The atomically thin nanosheets of graphitic carbon nitride (g-C 3 N 4 ) with mesopores have been successfully exfoliated with supercritical CO 2 (scCO 2 ). The thickness of the assynthesized samples could be directly tailored by simply regulating the scCO 2 pressure. The obtained bilayer mesoporous g-C 3 N 4 nanosheets doped with monatomic Co through a microwaveassisted 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 H 2 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.

Construction of Z‐scheme photocatalyst is an effective approach for using solar energy to produce hydrogen during water splitting. Herein, 2D/2D WO3/g‐C3N4 heterojunction photocatalyst was synthesized by a convenient and green method including exfoliation and heterojunction procedures, in the reverse microemulsion system via supercritical carbon dioxide (scCO2). The resultant W/CN‐10.3 composite exhibited enhanced photocatalytic activities towards the hydrogen evolution during water splitting with a hydrogen evolution rate of 688.51 μmol g−1 h−1, which was more than 16 times higher than bulk g‐C3N4 with the same loading amount of Pt as cocatalyst. Due to its effective separation of photogenerated carriers and prolonged lifetime, more photoexcited electrons with high reduction ability could contribute to the production of H2. Possible formation mechanism of 2D‐2D WO3/g‐C3N4 nanosheets via scCO2 in the reverse microemulsion system by the one‐pot method has been proposed. This work provides an efficient and green strategy to synthesize 2D‐2D heterojunction for the utilization in solar‐to‐fuel conversion.

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