BiVO₄ Microspheres Coated with Nanometer-Thick Porous TiO₂ Shells for Photocatalytic Water Treatment under Visible-Light Irradiation

Herein, we designed and synthesized well-defined BiVO 4 @porous TiO 2 shell microspheres, with different core diameters by a facile hydrothermal method, for efficient visible-light-driven photocatalysis. The developed complex particles contained single solid BiVO 4 cores and nanometer-thick porous TiO 2 shells, composed of many nanosheets, and showed high stability and excellent photocatalytic activity for degrading both organic dyes and colorless organic contaminants under visible-light irradiation, much better than the benchmark of commercial P25 and bare BiVO 4 microspheres of the same size. Compared to the bare BiVO 4 microspheres, the BiVO 4 @TiO 2 heterostructures showed improved photocatalytic activity, which was ascribed to (i) the formed BiVO 4 /TiO 2 heterojunction with a defect energy level generated by the Ti 3+ ions during the nanoporous TiO 2 shell formation, which greatly promoted the charge carrier seperation and transfer between the BiVO 4 and TiO 2 during the photocatalysis process; (ii) the unique core@porous-shell structure that led to the intimate contact between the BiVO 4 core and the TiO 2 shell, facilitating the interfacial charge transfer; and also more importantly, (iii) the unique nanostructured porous TiO 2 shell composed of numerous tiny TiO 2 nanosheets that provided a large surface area for the easy adsorption of organic molecules and made the separated charge carriers directly available to the reactants, largely suppressing the charge carrier recombination and further increasing the photocatalytic efficiency. This study provides a feasible approach for the rational design of high-efficiency core@porous-shell nanostructured photocatalysts for photocatalytic water and wastewater treatment under visible-light irradiation.