Selective wet-chemical etching to create TiO2@MOF frame heterostructure for efficient photocatalytic hydrogen evolution

Close heterojunction interface, open diffusion channel and the reactivity of the exposed facet are three key factors that affect the photocatalytic activity of porous heterojunction materials. It is significant to study the influence of these three factors on the photocatalytic activity of metal-organic framework (MOF)-based heterojunction systems. Herein, we synthesized the TiO2@NH2-MIL-125(Ti) frame structure (TiO2@MOF FS) by in-situ self-sacrificial hydrolytic etching approach with directional chemical protection, where four exposed facets are all active NH2-MIL-125(Ti) {100} facets. According to the structural characteristics of NH2-MIL-125(Ti) {100} facets, tannic acid was selected as the directional protective agent, and NH2-MIL-125(Ti) was etched from the inside out by the hydrolysis method. The obtained TiO2@MOF FS possessed tight heterojunction interface between TiO2 and NH2-MIL-125(Ti), while maintaining the open diffusion channels of NH2-MIL-125(Ti). Benefited from the improved electrical conductivity, open diffusion channels and high reactivity of the exposed facets, the obtained TiO2@MOF FS showed excellent photocatalytic hydrogen production efficiency under sun light illumination, without the deposition of any noble metal co-catalyst. This work provides a novel research idea for the fabrication of highly efficient MOF-based photocatalysts.