Modified bentonite adsorption of organic pollutants of dye wastewater

Materials Chemistry and Physics 202 (2017) 266e276

Contents lists available at ScienceDirect

Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys

Modified bentonite adsorption of organic pollutants of dye wastewater Zhihui Huang a, Yuzhen Li a, *, Wenjun Chen b, Jianhui Shi a, Ning Zhang a, Xiaojin Wang a, Zhen Li a, Lizhen Gao a, c, Yuxin Zhang a a b c

College of Environmental Science and Engineering, Taiyuan University of Technology, 79 Yingze Street, Yingze District, Taiyuan, 030024, China Shanxi Provincial People's Hospital, Taiyuan 030012, China School of Mechanical Engineering, University of Western Australia, 35 Stirling Highway, WA 6009, Australia

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Adsorption ability of different types of dyes onto CTAB-bentonite was investigated.
The relationship of structures and adsorption properties of adsorbent was explored.
The influence of different factors on the properties of the adsorbent was revealed.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 December 2016 Received in revised form 9 September 2017 Accepted 16 September 2017 Available online 19 September 2017

Removals of Rhodamine B (RhB) and Acid red 1 using the organic modification of bentonite from aqueous phase were optimized. The organobentonite was synthesized by replacing exchangeable Naþ ions in Nabentonite (Na-Bt) with cetyl trimethylammonium bromide (CTAB) and systematically explored for its adsorption behavior as an efficient adsorbent for the removal of dyes. Batch adsorption studies manifested that the maximum adsorption capacity of dyes were found to be 173.5 mg/g and 157.4 mg/g for RhB and Acid red 1 at the initial concentration of 300 mg/L at 30  C and pH 9 and 8, respectively. The investigations of adsorption isotherm and kinetics model showed that the adsorption isotherm data were fitted well to the Langmuir isotherm and the adsorption kinetic was better by pseudo-second-order kinetic model. Besides, the thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic. Furthermore, the properties of the obtained samples were characterized by Xray diffraction (XRD), Scanning electronic microscopy (SEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectrometry (FT-IR) and zeta potential analysis. The results of the characterization provided evidence of the morphological properties and how well the adsorption process performed. © 2017 Elsevier B.V. All rights reserved.

Keywords: Na-bentonite Organic modification Adsorption Dye wastewater

1. Introduction

* Corresponding author. Tel./fax: þ86 351 7686354. E-mail addresses: [email protected], [email protected] (Y. Li). https://doi.org/10.1016/j.matchemphys.2017.09.028 0254-0584/© 2017 Elsevier B.V. All rights reserved.

Dyes are applied widely in many industries as colorants, such as foods, paint, textiles, cosmetics, leather, paper-making, plastics, etc [1]. Dye wastewater has become one of the major hazardous

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

industrial wastewater [2e6]. Dyes can be sorted into natural and synthetic dyestuffs, and the synthetic dyestuff can be further divided into three categories: anionic dyes (direct, acid and reactive dyes), cationic dyes (basic dyes) and non-ionic dyes (disperse and vat dyes) [7]. Most of the organic structure contain aromatic rings in the wastewater and dyeing groups caused serious damage to the water environment, which were reported to generate carcinogens to fatally harm human health and could lead to negative influence to the environment and ecosystem as well [8e11]. Therefore, it is impending to take measures to reduce the degree of damage and even achieve risk-free level. Consequently, it is a herculean task of top priority to find an effective method for treatment of organic dyes in the dyeing and printing wastewater. Several technologies have been explored for dye removal including chemical method, adsorption, electrochemical oxidation, membrane separation and coagulation [12]. Currently, the wastewater treatment technology renovates ceaselessly, such as oxidation methods, biological methods, etc. However, the major disadvantage of using oxidation methods is that it may produce toxic byproducts even from biodegradable dyes in wastewater, which is not conducive to thoroughly remove pollutants [13,14]. In recent years, the results of biological treatment of dye wastewater showed that the removal efficiency of dyes was good and the removal process of dyes did not produce secondary pollution, but the biological methods removed only the dissolved dyes and demanding environment conditions [15e17]. Comparing to other technology, adsorption method come an economical and feasible method for dye wastewater decontamination due to the cheap adsorbents and efficient treatment effect. Various adsorbents can be used for the removal of dyes from chemical industry wastewater. Some low-cost or easy-accessibility materials have been investigated in many research studies, such as clay materials [18e22], layered double hydroxides [23e25], fly ash [26,27], resin [28], fruit peels [29], the biological strawhave [30]. In addition, photocatalytic method had also been used in the degradation of dye [31e33]. Good performance of adsorption materials play a vital role in wastewater purification. In recent years, raw mineral adsorbents occupy an irreplaceable position in wastewater treatment. Raw bentonite, as a representative nonmetallic clay mineral, is primarily based on montmorillonite, which is made up of two silicon oxygen tetrahedron clip a layer of alumina 2:1 type of octahedral crystal structure. The lamellar structure of montmorillonite crystal cell contains some cations, such as Cu2þ, Mg2þ, Naþ, Kþ, etc. However, the role of these cationic and montmorillonite crystal cell is very unstable and these cations are easier to be replaced by other cation. Therefore, bentonite has good performance in adsorbing cationic contaminants by cationic exchange [34]. It is the most common to prepare organobentonite by organic cationic surfactant inserting the bentonite between layers and external surface. It was studied that cationic surfactant cetyl trimethylammonium bromide (CTAB) modified bentonite removed four acid dyes from aqueous solution, the results showed that the modified bentonite layer spacing was bigger and had good adsorption effect of dyes, hence, organic cationic surfactant modified bentonite can strengthen the adsorption capacity [35]. Yaxin Zhang et al. have investigated the adsorption of cationic-nonionic mixed surfactant onto bentonite and its effect on bentonite structure. The result showed that the bentonite specific surface area, pore volume and the adsorption capacity was decreased [36]. Moreover, inorganic and compound modification have also been investigated by many researchers. Yaowen Gao et al. revealed that Iron modified bentonite (FeMB) was significantly ameliorated the adsorption property for Rhodamine B(RhB) [37]. In the present study, the natural Na-bentonite has been

