Mechanochemistry-Assisted Solvent-Free Supramolecular Engineering for Atomic-Layered Carbon Nitride Nanosheets with Enhanced Photocatalytic Hydrogen Evolution

Two-dimensional (2D) carbon nitride (C₃N₄) nanosheets hold significant potential for photocatalytic hydrogen evolution, yet their practical application remains hindered by energy-intensive exfoliation processes. Herein, a novel bottom-up synthesis strategy is proposed that combines solvent-free mechanochemistry with thermally controlled polycondensation to fabricate ultrathin 2D carbon nitride nanosheets (2DCN). Structural characterization and theoretical simulations reveal that the mechanochemical synthesis promotes planar-oriented growth of supramolecular crystals through in-plane hydrogen-bond-driven self-assembly, circumventing solvent interference that typically disrupts structural ordering in conventional solvothermal approaches. This unique assembly mechanism simultaneously achieves two critical structural advantages: 1) creation of a 2D architecture with 230.2 m² g⁻¹ surface area and abundant active sites, and 2) formation of interlayer C─N covalent bridges that facilitate cross-layer charge transfer while maintaining atomic layer thickness. The synergistic effects endow the 2DCN with exceptional electron–hole separation efficiency, yielding a remarkable hydrogen evolution rate of 6388 µmol h⁻¹ g⁻¹ under visible light (λ > 420 nm), representing a 20-fold enhancement over bulk C₃N₄ and outperforming most reported C₃N₄-based photocatalysts. This mechanochemistry-driven supramolecular engineering approach establishes a new paradigm for designing dimensionally controlled carbon-nitride materials with optimized photoelectronic properties, potentially extendable to other layered semiconductor systems for energy conversion applications.