
Fig. 2. Schematic diagram of adsorbent preparation.
Fig. 3 shows the probable synthesis reaction of carboxyl and amino functionalized CNTs. This figure illustrates that carboxyl group could be formed first and may have higher number of reactive sites that could lead to better interaction with polymers. 2.3. Adsorption experiments Batch adsorption experiments were performed in glass bottles with LAS solution (250 mL) of the mentioned concentration (i.e. 4 mg/L) and 25 mg of MWCNT-COOH was added to each bottle. The amount of MWCNT-COOH was kept constant in all experimental steps. According to a previous study [5], the concentration of detergent in Tehran surface water was 0.14–3.78 mg/L. Based on LAS concentration ranging from 1.5 to 4 mg/L was selected for this study [5]. The bottles were shaken using a magnetic shaker (IKA® RCT basic) at 25 °C until equilibrium. The pH of the solutions was adjusted by adding HCl or NaOH solutions. The solution pH ranges from 3 to 9. After achieving equilibrium (corresponding to the saturation of the adsorbent), the suspension was filtered through a 0.2 μm filter and the filtrate was analyzed using NO. 5540C standard method and spectrophotometer (Perkins-Elmer Lambeda 25-UV/Vis and 652 nm wavelengths with the thickness of cell 1 cm). 2.4. Surface characterization The morphology of the adsorbents was investigated using scanning electron microscopy (SEM, KYKY-EM3200) and X-ray diffraction (XRD, Quantachrome, NOVA2000).
2.2. Functionalization of MWCNTs Schematic diagram of adsorbents preparation is shown in Fig. 2. In order to functionalize MWCNTs, 0.3 g of MWCNTs were scattered in 25 mL of nitric acid (65 wt.%) in a 100 mL flask equipped with a condenser and scattering was refluxed under magnetic stirring for 48 h [23]. Then, the resulting scattering was diluted in water and filtered. The filtrate was rinsed to neutral pH and the sample was dried in vacuum at 40 °C overnight to obtain MWCNT-COOH.
Fig. 3. Schematic diagram for chemical fictionalization of MWCNTs.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
3
3. Results and discussion 3.1. Characterization of MWCNT-COOH SEM images and XRD spectra of MWCNT-COOH are shown in Fig. 4. As shown in Fig. 4(a), the peaks at 2θ = 20, 24, and 43° are related to graphite structure of CNTs that were sharper in functionalized nanotubes. According to the SEM images of the functionalized MWCNTs, the adsorbents have no porous structure. 3.2. Effect of contact time Fig. 5 shows the effect of the contact time on the removal efficiency of LAS using MWCNT-COOH. The removal efficiency increased with time until it reaches an equilibrium constant value after 45 min, corresponding to the saturation of the adsorbent. The removal of LAS was found to be rapid at the initial period of contact time, then, slow down with the increase of contact time. This is probably due to the initially abundant number of active sites on the sorbents, whereas, with the gradual increased occupancy of these sites, the sorption process becomes less efficient with increasing time [24,25].
Fig. 5. Effect of the contact time on LAS removal (adsorbent dosage 1 g/L, pH 3 and temperature = 24 °C).
The equation of Langmuir [26,27] can be expressed as: qe ¼
3.3. Effect of the initial solution pH on LAS removal The pH of the solution is an important factor controlling the surface charge of the adsorbent and the degree of ionization of the materials in the solution. To determine the optimum solution pH for maximum LAS removal, the equilibrium adsorption of LAS (for an initial concentration of 4 mg/L) was investigated for a solution pH ranging from 3 to 9 while the other parameters such as adsorbent dose (1 g/L) and contact time (45 min) were maintained constant. According to Fig. 6, the removal efficiency of LAS decreased with increasing solution pH. Therefore, we suggest that acidic medium favors the adsorption process of LAS by MWCNT-COOH. High adsorption of LAS at low pH indicates that due to the weak basicity of LAS, its acidic form (R–C6H4–CO3H) is predominant in acidic solutions and better adsorbed by MWCNTs. The percentage removal efficiency for LAS increased with increasing LAS concentration. These results indicate that energetically high favorable sites became involved in increasing LAS concentrations in the aqueous solution.
