Self-assembly hybridization of COFs and g-C3N4: Decipher the charge transfer channel for enhanced photocatalytic activity

[Display omitted] •A metal-free self-assembled covalent organic framework (TpMa)/ g-C3N4 (CN) heterojunction was prepared via π-π interaction.•A built-in electric field was formed at the interface of TpMa and CN.•The introduction of donor–acceptor conjugated TpMa leads to the enlarged visible-light absorption of CN.•TpMa/CN shows enhanced photocatalytic activity under visible-light irradiation. Organic semiconductors have been recognized as a new generation of photocatalysts for pollutants degradation and energy production. Herein, organic heterojunction (TpMa/CN) consisting of carbon nitride and β-ketoenamine-based covalent organic framework is fabricated via a controllable self-assembly approach. The as-prepared TpMa/CN heterojunctions show enlarged visible-light absorption. The optimum TpMa/CN-5 photocatalyst achieves the highest photocatalytic activity towards tetracycline degradation, and its photocatalytic degradation rate is improved by 2.3 and 4.3 times than TpMa and CN, respectively. As a multifunctional photocatalyst, TpMa/CN-5 sample also shows remarkable photocatalytic activity for hydrogen peroxide production (880.494 μM h−1), which is 49 times higher than that of CN. Experimental and theoretical investigations indicate that a built-in electric field is formed at the interface of composite, which enables an accelerated charge transfer and separation. This work develops an effective strategy to design difunctional photocatalyst and deciphers the electronic properties and mechanisms of g-C3N4-based organic photocatalysts, which spurs further interests for organic heterojunction photocatalysts in the future.