Plasma-surface modification on bentonite clay to improve the performance of adsorption of methylene blue

Applied Clay Science 116–117 (2015) 46–53

Contents lists available at ScienceDirect

Applied Clay Science journal homepage: www.elsevier.com/locate/clay

Research paper

Plasma-surface modification on bentonite clay to improve the performance of adsorption of methylene blue Ömer Şahin a, Mustafa Kaya a, Cafer Saka b,⁎ a b

Faculty of Engineering and Architecture, Siirt University, 56100 Siirt, Turkey School of Health, Siirt University, 56100 Siirt, Turkey

a r t i c l e

i n f o

Article history: Received 1 June 2015 Received in revised form 6 August 2015 Accepted 10 August 2015 Available online xxxx Keywords: Modification Cold plasma Bentonite Methylene blue

a b s t r a c t The present study consists of the cold plasma treatment was applied for the surface modification of bentonite to improve the removal of methylene blue (MB) from aqueous solution. To achieve the aim, the conditions for adsorption, including cold plasma application time, plasma gas effect, and pH were investigated with respect to the adsorption capacity of MB. The changes of the surface property before and after cold plasma treatment were discussed. Cold plasma treated bentonite is characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), BET surface area, and X-ray diffraction (XRD). Equilibrium adsorption data were analyzed by Freundlich and Langmuir equations. Langmuir isotherm exhibited the best fit with the experimental data. Adsorption kinetics were fitted with pseudo-first-order, and pseudo-second order. Cold plasma treated bentonite was exhibited largest adsorption capacity (303 mg/g) at 30 °C. © 2015 Elsevier B.V. All rights reserved.

1. Introduction There are nowadays more than 100,000 commercially available dyes with an estimated annual production of over 70,000 tons. Dyes are widely used in textile, paper, rubber, plastic, leather, cosmetic, and pharmaceutical and food industries. The discharge of wastewaters containing dyes into rivers and lakes even at very low concentrations is a source of esthetic pollution that increases toxicity and chemical oxygen demand of the effluent, and also reduces light penetration, which has a derogatory effect on photosynthetic phenomena (Nigam et al., 2000; Saka et al., 2012a,b,c). For all these reasons, colored effluents are a serious environmental problem and it is essential to develop proper treatment processes. Several treatment methods have been developed for dye removal including coagulation, chemical oxidation, membrane separation, electrochemical process, and adsorption technique. Among these processes, adsorption is an effective method for color removal. There are very different studies on the use of low-cost materials for removing dyes, such as various agricultural wastes (Saka and Şahin, 2011; Saka et al., 2011, 2012b,c, 2013), chitosan (Pitakpoolsil and Hunsom, 2014), fly ash (Mohan et al., 2002), kaolinite (Yavuz et al., 2003; Volzone and Ortiga, 2011; Yavuz and Saka, 2013), perlite (Doğan et al., 2004), sepiolite (Özdemir et al., 2006; Doğan et al., 2007), montmorillonite (Gemeay et al., 2002), zeolite (Meshko et al., 2001; Hernandez-Montoya et al., 2013), bentonite (Hong et al., 2009; Li et al., 2010; Hashemian et al., 2014; Musso et al., 2014; Rahni et al., 2014), other soils (Çöle et al., ⁎ Corresponding author at: School of Health, Hospital Street, 56100 Siirt, Turkey. E-mail address: [email protected] (C. Saka).

http://dx.doi.org/10.1016/j.clay.2015.08.015 0169-1317/© 2015 Elsevier B.V. All rights reserved.

2013; Quan et al., 2014; Yin and Shi, 2014), etc. Clay minerals have been increasingly receiving attention because it is promising low-cost adsorbent (Panneer et al., 2008). Clays are good adsorbents because of the existence of several types of active sites on the surface, which include Bronsted and Lewis acid sites and ion exchange sites. Clay minerals have different adsorption capacities for dyes. Adsorption capacities depend on the properties of the clay minerals and the adsorbate as well as experimental conditions. Clay minerals have many applications in industry due to their high surface area, porosity, thermal stability, specific active sites, and attractive adsorptive properties (Laszlo, 1987; Tanabe and Holderich, 1999; Varma, 2002). The application of clays, especially bentonite, has attracted more and more attention because of their low-cost, easy availability, high cation exchange capacity and surface area. Because of their low cost, abundance in most continents of the world, high adsorption properties and potential for ion exchange, clay materials are strong candidates as adsorbents. Bentonite is mainly composed of montmorillonite, which has interlayer cations to compensate the negative net charge on the surface. This negative charge is due to isomorphic substitutions on the montmorillonite structure. These inorganic cations can be replaced with cationic surfactants or polycationic species, and the resulting materials are regarded as organobentonite or pillared bentonite, respectively (Zhu et al., 2009). However, the studies about adsorption properties and optimal adsorption conditions of modified bentonite are limited. The adsorption capacity of bentonite may be enhanced by thermal or chemical modifications. Various surface modification methods such as, heat and acid

