One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO₂ photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO₂ surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO₂ composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H₂ production activities of the samples were studied in aqueous TiO₂ suspensions irradiated with near-UV light in the absence of dissolved O₂, with oxalic acid or methanol as the sacrificial agent. The H₂ evolution rates proved to be strongly dependent on Au particle size: the highest H₂ production rate was achieved when the Au particles measured ~6 nm.
Keywords: Au nanoparticle; H2 evolution; TiO2; oxalic acid; size-dependent activity.