Organic-Inorganic Dual-Coated TiO 2 Nanoparticles for Regulation of Photocatalytic Activity

Organic-inorganic dual-coated photocatalytic TiO2 nanoparticles (NPs) were obtained by two-step surface modification of i) an inner SiO2-coating and ii) outer alkylation through a silane coupling reaction, exhibiting tunable photocatalytic activity. Evaluation of the photocatalytic activity under ultraviolet ray irradiation revealed that the dual coating on the surface of the TiO2 NPs changed the reaction rate-determining step of the photocatalytic decomposition of methylene blue (MB) from an adsorption-limited manner to a diffusion-limited manner. Unmodified TiO2 NPs decomposed MB as soon as MB was adsorbed on the surface, while the decomposition reaction proceeded in the concentration-independent diffusion-controlled manner in the surface-modified NPs. The double shells might confine both outward excited electron diffusion and inward substance diffusion, preventing the generation of active oxygen on the surface of TiO2 NPs.