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

treatment may be used for improving the adsorption capacity of bentonite. However, most of these modifications are either prepared in certain conditions, e.g., high temperature and additional of chemicals which increase operation costs and their efficiency is low. Therefore, there is a need to develop low cost, easily available, effective and reusable adsorbents for the removal of dyes from the aqueous environment. Recently, cold plasma techniques have received special attention because of their advantages in comparison with the traditional modification techniques including high efficiency, simple operation, energy source saving and, non-pollution, which play an important role in pollution prevention. The surface properties of adsorbents are important for adsorption, because the adsorption process is about specific interactions between the target molecules and the adsorbents surface. Plasma includes less water usage and energy consumption, with very small material damage (Tusek et al., 2001; Lehocky et al., 2003; Grythe and Hansen, 2006; Ren et al., 2008; Sparavigna, 2008). Depending on the gas used for plasma generation and on the general treatment conditions it is possible to activate a surface by inserting active species, by surface abrasion or etching, by cross-linking processes or, in many cases, by obtaining combined effects (Ratner, 1995; Guruvenket et al., 2004; Lixon Buquet et al., 2010; Fatyeyeva et al., 2011). In the plasma treatment process, gases such as, Ar, O2, N2, CO2 are applied to a surface of materials. As a result, the surfaces of the materials are treated with chemical functionalities that bind polymers or other molecules to the surface in order to achieve desired surface properties (Desmet et al., 2009; Wen et al., 2012). During the plasma treatment, chemically active species, such as hydroxyl, carbonyl, and carboxylic acid occur only on the surface of adsorbents, which react at the adsorbent surface with specific chemical functions (Park and Kim, 2001; Shen et al., 2008). Until now, some studies have been reported in improving the surface properties of adsorbents using cold plasma and microwave radiation (Saka and Şahin, 2011; Saka et al., 2011, 2012b,c, 2013; Yavuz and Saka, 2013). However, no studies have been reported on the modification of bentonite using cold plasma. This paper is, to the best of knowledge, the first study on the modification of bentonite using cold plasma. The purpose of this study was to compare the effect of cold plasma modification on the surface of the bentonite in any way. The changes of the surface physical and chemical properties were characterized and analyzed by SEM, FT-IR, BET surface area and XRD after modification. MB is selected as a model dye. 2. Materials and analytical methods The clay used in this study as dye adsorbent was collected from the Eskisehir region of Turkey. The bulk chemical analysis (mass %) of the bentonite sample is: SiO2, 70.8; Al2O3, 16.2; Fe2O3, 0.70; TiO2, 0.18; MgO, 1.25; CaO, 1.62; Na2O, 0.11; K2O, 2.12; and loss on ignition, 6.63.

Fig. 1. Effect of cold plasma treatment time on bentonite surface.

47

Fig. 2. Effect of cold gas plasma on bentonite surface.

Cation exchange capacity determined by the methylene blue method was 837.5 mmol/kg (Özcan and Özcan, 2004). MB was chosen because of its known strong adsorptions onto solids. The adsorbate MB (C.I.: 52030, chemical formula: C16H18N3OS, MW: 333.6 g/mol) was supplied by Merck, Germany. Concentrations of dye were determined by measuring the absorbance at 663 nm with a spectrograph Perkin Elmer model, AAnalys 700 spectrophotometer. 2.1. Preparation of cold plasma treated bentonite Plasma Prep 5-plasma machine (GaLa Gabler Labor Instrumente, Bad Schwalbach, and Germany) was used to treat the sized samples. The gases of N2, Ar, and CO2 were employed in the Prep 5-plasma machine treatment. The output power was 80 W. Treatment times were 5, 15, 30, 45 and 60 min, respectively. Cold plasma treatment was applied on 3 g bentonite. The obtained material was stored in airtight plastic container for further use. 2.2. Characterization XRD patterns of the samples were acquired in a Bruker D8 Advance X-ray diffractometer with Cu Kα sources by using Cu Kα radiation (λ = 1.5418 Å), over the range of 2θ = 10–80°. The surface morphologies of the untreated and plasma treated bentonite were analyzed by means of scanning electron microscopy (SEM) (Zeiss EVO 50 Model). The FT-IR spectrum of the sample was recorded using a Model Perkin Elmer 1100 series Fourier transform infrared spectrometer operating in the range 4000–400 cm−1. The clay powder (5 mg) was mixed with KBr (100 mg).

Fig. 3. Yields of MB adsorption capacity for raw and cold plasma treated bentonite.