Equilibrium data, commonly known as adsorption isotherms, describe how the adsorbate interacts with adsorbents and gives a comprehensive understanding of the nature of interaction. Several isotherm equations have been developed and employed for such analysis, and the four important isotherms including Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin isotherms were applied in this study.
ð1Þ
It can conveniently be written in a linearized form as: Ce 1 1 þ ¼ Ce qe qm b qm
ð2Þ
where: qe is the adsorbed amount at equilibrium (mg/g), Ce is the adsorbate concentration at equilibrium (mg/L), qm is the maximum adsorption capacity and b is the Langmuir constant related to the energy of adsorption [28–30]; qm and b can be deduced from the slope and intercept, by plotting Ce/qe versus Ce. The influence of the adsorption isotherm shape can be discussed to examine whether adsorption is favorable in terms of RL, a dimensionless constant referred to as separation factor or equilibrium parameter. RL is defined by the following relationship: RL ¼
3.4. Adsorption isotherms
qm bC e 1 þ bC e
1 1 þ bC o
ð3Þ
RL values between 0 and 1 indicates favorable adsorption, while RL N 1, RL = 1, and RL = 0 indicate unfavorable, linear, and irreversible adsorption isotherms, respectively [31,32]. The Freundlich isotherm [33] can be expressed as: qe ¼ K f C 1=n e
ð4Þ
Fig. 4. XRD (a) and SEM (b) of MWCNT-COOH.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
4
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
adsorption capacity, Ce is the equilibrium concentration of LAS, K is the constant related to mean free energy, R is universal gas constant and T is the absolute temperature (K). The mean free energy of adsorption (E) was calculated from the constant “K” using the relation [36,37]: E ¼ ð2K Þ‐0:5
ð7Þ
It is defined as the free energy change when 1 mol of ion is transferred to the surface of the solid from infinity in solution. The Temkin isotherm [38,39] has been used for heterogeneous adsorption of adsorbate on a surface. The following is the linear form of the Temkin model: qe ¼ β ln K T þ βlnCe
Fig. 6. Effect of solution pH on the adsorption of LAS by MWCNT-COOH (adsorbent mass = 1 g/L, and temperature = 24 °C).
The equation is conveniently used in its linear form by taking the logarithm of both sides as: logqe ¼ logK f þ
1 logce n
ð5Þ
where: Kf and n are the Freundlich constants. For favorable adsorption, the value of n should be in the range from 1 to 10 [34,35]. In order to understand the adsorption type, equilibrium data were tested with D-R isotherm [36]. The linearised D-R equation can be written as: ln qe ¼ ln qs −Kε 2
ð6Þ
where: ε is polanyi potential, and is equal to RT ln(1 + 1/Ce), qe is the amount of LASadsorbed per unit mass of adsorbents, qs is the theoretical
ð8Þ
where KT is the equilibrium binding constant (L/mg) corresponding to the maximum binding energy and constant b = RT/β (KJ/mol) is related to the heat of adsorption. Isothermal studies of LAS removal are shown in Fig. (7). In this paper, the fit of experimental values by using the four isotherm models were patterned and the results are presented in Table 1. As can be seen from the correlation coefficients (R2), the Freundlich model fits the experimental values better than the other models. Conformation of the data into the Freundlich isotherm model demonstrated the formation of multilayer coverage of LAS at the outer surface of adsorbents and showed the heterogeneous nature of LAS adsorption onto adsorbents which suggests that adsorption sites are identical and energetically equivalent [33]. The values of KF and 1/n were calculated from the slope and intercept of the plot in Fig. (7B) and reported in Table 1. Kf is a constant indicates the adsorption capacity of the adsorbent; while n is an empirical constant related to the magnitude of the adsorption driving force [33,40]. Table 1 and Fig. (7B) show that the theoretical value of the adsorption capacity is 0.001. However, the Langmuir constant b, connected to the adsorption free energy and specifying the adsorbents affinity for LAS binding, is 0.016, indicating a favorable capability of LAS molecules to form a stable complex with MWCNTs. Furthermore, when the values of n are within 1 b n b 10 it means
