Kinetics and thermodynamics of lysozyme adsorption on mesoporous titanium dioxide

Mesoporous TiO₂ was prepared by calcinating H₂i₂O₅ at 773.15 K. The sample was characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) analysis. The adsorption behavior and mechanism of mesoporous TiO₂ for lysozyme were investigated by isothermal adsorption experiments. The results show that the equilibrium experimental data were correlated with the Langmuir isotherm equation. The adsorption capacity first increased and then decreased with increasing pH value. The capacity showed a maximum value of 72.5 mg∙g^-1 when the pH value was 7.2. Lysozyme adsorbed on mesoporous TiO₂ was extremely stable, and its amount on mesoporous TiO₂ maintained 81.6% of its initial value after five adsorption and regeneration cycles. Furthermore, kinetic analysis was conducted using pseudo-first and pseudo-second order models. The adsorption of lysozyme on mesoporous TiO₂ was described well by the pseudo-second order rate equation. The rate-determining step of the adsorption was the combined action of film diffusion and intraparticle diffusion. The adsorption thermodynamic analysis suggested ΔG⁰ < 0, ΔH⁰ > 0, and ΔS⁰ > 0, which indicated that the adsorption was a spontaneous and endothermic process with entropy increased.