48

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

the supernatant at corresponding maximum absorption wavelength (λmaxMB = 663 nm) by means of a UV–vis spectrophotometer. Experimental measurements were carried out twice. The pH effect of the initial solution on the equilibrium uptake of dye was analyzed over a range of pH 2–12. The pH effect of the solution adjusted by either 0.05 M NaOH or 0.05 M HCl solutions. Under the experimental conditions, the adsorption capacity for each concentration of dye at equilibrium was determined by using Eq. (1).

qe ¼

Fig. 4. Effect of pH on the adsorption of MB (initial concentration = 200 mg/L, agitation rate = 100 rpm, temperature = 30 °C contact time = 180 min and adsorbent dosage = 0.15 g/200 mL).

The pore structures of the samples were performed on a surface area analyzer (Quantachrome Corporation, USA) through N2 adsorption/ desorption at − 196 °C. Samples were degassed under vacuum at 200 °C for 2 h. The specific surface areas of the samples were calculated from the N2 adsorption/desorption isotherms using the Brunauer– Emmett–Teller (BET) equation in the relative pressure range p/p0 = 0.003–0.2. Pore volumes were calculated using the t-plot method.

2.3. Adsorption experiments A stock solution of 1000 ppm of MB was prepared by dissolving the necessary amount of MB in 1000 mL distilled water. Different concentrations (100, 150, 200, and 250 ppm) of MB solutions were prepared by further dilution from the stock solution. Adsorption kinetic experiments were carried out using 250 mL capped polyethylene bottles containing 200 mL of MB solutions at a constant dye concentration with 0.15 g of clay at a constant stirring speed of 100 rpm at 30 °C. Afterwards, all samples were centrifuged for 10 min at 5000 rpm and the concentration of MB was calculated from the measured absorbance in


 ðCi−CeÞ  V M

ð1Þ

qe (mg/g) is the amount of adsorbate adsorbed at equilibrium. Ci and Ce were the initial and final concentration of dyes in the solution respectively. V is the volume of solution (L) and M is the mass of adsorbent in (g) used. 3. Results and discussion 3.1. Effect of cold plasma application time on the bentonite surface Fig. 1 shows the effect of cold plasma application time on the adsorption capacity of MB. As shown in Fig. 1, the efficiency of the MB removal is dependent on the duration of plasma treatment. The efficiency of the MB removal on the bentonite surface with cold plasma increases rapidly from 5 to 10 min, and then decreases until reaching a shallow minimum after about 30 min. 3.2. Effects of plasma gases (Ar, CO2, and N2) To examine the effects of plasma gases, the MB adsorption efficiency on the bentonite surface was measured with 10 min plasma time and 80 W plasma power at 30 °C by using three different plasma gases, namely, argon (Ar), carbon dioxide (CO2) and nitrogen (N2) (Fig. 2). The best adsorption capacity is achieved by N2 plasma gas. We used N2 plasma gas in this study.

Fig. 5. XRD images of raw (a) and cold plasma treated bentonite (b).

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

3.3. Efficiency of adsorption capacity of MB with cold plasma Compared to raw bentonite, efficiency of adsorption capacity of MB with cold plasma was increased from 168 to 231 mg/g (Fig. 3). The active species such as high-energy electrons and reactive radicals generated in the plasma can activate the upper molecular layers of the interface. However, the surface subjected to plasma treatment degrades with time.

49

adsorption of MB at acidic pH is probably due to the presence of excess H+ ions competing with the cation groups on the dye for adsorption sites. Similar trend was observed for adsorption of MB onto various carbons (Kannan and Sundaram, 2001), steam activated bituminous coal (El Qada et al., 2006), coconut bunch waste (Hameed et al., 2008) and perlite (Doğan et al., 2004).

3.5. X-ray diffraction 3.4. Effect of pH pH of the aqueous solution is an important parameter in the adsorption process. Initial dye concentration was 200 mg/L and the adsorbent dose kept at 0.15 g/200 mL. The effect of solution pH on the adsorption of MB using the cold plasma treated bentonite was investigated and the results are presented in Fig. 4. The experiments were conducted over pH from 2 to 12. The dye uptake increases from 158 to 231 mg/g for an increase in pH from 2 to 12. Silanol groups at the surface become increasingly deprotonated as the pH increases. This increases the number of adsorption sites for MB (Hamdaoui, 2006; Almeida et al., 2009). Lower

XRD patterns of the bentonite before and after plasma treatment were compared in Fig. 5. The XRD patterns showed that the bentonite contains preponderantly montmorillonite. The XRD patterns also indicated the presence of calcite (2.08 Å, 2θ: 43.07), quartz (2.76 Å, 2θ: 32.40; 2.60 Å, 2θ: 34.42) and dolomite (1.69 Å, 2θ: 53.89) as impurities. According to XRD data, the surface of bentonite samples before and after N2 plasma treatment was showed the same characteristic diffraction peaks placed between 20° and 60° (2θ). However, after the sample was modified by the cold plasma of N2, the characteristic peaks became

Fig. 6. SEM images of raw (a, b, c) and cold plasma treated bentonite (d, e, f).