Fig. 7. (A) Langmuir; (B) Freundlich; (C) Dubinin Radushkevich and (D) Temkin adsorption isotherms of LAS.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx Table 1 Isotherm constants for the adsorption of LAS on MWCNT-COOH for different initial LAS concentrations at pH 3, adsorbent dose 1 g/L and contact time 45 min. Model
Parameter
Parameter
Freundlich MWCNTs Langmuir MWCNTs D-R MWCNTs Temkin MWCNTs
Kf(mg/g) 0.001 qm(mg/g) 62.5 qm(mg/g) 262.8 KT (L/g) 1189
n 0.632 b(L/mg) 0.016 E (kJ/mol) 2.67 β(mg/L) 0.016
Parameter
Parameter
RL(L/mg) 0.94 K (mol2 k/J) 7 × 10−8 b(KJ/mol) 154.84
R2 0.967 R2 0.679 R2 0.920 R2 0.920
favorable adsorption [24]. The value of constant RL is 0.86 and 0.94 l/mg indicating favorable adsorption. The monolayer adsorption capacity was 62.5 mg/g. The plot of ln(qe) against ε2 was almost linear with correlation coefficients R2 = 0.929 (Fig. 7). D-R isotherm constants K and qs were calculated from the slope and intercept of the plot, respectively. The value of K was found to be 7 × 10−8 mol2 k/J2 and that of qs was 262.8 mg/g. The value of E was found to be 2.67 kJ/mol. Table 1 depicts further that the experimental data had a relatively lower correlation with the Temkin isotherm (R2 = 0.92). 3.5. Adsorption kinetics studies The kinetic of adsorption describes the rate of LAS adsorption on adsorbent, which controls the equilibrium time and influences the adsorption mechanism. For an adsorption process, there are typically three major steps that take place at the solid–liquid interface: external diffusion, intra-particle diffusion and surface reaction. The “external diffusion” is not often decisive, especially when the experimental system is well agitated. In order to adequately correlate the experimental data, the pseudo-first order equation, pseudo-second order equation and intra-particle diffusion were used to investigate the kinetics of adsorption. The most accurate model was considered based on the regression coefficient (R2) and the comparison of the qe values to the experimental ones. Kinetics of LAS removal is shown in Fig. 8. The corresponding
5
parameters are collected in Table 2. By contrast, the experimental data of kinetic model were well-fitted by the pseudo-second-order model for all studied LAS concentrations. In addition, Fig. 8B and Table 2, show that the q values (qe,cal) determined from the pseudo secondorder model were closer to the experimental q values (qe,exp) than other models. This indicates that chemisorption was the ratecontrolling step. Fig. 8 showed that the adsorption of LAS was very fast in the first few minutes (0–5 min). Sharp slope curves of LAS adsorption onto MWCNT-COOH reveals an immediate adsorption which could be attributed to the effect of surface functional groups. Consequently, the adsorption behavior and mechanism of LAS was believed to happen via surface adsorption till the surface functional active sites were entirely occupied. Subsequently, LAS molecules diffused into the pores of the MWCNT-COOH for further adsorption [41]. The plot of qt versus t1/2 may present multi linearity [42], which indicates that two or more steps occur in the adsorption process. The first sharper stage is the external surface adsorption or instantaneous adsorption stage and the second portion is the gradual adsorption stage, where the intra-particle diffusion is rate-controlled. In Fig. 8C, the plot of qt versus t1/2 is depicted. The slope of the line in each stage is written as the rate parameter kip. The value of the rate constant for intra-particle transport increased with the increase in the initial LAS concentration (Table 2). Fig. 8C shows that the first stage has a quick diffusion rate at the highest studied concentration (i.e. 4 mg/L). The plots are linear but did not pass through the origin (Fig. 8C), indicating that external mass transfer is the main rate controlling step at the initial stages. 4. Conclusions Functionalized MWCNTs (MWCNT-COOH) have been employed as adsorbents for the removal of the LAS from aqueous solutions. Freundlich model for adsorption isotherms appeared to fit more accurately the experimental data. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Adsorption kinetics was successfully fitted to the pseudo-second-order kinetics model. Therefore, the results obtained point out MWCNT-COOH as a promising adsorbent for LAS removal.
