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

Two‐dimensional (2D) carbon nitride (C 3 N 4 ) 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 m 2 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 C 3 N 4 and outperforming most reported C 3 N 4 ‐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.