Efficient photosynthesis of hydrogen peroxide by triazole-modified covalent triazine framework nanosheets

Two-dimensional (2D) polymeric semiconductors, especially covalent triazine framework (CTF) nanosheets with aromatic triazine linkages are emerging as attractive metal-free photocatalysts owing to their predictable structures, good semiconducting properties, and high stability. However, the quantum size effect and ineffective electron screening of 2D CTF nanosheets cause an enlargement of electronic band gap and high excited electron-hole binding energies, which lead to low-level enhancements in photocatalytic performance. Herein, we present a novel triazole groups functionalized CTF nanosheet (CTF-LTZ) synthesized by facile combination of ionothermal polymerization and freeze-drying strategy from the unique letrozole precursor. The incorporation of the high-nitrogen-containing triazole group effectively modulates the optical and electronic properties, resulting in narrowed bandgap from 2.92 eV for unfunctionalized CTF to 2.22 eV for CTF-LTZ and dramatically improved charge separation, as well as highly-active sites for O₂ adsorption. As a result, CTF-LTZ photocatalyst exhibits excellent performance and superior stability in H₂O₂ photosynthesis, with a high H₂O₂ production rate of 4068 μmol h^-1 g^-1 and a remarkable apparent quantum efficiency of 4.5 % at 400 nm. This work provides a simple and effective approach for rational design highly-efficient polymeric photocatalysts for H₂O₂ production.