Effect of exposed active sites of semi-amorphous Fe-BTC on photocatalytic CO2 cycloaddition reaction under ambient conditions

The capture and efficient use of CO2 is an important issue because CO2 emissions by burning fossil fuels is a primary cause of greenhouse effect. One of the best solutions to this problem is to convert CO2 into valuable organic products through clean technologies. In this work, semi-amorphous material Fe-BTC with highly efficient photocatalytic CO2 cycloaddition reactions was prepared by adopting two strategies: the coordination of Fe ions with H2BDC affected by different solvents and the defect engineering controlled by relatively low temperatures. Combined with FT-IR, SEM, TGA and BET analysis, the two strategies change the properties of Fe-BTC to a certain extent. The NH3-TPD analysis confirmed that the Fe-BTC prepared in different solvents and temperatures had different number of Lewis acid sites, and more Lewis acid sites were beneficial to improve the yield of the reaction. In addition, DFT theoretical calculation also verified that the defective Fe-BTC obtained by relatively low temperature would expose more active sites. Finally, light also played an irreplaceable role in this reaction, as photogenerated charge carriers produced under light excitation could greatly activate CO2 and epoxides, thereby reducing the energy barrier of the reaction. Based on the above photocatalytic experimental results and characterization, the possible mechanism was proposed and explained. This work would provide an economical and effective strategy to obtain more active sites for CO2 cycloaddition reaction under mild conditions.