Role of platinum deposited on TiO₂ in phenol photocatalytic oxidation

Photooxidation of phenol has been studied in aqueous suspensions of titanium dioxide Hombikat UV100 and Degussa P25 loaded with various amounts of Pt. The rates of phenol decomposition and total carbon removal rose by a maximum factor of 1.5 when Hombikat was loaded with 1 wt % Pt; further increase of Pt deposition did not increase the photoactivity any more. The electron movement across the Pt - anatase junction is discussed, and the positive influence of Pt on phenol oxidation over Hombikat is explained by the increase of charge separation in agglomerates of primary particles. The photocatalytic activity of P25 was higher than that of platinized and pure Hombikat. But loading P25 with Pt resulted in a decrease of phenol decomposition and total carbon removal rates. The decrease of Degussa P25 activity after platinization means that Pt cannot further increase the efficiency of charge separation in this TiO₂, whose two-phase composition already provides a very efficient suppression of recombination in liquid photocatalytic reaction. The charge separation in P25 is illustrated with the scheme of P25's band structure. The possible side effects brought by Pt deposition are also discussed.