Fig. 8. (A) Pseudo-first order; (B) Pseudo-second order and (C) Intra-particle diffusion for LAS adsorption.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046
6
B. Heibati et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Table 2 Parameters of kinetic equations. LAS(mg/L)
1.5 4.0
Pseudo-first-order model
Pseudo-second-order model
Intra particle diffusion model
qe,exp. (mg/g)
qe,cal (mg/g)
k
R2
qe,cal (mg/g)
k
R2
kip (g/mg mind/2)
R2
14.31 39.18
14.09 38.37
0.287 0.325
0.999 0.998
14.55 39.59
0.043 0.018
0.999 0.999
0.992 2.604
0.923 0.885
Acknowledgments The authors thank Sakine Shekoohiyan, Mika Sillanpää, Shila Jafari and Chungsying Lu for their helpful suggestions in the modification methods. Also, AM, IT, SA and VKG, are thankful to the Department of Science and Technology, New Delhi, India, for the financial support under project grant DST/INT/South Africa/P-03/2014. Support of the Deanship of Scientific Research grant for the Research Group RGPVPP-292 at King Saud University is appreciated by M. Asif. References [1] M. Garcia, E. Campos, J. Sánchez-Leal, I. Ribosa, Effect of linear alkylbenzene sulphonates (LAS) on the anaerobic digestion of sewage sludge, Water Res. 40 (2006) 2958–2964. [2] M. Mösche, U. Meyer, Toxicity of linear alkylbenzene sulfonate in anaerobic digestion: influence of exposure time, Water Res. 36 (2002) 3253–3260. [3] G.-G. Ying, Fate, behavior and effects of surfactants and their degradation products in the environment, Environ. Int. 32 (2006) 417–431. [4] A.K. Mungray, P. Kumar, Fate of linear alkylbenzene sulfonates in the environment: a review, Int. Biodeterior. Biodegrad. 63 (2009) 981–987. [5] M. Ghoochani, S. Shekoohiyan, A. Mahvi, B. Haibati, M. Norouzi, Determination of detergent in Tehran ground and surface water, Am. Eurasian J. Agric. Environ. Sci. 10 (2011) 464–469. [6] A.K. Mungray, P. Kumar, Occurrence of anionic surfactants in treated sewage: risk assessment to aquatic environment, J. Hazard. Mater. 160 (2008) 362–370. [7] A. Bordoloi, B.M. Devassy, P. Niphadkar, P. Joshi, S. Halligudi, Shape selective synthesis of long-chain linear alkyl benzene (LAB) with AlMCM-41/beta zeolite composite catalyst, J. Mol. Catal. A Chem. 253 (2006) 239–244. [8] C. Verge, A. Moreno, J. Bravo, J.L. Berna, Influence of water hardness on the bioavailability and toxicity of linear alkylbenzene sulphonate (LAS), Chemosphere 44 (2001) 1749–1757. [9] K.K. Brandt, M. Hesselso, P. Roslev, K. Henriksen, J. So, Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation ofNitrosomonas and nitrosospira strains, Appl. Environ. Microbiol. 67 (2001) 2489–2498. [10] D. McAvoy, W. Eckhoff, R. Rapaport, Fate of linear alkylbenzene sulfonate in the environment, Environ. Toxicol. Chem. 12 (1993) 977–987. [11] R. Rapaport, W. Eckhoff, Monitoring linear alkyl benzene sulfonate in the environment: 1973–1986, Environ. Toxicol. Chem. 9 (1990) 1245–1257. [12] M. Carballa, G. Manterola, L. Larrea, T. Ternes, F. Omil, J.M. Lema, Influence of ozone pre-treatment on sludge anaerobic digestion: removal of pharmaceutical and personal care products, Chemosphere 67 (2007) 1444–1452. [13] Z. Ou, A. Yediler, Y. He, L. Jia, A. Kettrup, T. Sun, Adsorption of linear alkylbenzene sulfonate (LAS) on soils, Chemosphere 32 (1996) 827–839. [14] J. Kaleta, M. Elektorowicz, The removal of anionic surfactants from water in coagulation process, Environ. Technol. 