Abstract

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 (ΔGâ—¦), enthalpy (ΔHâ—¦) and entropy (ΔSâ—¦) were calculated. The negative values of ΔGâ—¦ indicate that the methylene blue adsorption process is spontaneous in nature and the positive value of ΔHâ—¦ shows the endothermic nature of the process.

Key words: Carbon nanotubes, methylene blue, basic dye, adsorption, equilibrium, kinetic, thermodynamics.