Influence of Metal/Metal Ion Concentration on the Photocatalytic Activity of TiO₂−Au Composite Nanoparticles

Gold-capped TiO 2 nanocomposite particles have been synthesized by reducing [AuCl 4 ] - on the surface of preformed TiO 2 colloids in acetonitrile. Such semiconductor−metal nanocomposites are considered to be beneficial toward improving the efficiency of the photocatalytic oxidation process. Whereas photogenerated electrons of TiO 2 colloids readily reduce Au(III) ions in deaerated solution, the photogenerated holes are capable of oxidizing the preexisting gold layer on TiO 2 particles in aerated solutions. The experimental conditions under which photocatalysis experiments are carried out dictate the net concentration of metal and metal ion species at the semiconductor/metal interface and hence the overall catalytic activity. Using photocatalytic oxidation of SCN - as a probe, we have investigated the influence of Au 0 and Au(III) on interfacial hole transfer. The ratio of metal/metal ion concentration (viz., [Au 0 ]/[Au(III)]) at the TiO 2 interface was found to dictate the overall photocatalytic process in the semiconductor/metal nanocomposite.