Crystallographic facet heterojunction of MIL-125-NH2(Ti) for carbon dioxide photoreduction

Facet exposure affects photocatalytic CO2 reduction reaction, but the insight remains unclear. Here, we report finely controlled six types of MIL-125-NH2(Ti) exposing single and co-exposing mixed low-index facets as model catalysts and provide an insight into facet effect on photoreduction of CO2. Facet surface heterojunction endows MIL-125-NH2(Ti) with a broadened light-absorption and accelerated charge migration. The MIL-125-NH2(Ti) with {110}/{111}-heterojunction yields ca. 10 and 18 times enhanced CO2 reduction to CO and CH4 compared with the single {001} facet exposed. Density functional theory (DFT) calculations provide an energetically favorable CO2 catalytic reduction pathway and identify the rate-limiting step on different low-index facets. This work aims at exploring facet-effect on CO2 photoreduction, understanding the facet-dependence and providing a paradigm for MOFs materials by regulating facet to enhance the general surface catalytic reaction activity.