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The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO2 photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO2 surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH4. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λmax = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H2 evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H2 formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H+/H2 redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H2 gas in the reaction mixture.

Photocatalysts were prepared by the deposition of noble metal nanoparticles (Au, Pt, Rh or Ru) on different commercially available titanias. The photocatalytic performance of these catalysts was studied for the evolution of H 2 during excitation with visible light. Experiments were carried out in irradiated suspensions containing various organic compounds. Noble metal nanoparticles can promote the lowering of the overvoltage of H ? reduction. The noble metal nanoparticles were deposited onto the TiO 2 surface by in situ chemical reduction in a quantity of 1 wt%. Three aspects were considered: (i) the photocatalytic performance of different bare TiO 2 deposited with Pt; (ii) the effect of the deposition of Au, Pt, Rh or Ru nanoparticles onto the TiO 2 surface; and (iii) choosing the most suitable H 2 production supporting organic compound. The rate of H 2 evolution proved to be strongly dependent on the quality of TiO 2 powder and the presence of different organics. The applied noble metal was also an efficiency determining factor during these photocatalytic reactions. With the best combination of the above mentioned circumstances, we achieved promising results to be able to effectively harvest the energy of sunlight.

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.