Lead-free halide perovskites and Bi-BTC frameworks: Engineering S-scheme heterojunctions for photocatalytic CO2 conversion

The photochemical transformation of CO 2 into valuable hydrocarbon fuels is a promising strategy to reduce anthropogenic CO 2 emissions whilst addressing the escalating energy demand in a sustainable manner. Lead-free halide perovskite photocatalysts show potential for CO 2 reduction, yet limitations such as slow charge kinetics, weak redox capability, rapid electron-hole annihilation, and limited CO 2 adsorption capacities hamper their advancement. In this study, an innovative S-scheme heterojunction composite based on lead-free Cs 3 Sb 0.5 Bi 1.5 Cl 4 Br 5 perovskite (CSBX) and a bismuth organic framework (BOF) was engineered for robust gas phase CO 2 photoreduction. Under simulated solar irradiation, the optimised CSBX/BOF heterostructure afforded a high photocatalytic activity without the need for a scavenger or cocatalyst, achieving CO and CH 4 yields of 135.22 and 13.52 μmol g –1 , respectively. The S-scheme charge transfer with a built-in electric field was cooperatively substantiated by comprehensive experimental characterisation studies and density functional theory (DFT) simulations. Further, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments unveiled the key reaction intermediates and plausible reaction pathway. This work expounds on the synergistic effects of the S-scheme mechanism and highlights its effectiveness in circumventing the traditional limitations of lead-free halide perovskite photocatalysts. These findings provide valuable insights for the development of efficient lead-free halide perovskite-based photocatalysts for CO 2 conversion and other challenging photocatalytic transformations. • S-scheme heterojunction of CSBX/BOF was constructed via in-situ growth strategy. • IEF at the interface enables effective directional electron transfer and charge separation. • S-scheme charge transfer validated via experiments and DFT simulation. • In situ DRIFTS revealed reaction intermediates and plausible reaction pathway.