TiO₂-supported Au₁₄₄ nanoclusters for enhanced sonocatalytic performance

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.