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

50

Fig. 7. FT-IR spectra of raw (a) and cold plasma treated bentonite (b).

sharper and more intense, compared with the raw sample. This observation is due to morphological changes at the surfaces of the bentonite particles.

3.6. SEM analysis Surface morphologies of plasma treated bentonite samples were investigated with SEM before (a) and after (b) N2 plasma treatments (Fig. 6). There were considerably small cavities, cracks, and attached fine particles on the bentonite surface. This clearly indicated that the plasma modification could affect the external surface structure on the micron scale. One of the possible mechanisms is etching. Thus, active species generated in the plasma can change the upper layers of the composites during plasma treatment.

3.8. Surface area measurement The specific surface area of clay generally increases during acid treatment (Temuujin et al., 2004; Nguetnkam et al., 2005). However, the specific surface area of clay generally decreases with a surfactant loading treatment. At higher surfactant concentrations, bentonites have lower BET surface area and mesopore volume (Park et al., 2011; Parolo et al., 2014). In the study, the surface area and pore volume of raw and cold plasma treated bentonite were 64.2 m2/g, 0.0923 cm3/g, 65.3 m2/g and 0.0929 cm3/g, respectively. The adsorption–desorption isotherms of the plasma treated samples have the similar shape. Furthermore, the BET surface area showed a very low increasing after the plasma treatment.

3.9. Adsorption kinetic studies 3.7. Fourier transformed infrared surface analysis The structure of the bentonite before and after N2 plasma treatment was characterized in the range 400–4000 cm−1 by FTIR, and the spectra are shown in Fig. 7. The IR spectrum of the untreated bentonite shows absorptions in several regions. The bands correspond to Al–Al–OH, bending vibrations are observed at 918 cm− 1. The (Si–O) bands are strongly evident in the silicate structure and can be readily recognized in the infrared spectrum by the very strong absorption bands in 1100–950 cm−1 regions. The band at 645 cm−1 is assigned to couple Al–O and Si–O out-of-plane vibrations. The band around 3440 is due to O–H stretching vibrations of adsorbed water. The band at about 1600 cm− 1 corresponds to the OH deformation of water to observe raw and modified bentonite.

The most commonly used adsorption kinetics models are the Lagergren pseudo-first-order and pseudo-second-order kinetic models. The pseudo-first-order kinetic model of Lagergren may be represented by (Lagergren, 1898):

ln ðqe −qt Þ ¼ lnqe −k1 t

ð2Þ

where qe and qt are the amounts of dye adsorbed per unit weight of adsorbent (mg/g) at equilibrium time and time t, respectively, and k1 is the pseudo-first-order rate constant (min−1). The adsorption rate constant was determined from the plot of ln(qe − qt) against t.

Table 1 Comparison of adsorption rate constants, experimental and calculated qe values for the pseudo-first- and -second-order reaction kinetics of removal of MB. Initial MB concentration (mg/L)

100 150 200 250

Pseudo-first-order

Pseudo-second-order

qe, exp (mg/g)

k1 (1/min)

qe, calculated (mg/g)

R2

Δq (%)

k2 (g/mg min)

qe, calculated (mg/g)

R2

Δq (%)

98.92 148 203 216

0.00247 0.0467 0.0322 0.0568

30.87 96.54 117.91 269.07

0.77 0.97 0.98 0.96

50.81

0.00247 0.0467 0.0322 0.0568

100 161.29 212.76 217.39

0.99 0.99 0.99 0.99

5.92

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

51

Table 3 Comparison of the maximum monolayer adsorption of MB onto adsorbents from various sources.

Fig. 8. Second-order kinetic equation for adsorption of MB on cold plasma treated bentonite.

The pseudo-second-order kinetics may be expressed as (Ho and Mckay, 1999). t 1 t ¼ þ qt k2 q2e qe

ð3Þ

where k2 (g/mg min) is the rate constant of second-order adsorption, qe is the amount of dye adsorbed at equilibrium (mg/g) and qt is the amount of dye adsorbed at time t (mg/g). The linear plot of t/qt versus t gave 1/qe as the slope and 1/k2q2e as the intercept. qe and k2 can be determined from the slope and intercepts of plot t/qt versus t. Table 1 presents the values of correlation coefficients (R2). Based on values of R2, it is evident that the pseudo-second-order kinetic model can best describe the adsorption of MB on cold plasma treated bentonite. The linear plots of t/q vs t show a good agreement of experimental data with the second-order kinetic model (Fig. 8). To compare the validity of each model, a normalized Standard deviation, Δq (%) was calculated using the following equation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi   exp 2 cal X qexp =qt t −q Δq ð%Þ ¼ 100x N−1

ð4Þ

where qexp and qcal are experimental and calculated amounts of methyt lene blue adsorbed on plasma treated bentonite at time ‘t’ and N is the number of measurements made. Table 1 presents the values of Δq (%) and correlation coefficients (R2). The values of Δq (%) for pseudo-firstorder kinetic models are low compared to that for pseudo-second-order kinetic models. Based on Δq (%) values, it is evident that the adsorption of methylene blue can be best described by the pseudo-second-order kinetic model.

