Rational combination of covalent-organic framework and nano TiO2 by covalent bonds to realize dramatically enhanced photocatalytic activity

[Display omitted] •For the first time, COFs and inorganic semiconductor were combined together by covalent bonds.•The combination of COFs and TiO2 efficiently improve photocatalytic H2 evolution.•It was confirmed that the connected covalence can largely improve the separation and transfer of photogenerated charges.•A high 7.6 % AQE was achieved in the TiO2−COFs hybrid system. Rationally combining the advantage of inorganic and organic semiconductors to construct a heterojunction is an effective way to boost the photocatalytic activity of materials, while it is still a great challenge to tightly integrate these two different components together. In this work, for the first time, the TpPa-1-COF, an excellent visible-light harvesting covalent-organic frameworks (COFs), and TiO2 were combined together by covalent bonds to construct a heterojunction. The resulting TiO2-TpPa-1-COF hybrid materials show efficient photocatalytic activity under visible light irradiation. Especially, TiO2-TpPa-1-COF (1:3) exhibits the optimized photocatalytic H2 evolution rate of 11.19 mmol g−1 h-1 and apparent quantum efficiency of 7.6 % at λ = 420 nm, which is 5.3 and 3.0 times higher than the TpPa-1-COF and TiO2/TpPa-1-COF, respectively. Further investigations confirm that the covalent connection between TiO2 and TpPa-1-COF components can largely improve the transfer of photogenerated charges of COF, leading to the efficient H2 evolution activity.