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 CO 2 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 CO 2 into CH 4 , 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/NiMOF V series, which exhibited superior performance for CO 2 photoreduction into CH 4 compared with pure NiMOFs in the presence of hole scavengers under visible light irradiation. The highest yielding rate of CH 4 (1 mmol g −1  h −1 ) and selectivity (97.58 %) were obtained using a CQDs-25/NiMOF V catalyst. Most importantly, in diluted CO 2 atmosphere, the yield of CH 4 was almost unchanged and the selectivity of CH 4 over CQDs-25/NiMOF V was higher than that in pure CO 2 . The superior performance of CQDs-25/NiMOF V 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 CH 4 , and (ii) oxygen vacancies can act as the electron trap to capture the photogenerated electrons to react with adsorbed CO 2 on Ni 2+ . This study offers a valuable strategy for designing efficient photocatalysts to convert CO 2 into CH 4 with superior selectivity.