267

modified by cetyl trimethylammonium bromide (CTAB) to apply to adsorb dyes from aqueous solution. The paper selected cationic dye RhB and anionic dye Acid Red 1 as the target pollutants (the general concentration of 10e600 mg/L for Rhodamine B [38e41]and 100e2500 mg/L [42] for Acid Red 1 respectively.). In order to investigate the effects of several parameters, a series of experiments were carried out, including effects of adsorbent dosage, contact time, initial dyes concentration, temperature and initial solution pH on the adsorption of RhB and Acid red 1 onto modified Na-bentonite. In addition, the adsorption kinetics, adsorption isotherms and thermodynamic studies were also achieved. 2. Materials and methods 2.1. Materials The Na-bentonite used in this study was purchased from Heng Sheng material co., LTD (Henan,China). According to the supplier, its chemical composition was found to be as follows: 63.43% SiO2, 3.05% MgO, 17.88% Al2O3, 0.9% K2O, 2.22% CaO, 2.06% Fe2O3, 0.98% Na2O, 0.13% TiO2 and 8.09% loss of ignition. The cation exchange capacity (CEC) of Na-bentonite was determined by the barium clay method. The CEC of Na-bentonite was 1.092 mmoL/g. The dyes Rhodamine and Acid red 1 used for this study were purchased from aladdin industrial corporation (Shanghai,China). The dyes were used without any further purification. The chemical structures and parameters of the selected dyes were shown in Table 1. Different aqueous solutions of dyes were prepared by dissolving definite amount of dyes in distilled water in order to attain concentrations of between 50 and 350 mg/L of each dye for separate tests that may be typical in waste-water from printing and dyeing chemical industry. The surfactant cetyl trimethyl ammonium bromide (CTAB) was purchased from Chemical reagent co., LTD (Shanghai,China) and the chemical structural formula of CTAB was shown in Table 1. All reagents were analytical grade. Deionized water was used in all experient. HCl and NaOH which was used for adjusting different pH were purchased from Chemical reagent co. 2.2. Preparation of organobentonite The surfactant CTAB intercalated Na-bentonite was synthesized as follows: the amount of CTAB corresponding to 100% of the CEC of Na-bentonite were dissolved in 1 L of distilled water at 60  C and stirred for 3 h. A total of 10 g Na-bentonite was added to 1 L surfactant solution. The dispersion was stirred for 3 h at 60  C. The separated sample was washed with distilled water several times, until the supernatant solution was free of bromide ions. The results were oven-dried at 80  C until the water was completely evaporated and the product was ground into powder. The final product was noted as CTAB-bentonite. 2.3. Characterization of organobentonite To study the change in the structure properties of CTABbentonite (CTAB-Bt), the distance between the layers of the modified Na-Bt was determined by X-ray diffraction analysis using a Shimadzu XRD-6000 at a scanning rate of 2 /min in 2 q ranging from 0.6 to 70 with CuKa radiation (l ¼ 0.154 nm), and advance diffractometer operating at the voltage of 40 kV and a 30 mA flux. Bragg's formula 2dsinq ¼ nl was used to compute the d001 of the examined samples. The surface morphology of Na-Bt and CTABbentonite was confirmed by SEM (Hitachi, S4800) analysis under 10 KV voltage and a 5 mA flux. The isotherm data of bentonite nanoparticles were measured by BET-analyzer (Kang Ta N22-27E) after degassing under vacuum at 80  C for 3 h. The specific

268

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

Table 1 Chemical parameters of materials. Dye name

Molecular formula

Molar masst

lmax (nm)

Rhodamin B

C28H31ClN2O3

479.01

554

Acid red 1

C18H13N3Na2O8S2

509.42

505

CTAB

C19H42BrN

364.44

e

Structural formula

surface area, the pore size and pore size were calculated by the BET method. The total pore volume was calculated from the maximum amount of nitrogen gas desorption at partial pressure (P/P0) ¼ 0.95. FT-IR spectra study were carried out using Bruker Tensor 27 spectrophotometer and recorded in the range of 4000e400 cm1 with KBr pellet technique. The zeta potential was measured by Laser Zeta meter Malvern Instruments (Nano-ZS-90).

2.4. Adsorption experiments To compare the adsorption capacity of the synthesized organobentonite, different amount of CTAB-bentonite were identified as (0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.6 and 1.0) g. For purpose of determining the period required to reach the adsorption equilibrium, each batch was conducted at various time intervals (10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, and 130) min. Adsorption studies were done by the optimum value of CTAB-bentonite with 50 mL of various dye solutions (50e350 mg/L) in a stoppered bottle and they were placed in a temperature controlled water bath shaker. The initial concentrations. The pH of solutions was adjusted to the range from 2.0 to 10.0 with small amount of NaOH/HCl solution. The solutions were then separated from adsorbates with low

speed centrifuge at the rotate speed of 3000 r/min for 15 min. The remaining concentrations of each solution were measured by visible spectrophotometer at 554 nm (the lmax value for Rhodamine B) and 505 nm (the lmax value for Acid red 1), respectively. The absorbance concentration profile was obtained by plotting the calibration curve between absorbance and dye concentration. The amount adsorbed of dye onto organo-bentonite (qe) can be estimated from the mass balance equation:

qe ¼

ðC0  CeÞ  V  100 m

(1)

where qe is the amount of dye adsorbed per unit mass of adsorbent (mg/L), C0 and Ce (mg/L) are initial and equilibrium dyes concentration, V (L) is the volume of dyes solution, and m (g) is the adsorbent mass. The removal eficiency of dye onto organo-bentonite at time t was calculated by

Removal eficiency ð%Þ ¼

C0  Ct  100 C0

where Ct (mg/L) is time t dyes concentration.

(2)

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

269

3. Result and discussion 3.1. Characterization of organobentonite 3.1.1. X-ray diffraction analysis XRD patterns is mainly used for material within the mineral composition and crystal structure analysis [43]. The XRD patterns of Na-bentonite and CTAB-bentonite were shown in Fig. 1. The basal spacing for Na-bentonite was 1.50 nm, representing the typical XRD pattern of Na-bentonite with the d001 plane presenting in peak at about 5.87 (see Fig. 1a). After modification with CTAB on the surface of Na-bentonite, the d001 peak in CTAB-bentonite shifted to 4.54 (see Fig. 1b), the corresponding interlayer spacing of CTABbentonite (d001) increased to 2.04 nm, manifesting these cations had been inserted into the layer of Na-bentonite by ion exchange [44]. This was attributed to the long alkyl chain inserted between layers of bentonite, which was advantageous to the interlamellar spacing of bentonite increase, and then promoting the adsorption of organic matters removal. The XRD results indicated that organic cation modification had given rise to structural changes in the Nabentonite [45]. 3.1.2. SEM analysis The surface morphology and microstructure of Na-bentonite and CTAB-bentonite were displayed by SEM. The SEM images of Na-bentnite and modified bentonite (Fig. 2) revealed significant changes on the surface morphology of the Na-bentonite after modifying with CTAB [46]. The SEM micrographs of Nabentonite showed a smooth and irregular appearance, and natural Na-bentonite presented the scattered and different sizes of block structure (see Fig. 2a). However, the surface morphology of modified bentonite was rough and accompanied by a small number of holes (see Fig. 2b). At the same time, the SEM images of CTAB-bentonite displayed the edge of the crimp morphology and Na-bentonite small pieces formed a larger block structure. Fig. 2. SEM images of (a) Na-bentonite and (b) CTAB-bentonite.

