Mesostructured Anatase $TiO2$ for Visible Light and UV Photocatalysis With Confinement Effect and Semiconductor Coupling

Hexagonal and cubic mesostructured $TiO2$ anatase were synthesized by a templating sol-gel method using triblock copolymers as structuring agents, and used as photocatalysts for providing geometrical assistance to a photocatalytic reaction. The visible light and UV photocatalytic removal of gas-phase concentrated toluene $(110ppm)$ within an annular flow-reactor was used as a tool to evidence the benefit to use mesostructured photocatalysts. The coupling of low amounts of $WO3$ with mesostructured anatase led to high efficiency using visible light and UV activation. The highly positive effect of $WO3$ on the toluene removal efficiency was attributed to the coupling between $TiO2$ and $WO3$ semiconductors, leading to an improved photogenerated charge separation and thus a weaker charge recombination. The hypothesis of a confinement effect of the reactants inside the mesostructured photocatalyst was put forward to explain the photocatalytic performances obtained under visible light and UV activation. This confinement effect would be based on the inner partial pressure concept. It consists of an increase in the partial pressure of the reactants next to the active sites inside the nanometric cavities of the ordered structure, while the apparent macroscopic partial pressures, outside the mesostructure, would remain unchanged. According to a traditional reaction rate law, such an increase results in the increase in the reaction rate. The photon-assisted reaction could be considered as “structure-assisted,” the geometrical assistance being provided by the surrounding ordered $TiO2$ walls of the mesostructure.