COMPARISON OF MULTIWALLED CARBON NANOTUBES AND ACTIVATED CARBON FOR EFFICIENT REMOVAL OF METHYL ORANGE: KINETIC AND THERMODYNAMIC INVESTIGATION

Commercially powdered activated carbon and multi-walled carbon nanotubes were used for the removal of methyl orange (MO) from aqueous solutions. The effects of solution pH, initial dye concentration, temperature and sorption time on MO removal were studied. The equilibrium sorption isotherms have been analyzed by Langmuir, Freundlich, Dubinin and Radushkevich (D-R), and Harkins-Jura (H-J) models, and Langmuir isotherms had the highest correlation coefficients. The apparent thermodynamic parameters were calculated, and the obtained values support the conclusion that MO molecules sorb by an entropy-driven, endothermic process. The kinetic of the sorption was analyzed using pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion kinetic models. The data showed that the second-order equation was the more appropriate one, although intraparticle diffusion is the rate-limiting factor.