34 (2013) 999–1005. [15] M.H. Dehghani, M.M. Taher, A.K. Bajpai, B. Heibati, I. Tyagi, M. Asif, S. Agarwal, V.K. Gupta, Removal of noxious Cr (VI) ions using single-walled carbon nanotubes and multi-walled carbon nanotubes, Chem. Eng. J. (2015) (DOI). [16] W. de Wolf, T. Feijtel, Terrestrial risk assessment for linear alkyl benzene sulfonate (LAS) in sludge-amended soils, Chemosphere 36 (1998) 1319–1343. [17] N. Narkis, B. Ben-David, Adsorption of non-ionic surfactants on activated carbon and mineral clay, Water Res. 19 (1985) 815–824. [18] V.K. Upadhyayula, S. Deng, M.C. Mitchell, G.B. Smith, Application of carbon nanotube technology for removal of contaminants in drinking water: a review, Sci. Total Environ. 408 (2009) 1–13. [19] I. Kowalska, Ion-exchange–ultrafiltration system for surfactants removal from water solutions, Desalin. Water Treat. 25 (2011) 47–53. [20] K. Hui, C. Chao, Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents, J. Hazard. Mater. 137 (2006) 401–409.
[21] A. Mittal, J. Mittal, Hen feather: a remarkable adsorbent for dye removal, green chemistry for dyes removal from wastewater: research trends and applications(DOI) 2015 409–457. [22] A. APHA, WEF. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA/AWWA/WEF, Washington, DC, 1998 (DOI). [23] A. Naghizadeh, S. Nasseri, S. Nazmara, Removal of Trichloroethylene from water by adsorption on to multiwall carbon nanotubes, Iran. J. Environ. Health Sci. Eng. 8 (2011). [24] B. Heibati, S. Rodriguez-Couto, A. Amrane, M. Rafatullah, A. Hawari, M.A. Al-Ghouti, Uptake of Reactive Black 5 by pumice and walnut activated carbon: chemistry and adsorption mechanisms, J. Ind. Eng. Chem. (2013) (DOI). [25] H. Daraei, A. Mittal, M. Noorisepehr, J. Mittal, Separation of chromium from water samples using eggshell powder as a low-cost sorbent: kinetic and thermodynamic studies, Desalin. Water Treat. 53 (2015) 214–220. [26] A.B. Albadarin, C. Mangwandi, A.A.H. Al-muhtaseb, G.M. Walker, S.J. Allen, M.N. Ahmad, kinetic and thermodynamics of chromium ions adsorption onto low-cost dolomite adsorbent, Chem. Eng. J. 179 (2012) 193–202. [27] J. Mittal, D. Jhare, H. Vardhan, A. Mittal, Utilization of bottom ash as a low-cost sorbent for the removal and recovery of a toxic halogen containing dye eosin yellow, Desalin. Water Treat. 