Photocatalytic properties of TiO₂ modified with gold nanoparticles in the degradation of 4-chlorophenol in aqueous solution

The degradation in aqueous solution of 4-chlorophenol photocatalyzed by band-gap-irradiated TiO₂ modified with nanoscopic gold particles has been studied as a function of Au particle size by means of HREM, DRIFTS, BET, and reactor measurements. 4-chlorocatechol is observed as a reaction intermediate, and the results indicate that gold particle size is an important parameter. At low metal loadings, very small Au particles (<3 nm diameter) are particularly effective in enhancing the pseudo first-order rate constant. Higher Au loadings result in much larger particles and a loss of catalytic efficiency. These findings are discussed in terms of possible effects on the rate of production and recombination of photogenerated electrons and holes. It is shown that elimination of adsorbed hydroxyl groups that act as effective hole traps has a deleterious effect on the catalytic efficiency.