Facet-dependent photocatalytic hydrogen generation over MOF NH2-MIL-125(Ti) under visible light was investigated, both experimentally and theoretically.

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 CO 2 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 CO 2 photocatalytic reduction activity with remarkable production rates of 808.2 μmol/g•h for CO and 427.5 μmol/g•h for CH 4 , 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 CO 2 reduction, supported by a set of complimentary photochemical and electrochemical methods.

It is deemed as a desired approach to utilize solar energy for the conversion of CO 2 into valuable products, and the majority of the MOFs-based photocatalytic reductions of CO 2 have focused on formic acid (HCOOH) production with an organic solvent as the reaction medium. Herein, we report a solvent-free reaction route for the photoreduction of CO 2 catalyzed by Fe-MOFs, namely, NH 2 -MIL-53(Fe)aminoterephthalic acid; G = guest and/or solvent molecules). Compared with the orthodox reaction route, the present out-of-the-way photocatalytic reduction of CO 2 with superior selectivity to CO occurs at the gas−solid interface. The reaction procedure is environmentally friendly and provides a possibility to address the CO 2 emission problem. Importantly, NH 2 -MIL-101(Fe) shows the highest photocatalytic activity among these Fe-MOFs due to its efficient charge separation and electron transfer.