3.1.3. N2 gas adsorption-desorption analysis Fig. 3 showed the N2 adsorption-desorption isotherms and pore size distribution of Na-bentonite and CTAB-bentonite (see insert). In Fig. 3, with relative pressure P/Po > 0.44, adsorptiondesorption isotherms of two materials began to slowly rising

Fig. 3. N2 adsorption-desorption isotherms of samples, (a) Na-bentonite, (b) CTABbentonite and their corresponding pore size distribution (insert).

Fig. 1. XRD patterns of samples. (a) Na-bentonite, (b) CTAB-bentonite.

trend and adsorption/desorption isotherms didn't maintain overlap, appearing the significant lag phenomenon of regression. Hysteresis loop was clearly visible in the regime of pore filling, and showed typical H3 characteristics attributed to interstices pores.

270

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

The reasons for this phenomenon was no obvious adsorption limit for flake particle materials (such as clay), or seam hole materials in the region of the high relative pressure. Furthermore, the surface area of the CTAB-bentonite was much low compared with other reported about adsorption materials [47,48], macromolecular cationic organic modifier (CTAB) and negative charge of the surface of Na-bentonite happened neutralization reaction, and reaction products attached on the surface of the bentonite, which made its surface area decrease significantly [49]. Surmnary of BET analysis results of samples (Table 2) can reveal that specific surface area, pore volume and pore size of the organic bentonite (32.735 m2/g, 0.078 cm3/g, 3.865 nm) was lower than Nabentonite (74.351 m2/g, 0.137 cm3/g, 3.866 nm), respectively. Indicating that organic molecules entered into the interlayers of bentonite and overlapped its surface, and blocked the channel between the layers, reducing the surface area, pore volume and pore size. 3.1.4. FT-IR analysis The FT-IR spectra (4000-400 cm1) of Na-bentonite and CTABbentonite were visualized in Fig. 4. Comparing Fig. 4a and b, FT-IR spectra of the modified bentonite and natural bentonite had roughly the same peak shape, which showed that the basic skeleton of bentonite had no obvious change in the process of modification. The bands of Na-Bt and CTAB-bentonite at 1041 cm1 and 810 cm1 were attributed to Si-O and Al-O stretching vibration absorption peak, respectively [50]. Also, a stretching vibration of structural -OH groups was showed at the wavenumber of 3417 cm1 in Na-bentonite and CTAB-bentonite. New peaks were observed after the adsorption of CTAB on Na-Bt at 2864 cm1 and 2934 cm1 in Fig. 4b, which correspond to the symmetric and asymmetric stretching vibrations of -CH2 and -CH3 of the aliphatic chain of the surfactant. And a bending vibration of the methylene groups can be seen at wavelength bands of 1480 cm1 [51]. The change of the infrared spectra of two kinds of materials proved that surfactant molecules inserted into between Na-bentonite layer.

Fig. 4. FT-IR spectra of samples. (a) Na-bentonite, (b) CTAB-bentonite.

3.2. Influencing factors for the adsorption performance of modified Na-bentonite 3.2.1. Effect of surface modification and adsorbent dose on the adsorption of dyes onto organobentonite Batch experiments were carried on in order to investigate the

3.1.5. Zeta potential analysis The permanent negative charge in the crystal structures of bentonite, make them suitable for surface modification by long chain and short chain organic cation surfactants. The zeta potential is a very important parameter for evaluating the stability of the Nabentonite and CTAB-bentonite in aqueous solution. Zeta potential analysis results showed that zeta potential of the Na-bentonite was 28.2 mV, and the Na-bentonite of charge increased to 37.2 mV by the addition of CTAB (at which the Zeta potential analysis were taken. PH is 7.7 for Na-bentonite and is 8.1 for CTABbentonite, respectively). In general, the particle dispersion system was more stable at the higher zeta potential, and boundaries of particle dispersion stability were þ30 mV or 30 mV in aqueous phase, that is to say, if the zeta potential of particles was greater than þ30 mV or less than 30 mV, then the decentralized system was relatively stable [52,53]. Therefore, Zeta potential analysis revealed that the CTAB modification of bentonite was stable in water.

Table 2 Summaries of texture parameters of samples. Samples

SA (m2/g)

PS (nm)

PV(cm3/g)

a b

74.351 32.735

3.866 3.865

0.137 0.078

Notes: SA is the surface area, PS the pore size and PV the pore volume.

Fig. 5. Effect of surface modification for the adsorption of RhB (A) and Acid red 1(B) onto organobentonite. (a) Na-bentonite, (b) CTAB-bentonite.

