silica composite

silica composite

Journal of Industrial and Engineering Chemistry 18 (2012) 1964–1969 Contents lists available at SciVerse ScienceDirect Journal of Industrial and Eng...

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Journal of Industrial and Engineering Chemistry 18 (2012) 1964–1969

Contents lists available at SciVerse ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Kinetics and isotherm studies of methylene blue adsorption onto polyaniline nanotubes base/silica composite Mohamad M. Ayad a,b,*, Ahmed Abu El-Nasr b, Jaroslav Stejskal c a

Chemical and Petrochemicals Engineering Department, Egypt-Japan University of Science and Technology, PO Box 179, New Borg El-Arab City, 21934, Alexandria, Egypt Department of Chemistry, Faculty of Science, University of Tanta, Tanta, Egypt c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Prague 6, Czech Republic b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 9 November 2011 Accepted 19 May 2012 Available online 26 May 2012

A cationic dye, such as methylene blue (MB), was adsorbed from water by using polyaniline nanotubes (PANI NTs) base/silica composite as adsorbent. Experiments were conducted by using the UV–visible spectroscopy and by varying parameters namely: initial concentration of MB and contact time. The percentage of color removal decreased with increase of initial dye concentration. Equilibrium data were fit to Langmuir isotherm. The Langmuir isotherm fits best the MB adsorption data on PANI NTs base/silica composite. The kinetic models: pseudo first order, pseudo-second order and the intraparticle diffusion models were applied to the experimental data. It was observed that pseudo-second order kinetic model described the adsorption process better than any other kinetic models. Results obtained indicate that PANI NTs base/silica composite could be employed as an efficient adsorbent much more than the conventional PANI base/silica composite powder for dye uptake. Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.

Keywords: Polyaniline nanotubes Silica Composite Methylene blue Adsorption isotherm Kinetics

1. Introduction The extensive use of dyes in dye-manufacturing industries creates significant problems due to the discharged of colored waste water. The presence of very small amounts of dyes in water is visible and affects the quality of water [1]. Dyes can be divided into several categories, based on their chemical nature, whether anionic or cationic dyes, and basic or reactive dyes. The discharge of dyes contributes appreciable concentrations of materials with highly biochemical oxygen demand [2]. Dyes can also cause deterioration in human’s health. Some of them are found to be toxic, mutagenic and carcinogenic [3]. Various techniques, such as precipitation, membrane filtration, coagulation, electrochemical and chemical oxidations, ion exchange, adsorption [4], etc., have been used for the removal of dyes from waste water. Adsorption is a procedure of choice for the removal of dyes from wastewater [5,6]. Several efficient and selective adsorbent materials have been developed such as waste orange peel [7], banana pith [8], rice husk [9], clay [10], and activated carbon [11]. Recently, a conducting polymer, polyaniline (PANI), was tested in adsorption of dye

* Corresponding author at: Chemical and Petrochemicals Engineering Department, Egypt-Japan University of Science and Technology, PO Box 179, New Borg ElArab City, 21934, Alexandria, Egypt. Tel.: +20 3 459 9520; fax: +20 3 459 9520. E-mail address: [email protected] (M.M. Ayad).

effluent [12]. Polyaniline is considered to be one of the most promising classes of organic conducting polymers due to their well-defined electrochemistry, easy protonation reversibility, excellent redox recyclability [13], and good environmental stability [14], and variety of nanostructured morphologies [15]. It was reported to be utilized as adsorbent for adsorption of protein [16] and DNA [17]. Polyaniline is obtained in conducting form, emeraldine salt (ES), when prepared in acid media. It may be converted to corresponding emeraldine base (EB) by treatment with an alkali solution or by rinsing with a large excess of water (Scheme 1). Polyaniline base is non-conducting but the conductivity is not the most important property in many applications that rely on other physicochemical processes, such as adsorption phenomena in the present case. Recently, we have explored the PANI-coated electrode of the quartz-crystal microbalance as chlorinated hydrocarbons and alcohols vapor sensors [18–20]. The diffusion and the adsorption kinetics of the vapors adsorbed onto the polymer were studied. The use of PANI powders, however, could be limited by the polymersurface area. This drawback of using the PANI powder may be overcome by using nanostructured PANI such as nanotubes (NTs). Polyaniline nanotubes (PANI NTs) have recently been used for the regioselective reduction of silver nitrate to produce PANI–silver composites [21]. The organic–inorganic composite materials are modern adsorbent materials, as the merits of organic and inorganic moieties can

1226-086X/$ – see front matter . Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry. http://dx.doi.org/10.1016/j.jiec.2012.05.012

M.M. Ayad et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1964–1969

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CH3 CH3

N

CH3 S N

N CH3 Cl

Scheme 2. The formula of methylene blue.

