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.

ZnO‐MgO composite catalysts were prepared by the coprecipitation method and used for the synthesis of methyl ethyl oxalate (EMO) from dimethyl oxalate (DMO) and ethanol (EtOH). The results of the SEM, XRD, FT‐IR and XPS confirmed that Zn2+ ions were incorporated into the cubic MgO lattice to form the solid solution structure over ZnO‐MgO composites catalysts with 6–18 mol% ZnO. The ZnO‐MgO composite catalysts with a solid solution structure have a large specific surface area, high medium acidic density, and medium basic density according to the results of N2 adsorption‐desorption, pyridine‐IR (Py‐IR) and NH3/CO2 temperature‐programmed desorption (NH3‐TPD/CO2‐TPD). The ZnxMg1‐xO solid solution with 18 mol% ZnO‐MgO (Zn0.18Mg0.82O) catalyst showed the highest catalytic activity with 71.98 % conversion of DMO and 67.36 % selectivity to EMO (DMO: EtOH molar ratio=1 : 2, reaction time=20 min, reaction temperature=80 °C and catalyst amount=1.5 wt%). The high catalytic activity was attributed to the solid solution structure with high medium acidic density and medium basic density. The conversion of DMO showed a positive linear correlation with the medium acidic density and medium basic density according to the correlation between catalytic activity and acidity‐basicity.

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