Kinetic behaviour of the adsorption and photocatalytic degradation of salicylic acid in aqueous TiO₂ microsphere suspension

Abstract

Abstract A new photocatalyst, named TiO 2 microspheres, prepared by a sol‐spraying‐calcination method, can freely suspend with air bubbling in its aqueous suspension and easily settle down from a water phase under gravity. The experimental results demonstrated that TiO 2 microspheres had better adsorption capacity than conventional TiO 2 powders, due to large surface area, large pore volume, and also a porous structure. The photocatalytic activity of TiO 2 microspheres in aqueous suspension was evaluated using salicylic acid (SA) as a model substrate. It was found that the Langmuir–Hinshelwood model in its integral form described the kinetics of SA photocatalytic degradation in the TiO 2 microsphere suspensions better than its simplified form as a first‐order reaction model, since the significant substrate adsorption on the catalysts was not negligible. The kinetics of SA photocatalytic degradation with different initial concentrations and pH was further investigated. The experiments demonstrated that the change of pH could significantly affect the adsorption of SA in the TiO 2 microsphere suspensions. The effects of substrate adsorption rate and photoreaction rate on the overall performance of photocatalytic degradation is also discussed on the basis of experimental data. Copyright © 2004 Society of Chemical Industry