Enhanced sonocatalytic degradation of azo dyes by Au/TiO₂

Au-loaded TiO₂ (Au/TiO₂) has been reported for the first time as a sonocatalyst. It was found that the catalyst Au/TiO₂, with a low Au loading 0.5 wt % and under common and commercial frequency (40 kHz) ultrasonic irradiation, greatly accelerated both the discoloration and total organic carbon (TOC) removal of azo dyes such as orange II (Org II), ethyl orange (EO), and acid red G (ARG), as compared to bare TiO₂ and nano-Au catalyst. About 80% TOC removal was achieved after complete discoloration of 2.5 × 10^-4 M Org II. H₂O ₂ and H₂ formation as well as their accumulation was greatly enhanced due to Au loading on TiO₂. Both oxidative and reductive degradation intermediates have been detected, and thus the mechanism involves both enhanced oxidation and enhanced reduction via the accelerated formation of active •OH and •H radicals due to Au loading on TiO ₂, which is supported by electron spin resonance (EPR) and other evidence. The study provides an admirable way to raise the efficiency of sonication and to treat azo dye-containing wastewaters with sonocatalytic processes.