Size Engineering of Metal–Organic Framework MIL-101(Cr)–Ag Hybrids for Photocatalytic CO2 Reduction

Particle size-tuned photocatalytic activity has been recognized for noble metals such as platinum; however, it is not established for metal–organic frameworks (MOFs). In this work, nanoscaled MOF MIL-101(Cr)–Ag nanoparticle hybrids with varied sizes ranging from 80 to 800 nm have been successfully achieved, and their size effect on photocatalytic CO2 reduction under visible light has been examined. We show that when the size of MIL-101(Cr)–Ag is reduced to 80 nm, the hybrid catalyst shows the highest CO2 photocatalytic reduction activity with remarkable production rates of 808.2 μmol/g·h for CO and 427.5 μmol/g·h for CH4, representing one of the most efficient hybrid catalysts. The high catalytic activity of the small-sized hybrid catalyst can be ascribed to the high density of unit cells on corners and edges of the catalyst, which are favorable for electron transfer in the photocatalytic CO2 reduction, supported by a set of complimentary photochemical and electrochemical methods.