Lead-free perovskite Cs2AgBiBr6@g-C3N4 Z-scheme system for improving CH4 production in photocatalytic CO2 reduction

[Display omitted] •Novel lead-free perovskite Cs2AgBiBr6@C3N4-10% type-II heterojunction and Cs2AgBiBr6@C3N4-82% Z-scheme system were successfully developed by in situ assembled g-C3N4 on the surface of Cs2AgBiBr6 nanoparticles.•Through regulating the surface coverage of g-C3N4, the composite samples show highly selective yielding of CO over 90% or CH4 about 70% by Cs2AgBiBr6@g-C3N4-10% type-II system or Cs2AgBiBr6@g-C3N4-82% Z-scheme system, respectively.•The Cs2AgBiBr6@g-C3N4 photocatalyst exhibits superior CH4 production in photocatalytic CO2 reduction, which improves the activity by 26-fold and 10-fold higher than pure Cs2AgBiBr6 and pure g-C3N4, respectively. Solar-energy-driven CO2 conversion into value-added chemical fuels holds great potential renewable energy generation. However, most of the photocatalysts facilitate a two-electron reduction process producing CO, hard for the eight-electron CH4 production pathways which can stockpile more solar energy for further utilization. Herein, we developed an in situ assembly strategy to fabricate the lead-free perovskite Cs2AgBiBr6@g-C3N4 Z-scheme system in toluene and the Cs2AgBiBr6@g-C3N4 type-II heterojunction structure in CH2Cl2. By combining the reducing ability of the conduction band of g-C3N4 and the oxidizing ability of the valence band of Cs2AgBiBr6 perovskite, this Z-scheme system exhibits superior CH4 production in photocatalytic CO2 reduction, in contrast to the high CO selectivity for the heterojunction photocatalysts, which is 10-fold and 16-fold higher than that of pure g-C3N4 and pure CABB, respectively. The stability (four consecutive photocatalytic cycles in solvent methanol as sacrificial reagent without obvious decrease of efficiency) and the mechanism (the prominent activity and the high CH4 production selectivity boosted by Z-scheme system) were demonstrated. In this work, the first report for constructing lead-free halide perovskite Z-scheme and type-II photocatalytic systems for the regulation products selectivity of CO2 reduction reaction provides a promising strategy for the fabrication other types of inorganic/organic heterojunction systems.