Interlayer interaction in ultrathin nanosheets of graphitic carbon nitride for efficient photocatalytic hydrogen evolution

Two-dimensional graphitic carbon nitride (g-C₃N₄) nanosheets (CNNS) have attracted intense interest in photocatalysis, given their small thickness and high specific surface area favoring charge transfer and surface reactions. Herein, a facile strategy of breaking and following repolymerizing the heptazine units in bulk g-C₃N₄ (BCN) is developed to synthesize ultrathin CNNS with thickness of 1 nm in relatively high product yield (∼24%). The as-prepared 1 nm-thick CNNS show significantly enhanced photocatalytic performance for hydrogen evolution than BCN and even the 3 nm-thick CNNS acquired by thermal oxidation etching of BCN. It is evidenced that the disordered layer structure of the obtained ultrathin CNNS causes strong interlayer C–N interaction, tunneling electron transport between the C–N layers. Meanwhile, the broken in-plane C–N bonds create more unsaturated N sites in the 1 nm-thick CNNS, facilitating the electron excitation from the occupied states in g-C₃N₄ to its unoccupied states for water reduction reaction.