Nanocages of Polymeric Carbon Nitride from Low-Temperature Supramolecular Preorganization for Photocatalytic CO₂ Reduction

Polymeric carbon nitride (CN) is considered as one of the most promising photocatalysts to solve energy and environmental crises by solar-to-fuel conversion. However, the traditional thermal condensation of monomers usually leads to the disorganized agglomerate structure with a high recombination rate of electron–hole pairs. Herein, the effective synthesis of CN using supramolecular complexes of melamine and cyanuric acid with strengthened hydrogen bonding is presented, which are treated under freeze-drying conditions as precursors. The as-prepared CN exhibits a unique nanocage structure, which facilitates the scattering and reflection of incident light and improves the light-harvesting efficiency. The charge transfer and CO₂ adsorption of CNs is improved because of the extended π-delocalization, conjugated aromatic system with more exposed lone-pair electrons and a relatively enlarged specific surface area, caused by the more stretchable and distorted structure of CNs. Consequently, the nanocage-like CN shows improved performance for photocatalytic CO₂ reduction. This work provides a protocol for tailoring the microstructure of CNs via tuning the weak intermolecular interaction, with the aim of designing high-performance CN-based photocatalysts.