Enhanced Photocatalytic CO2 Reduction Activity over NH2-MIL-125(Ti) by Facet Regulation

Designation and optimization of facets of photocatalysts is an effective strategy to address the issue of facet-dependent photocatalytic reactions. However, studies regarding the facet effect of metal–organic frameworks (MOFs) on the photocatalytic process are in infancy. In this study, NH2-MIL-125 (Ti) with different ratios of 001 and 111 facets was exactly controlled and synthesized, and it was found that the activity in photoreduction of CO2 is enhanced with gradually increasing exposed proportion of 111 facets. The 111 facets exhibit photocatalytic activity with the maximal CO and CH4 yields of 8. 25 and 1. 01 μmol g–1 h–1, which are 9 and 5 times higher than those of 001 facets, respectively. Also, the 111 facets give the highest quantum yields of 0. 14 and 0. 07% for CO and CH4 production, respectively. Steady-state and time-resolved fluorescence spectra reveal the importance of inhibiting the recombination of photoinduced electrons and holes for the sample with 111 facets. Besides, TiIII formed during the reaction process exhibits strong reducibility for CO2. Starting from NH2-MIL-125 (Ti), the photocatalytic performance can be enhanced by regulating exposed 111 facets. This work not only provides a strategy for further enhancing photocatalytic performance by tuning the exposed active facets of MOFs, but also provides a deep understanding of the factors for improving the photocatalytic reduction of CO2.