Precursor-Concentration-Controlled Interface Engineering in Bi2O3/Bi2O2CO3/BiOCOOH Nanostructures for Improved CO2 Photoreduction

Engineering heterophase interfaces is an effective strategy for regulating charge dynamics, reactant chemisorption, and reaction pathways in photocatalytic CO2 reduction. Herein, Bi2O3/Bi2O2CO3/BiOCOOH heterophase photocatalysts were synthesized through a simple ethanol-mediated solvothermal method by controlling the precursor concentration. Lower precursor concentrations promoted the formation of crystalline Bi2O3 intimately integrated with semicrystalline Bi2O2CO3/BiOCOOH domains, whereas higher concentrations yielded predominantly crystalline BiOCOOH nanoflakes. The optimized BCH-0.05 catalyst exhibited enhanced light harvesting, suppressed electron–hole recombination, and reduced interfacial charge-transfer resistance. Furthermore, in situ EPR analysis revealed the formation of reactive Bi-associated paramagnetic species through H2O-induced surface hydroxylation, while the chemisorbed CO2 efficiently accepted photogenerated electrons from the Bi active sites under illumination, thereby facilitating CO2 activation and reduction. These properties contributed to the high activity of BCH-0.05, achieving CO and CH4 production rates of 27.83 ± 0.94 and 3.47 ± 0.48 μmol/g-h, respectively, corresponding to an 8.5-fold higher surface-area-normalized activity than the BiOCOOH-dominant BCH-0.4 catalyst. In situ DRIFTS analysis identified that CO was produced through Bi–COO–Bi and Bi–CO intermediates, whereas CH4 formation proceeded via bidentate CO32– and Bi–OCH3 intermediates. Although photocatalysis gradually induced crystallization through structural reconstruction, the Bi2O3/Bi2O2CO3/BiOCOOH heterophase remained intact, preserving efficient interfacial charge transfer and high photocatalytic activity.