Commonly Existing Hole-Capturer Organics Adsorption-Induced Recombination over Metal/Semiconductor Perimeters: A Possible Important Factor Affecting Photocatalytic Efficiencies

Photocatalysis is a physiochemical effect arising from the relaxation of photoinduced electrons from the conduction band to the valence band. Controlling the electron relaxation to occur through photocatalytic pathways and prohibiting other relaxations is the main scientific thought for photocatalytic studies. It is needed to know the parallel relaxation pathways that can compete with photocatalytic reactions. By means of in situ photoconductances (PCs) and photoinduced absorptions (PAs), the current research studied the photoinduced electron relaxations of the Au/TiO2 in different atmospheres and at different temperatures. The PC and PA relaxations became different and fast when methanol, ethanol, isopropanol, and acetone were introduced; they also tend to decrease as temperature increases, while that of the undecorated TiO2 in all atmospheres and the Au/TiO2 in pure N-2 increased. The results indicated that the organic adsorptions over the Au/TO2 perimeters change the relaxation pathway, and a hole-capturing organics adsorption-induced recombination over the Au/TiO2 perimeter was proposed to explain the relaxations. We found that this relaxation also exists for Ag/TiO2, Pt/TiO2, and Au/ZnO, so it is a commonly existing physical course for the metal/semiconductor (M/S) materials. The effect of the organics and M/S structures on the relaxation was discussed, and the relationship with photocatalytic reactions was also analyzed. Our finding means that blocking this relaxation pathway is an effective way to increase photocatalytic activities, which might open a door for highly active photocatalyst developments.