Adsorption of methylene blue onto hazelnut shell: Kinetics, mechanism and activation parameters

The adsorption kinetics of methylene blue (MB) on the hazelnut shell with respect to the initial dye concentration, pH, ionic strength, particle size and temperature were investigated. The rate and the transport/kinetic processes of MB adsorption were described by applying the first-order Lagergren, the pseudo-second-order, mass transfer coefficient and the intraparticle diffusion models. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. Significant increases in initial adsorption rate were observed with the increase in temperature followed by pH and initial MB concentration. The intraparticle diffusion was found to be the rate-limiting step in the adsorption process. Adsorption activation energy was calculated to be 45.6 kJ mol−1. The values of activation parameters such as free energy (ΔG*), enthalpy (ΔH*) and entropy (ΔS*) were also determined as 83.4 kJ mol−1, 42.9 kJ mol−1 and −133.5 J mol−1 K−1, respectively.