Oxygenated Triazine‐Heptazine Heterostructure Creates an Enormous Ascension to the Visible Light Photocatalytic Hydrogen Evolution Performance of Porous C3N4 Nanosheets

A highly efficient g‐C3N4 photocatalyst is developed by a novel one‐pot thermal polymerization method under a salt fog environment generated by heating the aqueous solution of urea and mixed metal salts of NaCl/KCl, namely SF‐CN. Thanks to the synergistic effect of the oxygenation and chemical etching of the salt fog, the obtained SF‐CN is an oxygenated ultrathin porous carbon nitride with an intermolecular triazine‐heptazine heterostructure, meanwhile, shows enlarged specific surface area, greatly enhanced absorption of visible light, narrowed band gap with a lower conduction band, and an increased photocurrent response due to the effective separation of photogenerated holes and electrons, comparing to those of pristine g‐C3N4. The theoretical simulations further reveal that the triazine‐heptazine heterostructure possesses better photocatalytic hydrogen evolution (PHE) capability than pure triazine and heptazine carbon nitrides. In turn, SF‐CN demonstrates an excellent visible light PHE rate of 18.13 mmol h−1 g−1, up to 259.00 times of that of pristine g‐C3N4. Porous g‐C3N4 ultrathin nanosheets with a distinct intermolecular triazine‐heptazine heterostructure have been judiciously developed via a facile one‐pot thermal polymerization technique under a salt fog environment of urea and mixed metal salts. Benefitting from the unique structural merits, the resulting g‐C3N4 photocatalyst demonstrates a very high‐efficient visible light hydrogen production activity.