Scheme 1. Protonated (doped) PANI salt is deprotonated (dedoped) by treatment with an alkali to PANI base.

the stock solution with distilled water to give the appropriate concentration of the working solutions. 2.4. Adsorption experiments

be combined in the composites. For example, PANI–silica (SiO2) composite can be used. The properties of PANI can be improved by incorporating other functional materials, including oxides, heteropolyacidic anions, etc. [22,23]. Among these materials, SiO2 has received great attention because of their unique properties and wide applications [24]. SiO2 particles have been included in the composites by many ways, including surface polymerization of aniline adsorbed onto silica surfaces [25–27], in situ hydrolysis and condensation of tetraethoxysilane in PANI solutions or on solid PANI surfaces [28], etc. The present paper is devoted to study the adsorption of the cationic dye methylene blue (MB) as a model dye into PANI NTs base/silica composite. The difference between PANI NTs base/silica composite and the conventional PANI base/silica composite toward the adsorption of MB was studied. The kinetics and the isotherm adsorption models were investigated. 2. Experimental

The initial and final concentrations of MB solutions were determined by measuring the absorbance at 664 nm by using UV– visible absorption spectrometer (Labomed, Inc). 100 mL of MB solutions of various concentrations were mixed with 0.05 g of PANI NTs base/silica composite or conventional PANI base/silica composite and were stirred at 700 rpm by magnetic stirrer in dark at 25 8C. The suspension of the polymer and dye solution was separated by a centrifugation (Hettich, EBA 20). 3. Results and discussion The morphological information of PANI NTs base/silica composite was provided by scanning electron microscopy. The NTs bases are of 100–250 nm diameters, their lengths 2– 40 mm. The inner diameter differed substantially among individual NTs, in the range 20–100 nm [31]. Fig. 1 shows the SEM image of the PANI NTs base/silica composite with silica particles distributed among PANI NTs. Silica particles are coated with a thin PANI film [30].

2.1. Chemicals 3.1. Adsorption of methylene blue into the PANI NTs base/silica Aniline (ADWIC, Egypt) was distilled twice under atmospheric pressure in the presence of zinc dust. Ammonium peroxydisulfate (APS; MP Biomedicals, LLC), acetic acid (ADWIC, Egypt), sulfuric acid (ADWIC, Egypt), ammonium hydroxide (ADWIC, Egypt), silica (60–120 mesh, Aldrich, USA) and methylene blue (MB; Aldrich, USA) were used without further purification. 2.2. Preparation of PANI NTs base/silica composite and conventional PANI base/silica composite Typical solutions used for the preparation PANI NTs contained 0.2 mol L1 aniline and 0.25 mol L1 APS in 500 mL of 0.5 mol L1 acetic acid [29] with 15 g suspended silica. In the present investigation, the composite was prepared as PANI NTs/silica in conducting salt form. Following day, the precipitate was collected on a filter paper, rinsed with 0.5 mol L1 acetic acid, and dried. The PANI NTs salt/silica composite was deprotonated with excess 0.1 mol L1 ammonia, and the resulting PANI NTs base/silica composite was again dried in dynamic vacuum. The conventional PANI base/silica composite was prepared in the bulk solution as described earlier for the PANI NTs base/silica composite, except 0.5 mol L1 acetic acid was exchanged for 0.1 mol L1 sulfuric acid [30].

3.1.1. Adsorption studies The adsorption of MB into the PANI NTs base/silica composite and conventional PANI base/silica composite was followed by using UV– visible spectroscopy. Addition of 0.05 g of different substrates such as PANI NTs base/silica composite, conventional globular PANI base/ silica composite, PANI NTs base and conventional PANI base to 100 mL of 3.1 mg L1 MB solution at the same conditions leads to decrease in absorbance of MB with increasing time as shown in Fig. 2a–d, respectively. The amount of dye adsorbed, Qe (mg g1) onto unit mass of PANI NTs base/silica composite, PANI NTs base, conventional PANI base/silica composite and conventional PANI base at equilibrium are equal to 5.38 mg g1, 4.48 mg g1,

2.3. Preparation of methylene blue solution Methylene blue (Scheme 2) has a formula C16H18N3ClS and molecular weight 319.85. It is a water-soluble non-toxic dye, which is blue in color (lmax = 664 nm). A stock solution was prepared by dissolving an appropriate quantity of MB in a volume of distilled water. The working solutions were prepared by diluting

Fig. 1. SEM image of PANI NTs base/silica composite.

