Covalently integrated TiO₂-COF heterostructure with promoted intramolecular charge transfer for effective photocatalytic hydrogen production

Constructing a tight heterojunction between inorganic semiconductor and covalent organic framework (COF) to boost photocatalytic performance is a strategy with great potential but also extremely challenging in terms of synthesis. Herein, a series of covalently integrated TiO₂-TpPy-COF S-scheme heterostructures with a closely-contacted interface were synthesized by a simple hydrothermal reaction between aldehyde modified TiO₂ (CHO-TiO₂) nanosheets and TpPy-COF. The resulting TiO₂-TpPy-COF (1:2) composite demonstrates markedly enhanced activity with a hydrogen evolution rate (HER) of 8203.8 μmol g⁻¹ h⁻¹, which is 9.1 times that of TpPy-COF, 8.9 times that of the physical mixture, and 6.9 times that of TiO₂/TpPy-COF which is constructed by aminopropyltriethoxysilane (APTES) modified TiO₂(APTES-TiO₂). The superior performance is ascribed to the synergistic effects of the strong covalent interfacial coupling and the formed S-scheme heterojunction, which ensures efficient electron transfer at interface, spatial separation of carriers, and retention of high-energy electrons. This rational covalent binding strategy provides a scalable prospect for constructing other efficient COF-based heterostructure photocatalysts.