Covalent　triazine-based　frameworks　(CTFs)　are　typically　produced　by　the　salt-melt　polycondensation　of　aromatic　nitriles　in　the　presence　of　ZnCl2.　In　this　reaction,　molten　ZnCl2　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-ZnCl2　eutectic　salt　(ES)　mixture　with　a　melting　point　of　approximately　200　°C.　This　temperature　is　lower　than　the　melting　point　of　pure　ZnCl2　(318　°C),　thus　providing　milder　salt-melt　conditions.　These　conditions　facilitated　the　polycondensation　process,　while　avoiding　carbonization　of　the　polymeric　backbone.　The　resulting　CTF-ES200　exhibited　enhanced　optical　and　electronic　properties,　and　displayed　remarkable　photocatalytic　performance　in　the　hydrogen　evolution　reaction.　©　2022　Wiley-VCH　GmbH.