Kinetics and Thermodynamic Studies of Adsorption of Methylene Blue from Aqueous Solutions onto Paliurus spina-christi Mill. Frutis and Seeds

Abstract

In the present study, Paliurus spina-christi Mill. Frutis and Seeds (PSCFS) was used as an adsorbent for the investigation of the adsorption kinetics and thermodynamic parameters of methyleneblue (MB) from aqueous solution at various temperatures and concentrations. Six kinetic models, the pseudo-first-order, pseudo-second-order, intra-particle diffusion, Elovich, Bangham and Avrami equations were used to predict the adsorption rate constants. It was found that the kinetics of the adsorption of MB onto PSCFS at different operating conditions was the best described by the pseudo-second-order model. The rate parameters of the other kinetic models for adsorption were also evaluated and compared to identify the adsorption mechanisms. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy. Thermodynamic analysis showed that adsorption was favourable and spontaneous, endothermic physical adsorption and increased disorder and randomness at the solid-solution interface of MB onto PSCFS.