Investigation of the photodecomposition of phenol in near-UV-irradiated aqueous TiO2 suspensions. I: Effect of charge-trapping species on the degradation kinetics

The effects of charge-trapping species on the kinetics of phenol decomposition were studied in near-UV-irradiated aqueous TiO₂ (anatase) suspensions in a batch photoreactor. The influence of catalyst loading, initial phenol concentration, dissolved O₂ concentration, Ag⁺ content and H₂O₂ concentration on the rate of phenol degradation is reported. The observed heterogeneous degradation of phenol followed apparently zero-order kinetics up to ca. 70% conversion. The Langmuir–Hinshelwood kinetic model successfully described the influence of the initial phenol concentration and dissolved O₂ concentration on the rate of heterogeneous photooxidation of phenol. The data obtained by applying the Langmuir–Hinshelwood treatment are consistent with the available kinetic parameters. The results of the experiments in the presence of Ag⁺ indicated that the phototransformation of phenol can proceed via direct electron transfer, neither dissolved O₂ nor its reduction forms playing a significant role in the degradation mechanism.