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Fig. 2. Time resolved absorption spectra of the adsorption of MB dye [100 mL of 3.1 mg L1] with 0.05 g PANI NTs base/silica composite (a), 0.05 g conventional globular PANI base/silica composite (b), 0.05 g PANI NTs base (c) and 0.05 g conventional PANI base (d) in dark.

4.75 mg g1 and 0.61 mg g1, respectively. Qe was calculated from the mass balance equation given by: Q e ¼ ðC 0  C e ÞVm1

(1)

where C0 is the initial dye concentration in liquid phase, Ce is the liquid phase dye concentration at equilibrium, V is the volume of dye solution used, and m is the mass of adsorbent used. It is observed that adsorbed amount of MB increases in the following series: PANI NTs base/silica composite > PANI NTs base > convenconventional PANI base/silica composite > conventional PANI base. The adsorption of MB dye onto the PANI NTs base/silica composite is highly accessible is a comparison to the other substrates. This result is explained by the higher surface area of the PANI NTs base/silica composite. The binding sites of the interactions available in the PANI NTs base/silica composite would be larger; hence, more intensive interaction with the cationic dye MB occurs. Fig. 3 shows the decreasing in MB concentration at different times in the presence of PANI NTs base/silica composite. The dyeadsorption kinetics and isotherms of the PANI NTs base/silica composite are reported in detail below.

3.1.2. Adsorption kinetics In order to evaluate the mechanism which controls the process, the pseudo-first order [32], pseudo-second order [33] and intraparticle diffusion [34] models were tested: Pseudo-first order rate equation: logðQ e  Q t Þ ¼ log Q e 

k1 t 2:303

(2)

Pseudo-second-order equation: t 1 t ¼ þ Q t k2 Qe2 Q e

(3)

Intraparticle diffusion model: Q t ¼ ki t 1=2 þ C

(4)

where Qe and Qt refer to the amount of dye adsorbed at equilibrium and time t, respectively, k1 is the rate constant, k2 is the rate constant of pseudo-second-order model, ki is an intraparticle diffusion rate parameter and C is the constant. The validity of the models was verified by the linear equation analysis of log (Qe  Qt)

M.M. Ayad et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1964–1969

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Table 1 Kinetic parameters for the adsorption of MB on PANI NTs base/silica composite (initial MB concentration = 3.1 mg L1). Models

Fig. 3. Concentration profiles of MB dye with time in the presence of PANI NTs base/ silica composite where dye concentration is 3.1 mg L1 and adsorbent dose is 0.05 g in 100 mL.

vs. t, (t/Qt) vs. t and Qt vs. t1/2, as shown in Fig. 4a–c, respectively. The correlation coefficient (R2) of the curve-fitting plots was calculated. Good correlation with the kinetic data explains the dye adsorption mechanism in the solid phase [32]. The fitting with the excellent linearity (R2 = 0.999), confirming the applicability of the pseudo second-order equation. Weber and Morris [35] stated that, if intraparticle diffusion is the rate-controlling factor, uptake of the adsorbate varies with the square root of time. It can be shown in Fig. 4c, that the external surface adsorption (stage 1) is the fastest and completed before 5 min and then the stage of intraparticle diffusion control (stage 2) is attained and continues from 5 to 30 min. The slope of the first linear portion (stage 2) characterizes the rate parameter corresponding to the intraparticle diffusion, whereas the intercept of this portion is proportional to the boundary layer thickness. The R2 value for this diffusion model is 0.977 (Table 1). This indicates that the adsorption of MB onto PANI NTs base/silica composite can be followed by an intraparticle diffusion in about 60 min. 3.1.3. Adsorption isotherms The most common sorption model was used to fit the experimental data is Langmuir isotherm [36]: Ce 1 al C e ¼ þ Q e Kl Kl

(5)