52 (2014) 4508–4519. [28] A. Bhatnagar, E. Kumar, M. Sillanpää, Nitrate removal from water by Nano-alumina: characterization and sorption studies, Chem. Eng. J. 163 (2010) 317–323. [29] Ş.S. Bayazit, Ö. Kerkez, Hexavalent chromium adsorption on superparamagnetic multi-wall carbon nanotubes and activated carbon composites, Chem. Eng. Res. Des. (2014) (DOI). [30] G. Sharma, M. Naushad, D. Pathania, A. Mittal, G. El-desoky, Modification of hibiscus cannabinus fiber by graft copolymerization: application for dye removal, desalination and water treatment(DOI) 2014 1–8. [31] M.L. Paul, J. Samuel, S.B. Das, S. Swaroop, N. Chandrasekaran, A. Mukherjee, Studies on Cr (VI) removal from aqueous solutions by nanoalumina, Ind. Eng. Chem. Res. 51 (2012) 15242–15250. [32] H. Daraei, A. Mittal, J. Mittal, H. Kamali, Optimization of Cr (VI) removal onto biosorbent eggshell membrane: experimental & theoretical approaches, Desalin. Water Treat. 52 (2014) 1307–1315. [33] A.B. Albadarin, Z. Yang, C. Mangwandi, Y. Glocheux, G. Walker, M. Ahmad, experimental design and batch experiments for optimization of cr (vi) removal from aqueous solutions by hydrous cerium oxide nanoparticles, Chem. Eng. Res. Des. (2013) (DOI). [34] M. Naushad, A. Mittal, M. Rathore, V. Gupta, Ion-exchange kinetic studies for Cd (II), Co (II), Cu (II), and Pb (II) metal ions over a composite cation exchanger, desalination and water treatment(DOI) 2014 1–8. [35] A. Mital, L. Kurup, Column operations for the removal and recovery of a hazardous DyeAcid red-27'from aqueous solutions, using waste materials-bottom ash and De-oiled soya, Ecol. Environ. Conserv. 12 (2006) 181. [36] M. Islam, P.C. Mishra, R. Patel, Fluoride adsorption from aqueous solution by a hybrid thorium phosphate composite, Chem. Eng. J. 166 (2011) 978–985. [37] B. Heibati, S. Rodriguez-Couto, M.A. Al-Ghouti, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, Kinetics and thermodynamics of enhanced adsorption of the dye AR 18 using activated carbons prepared from walnut and poplar woods, J. Mol. Liq. 208 (2015) 99–105. [38] M.I. Tempkin, V. Pyzhev, Kinetics of ammonia synthesis on promoted iron catalyst, J. Phys. Chem. (USSR) 13 (1939) 851–867. [39] B. Heibati, S. Rodriguez-Couto, O. Ozgonenel, N.G. Turan, A. Aluigi, M.A. Zazouli, M.G. Ghozikali, M. Mohammadyan, A.B. Albadarin, A modeling study by artificial neural network on ethidium bromide adsorption optimization using natural pumice and iron-coated pumice, desalination and water treatment(DOI) 2015 1–12. [40] B. Heibati, S. Rodriguez-Couto, N.G. Turan, O. Ozgonenel, A.B. Albadarin, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, Removal of noxious dye—acid orange 7 from aqueous solution using natural pumice and fe-coated pumice stone, J. Ind. Eng. Chem. (2015) (DOI). [41] M.A. Al-Ghouti, M.A. Khraisheh, M.N. Ahmad, S. Allen, Adsorption behaviour of methylene blue onto Jordanian diatomite: a kinetic study, J. Hazard. Mater. 165 (2009) 589–598. [42] S. Allen, G. McKay, K. Khader, Intraparticle diffusion of a basic dye during adsorption onto sphagnum peat, Environ. Pollut. 56 (1989) 39–50.
Please cite this article as: B. Heibati, et al., Removal of linear alkyl benzene sulfonate from aqueous solutions by functionalized multi-walled carbon nanotubes, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.046