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

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.