Catalytic degradation of methylene blue by biosynthesized Au nanoparticles on titanium dioxide (Au@TiO2)

The degradation of methylene blue is a critical procedure in its wastewater remediation and thus has inspired wide catalysis research with semiconductors such as titanium dioxide (TiO2) and rare metals such as gold (Au). In this study, we report bacterial cells assisting biosynthesis for Au@TiO2 as an efficient catalyst for the catalytic degradation of methylene blue. Multiple complementary characterization for bio-Aux@TiO2 evidenced the evenly distributed Au nanoparticles (NPs) on the bio-TiO2 layers. Meanwhile, bio-Au2@TiO2 displayed the superior catalytic activity in the degradation of methylene blue with the highest kinetics constant (kapp) value of 0.195 min-1. In addition, bio-Au2@TiO2 keeps stable catalytic activity for up to 10 cycles. The origin of the catalytic activity was investigated by the hydroxyl radical fluorescence quantitative analysis and optical band gap analysis. In the bio-Au2@TiO2 catalytic system, Au NPs decreased the band gap energy of TiO2 and enabled the generation of abundant photogeneration hydroxyl radicals, resulting in an enhanced photocatalytic activity. Our microbial synthesized bio-TiO2 and bio-Aux@TiO2 study would be useful for developing green synthesis catalyst technology.