Fabrication of p- n Heterostructured Photocatalysts with Triazine-Based Covalent Organic Framework and CuInS₂ for High-Efficiency CO₂ Reduction

The application of covalent organic frameworks (COFs) for the photocatalytic reduction of CO₂ is mostly limited by severe charge recombination and low sunlight utilization. Herein, a triazine-based COF with an electron-rich and large π-conjugated system (TCOF) was employed as a building block and integrated with CuInS₂ (CIS) to construct a noble-metal-free and high-efficiency photocatalyst for CO₂ reduction. The in situ growth of CIS nanosheets on TCOF creates a p-n heterojunction, named CIS@TCOF. Compared with TCOF, the CIS@TCOF heterostructure exhibits a dramatically boosted photocatalytic performance in the reduction of CO₂. The produced HCOOH yield over 10 wt % CIS@TCOF can be up to 171.2 μmol g^-1 h^-1 under visible light irradiation with good reproducibility, which is about 3 times as high as that over TCOF. Further in-depth studies indicate that the introduction of CIS not only enhances the visible light utilization but also restrains the recombination of photogenerated electron-hole pairs efficiently and facilitates the photoinduced charge transfer via the p-n heterojunction system due to the unique structural and compositional features. This research shows the great potential of COFs as efficient photocatalytic carbon fixation materials and provides a versatile route to construct semiconductor-COF heterostructures for photocatalysis.