Controllable Synthesis of MIL-101(Cr)@TiO2 Core–Shell Nanocomposites for Enhanced Photocatalytic Activity

Incorporating high surface area and high CO2 adsorption capacity of metal–organic frameworks (MOFs) together with highly efficient semiconductor photocatalysts provides an ideal strategy for designing CO2 reduction photocatalysts. Controllable growth of TiO2 nanoparticles on MIL-101(Cr) can be obtained and yields MIL-101(Cr)@TiO2 core–shell photocatalysts via a fluoride-assisted solvothermal method. Corrosion occurs on the surface of MIL-101(Cr) by the action of F– and generates an activated surface, facilitating the growth of a TiO2 shell. MIL-101(Cr)@TiO2 nanocomposites with different TiO2 contents are remarkably fabricated by controlling the reaction conditions. The morphology, structure, surface area, and composition of the as-prepared MIL-101(Cr)@TiO2 nanocomposites are investigated by various characterization methods. The EDS mapping images reveal that the Ti and O elements are uniformly distributed on the shell, but Cr and C elements are mainly situated at the core of the composite, which further indicates the successful synthesis of the MIL-101(Cr)@TiO2 core–shell structure. The photocatalytic conversion of CO2 into CH4 is noticeably enhanced by the produced MIL-101(Cr)@TiO2 octahedra inheriting both large surface area (387.3 m2 g–1) and high CO2 adsorption capacity. Compared to pure TiO2 nanoparticles under the same conditions, the optimized MIL-101(Cr)@TiO2 photocatalyst exhibits a much greater CO2 conversion efficiency, with a CH4 generation rate of 0.22 μmol h–1 g–1. This work will advance the experimental and theoretical basis for exploring highly efficient CO2 reduction photocatalysts.