Integrating carbon quantum dots with oxygen vacancy modified nickel-based metal organic frameworks for photocatalytic CO2 reduction to CH4 with approximately 100 % selectivity

Solar-light-driven reduction of CO2 into renewable fuels has great potential in the production of sustainable energy, addressing the energy crisis and environmental problems simultaneously. However, it is a significant challenge to achieve high selectivity for the conversion of CO2 into CH4, which is a type of fuel with a high calorific value. Herein, carbon quantum dots (CQDs) were integrated with an oxygen vacancy modified nickel-based metal organic frameworks (NiMOFs) to form the CQDs-X/NiMOFV series, which exhibited superior performance for CO2 photoreduction into CH4 compared with pure NiMOFs in the presence of hole scavengers under visible light irradiation. The highest yielding rate of CH4 (1 mmol g(-1) h(-1)) and selectivity (97.58 %) were obtained using a CQDs-25/NiMOFV catalyst. Most importantly, in diluted CO2 atmosphere, the yield of CH4 was almost unchanged and the selectivity of CH4 over CQDs-25/NiMOFV was higher than that in pure CO2. The superior performance of CQDs-25/NiMOFV may be attributed to the following two factors: (i) both CQDs and oxygen vacancies facilitate the transmission of electrons to promote the eight-electron reaction producing CH4, and (ii) oxygen vacancies can act as the electron trap to capture the photogenerated electrons to react with adsorbed CO2 on Ni2+. This study offers a valuable strategy for designing efficient photocatalysts to convert CO2 into CH4 with superior selectivity.