Retarding effect of surface hydroxylation on titanium(IV) oxide photocatalyst in the degradation of phenol

Nanosized powders of TiO2 (anatase) were prepared by the hydrothermal method, acid-medium hydrolysis or by vacuum freeze-drying of sols, and annealing at temperatures <700-degrees-C. Photocatalytic activities of these powders in the mineralization of phenol, were evaluated in comparison to that of Degussa P25. Kinetic data indicated that surface hydroxylation had a retarding effect on the degradation of phenol. Formation of stable peroxotitanium species were observed on hydroxylated powders, whereas only V(Ti)-O- hole trap centres were detected by EPR on the heat treated samples. The data supports direct hole oxidation of the substrate preadsorbed on the photocatalyst, which is otherwise blocked by surface hydroxyls.