Adsorption of methylene blue onto spent alchemilla vulgaris leaves: characterization, isotherms, kinetic and thermodynamic studies

In this study, the removal of methylene blue dye, which is widely used in the textile industry, from aqueous solutions prepared synthetically using spent Alchemilla Vulgaris leaves was investigated. The effects of initial pH, initial dye concentration, adsorbent concentration, particle size and temperature on the adsorption efficiency were examined and the suitability of the adsorption data to the adsorption models of Langmuir, Freundlich, BET and Temkin was evaluated. The highest removal efficiency was obtained as 87.85% in the experiments using 0.5 g L-1 adsorbent concentration and 10 mg L-1 dye concentration. Experimental data were consistent with the Freundlich isotherm model. As a result of the kinetic study, it was observed that the adsorption of methylene blue conformed to the pseudo-second-order kinetic rate expression. The reaction enthalpy was determined as increment H-o = 8.54 kJ mol(-1) and the reaction entropy as increment S-o = - 12.283 J mol(-1). Because the activation energy of adsorption is Ea = 25.535 kJ mol(-1), the process has been determined to be an exothermic reaction that occurs physically.