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

influence of surface modification on the efficiency of dyes removal. Fig. 5 showed the removal efficiency of dyes from aqueous solutions with the impact of adsorbent dose for initial dyes (Rhodamine B and Acid red 1) concentration of 50 mg/L at 30  C. In Fig. 5A(b), as the increase of CTAB-bentonite dose from 0 to 0.1 g with the removal rate of RhB increased from 0 to 94.2%, however, when the adsorption dosage increased to 0.1 g, the dyes removal rate tended to maintain a stable progression and reached its maximum (94.2%). Compared in terms of CTAB-bentonite, the dosage of Na-bentonite increased from 0 to 0.1 g, the removal rate of RhB increased from 0 to 67.9%, and the best adsorption effect was obtained in the dosage of 0.1 g (see Fig. 5A(a)). The most value was significantly lower than adsorption of RhB onto the CTAB-bentonite. However, removal rate of acid red 1 onto the CTAB-bentonite was higher than which the RhB. From Fig. 5B, For the dose of CTAB-bentonite and Na-bentonite from 0 to 0.1 g, their adsorption increased to 94.1% and 44.2%, respectively. When adsorption dose exceeded 0.1 g, the adsorption reached equilibrium and the removal rate no longer increased. Fig. 5 indicates that cationic surfactant modified bentonite of adsorption performance was superior to Na-bentonite. It was seen that CTAB-bentonite was 1.4 and 1.9 times adsorption capacity than Na-bentonite for the removal of RhB and Acid red 1, respectively. This was due to the fact that after modification, Na-bentonite layer spacing increased and the hydrophilic surface of Na-bentonite transformed into a hydrophobic surface to improve adsorptive property [54]. Furthermore, the maximum removal rate of Acid red 1 onto CTAB-bentonite was greater than RhB, which was because the -SO3H of Acid red 1 was easy to combine with cation of CTABbentonite and cation of RhB and CTAB-bentonite generated electrostatic repulsion [55]. In conclusion, dye molecules were well separated from the dye wastewater and adsorbent dose was identified as 0.1 g for the next experiment.

3.2.2. Effect of contact time on dyes removal The adsorption capacity of CTAB-bentonite of RhB and Acid red 1 versus the contact time was shown in Fig. 6. From Fig. 6, it was clearly observed that the adsorption process of dyes onto CTABbentonite was relatively fast rapidly at initial time intervals, but with the increase of contact time, the dye adsorption amount increased slowly and gradually tended to equilibrium. As shown in Fig. 6a, the equilibrium time was found to be 90 min for Acid red 1, and the equilibrium time of RhB was 40 min (see Fig. 6b). In Fig. 6a,

Fig. 6. Effect of contact time on the adsorption of Acid red 1 (a) and RhB (b) onto CTABbentonite.

271

the amount adsorbed of Acid red 1 at equilibrium was found to be 44.2 mg/g at the initial concentration of 100 mg/L at 30  C. In the same conditions, the amount adsorbed was 55.4 mg/g for RhB (see Fig. 6b). The high efficiency in uptake at an initial process was due to the abundant availability of adsorption sites on the surface of CTAB-bentonite. After the rapid adsorption, the adsorption quantity of dyes reached a constant value. Therefore, the adsorption time of 90 min was used as subsequent experiments. 3.2.3. Effect of initial dye concentration and temperature on dyes adsorption amount The effect of dye concentration and temperature on the adsorption by CTAB-bentonite were investigated by varying the initial dye concentration from 50 to 350 mg/L and the temperature from 30  C to 50  C at contact time 90 min (see Fig. 7). In Fig. 7A, amount adsorbed maximum value of RhB and Acid red 1 were 156.2 mg/g (see Fig. 7A(b)) and 152.8 mg/g (see Fig. 7A(a)) in initial concentration 300 mg/L, respectively. Amount adsorbed quickly increased with initial dyes concentration of from 50 to 300 mg/L. However, when initial dyes concentration were 300e350 mg/L, adsorption process reached steady state. This was due to the initial dyes concentration furnishing a significant driving force to surmount all of the mass transfer limitations of dyes between the aqueous and solid phases [56]. In addition, amount adsorbed of dyes slightly increased as the temperature changed range from 30  C to 50  C. From Fig. 7B, the maximum adsorption amount of RhB and Acid red 1 were 156.3 mg/g (see Fig. 7B(b)) and 155.3 mg/g (see Fig. 7B(a)), respectively, which were 159.1 mg/g and 157.7 mg/g at 50  C in Fig. 7C. Therefore, in order to reduce energy consumption, the next experiments condition was identified as initial dyes concentration of 300 mg/L and 30  C solution temperature. 3.2.4. Effect of pH on adsorption performance In order to explore the effect of pH on the adsorption of dyes onto CTAB-bentonite, solutions were prepared by 0.1 moL/L solution of HCl and NaOH adjusting different pH values ranging from 2.0 to 10.0 at initial dyes concentration of 300 mg/L at 30  C. The effect of pH for the adsorption of RhB and Rcid red 1 onto CTABbentonite was shown in Fig. 8. It was clear that the adsorption of RhB and Rcid red 1 was pH-dependent. Fig. 8b demonstrated that the adsorption capacity of RhB was aggrandized from 150.2 to 173.5 mg/g with the solution pH increasing from 2.0 to 9.0. When the pH was between 2.0 and 6.0, the increment speed of amount adsorbed was relatively laggardly, adsorption quantity increased fast at the pH of solution from 6.0 to 9.0. But with pH more than 9.0, the adsorption quantity almost no longer increased even tended to decrease slowly. In Fig. 8a, the adsorption amonut of Acid red 1 reached maximum value (157.4 mg/g) at pH 8.0. In Fig. 8, the adsorption amonut of Acid red 1 gradually increased at pH from 2.0 to 6.0, compared with rhodamine B, the adsorption quantity of Acid red 1 increased faster than that of rhodamine B with increasing pH from 6.0 to 8.0. However, the pace of decline of Acid red 1 was greater than that's rhodamine B at pH 8.0e9.0, and adsorption tended to a stable state with pH value exceeding 9.0. Modified bentonite to the affinity of dye based on amonut adsorbed of dyes was as follows: RhB > Acid red 1, which was due to the fact that different dyes will have different physical, chemical and electrostatic forces according to their structure, molecular size and functional groups [57]. Adsorption of dyes onto CTABbentonite may take place through ion exchange electrostatic force and partition. For RhB, with the solution of pH under 7, cationexchange action played an important role in the adsorption process, so amount adsorbed of RhB was much higher than Acid red 1 (electrostatic force occurred through the interaction of the organic solutes with organic fraction of the organobentonite). However,

272

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

Fig. 8. Effect of pH on the adsorption of Acid red 1 (a) and RhB (b) onto CTABbentonite.

increased and reached a maximum value at pH 8. Furthermore, for organoclay, the CTAB surfactant obviously improved lamellar space by close packing of the alkyl chains to create hydrophobic regions, which will create an effective organic environment, resulting in good affinity for organic compounds [58]. 3.3. Adsorption isotherms The adsorption isotherm is significant for the depicting of how the adsorbate will interact with the adsorbent. Furthermore, it gives an idea of the adsorption capacity of the adsorbent. RhB and Acid red 1 adsorption isotherms obtained for different initial dye concentrations (50, 100, 150, 200, 250, 300 and 350) mg/L were applied to fit the models of Freundlich (Eq. (3)) and Langmuir (Eq. (4)). The linear form of the Freundlich and the Langmuir equation is as follows:

