Reversing CO₂ photoreduction selectivity from CO to near 100 % CH₄ using cation vacancy-induced pair sites in thinned MOFs

Metal-organic frameworks (MOFs) with customizable components can photo-reduce CO₂ into various products; however, tuning the distribution of these products through modification engineering remains challenging. In this study, we propose a novel bottom-up surfactant-assisted preorganization strategy to simultaneously disrupt inner Van der Waals forces and induce Ti cation vacancies in the well-known NH₂-MIL-125 MOF. The resulting Ti-deficient NH₂-MIL-125 nanosheets, featuring unpaired electrons on O atoms and residual Ti sites, not only significantly enhance photo-generated charge migration but also facilitate the further protonation of CO* to CHO* during CO₂ photoreduction. Unlike NH₂-MIL-125, which predominantly converts CO₂ to CO, the Ti-deficient NH₂-MIL-125 nanosheets achieve an impressive selectivity of 95.7 % for CH₄ production, with an electron consumption rate of 51.0 mol·g⁻¹·h⁻¹ for the first time. This approach of creating metal-cation vacancies to synergistically modulate charge separation dynamics and catalytic reaction kinetics offers a new pathway to refine the activity and selectivity of multifaceted competitive catalytic reactions.