TiO 2 -supported Au 144 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 2 , has excellent potential for use in sonodynamic therapy and for the sonocatalytic degradation of pollutants. However, TiO 2 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 2 -supported Au nanoclusters (NCs) (Au NCs/TiO 2 ) by monitoring the production of hydroxyl radicals (•OH) under ultrasonication conditions. The deposition of Au 144 NCs on TiO 2 NPs was found to enhance sonocatalytic activity for •OH production by approximately a factor of 2. Electron-hole recombination in ultrasonically excited TiO 2 NPs is suppressed by Au 144 NCs acting as an electron trap; this charge separation resulted in enhanced •OH production. In contrast, the deposition of Au 25 NCs on TiO 2 NPs resulted in lower sonocatalytic activity due to less charge separation, which highlights the effectiveness of combining Au 144 NCs with TiO 2 NPs for enhancing sonocatalytic activity. The sonocatalytic action that forms electron-hole pairs on the Au 144 /TiO 2 catalyst is due to both heat and sonoluminescence from the implosive collapse of cavitation bubbles. Consequently, the ultrasonically excited Au 144 (3 wt. %)/TiO 2 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.