Generation of reactive oxygen species and charge carriers in plasmonic photocatalytic Au@TiO2 nanostructures with enhanced activity

Abstract

The combination of semiconductor and plasmonic nanostructures, endowed with high efficiency light harvesting and surface plasmon confinement, has been a promising way for efficient utilization of solar energy. Although the surface plasmon resonance (SPR) assisted photocatalysis has been extensively studied, the photochemical mechanism, e.g. the effect of SPR on the generation of reactive oxygen species and charge carriers, is not well understood. In this study, we take Au@TiO₂ nanostructures as a plasmonic photocatalyst to address this critical issue. The Au@TiO₂ core/shell nanostructures with tunable SPR property were synthesized by the templating method with post annealing thermal treatment. It was found that Au@TiO₂ nanostructures exhibit enhanced photocatalytic activity in either sunlight or visible light (λ > 420 nm). Electron spin resonance spectroscopy with spin trapping and spin labeling was used to investigate the enhancing effect of Au@TiO₂ on the photo-induced reactive oxygen species and charge carriers. The formation of Au@TiO₂ core/shell nanostructures resulted in a dramatic increase in light-induced generation of hydroxyl radicals, singlet oxygen, holes and electrons, as compared with TiO₂ alone. This enhancement under visible light (λ > 420 nm) irradiation may be dominated by SPR induced local electrical field enhancement, while the enhancement under sunlight irradiation is dominated by the higher electron transfer from TiO₂ to Au. These results unveiled that the superior photocatalytic activity of Au@TiO₂ nanostructures correlates with enhanced generation of reactive oxygen species and charge carriers.