Synthesis of Atomically Thin g-C3N4 Nanosheets via Supercritical CO2 Doping with Single-Atom Cobalt for Photocatalytic Hydrogen Evolution.

The atomically thin nanosheets of graphitic carbon nitride (g-C3N4) with mesopores have been successfully exfoliated with supercritical CO2 (scCO2). The thickness of the as-synthesized samples could be directly tailored by simply regulating the scCO2 pressure. The obtained bilayer mesoporous g-C3N4 nanosheets doped with monatomic Co through a microwave-assisted approach havve been employed as single-atom catalysts to enhance the photocatalytic hydrogen evolution performance. The as-prepared Co/P/CN-sc sample exhibited a boosted H2 production performance due to its unique structural advantages by exposing more active sites and facilitating the separation of charge carriers. Based on X-ray photoelectron spectroscopy, steady-state and time-resolved photoluminescence spectroscopy, X-ray absorption fine structure measurement, and density functional theory (DFT) calculations, a possible mechanism has been proposed. The work shows a new perspective for designing an inexpensive photocatalyst with a unique structure through a facile and green approach for photocatalytic hydrogen evolution.