Cs3Bi2Br9/g-C3N4 Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO2 to CO.

Lead-free halide perovskite derivative Cs3Bi2Br9 has recently been found to possess optoelectronic properties suitable for photocatalytic CO2 reduction reactions to CO. However, further work needs to be performed to boost charge separation for improving the overall efficiency of the photocatalyst. This report demonstrates the synthesis of a hybrid inorganic/organic heterojunction between Cs3Bi2Br9 and g-C3N4 at different ratios, achieved by growing Cs3Bi2Br9 crystals on the surface of g-C3N4 using a straightforward antisolvent crystallization method. The synthesized powders showed enhanced gas-phase photocatalytic CO2 reduction in the absence of hole scavengers of 14.22 (±1.24) µmol CO g-1 h-1 with 40 wt % Cs3Bi2Br9 compared with 1.89 (±0.72) and 5.58 (±0.14) µmol CO g-1 h-1 for pure g-C3N4 and Cs3Bi2Br9, respectively. Photoelectrochemical measurements also showed enhanced photocurrent in the 40 wt % Cs3Bi2Br9 composite, demonstrating enhanced charge separation. In addition, stability tests demonstrated structural stability upon the formation of a heterojunction, even after 15 h of illumination. Band structure alignment and selective metal deposition studies indicated the formation of a direct Z-scheme heterojunction between the two semiconductors, which boosted charge separation. These findings support the potential of hybrid organic/inorganic g-C3N4/Cs3Bi2Br9 Z-scheme photocatalyst for enhanced CO2 photocatalytic activity and improved stability.

Lead-Free Halide Perovskite Cs2AgBiBr6/Bismuthene Composites for Improved CH4 Production in Photocatalytic CO2 Reduction.

CO2 photocatalytic conversion into value-added fuels through solar energy is a promising way of storing renewable energy while simultaneously reducing the concentration of CO2 in the atmosphere. Lead-based halide perovskites have recently shown great potential in various applications such as solar cells, optoelectronics, and photocatalysis. Even though they show high performance, the high toxicity of Pb2+ along with poor stability under ambient conditions restrains the application of these materials in photocatalysis. In this respect, we developed an in situ assembly strategy to fabricate the lead-free double perovskite Cs2AgBiBr6 on a 2D bismuthene nanosheet prepared by a ligand-assisted reprecipitation method for a liquid-phase CO2 photocatalytic reduction reaction. The composite improved the production and selectivity of the eight-electron CH4 pathway compared with the two-electron CO pathway, storing more of the light energy harvested by the photocatalyst. The Cs2AgBiBr6/bismuthene composite shows a photocatalytic activity of 1.49(±0.16) µmol g-1 h-1 CH4, 0.67(±0.14) µmol g-1 h-1 CO, and 0.75(±0.20) µmol g-1 h-1 H2, with a CH4 selectivity of 81(±1)% on an electron basis with 1 sun. The improved performance is attributed to the enhanced charge separation and suppressed electron-hole recombination due to good interfacial contact between the perovskite and bismuthene promoted by the synthesis method.