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 CN interaction, tunneling electron transport between the CN layers. Meanwhile, the broken in-plane CN 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.