Model parameters

R2

Pseudo-first order

Qe = 2.69 mg g k1 = 0.69 min1

R2 = 0.952

Pseudo-second order

Qe = 5.7 mg g1 k2 = 0.09 g mg1 min1

R2 = 0.999

Intraparticle diffusion

ki = 0.9 mg g1 min1 t1/2 = 3.55 min C = 1.659 mg g1

R2 = 0.977

1

where Ce is the equilibrium concentration of the adsorbate, Qe was previously defined, Kl and al are Langmuir constants. A linear plot was obtained when Ce/Qe was plotted against Ce as shown in Fig. 5a. The equilibrium data obtained were fitted to the above isotherm equation and the parameters evaluated are presented in Table 2 along with the correlation coefficient value. The Langmuir sorption isotherm is indeed the most widely used for the sorption of the dye from a liquid solution assuming that the sorption takes place at specific homogeneous sites within the adsorbent [37]. The essential feature of the Langmuir isotherm can be expressed in terms of a dimensionless factor called separation factor (Rl) which is defined by the following equation [38]: Rl ¼

1 1 þ al C 0

(6)

where C0 is the initial adsorbate concentration. The value of Rl indicates the shape of the isotherm to be either unfavorable (Rl > 1), linear (Rl = 1), favorable (0 < Rl < 1) or irreversible (Rl = 0). Fig. 5b shows the variation of Rl with initial MB concentrations. The results indicate that Rl values were in the range of 0–1, i.e. that the adsorption of MB onto PANI NTs base/silica composite is favorable. The observed rate constant Kobs, was calculated using the following equation: ln

A0 ¼ Kt A

(7)

where A0 is the initial concentration of MB and A is the concentration of MB after different times t. Fig. 6 shows the linear plots of the right hand side and t. The slope Kobs equals to 0.13 min1.

Fig. 4. The pseudo-first order (a), pseudo-second-order and (b) and intraparticle diffusion kinetic plot for adsorption of MB on PANI NTs base/silica composite (c). Dye concentration is 3.1 mg L1 and adsorbent dose is 0.05 g in 100 mL.

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Fig. 5. Langmuir isotherm model (a) and separation factor vs. initial MB concentration (b).

Fig. 6. The observed rate constant Kobs, at MB concentration is 3.1 mg L1 and adsorbent dose is 0.05 g in 100 mL.

Fig. 7. Effect of initial concentration (mg L1) and time on the adsorption of MB by PANI NTs base/silica composite.

3.2. Effect of initial MB concentration

concentrations, lower adsorption yields were observed because of the saturation of the adsorption sites.

Experiment was conducted with different initial concentrations of MB in the presence of 0.05 g of PANI NTs base/silica composite for 60 min. When the initial concentration of the dye was 0.95 mg L1, the dye was completely adsorbed in 10 min. At higher concentrations, the dye was not completely adsorbed, indicating that there is a saturation limit for the polymer above which it does not remove the dye from solution. The effects of initial concentration and time on the adsorption of MB by PANI NTs base/silica composite are shown in Fig. 7. At lower concentrations all MB present in the adsorption medium could interact with the binding sites on the surface of adsorbent so higher adsorption yields were obtained. At higher Table 2 Summary of the Langmuir isotherm analysis, separation factors (Rl) and linear (R2) regression coefficient. Model

Parameters

Langmuir

Qo = 10.31 mg g1 Kl = 37.03 L g1 Al = 3.59 L mg1 Rl = 0.081 R2 = 0.998

4. Conclusions The results presented in this work have shown that the PANI NTs base/silica composite can be used for the adsorption of MB more pronounced than the corresponding occurred into the conventional PANI base/silica composite. In the absence of silica, the MB adsorption into the PANI NTs base is much more efficient adsorbent than in the case of conventional PANI base. Adsorption rate increase in the following order: PANI NTs base/silica composite > PANI NTs base > conventional PANI base/silica composite > conventional PANI base. This is probably due to the increase in the surface area of polymer nanotubes substrates. Kinetic studies point to the fact that the adsorption dynamics of phenols are predicted more accurately by the pseudo-second order model. The equilibrium data have been analyzed using Langmuir isotherm model and represented the equilibrium adsorption data. References [1] I.M. Banat, P. Nigam, D. Singh, R. Marchant, Bioresource Technology 58 (1996) 217. [2] G. Mckay, Journal of Chemical Technology and Biotechnology 34A (1984) 294.

