Solid-Phase Photocatalysts: Physical Vapor Deposition of Au Nanoislands on Porous TiO2 Films for Millimolar H2O2 Production within a Few Minutes

The production of hydrogen peroxide (H2O2) using photocatalytic nanoparticles is an emerging field with applications in organic synthesis, biosensors, and fuel cells. Colloidal photocatalysts are, however, limited in their applications because of poor efficiency and stability. In this study, millimolar production of H2O2 was achieved within 5 min using solid-phase photocatalysts—Au nanoislands (NIs) on porous TiO2 films—without supplying O2 or stirring the solution. Au/TiO2 showed an almost 80-fold greater productivity than TiO2, which can be explained by considering two factors. First, the physical-vapor-deposited Au resulted in the formation of Au NIs of various sizes on TiO2, whose work functions were size-dependent. Thus, the combination of small Au NIs, TiO2, and large Au NIs allowed the introduction of potential gradients through TiO2, and also the reduced potential barriers at the small Au NI/TiO2 junctions; thereby minimizing the recombination of electron–hole pairs, and effectively extracting them. Second, the porous TiO2 films may effectively scatter UV light, leading to enhanced electron–hole pair generation. The inherent properties of the solid-phase photocatalysts could also circumvent stability issues caused by aggregation. These solid-phase photocatalysts should facilitate the development of high-efficiency H2O2 generation and promote technology based on H2O2-mediated processes.