Boosting CO ₂ Conversion Efficiency Using Bi ₂ S ₃ Nanocatalysts with Tailored Platelet, Polyhedral, and Flower-Like Structures

This study investigates the influence of varying Bi-metal contents (58%, 66%, and 81%) on the optical and impedance characteristics of bismuth sulfide (Bi 2 S 3 ) nanoparticles synthesized via a wet chemical method. The catalysts exhibit a distinct morphology transition from platelets to polyhedral and flower-like nanosheets, establishing strong structure–property correlations for CO 2 photoreduction. Raman and FTIR spectroscopy revealed distinctive vibrational modes, whereas XRD verified the production of orthorhombic phases. At greater Bi loading, SEM showed improved surface area and crystallinity. Reduced crystallite size and quantum confinement (band gap adjusted from 2.07 to 2.11 eV) were compatible with the blue-shifted absorption edge observed in UV–vis spectra upon Bi enrichment. Dielectric and impedance measurements indicated reduced energy loss and charge-transfer resistance, supporting efficient carrier transport and enhanced photocatalytic stability. Photocatalytic reduction of CO 2 was investigated for 5 h under a xenon solar simulator (ABET 2000, 150 mW·cm –2, λ > 420 nm) in a sealed quartz reactor containing 50 mg catalyst in 50 mL H 2 O, with continuous CO 2 purging in a sealed 12.5 mL reaction container. The highest yields were obtained by the Bi 2 S 3 sample with 81% Bi, which produced 284.22 μmol CH 3 OH and an apparent quantum yield (AQY) of 0.114% (measured at 1.5 h). With approximately 88% activity retention after five reuse cycles and a competitive AQY compared to several recently reported Bi-based photocatalysts under visible light, compositionally tailored Bi 2 S 3 demonstrates strong potential as a practical and scalable catalyst for solar-to-fuel conversion.