TiO2-supported Au144 nanoclusters for enhanced sonocatalytic performance.

Abstract

The production of reactive oxygen species (ROS), such as hydroxyl radicals, by ultrasonic activation of semiconductor nanoparticles (NPs), including TiO2, has excellent potential for use in sonodynamic therapy and for the sonocatalytic degradation of pollutants. However, TiO2 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 TiO2-supported Au nanoclusters (NCs) (Au NCs/TiO2) by monitoring the production of hydroxyl radicals (•OH) under ultrasonication conditions. The deposition of Au144 NCs on TiO2 NPs was found to enhance sonocatalytic activity for •OH production by approximately a factor of 2. Electron-hole recombination in ultrasonically excited TiO2 NPs is suppressed by Au144 NCs acting as an electron trap; this charge separation resulted in enhanced •OH production. In contrast, the deposition of Au25 NCs on TiO2 NPs resulted in lower sonocatalytic activity due to less charge separation, which highlights the effectiveness of combining Au144 NCs with TiO2 NPs for enhancing sonocatalytic activity. The sonocatalytic action that forms electron-hole pairs on the Au144/TiO2 catalyst is due to both heat and sonoluminescence from the implosive collapse of cavitation bubbles. Consequently, the ultrasonically excited Au144 (3 wt.%)/TiO2 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.