Light-Assisted Conversion of Aqueous CO₂ (Bicarbonate) into Surface Reduced Species by a CeO₂-SnO₂ Hybrid

Understanding the interfacial chemistry of bicarbonate at oxide surfaces is central to advancing photodriven carbon transformation processes. Here, a CeO₂-SnO₂ hybrid oxide synthesized via a simple solid-state route is investigated as a model system for UV-visible-light-assisted bicarbonate conversion at a fundamental, proof-of-concept level. Surface-sensitive ATR-FTIR spectroscopy reveals a progressive enhancement of formate-related vibrational features under UV-visible-light irradiation of the hybrid material, whereas dark-treated samples and physical mixtures of the parent oxides remain dominated by overlapping carbonate- and water-related absorptions. Bayesian inference applied to overlap-corrected FTIR band areas, independently corroborated by unsupervised self-organizing map analysis of the full spectral fingerprints, indicates that the sustained accumulation of formate-like species is intrinsic to the hybrid surface chemistry rather than inherited from the individual oxides. Total organic carbon measurements show no measurable accumulation of dissolved organic species, consistent with preferential stabilization of reduced carbon species at the solid-liquid interface, while inorganic carbon concentrations decrease significantly between 24 and 48 h of irradiation, a trend supported by both classical statistics and Bayesian inference (posterior probability P ≈ 0.97) and plausibly associated with progressive bicarbonate consumption through surface-mediated pathways. Thermal regeneration experiments further demonstrate partial reversibility of the irradiation-induced spectral features, supporting their surface-bound nature. Taken together, these results establish CeO₂-SnO₂ hybrids as useful model systems for fundamental studies of bicarbonate-to-formate-like surface processes and highlight the value of probabilistic and unsupervised analytical frameworks for resolving subtle, irradiation-driven interfacial transformations.