Adsorbents

Maximum monolayer adsorption capacity (mg/g)

References

Cotton stalk Carbon nanotube Magnetic chitosan/graphene oxide Montmorillonite clay modified with iron oxide Diatomite treated with sodium hydroxide Dodecyl sulfobetaine surfactant-modified montmorillonite Microwave heating treated onion skins Pre-boiling treated onion skins Cold plasma treated onion skins Formaldehyde treated onion skins Plasma treated bentonite

147.06 46.20 95.16 71.12

Deng et al. (2011) Yao et al., 2010 Fan et al. (2012) Cottet et al. (2014)

27.86

Zhang et al. (2013)

150.2

Fan et al. (2014)

142.67 55.55 250 166.67 303

Saka et al. (2012b) Saka et al. (2012b) Saka and Şahin (2011) Saka and Şahin (2011) This study

a certain temperature. Langmuir and Freundlich models are two of the most commonly used adsorption models. The Langmuir model assumes that uptake of the MB dye occurs on a homogenous surface by monolayer adsorption without any interaction between adsorbed ions. The Langmuir equation (Langmuir, 1918) may be written as: Ce 1 Ce ¼ þ qe bqm qe

ð5Þ

where qm (mg/g) and b (Lm/g) are the Langmuir constants related to adsorption capacity and energy of adsorption, respectively. The plot of Ce/qe versus Ce employed to generate the intercept value of 1/bqm and slope of 1/qm. By using a dimensionless constant called separation factor or equilibrium parameter (R L) which is defined as (Weber and Chakravorti, 1974): RL ¼ 1=ð1 þ bC 0 Þ

ð6Þ

where C0 is the initial MB dye concentration. If RL value is between 0 and 1, the adsorption is favorable. RL value of 0.087 indicates a favorable adsorption of MB onto cold plasma treated bentonite. Freundlich model assumes that the stronger binding sites are occupying first and that the binding strength decreases with the increasing degree of site occupation. The expression for Freundlich isotherm model (Freundlich, 1906) was given as: lnqe ¼ lnK F þ



1 lnCe : n

ð7Þ

3.10. Adsorption isotherms Adsorption isotherms describe the relationship of the equilibrium adsorption quantity (qe) with the equilibrium concentration (Ce) under

Table 2 Isotherm parameters for removal of MB onto cold plasma treated bentonite. Isotherm model

Cold plasma treated bentonite

Langmuir qm (mg/g) b (L/mg) RL R2

303 0.052 0.087 0.99

Freundlich KF (mg/g(L/mg)1/n) n R2

31.58 1.88 0.92

KF and n represent adsorption capacity and intensity, respectively. KF is an important constant used as a measure for adsorption efficiency. The slope of 1/n ranging between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero. The value of 1/n below one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption. Table 2 shows the value of n for cold plasma treated bentonite is 1.88, indicating that the dye is favorably physical adsorbed on cold plasma treated bentonite. In order to determine the best-fit isotherm model the correlation factors for two studied isotherm models were compared. The Langmuir and Freundlich isotherm parameters for the MB adsorption of raw and cold plasma treated bentonite are given in Table 2. The correlation coefficients for Langmuir isotherm were highest in comparison to the values obtained for Freundlich isotherm. Therefore, Langmuir isotherm was found to best fit the equilibrium data for adsorption of MB onto cold plasma treated bentonite. Although one work has been reported on

