Catalytic degradation of methylene blue by biosynthesized Au nanoparticles on titanium dioxide (Au@TiO 2 ).

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 (TiO 2 ) and rare metals such as gold (Au). In this study, we report bacterial cells assisting biosynthesis for Au@TiO 2 as an efficient catalyst for the catalytic degradation of methylene blue. Multiple complementary characterization for bio-Au x @TiO 2 evidenced the evenly distributed Au nanoparticles (NPs) on the bio-TiO 2 layers. Meanwhile, bio-Au 2 @TiO 2 displayed the superior catalytic activity in the degradation of methylene blue with the highest kinetics constant (k app ) value of 0.195 min -1 . In addition, bio-Au 2 @TiO 2 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-Au 2 @TiO 2 catalytic system, Au NPs decreased the band gap energy of TiO 2 and enabled the generation of abundant photogeneration hydroxyl radicals, resulting in an enhanced photocatalytic activity. Our microbial synthesized bio-TiO 2 and bio-Au x @TiO 2 study would be useful for developing green synthesis catalyst technology.