Methylene blue removal using Salix babylonica (Weeping willow) leaves powder as a low-cost biosorbent in batch mode: Kinetic, equilibrium, and thermodynamic studies

In this article, Salix babylonica leaves powder (SBLP) has been used for the removal methylene blue (MB) from aqueous solutions by adsorption process. The surface of SBLP analyzed by scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR). The effects of changing parameters such as adsorbent dosage, contact time, pH, temperature, and initial dye concentration on methylene blue adsorption were investigated. Three isotherm equations, Langmuir, Freundlich, and Temkin, have been tested in order to describe the equilibrium characteristics of adsorption. The experimental data fitted well by Langmuir isotherm, with maximum adsorption capacity 60.97 mg/g. The experimental data were fitted using pseudo-first-order and pseudo- second-order and intraparticle diffusion models. The experimental results were fitted better with pseudo-second-order model compared to the other two models. The amount of thermodynamic parameters such as Gibbs free energy (∆ G°), change in enthalpy of adsorption (∆ H°), and change in entropy (∆ S°) were calculated and this parameter showed that MB adsorption on SBLP is spontaneous and exothermic in nature. The result of experimental shows that SBLP is suitable low-cost adsorbent for removal of methylene blue from aqueous solutions.