52

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53

adsorption of MB (Hong et al., 2009) including pure bentonite, the maximum adsorption capacities of MB for the adsorbents used in this study was 151 mg/g. According to the results obtained in our study, the maximum adsorption capacity was 303 mg/g for cold plasma treated bentonite. The adsorption capacity of cold plasma treated bentonite is considerably bigger than that adsorption capacity of raw bentonite. Comparisons of the maximum monolayer adsorption of methylene blue onto adsorbents from various sources are presented in Table 3 (Yao et al., 2010; Deng et al., 2011; Fan et al., 2012; Zhang et al., 2013; Cottet et al., 2014; Fan et al., 2014). 4. Conclusions The adsorbent obtained from cold plasma treated bentonite can be used as efficient low-cost adsorbent for the removal of MB from aqueous solutions. The surface properties of bentonite treated with cold plasma were investigated by SEM, FT-IR, BET surface area and XRD analysis. The results showed that the cold plasma treatment changed the surface of bentonite adsorbent. Langmuir isotherm fits better than Freundlich isotherm. The largest monolayer adsorption capacity was obtained at 30 °C (303 mg/g). Adsorption of MB onto cold plasma treated bentonite follows the pseudo-second-order kinetic. Based on the present investigation, it could be concluded that the modified cold plasma treated bentonite can be used efficiently in the removal of MB from aqueous solutions. Acknowledgment The authors are grateful to the Research Foundation of Siirt University for financial support under Project 2013-SİÜSYO-SH1. References Almeida, C.A.P., Debacher, N.A., Downs, A.J. Cottet, Mello, L., CAD, 2009. Removal of methylene blue from colored effluents by adsorption on montmorillonite clay. J. Colloid Interface Sci. 332, 46–53. Çöle, G., Gök, M.K., Güçlü, G., 2013. Removal of basic dye from aqueous solutions using a novel nanocomposite hydrogel: N-vinyl 2-pyrrolidone/itaconic acid/organo clay. Water Air Soil Pollut. 224, 1760. Cottet, L., Almeida, C.A.P., Naidek, N., Viante, M.F., Lopes, M.C., Debacher, N.A., 2014. Adsorption characteristics of montmorillonite clay modified with iron oxide with respect to methylene blue in aqueous media. Appl. Clay Sci. 95, 25–31. Deng, H., Lu, J., Li, G., Zhang, G., Wang, X., 2011. Adsorption of methylene blue on adsorbent materials produced from cotton stalk. Chem. Eng. J. 172, 326–334. Desmet, T., Morent, R., De Geyter, N., Leys, C., Schacht, E., Dubruel, P., 2009. Nonthermal plasma technology as a versatile strategy for polymeric biomaterials surface modification: a review. Biomacromolecules 10, 2351–2378. Doğan, M., Alkan, M., Türkyilmaz, A., Özdemir, Y., 2004. Kinetics and mechanism of removal of methylene blue by adsorption onto perlite. J. Hazard. Mater. 2004, 141–148. Doğan, M., Özdemir, Y., Alkan, M., 2007. Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite. Dyes Pigments 75, 701–713. El Qada, E.N., Allen, S.J., Walker, G.M., 2006. Adsorption of Methylene Blue onto activated carbon produced from steam activated bituminous coal: a study of equilibrium adsorption isotherm. Chem. Eng. J. 124, 103–110. Fan, L., Luo, C., Li, X., Lu, F., Qiu, H., Sun, M., 2012. Fabrication of novel magnetic chitosan grafted with graphene oxide to enhance adsorption properties for methyl blue. J. Hazard. Mater. 215–216, 272–279. Fan, H., Zhou, L., Jiang, X., Huang, Q., Lang, W., 2014. Adsorption of Cu2 + and methylene blue on dodecyl sulfobetaine surfactant-modified montmorillonite. Appl. Clay Sci. 95, 150–158. Fatyeyeva, K., Bigarre, J., Blondel, B., Galiano, H., Gaud, D., Lecardeur, M., Poncin-Epaillard, F., 2011. Grafting of p-styrene sulfonate and 1, 3-propane sulfone onto Laponite for proton exchange membrane fuel cell application. J. Membr. Sci. 366, 33–42. Freundlich, H.Z., 1906. Over the adsorption in solution. J. Phys. Chem. 57A, 385–470. Gemeay, A.H., El-Sherbiny, A.S., Zaki, A.B., 2002. Adsorption and kinetic studies of the intercalation of some organic compounds onto Na+–montmorillonite. J. Colloid Interface Sci. 245, 116–125. Grythe, K.F., Hansen, F.K., 2006. Surface modification of EPDM rubber by plasma treatment. Langmuir 22, 6109–6124. Guruvenket, S., Rao, G.M., Komath, M., Raichur, A.M., 2004. Plasma surface modification of polystyrene and polyethylene. Appl. Surf. Sci. 236, 278–284. Hamdaoui, O., 2006. Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick. J. Hazard. Mater. 135, 264–273. Hameed, B.H., Mahmoud, D.K., Ahmad, A.L., 2008. Equilibrium modeling and kinetic studies on the adsorption of basic dye by a low-cost adsorbent: coconut (Cocos nucifera) bunch waste. J. Hazard. Mater. 158, 65–72.