M.M. Ayad et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1964–1969 [3] K.C. Chen, J.Y. Wu, C.C. Huang, Y.M. Liang, S.C.J. Hwang, Journal of Biotechnology 101 (2003) 241. [4] M.S. Chiou, G.S. Chuang, Chemosphere 62 (2006) 731. [5] E. Forgacs, C. Tibor, O. Gyula, Environment International 30 (2004) 953. [6] G. Annadurai, M. Chellapandian, M.R.V. Krishnan, Environmental Monitoring and Assessment 59 (1999) 111. [7] C. Namasivayam, N. Muniasamy, K. Gayatri, M. Rani, K. Ranganathan, Bioresource Technology 57 (1996) 37. [8] C. Namasivayam, D. Prabha, M. Kumutha, Bioresource Technology 64 (1998) 77. [9] G. McKay, G. Ramprasad, P.P. Mowli, Water, Air, and Soil Pollution 29 (1986) 273. [10] K.R. Ramkrishna, T. Viaraghavan, Water Science and Technology 36 (1997) 189. [11] Y.C. Sharma, S.N. Uma, Upadhyay, F. Gode, Journal of Applied Sciences in Environmental Sanitation 4 (2009) 21. [12] A.N. Chowdhury, S.R. Jesmeen, M.M. Hossain, Polymers for Advanced Technologies 15 (2004) 633. [13] M.S. Wu, T.C. Wen, A. Gopalan, Materials Chemistry and Physics 74 (2002) 58. [14] J.L. Camalet, J.C. Lacroix, S. Aeiyach, K. Chane-ching, P.C. Lacaze, Synthetic Metals 93 (1998) 133. [15] J. Stejskal, I. Sapurina, M. Trchova´, Progress in Polymer Science 35 (2010) 1420. [16] B. Miksa, S. Slomkowski, Colloid and Polymer Science 273 (1995) 47. [17] B. Saoudi, N. Jammul, M.L. Abel, M.M. Chehimi, G. Dodin, Synthetic Metals 87 (1997) 97. [18] M.M. Ayad, G. El-Hefnawey, N.L. Torad, Sensors and Actuators B: Chemical 134 (2008) 887. [19] M.M. Ayad, G. El-Hefnawey, N.L. Torad, Journal of Hazardous Materials 168 (2009) 85. [20] M.M. Ayad, N.L. Torad, Talanta 78 (2009) 1280.

1969

[21] M.M. Ayad, N. Prastomo, M. Matsuda, J. Stejskal, Synthetic Metals 160 (2010) 42. [22] X.X. Liu, L.J. Bian, L. Zhang, L.J. Zhang, Journal of Solid State Electrochemistry 11 (2007) 1279. [23] N. Prastomo, M.M. Ayad, G. Kawamura, A. Matsuda, Journal of the Ceramic Society of Japan 119 (2011) 342. [24] P. Liu, W.M. Liu, Q.J. Xue, Materials Chemistry and Physics 87 (2004) 109. [25] S. Fedorova, J. Stejskal, Langmuir 18 (2002) 5630. [26] J. Stejskal, M. Trchova´, S. Fedorova, I. Sapurina, J. Zemek, Langmuir 19 (2003) 3013. [27] X.M. Feng, G. Yang, Y.G. Liu, W.H. Hou, J.J. Zhu, Journal of Applied Polymer Science 101 (2006) 2088. [28] Z. Niu, Z. Yang, Z. Hu, Y. Lu, C.C. Han, Advanced Functional Materials 13 (2003) 949. [29] E.N. Konyushenko, J. Stejskal, I. Sˇedeˇnkova´, M. Trchova´, I. Sapurina, M. Cieslar, Polymer International 55 (2006) 31. [30] J. Stejskal, I. Sapurina, M. Trchova´, E.N. Konyushenko, Macromolecules 41 (2008) 3530. [31] M.M. Ayad, A. Abu El-Nasr, Journal of Physical Chemistry C 114 (2010) 14377. [32] F. Wu, R. Tseng, R. Juang, Water Research 35 (2001) 613. [33] M.S. Chiou, H.Y. Li, Journal of Hazardous Materials 93 (2002) 233. [34] I. Uzun, Dyes Pigments 70 (2006) 76. [35] W.J. Weber, J.C. Morris, Journal of Sanitary Engineering Division ASCE 89 (1963) 31. [36] I. Langmuir, Journal of the American Chemical Society 40 (1918) 1361. [37] I. Langmuir, Journal of the American Chemical Society 38 (1916) 2221. [38] T.W. Weber, R.K. Chakravorti, Journal of American Institute of Chemical Engineering 20 (1974) 228.