Ionothermal Synthesis of Covalent Triazine Frameworks in a NaCl‐KCl‐ZnCl2Eutectic Salt for the Hydrogen Evolution Reaction

Abstract Covalent triazine‐based frameworks (CTFs) are typically produced by the salt‐melt polycondensation of aromatic nitriles in the presence of ZnCl 2 . In this reaction, molten ZnCl 2 salt acts as both a solvent and Lewis acid catalyst. However, when cyclotrimerization takes place at temperatures above 300 °C, undesired carbonization occurs. In this study, an ionothermal synthesis method for CTF‐based photocatalysts was developed using a ternary NaCl‐KCl‐ZnCl 2 eutectic salt (ES) mixture with a melting point of approximately 200 °C. This temperature is lower than the melting point of pure ZnCl 2 (318 °C), thus providing milder salt‐melt conditions. These conditions facilitated the polycondensation process, while avoiding carbonization of the polymeric backbone. The resulting CTF‐ES 200 exhibited enhanced optical and electronic properties, and displayed remarkable photocatalytic performance in the hydrogen evolution reaction.