Synthesis of Hollow Mesoporous TiO 2 Microspheres with Single and Double Au Nanoparticle Layers for Enhanced Visible-Light Photocatalysis.

A facile method was used to prepare hollow mesoporous TiO2 and Au@TiO2 spheres using polystyrene (PS) templates. Au nanoparticles (NPs) were simultaneously synthesized and attached on the surface of PS spheres by reducing AuCl4 - ions using sodium citrate which resulted in the uniform deposition of Au NPs. The outer coating of titania via sol-gel produced PS@Au@TiO2 core-shell spheres. Removing the templates from these core-shell spheres through calcination produced hollow mesoporous and crystalline Au@TiO2 spheres with Au NPs inside the TiO2 shell in a single step. Anatase spheres with double Au NPs layers, one inside and another outside of TiO2 shell, were also prepared. Different characterization techniques indicated the hollow mesoporous and crystalline morphology of the prepared spheres with Au NPs. Hollow anatase spheres with Au NPs indicated enhanced harvesting of visible light and therefore demonstrated efficient catalytic activity toward the degradation of organic dyes under the irradiation of visible light as compared to bare TiO2 spheres.