Tailoring chemical structures and intermolecular interactions of melem intermediates for highly efficient photocatalytic hydrogen evolution of g-C₃N₄

Additional pre-modification on precursors or post-treatment on polymeric graphitic carbon nitride (g-C₃N₄) induces variation in physicochemical and optoelectronic properties. However, the enhancement is still limited because the treatment is done either before the formation of the repeated units melem or after the formation of the polymer plane. Accordingly, the tailoring of the crystalline phase, nanomorphology and electronic band structure on g-C₃N₄ is less efficient. Herein, we propose a novel strategy to obtain highly efficient g-C₃N₄ by tailoring of molecular structures and intermolecular interactions of intermediates. A protonated melem derived g-C₃N₄ (PM-CN) is fabricated via recalcination of HNO₃-treated melem intermediates. The HNO₃ treatment induces oxygen-containing functional groups on melem molecules and NO₃^– inserted into adjacent stacking layers, which results in a favorable crystalline order. In addition, porous structure with large specific surface area is obtained since release of gases occurs during recalcination of HNO₃-treated melem. These features endow favorable charge transport conditions and large driving force for hydrogen production. The prepared PM-CN exhibits a promising photocatalytic activity under visible light with a hydrogen production rate up to 3.085 mmol h⁻¹ g⁻¹. This study provides a novel strategy for optimize the crystalline phase and nanostructure of polymers for energy-related applications.