Schottky-junction-mediated interfacial charge regulation in Ag-decorated NH2-MIL-125(Ti) for effective photoreduction of gas-phase CO2.

Photocatalytically reducing CO2 is a mild and sustainable pathway for transforming greenhouse gases into value-added chemical compounds and fuels by utilizing renewable light energy. Herein, Ag-decorated NH2-MIL-125(Ti) composite compounds (denoted as Ti-MOF-xAg) with engineered metal-semiconductor interfaces were rationally fabricated via UV-assisted photodeposition. The photocatalytic performance was evaluated in a gas-solid CO2/H2O (vapor) system under UV irradiation. All Ti-MOF-xAg samples exhibit markedly better photocatalytic properties in comparison to Ag-free NH2-MIL-125(Ti). Ti-MOF-5Ag achieves the optimal performance, delivering an accumulated 218 µmol·g- 1 CO yield and 26.4 µmol·g- 1 CH4 yield within 180 min, together with apparent quantum yield and energy return on energy invested values of 7.40‰ and 2.71‰, respectively. The catalyst also maintains stable performance over consecutive cycling tests, exhibiting excellent robustness and stability. Systematic spectroscopic and electrochemical analyses reveal that the performance enhancement originates primarily via the Schottky junction at the Ag/NH2-MIL-125(Ti) interface driving directional photogenerated electron transfer from the NH2-MIL-125(Ti) LUMO to Ag and promoting electron accumulation on Ag active sites. This interfacial electron extraction effectively suppresses charge recombination and accelerates the CO2 reduction process. This work highlights noble-metal interfacial engineering as an effective strategy to boost the gas-phase CO2 photoreduction capability of Ti-based MOFs.