A multi-centre metal-free COF@g-C3N4 catalyst assembled with covalent bonds for photocatalytic CO2 reduction†

Abstract

Photocatalytic carbon dioxide (CO₂) reduction technology using solar energy can convert carbon dioxide into fuels and chemicals, and is one of the most effective strategies to mitigate the energy crisis and greenhouse effect. In recent years, covalent organic frameworks (COFs) have flourished due to their unique advantages and have received extensive attention in the field of photocatalytic reduction of CO₂. Here, we use the pre-designability of COFs to preserve the aldehyde group at the end of the COF skeleton by the motif strategy, while ensuring its excellent photosensitivity. This facilitates further assembly with amino-terminated g-C₃N₄ through covalent bonding, resulting in composite catalysts (COF@g-C₃N₄). This COF@g-C₃N₄ material can take g-C₃N₄ as the active center to undertake the main catalytic reaction function, COF as the photosensitive center to absorb light energy and generate photogenerated carriers, and covalent bonds as electron transport bridges, effectively facilitating the transfer of electrons. These three components operate independently yet synergistically to accomplish the photocatalytic CO₂ reduction reaction. In addition, by integrating theoretical calculations with experimental results, the electron transfer and reaction mechanism in the photocatalytic process of COF@g-C₃N₄ were thoroughly explored, and a rational photocatalytic process was proposed. This multi-center metal-free catalyst, COF@g-C₃N₄, not only exhibits good photocatalytic performance but also is more economical and environmentally friendly, which is worthy of attention.