Solid-Phase Photocatalysts: Physical Vapor Deposition of Au Nanoislands on Porous TiO 2 Films for Millimolar H 2 O 2 Production within a Few Minutes

The production of hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 was achieved within 5 min using solid-phase photocatalysts—Au nanoislands (NIs) on porous TiO 2 films—without supplying O 2 or stirring the solution. Au/TiO 2 showed an almost 80-fold greater productivity than TiO 2, 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 TiO 2, whose work functions were size-dependent. Thus, the combination of small Au NIs, TiO 2, and large Au NIs allowed the introduction of potential gradients through TiO 2, and also the reduced potential barriers at the small Au NI/TiO 2 junctions; thereby minimizing the recombination of electron–hole pairs, and effectively extracting them. Second, the porous TiO 2 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 H 2 O 2 generation and promote technology based on H 2 O 2 -mediated processes.