Fig. 7. Effect of initial concentration and temperature on the adsorption of Acid red 1 (a) and RhB (b) onto CTAB-bentonite. (A) at 30  C, (B) at 40  C, (C) at 50  C.

partition played a vital role in the pH more than 7, and with adsorption sites decreasing, adsorption capacity of CTAB-bentonite was saturated. Acid red 1 belongs to anionic dyes, partition became dominant part for dyes adsorption onto CTAB-bentonite under the alkaline conditions, but due to electrostatic repulsion in between OH and Acid red 1, amount adsorbed of Acid red 1 slowly

1 ln qe ¼ ln Kf þ ln Ce n

(3)

Ce 1 Ce ¼ þ qe qmaxkL qmax

(4)

where qe is the amount of dye adsorbed on the adsorbent (mg/g) at equilibrium, Ce the equilibrium dye concentration in solution (mg/ L), while Kf (L/g) and n are the Freundlich adsorption constants. Where qmax is the maximum adsorption amount for the adsorbent (mg/g) and KL is the Langmuir adsorption constant (L/mg), while all other symbols are the same as in Eq. (3). The Freundlich equation is applied to describe heterogeneous systems and reversible adsorption and is not confined within the formation of monolayers, while the Langmuir adsorption isotherm assumes that the adsorption occurs at specific homogenous sites within the adsorbent and is the most suitable for monolayer adsorption [59]. The essential characteristics of the Langmuir equation can be expressed by a dimensionless constant called the Langmuir equilibrium parameter RL. RL expression equation is as follows:

RL ¼

1 ð1 þ KLC0Þ

(5)

The value of RL indicates the type of isotherm either to be unfavorable (RL > 1), linear (RL ¼ 1), favorable (0 < RL < 1)or irreversible (RL ¼ 0).

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

273

The experimental data were fitted by the Langmuir (Fig. 9) and the Freundlich (Fig. 10) models, corresponding constants were calculated from the intercepts and slopes, and are shown in Table 3. According to results displayed in Table 3, the correlation coefficient (R2) in the Langmuir model was closer to unity than the Freundlich. Therefore, the Langmuir model was more appropriate for adsorption of RhB and Acid red 1 onto CTAB-bentonite (The responding correlation coefficient R2 was 0.99807 for RhB and 0.99008 for Acid Red 1, respectively.). At the same time, it can be seen that RhB and Acid red 1 of the values of RL were 0.0427 and 0.1911, respectively (see Table 3), RL ¼ 0.0427 and RL ¼ 0.1911 lie within the favorable limits. It well known that Langmuir model assumed that the adsorption process occurs at a homogeneous surface. Therefore, each adsorbate molecule fairly distributed on active sites of organobentonite. 3.4. Adsorption kinetics Adsorption kinetics is highly important in the design and evaluation of adsorbents in removing RhB and Acid red 1 from the solution. The pseudo-first and pseudo-second order models were employed to correlate the kinetics data. The pseudo-first-order kinetics adsorption model was described for the adsorption of solid/liquid systems [60] and can be expressed in linear form using the following Eq. (6):

lnðqe  qtÞ ¼ ln qe  tK1

(6)

where K1 is the rate constant of adsorption (min1), qe and qt are the adsorption loading of RhB and Acid red 1 (mg/g) at equilibrium and at time t (min), respectively. If the pseudo-first-order kinetics is applicable, plotting ln (qeqt) versus t (Fig. 11) should provide a straight line and K1 can be determined from the slope. The pseudo-second-order kinetics model is as follows:

t 1 t ¼ þ qt qe2 K2 qe

Fig. 10. The Freundlich adsorption isotherms of Acid red 1 (a) and RhB (b) onto CTABbentonite.

Table 3 Isotherm parameters analysis coefficient for the adsorption of RhB and Acid red 1 onto organoclay. Isotherm constants Langmuir qmax (mg/g) KL (L/mg) R2 RL Freundlich Kf (L/g) n R2

RhB

Acid Red 1

156.3169 0.0641 0.99807 0.0427

156.1865 0.0121 0.99008 0.1911

0.0051 0.1422 0.69496

0.0019 0.2793 0.89085

(7)

where K2 (g$ mg1min1) is the rate constant of pseudo-secondorder adsorption, and all other symbols are the same as in Eq. (6). Plotting t/qt against t (Fig. 12), a straight line is obtained and the rate constant K2 can be calculated according to the straight line of intercept. The pseudo-second-order model is based on the assumption that the rate limiting step may be chemical adsorption

Fig. 11. The pseudo-first-order kinetic for the adsorption of Acid red 1 (a) and RhB (b) onto CTAB-bentonite.

Fig. 9. The Langmuir adsorption isotherms of Acid red 1 (a) and RhB (b) onto CTABbentonite.

which concerns valence forces by sharing or electron exchange between the adsorbent and the adsorbate [61]. Kinetics of related parameters (qe, K1, K2) and the correlation coefficient R2 were shown in Table 4. It can be observed that the R2 values for the pseudo-second-order were higher than that of the pseudo-firstorder model. These imply that the adsorption of RhB and Acid red 1 accorded with the pseudo-second-order model.

274

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

3.5. Thermodynamic study Thermodynamic parameters such as standard free energy change (DG ), standard enthalpy change (DH ) and standard entropy change (DS ) can be obtained on the basis of the following equations:

DG ¼ RT ln Kc

(8)

DG ¼ DH  T DS

(9)

DG

ln Kc ¼ 

Fig. 12. The pseudo-second-order kinetic for the adsorption of Acid red 1 (a) and RhB (b) onto CTAB-bentonite.