Hashemian, S., Saffari, H., Ragabion, S., 2014. Adsorption of Cobalt(II) from aqueous solutions by Fe3O4/bentonite nanocomposite. Water Air Soil Pollut. 226, 2212. Hernandez-Montoya, V., Perez-Cruz, M.A., Mendoza-Castillo, D.I., Moreno-Virgen, M.R., Bonilla-Petriciolet, A., 2013. Competitive adsorption of dyes and heavy metals on zeolitic structures. J. Environ. Manag. 116, 213–222. Ho, Y.S., Mckay, G., 1999. Comparative sorption kinetic studies of dyes and aromatic compounds onto fly ash. J. Environ. Sci. Health A34, 1179–1204. Hong, S., Wen, C., He, J., Gan, F., Ho, Y.-S., 2009. Adsorption thermodynamics of Methylene Blue onto bentonite. J. Hazard. Mater. 167, 630–633. Kannan, N., Sundaram, M.M., 2001. Kinetics and mechanism of removal of methylene blue by adsorption on various carbons—a comparative study. Dyes Pigments 51, 25–40. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. Kungliga Svenska Vetenskapsakademiens Handlingar 24, 1–39. Langmuir, I., 1918. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 40, 1361–1403. Laszlo, P., 1987. Chemical reactions on clays. Science 235, 1473–1477. Lehocky, M., Drnovska, H., Lapcikova, Barbora, Barros-Timmons, A.M., Trindade, T., Zembala, M., Lapcik Jr., L., 2003. Plasma surface modification of polyethylene. Colloids Surf., A 222, 125–131. Li, Q., Yue, Q.-Y., Sun, H.-J., Su, Y., Gao, B.-Y., 2010. A comparative study on the properties, mechanisms and process designs for the adsorption of non-ionic or anionic dyes onto cationic-polymer/bentonite. J. Environ. Manag. 91, 1601–1611. Lixon Buquet, C., Fatyeyeva, K., Poncin-Epaillard, F., Schaetzel, P., Dargent, E., Langevin, D., Nguyen, Q.T., Marais, S., 2010. New hybrid membranes for fuel cells: plasma treated laponite based sulfonated polysulfone. J. Membr. Sci. 35, 1–10. Meshko, V., Markovska, L., Mincheva, M., Rodrigues, A.E., 2001. Adsorption of basic dyes on granular activated carbon and natural zeolite. Water Res. 35, 3357–3366. Mohan, D., Singh, K.P., Singh, G., Kumar, K., 2002. Removal of dyes from wastewater using fly ash. Ind. Eng. Chem. Res. 41, 3688–3695. Musso, T.B., Parolo, M.E., Pettinari, G., Francisca, F.M., 2014. Cu(II) and Zn(II) adsorption capacity of three different clay liner materials. J. Environ. Manag. 146, 50–58. Nguetnkam, J.-P., Kamga, R., Villieras, F., Ekodeck, G.-E., Razafitianamaharavo, A., Yvon, J., 2005. Assessment of surface areas of silica and clay in acid-leached clay materials using concepts of adsorption on heterogeneous surfaces. J. Colloid Interface Sci. 289, 104–115. Nigam, P., Armour, G., Banat, I.M., Singh, D., Marchant, R., 2000. Physical removal of textile dyes from effluents and solid-state fermentation of dye-adsorbed agricultural residues. Bioresour. Technol. 72, 219–226. Özcan, A.S., Özcan, A., 2004. Adsorption of acid dyes from aqueous solutions onto acidactivated bentonite. J. Colloid Interface Sci. 276, 39–46. Özdemir, Y., Doğan, M., Alkan, M., 2006. Adsorption of cationic dyes from aqueous solutions by sepiolite. Microporous Mesoporous Mater. 96, 419–427. Panneer, S.P., Preethi, S., Basakaralingam, P., Thinakaran, N., Sivasamy, A., Sivanesan, S., 2008. Removal of Rhodamine B from aqueous solution by adsorption onto sodium montmorillonite. J. Hazard. Mater. 155, 39–44. Park, S.J., Kim, J.S., 2001. Influence of plasma treatment on microstructures and acid–base surface energetics of nanostructured carbon blacks: N2 plasma environment. J. Colloid Interface Sci. 244, 336–341. Park, Y., Ayoko, G., Frost, R., 2011. Characterisation of organoclays and adsorption of p-nitrophenol: environmental application. J. Colloid Interface Sci. 360, 440–456. Parolo, M.E., Pettinari, G.R., Musso, T.B., Sanchez-Izquierdo, M.P., Fernandez, L.G., 2014. Characterization of organo-modified bentonite sorbents: The effect of modification conditions on adsorption performance. Appl. Surf. Sci. 320, 356–363. Pitakpoolsil, W., Hunsom, M., 2014. Treatment of biodiesel wastewater by adsorption with commercial chitosan flakes: parameter optimization and process kinetics. J. Environ. Manag. 133, 284–292. Quan, G., Zhang, J., Guo, J., Lan, Y., 2014. Removal of Cr(VI) from Aqueous Solution by Nanoscale Zero-Valent Iron Grafted on Acid-Activated Attapulgite. Water Air Soil Pollut. 225, 1979. Rahni, S.Y., Mirghaffari, N., Rezaei, B., Ghaziaskar, H.S., 2014. Removal of phosphate from aqueous solutions using a new modified bentonite-derived hydrogel. Water Air Soil Pollut. 225, 1916. Ratner, B.D., 1995. Surface modification of polymers: chemical, biological and surface analytical challenges. Biosens. Bioelectron. 10, 797–804. Ren, C.S., Wang, K., Nie, Q.Y., Wang, D.Z., Guo, S.H., 2008. Surface modification of PE film by DBD plasma in air. Appl. Surf. Sci. 255, 3421–3425. Saka, C., Şahin, Ö., 2011. Removal of methylene blue from aqueous solutions by using cold plasma and formaldehyde treated onionskins. Color. Technol. 127, 246–255. Saka, C., Şahin, Ö., Demir, H., Kahyaoğlu, M., 2011. Removal of Pb(II) from aqueous solutions using pre-boiled and formaldehyde treated onion skins as a new adsorbent. Sep. Sci. Technol. 46, 507–517. Saka, C., Şahin, Ö., Adsoy, H., Akyel, M.S., 2012a. Removal of methylene blue from aqueous solutions by using cold plasma, microwave radiation and formaldehyde treated acorn shells. Sep. Sci. Technol. 47, 1542–1551. Saka, C., Şahin, Ö., Çelik, M.S., 2012b. Removal of methylene blue from aqueous solutions by using microwave heating and preboiling treated onion skins as a new adsorbent. Energy Sources, Part A 34, 1577–1590. Saka, C., Şahin, Ö., Küçük, M.M., 2012c. Applications on agricultural and forest waste adsorbents for the removal of lead (II) from contaminated waters. Int. J. Environ. Sci. Technol. 9, 379–394. Saka, C., Şahin, Ö., Kutluay, S., 2013. Cold plasma and microwave radiation applications on almond shell surface and its effects on the adsorption of Eriochrome Black T. J. Ind. Eng. Chem. http://dx.doi.org/10.1016/j.jiec.2013.01.032. Shen, W., Li, Z., Liu, Y., 2008. Surface chemical functional groups modification of porous carbon. Recent Pat. Chem. Eng. 1, 27.

