Effect of Copper and Silver Modification of NH2-MIL-125(Ti) on the Photoreduction of Carbon Dioxide to Formic Acid over this Framework under Visible-Light Irradiation

Cu and Ag enhance the photocatalytic activities of metal–organic frameworks (MOFs) toward CO2 conversion because of their CO2 adsorption capacities and effects on the lowest unoccupied molecular orbital (LUMO) overpotentials of MOFs. However, to date, targeted introduction of metals into MOFs to achieve visible (Vis)-light-active photocatalysts for CO2 photoconversion has not been realized. Herein, a series of amine-functionalized Ti MOF (NH2-MIL-125(Ti))-based photocatalysts were successfully synthesized using metalation, incorporation, and photodeposition, allowing Cu and Ag incorporation into NH2-MIL-125(Ti) and attainment of ultraviolet- and Vis-light-active photocatalysts. Notably, the most active photocatalyst obtained by post-synthetic metalation of NH2-MIL-125(Ti) by Cu2+ (MOF_met_0.5%Cu) demonstrated excellent performance in photoreducing CO2 to HCOOH: a conversion rate of 30.1 umolg-1h-1 and quantum yield of 1.18% at 380nm. Photoconversion of CO2 to HCOOH was further confirmed using 13CO2. The novel approach proposed herein is a significant step toward clean energy production and environmental pollutant elimination.