Comprehensive insight into the support effect of graphitic carbon nitride for zinc halides on the catalytic transformation of CO2 into cyclic carbonates

Chemical fixation of CO2 to high-valued chemicals is currently a significant research topic in both the environment and chemistry, and cycloaddition of CO2 with epoxides is regarded as a sustainable route for the manufacture of cyclic carbonates. Homogeneous catalysts including ionic liquids and organic metal complexes suffer from difficulty in catalyst-product separation despite their excellent catalytic activities. In this work, we utilized graphitic carbon nitride (g-C3N4) as a novel support to immobilize zinc halides (ZnX2) through a simple preparation method. Based on the detailed design of the synthesis of ZnX2/g-C3N4, the chemical bonding information of ZnX2 on g-C3N4 was comprehensively investigated by XPS and FT-IR techniques. In addition to activation of CO2, g-C3N4 can anchor zinc halides via interaction between zinc and nitrogen, thereby effectively alleviating potential leaching of zinc halides. As heterogeneous catalysts, ZnX2/g-C3N4 materials showed good catalytic activities in the cycloaddition reactions of CO2 with propylene oxide. Furthermore, a wide range of epoxides can be converted to the corresponding cyclic carbonate with good selectivities (>93%) and moderate conversions (50-88%).