Asian Journal of Chemical Sciences

In this study, the thermodynamic parameters and adsorption kinetic of catalase onto diatomite were investigated in aqueous solution for determining the effect of contact time, stirring speed, initial enzyme concentration, initial concentration of sodium phosphate buffer, temperature and pH. Maximum adsorption capacity values (q_m) showed a great dependence on pH. It was found that q_m–pH curves reached a maximum at around isoelectric point (iep) of catalase. It can be said that the maximum adsorption takes place because the electrostatic attraction is the most suitable at pH values close to the isoelectric point. Both structural and electrostatic effects must be invoked to explain the diminution of adsorbed catalase enzyme on either side of the iep. Also characterization of diatomite and catalase adsorbed diatomite were performed by SEM, FTIR-ATR, TGA and BET aparatus. Three different kinetic models, pseudo-first and -second-order and intraparticle diffusion were used to fit the kinetics data. The pseudo-second-order model best described the experimental data. The thermodynamic activation parameters, such as activation energy, enthalpy, entropy, and Gibbs free energy were determined.