Table 4 Kinetic models parameters obtained in adsorption of RhB and Acid red 1 onto CTABbentonite. Dynamics constants Pseudo-first-order qe (mg/g) K1 (min1) R2 Pseudo-second-order qe (mg/g) K2 (g$ mg1min1) R2

RhB

Acid Red 1

55.3326 0.1570 0.95379

44.1818 0.0710 0.96108

55.3326 0.0199 0.99996

44.1818 0.0035 0.99831

RT

¼

DS R



DH

(10)

RT

where Kc is the equilibrium constant resulting from the ratio of the equilibrium concentration of the dyes attached to adsorbent compared to the equilibrium the dyes concentration in solution. The values of DH and DS were calculated from slope and intercept of the plot of lnKc against 1/T (Fig. 13). Table 5 summarizes the thermodynamic parameters at different temperatures for the adsorption of RhB and Acid red 1 onto CTAB-bentonite. It can be observed that the DH and DS values of RhB and Acid red 1 were greater than zero. Positive DH values indicated that the adsorption of RhB and Acid red 1 onto CTAB-bentonite was an endothermic process in nature, and that the increase of temperature was advantageous to the dyes adsorption. In the meantime, positive DS values implied that randomness of the solid/solution interface was enhanced during the adsorption of dyes onto CTABbentonite, manifesting that some structural exchange took place among the active sites of the adsorbent and the dyes [62]. From Table 5, the DG values of RhB and Acid red 1 were less than zero at various temperatures. The negative values of Gibbs energy of RhB and Acid red 1 showed that adsorption process was spontaneous and feasible for the modified bentonite.

4. Conclusions

Fig. 13. Plots of ln Kc versus 1/T for Acid red 1 (a) and RhB (b) onto CTAB-bentonite.

Organoclay was prepared with CTAB equivalent to 1.0 CEC of Nabentonite and was used to remove ionic dyes from aqueous phase. Characterization results demonstrat that CTAB brought some changes to the structure and surface properties of natural Nabentonite. CTAB intercalated into Na-bentonite and formed a more hydrophobic partition medium, which was more conducive to increase the adsorption capacity of bentonite for RhB and Acid red 1. Dyes adsorption were also affected by pH and concentration. Higher pH will generally generate higher adsorption amonut for RhB and Acid red 1. The maximum adsorption amonut of RhB and Acid red 1 were 173.5 mg/g (pH ¼ 9.0) and 157.4 mg/g (pH ¼ 8.0), respectively. The adsorption of RhB and Acid red 1 onto surfactant modified Na-bentonite equilibrated within 40 min and 90 min, respectively. The adsorption data of RhB and Acid red 1 onto CTABbentonite was well described by the pseudo-second-order kinetic model and the Langmuir isotherm model. Thermodynamic pa-

Table 5 Thermodynamic parameters for the adsorption of RhB and Acid red 1 by CTAB-bentonite. T

RhB

(K) 303 313 323

DH (kJ/mol)

DS (J/k mol)

Acid red 1

6.0966

31.4839

DG (kJ/mol) 3.4430 3.7579 4.0727

DH (kJ/mol) 9.3429

DS (J/k mol) 40.9133

DG (kJ/mol) 3.0538 3.4630 3.8721

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276

rameters indicate that the adsorption of RhB and Acid red 1 was spontaneous and endothermic process. This study is promising for designing on the basis of bentonite organoclay as adsorbents for purification of organic pollutants similar to RhB and Acid red 1.

[20]

[21]

Acknowledgements [22]

This work was supported by the National Natural Science Foundation of China (21203136), the Project for Importing Talent of Taiyuan University of Technology (tyut-rc201120a) and the Natural Science Foundation of Shanxi (2015021060), the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (2015135, 2015128), the College Students Innovations Special Project funded by Taiyuan University of Technology (8003-02030381), and the Shanxi Provincial Key Research and Development Plan (general) Social Development Project(201703D321009-5). References [1] R. Koswojo, R.P. Utomo, Y.H. Ju, A. Ayucitra, F.E. Soetaredjo, J. Sunarso, S. Ismadji, Acid Green 25 removal from wastewater by organo-bentonite from Pacitan, Appl. Clay Sci. 48 (2010) 81e86. [2] C.D. Raman, S. Kanmani, Textile dye degradation using nano zero valent iron: a review, J. Environ. Manag. 177 (2016) 341e355. [3] R.D.C. Soltani, S. Jorfi, M. Safari, M.S. Rajaei, Enhanced sonocatalysis of textile wastewater using bentonite-supported ZnO nanoparticles: response surface methodological approach, J. Environ. Manag. 179 (2016) 47e57. [4] C.J. Wang, X.H. Jiang, L.M. Zhou, G.Q. Xia, Z.J. Chen, M. Duan, X.M. Jiang, The preparation of organo-bentonite by a new gemini and its monomer surfactants and the application in MO removal: a comparative study, Chem. Engin. J. 219 (2013) 469e477. [5] H.H. Hammud, A. Shmait, N. Hourani, Removal of Malachite Green from water using hydrothermally carbonized pine needles, RSC Adv. 5 (2015) 7909e7920. [6] S.P. Patil, B. Bethi, G.H. Sonawane, V.S. Shrivastava, S. Sonawane, Efficient adsorption and photocatalytic degradation of Rhodamine B dye over Bi2O3bentonite nanocomposites: a kinetic study, J. Ind. Eng. Chem. 34 (2016) 356e363. [7] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative, Bioresour. Technol. 77 (2001) 247e255. [8] L.G. Yan, L.L. Qin, H.Q. Yu, S. Li, R.R. Shan, B. Du, Adsorption of acid dyes from aqueous solution by CTMAB modified bentonite: kinetic and isotherm modelin, J. Mol. Liq. 211 (2015) 1074e1081. [9] Y.C. Xu, Z.X. Wang, X.Q. Cheng, Y.C. Xiao, L. Shao, Positively charged nanofiltration membranes via economically mussel-substance-simulated codeposition for textile wastewater treatment, Chem. Eng. J. 303 (2016) 555e564. [10] S. Olivera, H.B. Muralidhara, K. Venkatesh, V.K. Gunab, K. Gopalakrishna, K.K. Yogesh, Potential applications of cellulose and chitosan nanoparticles/ composites in wastewater treatment: a review, Carbohydr. Poly 153 (2016) 600e618. [11] H. Kono, K. Ogasawara, R. Kusumoto, K. Oshima, H. Hashimoto, Y. Shimizu, Cationic cellulose hydrogels cross-linked by poly(ethylene glycol): preparation, molecular dynamics, and adsorption of anionic dyes, Carbohydr. Poly 152 (2016) 170e180. [12] A. Latif, S. Noor, Q.M. Sharif, M. Najeebullah, Different techniques recently used for the treatment of textile dyeing effluents: a review, J. Chem. Soc. Pak 32 (2010) 115e124. [13] C.R. Holkar, A.J. Jadhav, D.V. Pinjari, N.M. Mahamuni, A.B. Pandit, A critical review on textile wastewater treatments: possible approaches, J. Environ. Manag. 182 (2016) 351e366.
rez, S.M. Ricardo, S. Malato, Is [14] S. Miralles-Cuevas, I. Oller, A. Agüera, J.A.S. Pe the combination of nanofiltration membranes and AOPs for removing microcontaminants cost effective in real municipal wastewater effluents, Environ. Sci. Water Res. Technol. 2 (2016) 511e520. [15] J. Kanagaraj, T. Senthilvelan, R.C. Panda, Degradation of azo dyes by laccase: biological method to reduce pollution load in dye wastewater, Clean. Technol. Environ. Policy 17 (2015) 1443e1456. € za, S. Atalaya, J. Forssb, U. Welander, The treatment of azo [16] O. Türgaya, G. Erso dyes found in textile industry wastewater by anaerobic biological method and chemical oxidation, Sep. Purif. Technol. 79 (2011) 26e33. [17] L.Q. Qi, X.J. Wang, Q.K. Xu, Coupling of biological methods with membrane filtration using ozone as pre-treatment for water reuse, Desalination 270 (2011) 264e268. [18] A. Khataee, M. Sheydaei, A. Hassani, M. Taseidifar, S. Karaca, Sonocatalytic removal of an organic dye using TiO2/Montmorillonite nanocomposite, Ultrason. Sonochem 22 (2015) 404e411. [19] C.X. Li, H. Zhong, S. Wang, J.R. Xue, Z.Y. Zhang, Removal of basic dye

