Cs 3 Bi 2 Br 9 /g-C 3 N 4 Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO 2 to CO.

Lead-free halide perovskite derivative Cs 3 Bi 2 Br 9 has recently been found to possess optoelectronic properties suitable for photocatalytic CO 2 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 Cs 3 Bi 2 Br 9 and g-C 3 N 4 at different ratios, achieved by growing Cs 3 Bi 2 Br 9 crystals on the surface of g-C 3 N 4 using a straightforward antisolvent crystallization method. The synthesized powders showed enhanced gas-phase photocatalytic CO 2 reduction in the absence of hole scavengers of 14.22 (±1.24) μmol CO g -1 h -1 with 40 wt % Cs 3 Bi 2 Br 9 compared with 1.89 (±0.72) and 5.58 (±0.14) μmol CO g -1 h -1 for pure g-C 3 N 4 and Cs 3 Bi 2 Br 9 , respectively. Photoelectrochemical measurements also showed enhanced photocurrent in the 40 wt % Cs 3 Bi 2 Br 9 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-C 3 N 4 /Cs 3 Bi 2 Br 9 Z-scheme photocatalyst for enhanced CO 2 photocatalytic activity and improved stability.