Highly crystalline carbon nitride by covalent remedy for CO2 photoreduction

The conventional carbon nitride (NH2-CN) synthesized through high-temperature thermal polymerization, possesses numerous unreacted NH2 or NH groups and abundant in-plane defects. These inherent imperfections trigger a high charge transfer resistance and deficient active sites, which collectively undermine the CO2 photoreduction performance of NH2-CN. To address these limitations, 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) is employed to rectify the in-plane defects of NH2-CN and fabricate highly crystalline TpCN. The light absorption capacity of NH2-CN is enhanced by the O 2p orbital of Tp, which elevates the density of states (DOS) occupation of the valence band. In addition, the facilitated separation of excitons and photogenerated charges both in-plane and interlayer is confirmed through femtosecond transient absorption spectroscopy (fs-TAS) and time-resolved fluorescence spectroscopy (TRPL). Moreover, The Gibbs free energy profile shows that the energy barrier for CO2 hydrogenation reduction to *COOH on TpCN is lowered, thereby augmenting the CO2 photoreduction process. As anticipated, the photoconversion of CO2 to CO for TpCN is 176.9 μmol g–1h−1, which is 18.2 folds that of NH2-CN (9.7 μmol g–1h−1). This work provides a reference for the synthesis of highly crystalline carbon nitride for CO2 photoreduction achieved through covalent repair.