TiO-supported Au nanoclusters for enhanced sonocatalytic performance.

The production of reactive oxygen species (ROS), such as hydroxyl radicals, by ultrasonic activation of semiconductor nanoparticles (NPs), including TiO, has excellent potential for use in sonodynamic therapy and for the sonocatalytic degradation of pollutants. However, TiO NPs have limitations including low yields of generated ROS that result from fast electron-hole recombination. In this study, we first investigated the sonocatalytic activity of TiO-supported Au nanoclusters (NCs) (Au NCs/TiO) by monitoring the production of hydroxyl radicals (•OH) under ultrasonication conditions. The deposition of Au NCs on TiO NPs was found to enhance sonocatalytic activity for •OH production by approximately a factor of 2. Electron-hole recombination in ultrasonically excited TiO NPs is suppressed by Au NCs acting as an electron trap; this charge separation resulted in enhanced •OH production. In contrast, the deposition of Au NCs on TiO NPs resulted in lower sonocatalytic activity due to less charge separation, which highlights the effectiveness of combining Au NCs with TiO NPs for enhancing sonocatalytic activity. The sonocatalytic action that forms electron-hole pairs on the Au/TiO catalyst is due to both heat and sonoluminescence from the implosive collapse of cavitation bubbles. Consequently, the ultrasonically excited Au (3 wt. %)/TiO catalyst exhibited higher catalytic activity for the production of •OH because of less light shadowing effect, in contrast to the lower catalytic activity when irradiated with only external light.