Boosting photocatalytic reduction of the diluted CO2 over covalent organic framework

Photocatalytic reduction of the diluted CO2 into the value-added chemicals and fuels is one of promising approaches for the utilization of anthropogenic CO2, but it is still great challenges to achieve high photocatalytic efficiency. Herein, we reported covalent organic framework nanosheets (CON) containing bis-chelating Ni coordination sites for selective photoreduction of the diluted CO2 (15 %). X-ray absorption and X-ray photoelectron spectroscopy fine structure analysis corroborate chemical environments of Ni active sites. Strong bis-chelation with metal active sites improves the stability and conjugation degree of CON, which promise high CO production of 8721 μmol g−1 in 2 h with 95 % selectivity over H2 generation in the diluted CO2. The apparent quantum efficiency over Ni-TP-CON is 1.2 % upon 420 nm irradiation with CO turnover number of 28.7 in 5 h in the atmosphere of 15 % CO2. The experimental and theoretical results show that bis-chelating metal coordination units in CON are more favorable active sites for the diluted CO2 photoreduction when compared with mono-chelating coordination mode, which effectively reduces the energy barrier, expedites the formation of reaction radicals *COOH and facilitates the charge transportation. Our findings provide prospects toward the application of bis-chelating metal coordination modes in solar-to-chemical energy conversion.