Novel covalent triazine frameworks incorporating thiophene moiety for enhanced photocatalytic hydrogen production

The increasing global demand for renewable and sustainable energy has made the development of clean and renewable energy sources crucial in addressing both global energy security and environmental challenges. Among all fuel options, hydrogen stands out due to its high energy density and emission of only water when burned, making it a highly regarded clean and promising alternative energy source. Moreover, the utilization of solar energy to produce hydrogen by efficient photolysis of water is a very promising strategy. Covalent triazine frameworks (CTFs) materials are a novel class of porous organic polymer materials that have garnered significant attention from researchers due to their exceptional characteristics, including high specific surface area, porosity, stability, and tunable active sites. In the realm of photocatalysis, CTFs exhibit remarkable light responsiveness owing to their planar π-conjugated structure and π-π stacking arrangement, which facilitate efficient charge carrier separation and migration within the material. The application of CTFs in the field of photocatalysis has received extensive attention. However, the reaction conditions for traditional high temperature ionic thermal synthesis of CTFs are harsh, which makes the material lose its photoresponsiveness. Consequently, the design and synthesis of CTF materials with exceptional photocatalytic properties remain highly challenging. The ideal photocatalyst should possess high light absorption capability and efficient carrier separation and transport efficiency. In order to enhance these properties, apart from altering the catalyst material, the incorporation of an electron donor-acceptor (D-A) junction is also a highly effective strategy. The D-A junction can precisely regulate the electron affinity between the D and A units at a molecular level to achieve charge separation and transfer. Moreover, the structural characteristics of the catalyst can significantly increase the number of active interfaces, thereby further enhancing its charge participation capability in the reaction. In CTFs materials, D-A structures also show extensive potential due to the excellent tunability of the CTFs skeleton structure. By adjusting the structure and proportion of D and A units, it becomes possible to modify the distribution position of LUMO and HOMO levels within the material, thereby accurately controlling the band structure and photoelectric properties at a molecular level. This precise control facilitates enhanced charge separation, transport, and ultimately leads to more efficient photocatalytic reactions. A novel CTFs was synthesized via amidine polycondensation under mild conditions, and D-A junctions were constructed at the molecular level through the controlled design of monomers to improve the photocatalytic hydrogen production. Herein, we successfully constructed three types of CTFs (CTF-PP, CTF-PTP and CTF-TPT). The photocatalytic hydrogen production activity of D-A type CTF-TPT with stronger electron donor capacity was as high as 15650 μmol/(g·h). The photocatalytic hydrogen production activity of CTF-PP without electron donor group was only 6172 μmol/(g·h). In addition, by means of electrochemical analysis and calculation, it has been determined that the thiophene moiety can serve as an effective electron donor unit, while the triazine moiety can function as an effective acceptor unit. Moreover, the incorporation of a donor-acceptor junction enables precise regulation of the bandgap position in CTFs at the molecular level, thereby facilitating charge separation and transport processes and ultimately enhancing photocatalytic performance.