International Journal of Water Resources and Environmental Engineering Vol.2 (2), pp. 016-028, March, 2010 Available online at http://www.academicjournals.org/ijwree © 2010 Academic Journals Full Length Research Paper Experimental study of methylene blue adsorption from aqueous solutions onto carbon nano tubes Zohre Shahryari, Ataallah Soltani Goharrizi* and Mehdi Azadi Department of Chemical Engineering, College of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran. Accepted 28 December, 2009 In this work, batch adsorption experiments were carried out for the removal of methylene blue as a basic dye from aqueous solutions using carbon nanotubes (CNTs). The effects of major variables governing the efficiency of the process such as, temperature, initial dye concentration, CNTs dosage, and pH were investigated. Experimental results have shown that, the amount of dye adsorption increased with increasing the initial concentration of the dye, CNTs dosage, and temperature. The dye removal using 400 mg L-1 of CNTs was more than 90%. This dosage (400 mg L-1) was considered as the optimum dosage of CNTs to remove methylene blue. The adsorption kinetic data were analysed using pseudo-first-order, pseudo-second-order and Elovich models. It was found that the pseudo-second- order kinetic model was the most appropriate model, describing the adsorption kinetics. Adsorption isotherm of methylene blue onto the CNTs was determined at 290, 300 and 310 K with 10 mg L-1 as initial concentration of methylene blue. Adsorption equilibrium was attained within 120 min. Equilibrium data were fitted to the Langmuir, Freundlich, Temkin and Sips isotherm models and isotherm constants were determined. The equilibrium data were best represented by the Sips isotherm model. Thermodynamic parameters such as changes in the free energy of adsorption (G), enthalpy (H) and entropy (S) were calculated. The negative values of G indicate that the methylene blue adsorption process is spontaneous in nature and the positive value of H shows the endothermic nature of the process. Key words: Carbon nanotubes, methylene blue, basic dye, adsorption, equilibrium, kinetic, thermodynamics. INTRODUCTION Synthetic dyes are one of the main pollutant groups of water and wastewater. Dye contamination in wastewater causes problems in several ways: the presence of dyes in water, even in very low quantities, is highly visible and undesirable; color interferes with penetration of sunlight into waters; retards photosynthesis; inhibits the growth of aquatic biota and interferes with gas solubility in water bodies (Garg et al., 2004; Robinson et al., 2002; Wang et al., 2005a; Hamdaoui, 2006; O¨zer and Dursun, 2007). These materials are the complicated organic compounds and they resist against light, washing and microbial invasions. Thus, they cannot be decomposed easily *Corresponding author. E-mail address: a.soltani@mail.uk.ac.ir. Tel.:+98-913-343-5504. Fax: +98-341-2118298. (Wang et al., 2008b; Baldez et al., 2008). Direct discharge of dyes containing effluents into municipal environment may cause the formation of toxic carcinogenic breakdown products. The highest rates of toxicity were found amongst basic and diazo direct dyes (Lata et al., 2007; Wang et al., 2008a). Therefore, it is highly necessary to reduce dye concentration in the wastewater. The conventional methods for treating dye- containing wastewaters are electrochemical treatment (Fan et al., 2008; G¨urses et al., 2002), coagulation and flocculation (Tak-Hyun et al., 2004), chemical oxidation (Oguz and Keskinler, 2007), liquid–liquid extraction (Muthuraman et al., 2008) and adsorption (Wang et al. 2005a; Wang et al., 2005b; Mohan et al., 2002; G¨urses et al., 2006). Adsorption has been shown to be an effective way for removing organic matter from aqueous solutions in terms of initial cost, simplicity of design, ease