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31] [32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45] [46]

275

(methylene blue) from aqueous solution using zeolite synthesized from electrolytic manganese residue, J. Ind. Eng. Chem. 23 (2015) 344e352. K. Dong, F.X. Qiu, X.R. Guo, J.C. Xu, D.Y. Yang, K.C. He, Polyurethane- attapulgite porous material: preparation, characterization, and application for dye adsorption, J. Apply Poly. Sci. 129 (2013) 1697e1706. V. Vimonses, B. Jin, W.K. Christopher, Insight into removal kinetic and mechani- sms of anionic dye by calcined clay materials and lime, J. Hazard. Mater 177 (2010) 420e427. lu, M. Dog an, M. Alkan, Kinetic analysis of reactive blue 221 M.H. Karaog adsorption on kaolinite, Desalination 256 (2010) 154e165. A. Srikhaow, S.M. Smith, Preparation of Cu2(OH)3NO3/ZnO, a novel catalyst for methyl orange oxidation under ambient conditions, Appl. Cataly. B Environ. 130e131 (2013) 84e92. Y. Lin, Z.K. Zeng, J.R. Zhu, Y. Wei, S. Chen, X. Yuan, L. Liu, Facile synthesis of ZnAl-layered double hydroxide microspheres with core-shell structure and their enhanced adsorption capability, Mater. Lett. 156 (2015) 169e172. S.X. Yang, L.Y. Wang, X.D. Zhang, W.J. Yang, G.L. Song, Enhanced adsorption of Congo red dye by functionalized carbon nanotube/mixed metal oxides nanocomposites derived from layered double hydroxide precursor, Chem. Eng. J. 275 (2015) 315e321. C.J. An, S.Q. Yang, G.H. Huang, S. Zhao, P. Zhang, Y. Yao, Removal of sulfonated humic acid from aqueous phase by modified coal fly ash waste: equilibrium and kinetic adsorption studies, Fuel 165 (2016) 264e271. M. Visa, L. Isac, A. Duta, New fly ash TiO2 composite for the sustainable treatment of wastewater with complex pollutants load, Appl. Surf. Sci. 339 (2015) 62e68. M. Greluk, Z. Hubicki, Efficient removal of Acid Orange 7 dye from water using the strongly basic anion exchange resin Amberlite IRA-958, Desalination 278 (2011) 219e226. R. Mallampati, X.J. Li, A. Adin, S. Valiyaveettil, Fruit peels as efficient renewable adsorbents for removal of dissolved heavy metals and dyes from water, ACS Sustain. Chem. Eng. 3 (2015) 1117e1124. M. Cheng, G.M. Zeng, D.L. Huang, C. Lai, Z. Wei, N.J. Li, P. Xu, C. Zhang, Y. Zhu, X.X. He, Combined biological removal of methylene blue from aqueous solutions using rice straw and Phanerochaete chrysosporium, Appl. Microbiol. Biotechnol. 99 (2015) 5247e5256. Q.J. Xiang, J.G. Yu, M. Jaroniec, Graphene-based semiconductor photocatalysts, Chem. Soc. Rev. 41 (2012) 782e796. S. Thangavel, K. Krishnamoorthy, S.J. Kim, G. Venugopal, Designing ZnS decorated reduced graphene-oxide nanohybrid via microwave route and their application in photocatalysis, J. Alloys Comp. 683 (2016) 456e462. S. Thangavel, K. Krishnamoorthy, V. Krishnaswamy, N. Raju, S.J. Kim, G. Venugopal, GraphdiyneZnO nanohybrids as an advanced photocatalytic material, J. Phys. Chem. C 119 (2015) 22057e22065. T.S. Anirudhan, M. Ramachandran, Adsorptive removal of basic dyes from aqueous solutions by surfactant modified bentonite clay (organoclay): kinetic and competitive adsorption isotherm, Proc. Saf. Environ. Prot. 95 (2015) 215e225. D.M. Chen, J. Chen, X.L. Luan, H.P. Ji, Z.G. Xia, Characterization of anionecationic surfactants modified montmorillonite and its application for the removal of methyl orange, Chem. Eng. J. 171 (2011) 1150e1158. Y.X. Zhang, Y. Zhao, Y. Zhu, H.Y. Wu, H.T. Wang, W.J. Lu, Adsorption of mixed cationic-nonionic surfactant and its effect on bentonite structure, J. Environ.Sci. 24 (2012) 1525e1532. Y.W. Gao, Y.Z. Guo, H. Zhang, Iron modified bentonite: enhanced adsorption performance for organic pollutant and its regeneration by heterogeneous visible light photo-Fenton process at circumneutral pH, J. Hazard. Mater 302 (2016) 105e113. K. Kadirvelu, C. Karthika, N. Vennilamani, S. Pattabhi, Activated carbon from industrial solid waste as an adsorbent for the removal of Rhodamine-B from aqueous solution: kinetic and equilibrium studies, Chemosphere 60 (2005) 1009e1017. D.L. Postai, C.A. Demarchi, F. Zanatta, D.C.C. Melo, C.A. Rodrigues, Adsorption of rhodamine B and methylene blue dyes using waste of seeds of Aleurites Moluccana, a low cost adsorbent, Alex. Eng. J. 55 (2016) 1713e1723. A.I. Hettige, M.I.M. Mowjood, Reduction of colour in treated wastewater from textile industry using sawdusts as bio-sorbents, Trop. Agric. Res. 26 (2015) 666e676. M.K. Dahri, M.R.R. Kooh, L.B.L. Lim, Remediation of rhodamine B dye from aqueous solution using Casuarina equisetifolia cone powder as a low-cost adsorbent, Adv. Phys. Chem. 2016 (2016) 1e7. Leite, A.J.B.; Lima, E. C.; Reis, G. S. D.; Thue, P.S.; Saucier, C.; Rodembusch, F. S.; Dias, S.L.P.; Umpierres, C. S.; Dotto, G. L.. Hybrid adsorbents of tannin and APTES (3-aminopropyltriethoxysilane) and their application for the highly efficient removal of acid red 1 dye from aqueous solutions. J. Environ. Chem. Eng. http://dx.doi.org/10.1016/j.jece.2017.08.022. Y. Park, G.A. Ayoko, R.L. Frost, Characterisation of organoclays and adsorptionof p-nitrophenol: environmental application, J. Colloid Interface Sci. 360 (2011) 440e456. Y.F. Xi, R. Frost, H.P. He, Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides, J. Colloid Interf. Sci. 305 (2007) 150e158. S.X. Zha, Y. Zhou, X.Y. Jin, Z.L. Chen, The removal of amoxicillin from wastewater using organobentonite, J. Environ. Manag. 129 (2013) 569e576. S. Thangavel, S. Thangavel, N. Raghavan, K. Krishnamoorthy, G. Venugopal,