Ö. Şahin et al. / Applied Clay Science 116–117 (2015) 46–53 Sparavigna, A., 2008. Plasma treatment advantages for textile. Cornell University Library, pp. 1–16 (arXiv:0801.3727v1 (physics.pop-ph)). Tanabe, K., Holderich, W., 1999. Industrial application of solid acid–base catalysts. Appl. Catal. A Gen. 181, 399–434. Temuujin, J., Jadambaa, T.-S., Burmaa, G., Erdenechimeg, S., Amarsanaa, J., MacKenzie, K.-J.-D., 2004. Characterisation of acid activated montmorillonite clay from Tuulant (Mongolia). Ceram. Int. 30, 251–255. Tusek, L., Nitschke, M., Werner, C., Stana-Kleinschek, K., Ribitsch, V., 2001. Surface characterisation of NH3 plasma treated polyamide 6 foils. Colloids Surf., A 195, 81–95. Varma, R.S., 2002. Clay and clay-supported reagents in organic synthesis. Tetrahedron 58, 1235–1255. Volzone, C., Ortiga, J., 2011. SO2 gas adsorption by modified kaolin clays: influence of previous heating and time acid treatments. J. Environ. Manag. 92, 2590–2595. Weber, T.W., Chakravorti, P.K., 1974. Pore and solid diffusion model for fixed bed adsorbent. J. Am. Inst. Chem. Eng. 20, 228–235.

53

Wen, Y., Shen, C., Ni, Y., Tong, S., Yu, F., 2012. Glow discharge plasma in water: a green approach to enhancing ability of chitosan for dye removal. J. Hazard. Mater. 201–202, 162–169. Yao, Y., Xu, F., Chen, M., Xu, Z., Zhu, Z., 2010. Adsorption behavior of methylene blue on carbon. nanotubes Bioresour. Technol. 101, 3040–3046. Yavuz, Ö., Saka, C., 2013. Surface modification with cold plasma application on kaolin and its effects on the adsorption of methylene blue. Appl. Clay Sci. 85, 96–102. Yavuz, Ö., Altunkaynak, Y., Güzel, F., 2003. Removal of copper, nickel, cobalt and manganese from aqueous solution by kaolinite. Water Res. 37, 948–952. Yin, P., Shi, L., 2014. Remediation of Cd, Pb, and Cu-contaminated agricultural soil using three modified industrial by-products. Water Air Soil Pollut. 225, 2194. Zhang, J., Ping, Q., Niu, M., Shi, H., Li, N., 2013. Kinetics and equilibrium studies from the methylene blue adsorption on diatomite treated with sodium hydroxide. Appl. Clay Sci. 83–84, 12–16. Zhu, R.L., Zhu, L.Z., Zhu, J.X., Ge, F., Wang, T., 2009. Sorption of naphthalene and phosphate to the CTMAB–Al13 intercalated bentonites. J. Hazard. Mater. 168, 1590–1594.