Sensitization of Pt/TiO 2 Using Plasmonic Au Nanoparticles for Hydrogen Evolution under Visible-Light Irradiation.

Au nanoparticles with different sizes (10, 20, 30, and 50 nm) were synthesized using a seed-assisted approach and anchored onto Pt/TiO2 employing 3-mercaptopropionic acid as the organic linker. The sizes of the Au nanoparticles were controlled within a narrow range so that the size-dependent surface plasmonic resonance effect on sensitizing Pt/TiO2 can be thoroughly studied. We found that 20 nm Au nanoparticles (Au20 ) gave the best performance in sensitizing Pt/TiO2 to generate H2 under visible-light illumination. Photoelectrochemical measurements indicated that Au20 -Pt/TiO2 exhibited the most efficient "hot" electrons separation among the studied catalysts, correlating well with the photocatalytic activity. The superior performance of Au-supported Pt/TiO2 (Au20 -Pt/TiO2 ) compared with Au anchored to TiO2 (Au20 /TiO2 ) revealed the important role of Pt as a cocatalyst for proton reduction. To elucidate how the visible-light excited hot electrons in Au nanoparticles involved in the proton-reduction reaction process, Au20 /TiO2 was irradiated by visible light (λ > 420 nm) with the presence of Pt precursor (H2 PtCl6 ) in a methanol aqueous solution under deaerated condition. Energy-dispersive X-ray spectroscopy mapping analysis on the recovered sample showed that Pt ions could be reduced on the surfaces of both Au nanoparticles and TiO2 support. This observation indicated that the generated hot electrons on Au nanoparticles were injected into the TiO2 conduction band, which were then subsequently transferred to Pt nanoparticles where proton reduction proceeded. Besides, the excited hot electrons could also participate in the proton reduction on Au nanoparticles surface.