276

[47]

[48]

[49]

[50]

[51]

[52]

[53]

Z. Huang et al. / Materials Chemistry and Physics 202 (2017) 266e276 Visible-light driven photocatalytic degradation of methylene-violet by rGO/ Fe3O4/ZnO ternary nanohybrid structures, J. Alloys Comp. 665 (2016) 107e112. A. Gopalakrishnan, R. Krishnan, S. Thangavel, G. Venugopal, S.J. Kim, Removal of heavy metal ions from pharma-effluents using graphene-oxide nanosorbents and study of their adsorption kinetics, J. Ind. Eng. Chem. 30 (2015) 14e19. C.H. Xu, X.H. Huang, C.H. Li, Y.K. Chen, B.F. Lin, X.Q. Liang, Design of “Zn2þ saltbondings” cross-linked carboxylated styrene butadiene rubber with reprocessing and recycling ability via rearrangements of ionic cross-linkings, ACS Sus. Chem. Eng. 4 (2016) 6981e6990. C.H. Xu, L.M. Cao, B.F. Lin, X.Q. Liang, Y.K. Chen, Design of self-healing supramolecular rubbers by introducing ionic cross-links into natural rubber via a controlled vulcanization, ACS Appl. Mater. Interfaces 8 (2016) 17728e17737. Y.M. Li, M.L. Bi, Z.P. Wang, R. Li, K.L. Shi, W.S. Wu, Organic modification of bentonite and its application for perrhenate (an analogue of pertechnetate) removal from aqueous solution, J. Taiwan Inst. Chem. Eng. 62 (2016) 104e111.  B. Schampera, R. Solc, D. Tunega, S. Dultz, Experimental and molecular dynamics study on anion diffusion in organically modified bentonite, Appl. Clay Sci. 120 (2016) 91e100. S. Thangavel, G. Venugopal, Understanding the adsorption property of graphene-oxide with different degrees of oxidation levels, Powder Tech. 257 (2014) 141e148. N.N. Ab Kadir, M. Shahadat, S. Ismail, Formulation study for softening of hard water using surfactant modified bentonite adsorbent coating, Appl. Clay Sci. 137 (2017) 168e175.

[54] A. Mierczynska-Vasilev, P.A. Smith, Surface modification influencing adsorption of red wine constituents: the role of functional groups, Appl. Surf. Sci. 386 (2016) 14e23. [55] Y.F. Hao, L.G. Yan, H.Q. Yu, K. Yang, S.J. Yu, R.R. Shan, B. Du, Comparative study on adsorption of basic and acid dyes by hydroxy-aluminum pillared bentonite, J. Mol. Liq. 199 (2014) 202e207. [56] K.L. Lin, J.Y. Pan, Y.W. Chen, R.M. Cheng, X.C. Xu, Study the adsorption of phenol from aqueous solution on hydroxyapatite nanopowders, J. Hazard. Mater 161 (2009) 231e240. [57] K. Chinoune, K. Bentaleb, Z. Bouberka, A. Nadimb, UlrichMaschke, Adsorption of reactive dyes from aqueous solution by dirty bentonite, Appl. Clay Sci. 123 (2016) 64e75. [58] F.P. Zhao, E. Repo, D.L. Yin, Y. Meng, S.L. Jafari, M. Sillanpa, EDTA- cross- linked b-cyclodextrin: an environmentally friendly bifunctional adsorbent for simultaneous adsorption of metals and cationic dyes, Environ. Sci. Technol. 49 (2015) 10570e10580. [59] J.J. Natasa, A.M. Nikolic, I. Gr zetic, D. Jovanovic, Organobentonite as efficient textile dye sorbent, Chem. Eng. Technol. 31 (2008) 567e574. [60] H. Zaghouane-Boudiaf, M. Boutahala, S. Sahnoun, C. Tiar, F. Gomri, Adsorption characteristics, isotherm, kinetics, and diffusion of modified natural bentonite for removing the 2,4,5-trichlorophenol, Appl. Clay Sci. 90 (2014) 81e87. [61] M. Toor, B. Jin, Adsorption characteristics, isotherm, kinetics, and diffusion of modified natural bentonite for removing diazo dye, Chem. Eng. J. 187 (2012) 79e88. [62] M. Abbasa, M. Trari, Kinetic, equilibrium and thermodynamic study on the removal of Congo Red from aqueous solutions by adsorption onto apricot stone, Proc. Saf. Environ. Prot. 98 (2015) 424e436.