Engineering Electron/Hole Traps via Atomically Dispersed Bi Sites for Photocatalytic Glycerol Oxidation to Glyceric Acid

Abstract Converting glycerol (GLY), a byproduct of biodiesel production, into high-value product glyceric acid (GLA) under mild conditions shows significant potential for resource utilization. However, this process is hindered by facile C–C bond cleavage and poor oxidation efficiency of the glyceraldehyde (GLAD) intermediate. Herein, we synthesized Bi single atoms (BiSA) incorporated into CdS nanorods with sulfur vacancies (SV) and unsaturated Cd (CdUS) sites. The optimized Bi-CdS achieves a GLA production rate of 1182.99 μmol g–1 h–1 with 61.2% selectivity in the presence of H2O2, roughly 3.4 times higher than that of CdS, while maintaining high stability (over 97.5% activity retention after four cycles). Combined in situ characterizations and density functional theory (DFT) calculations reveal that Cd(s/p)–S(p)–Bi(p) orbital hybridization optimizes the electronic structure, enabling rapid and directional charge carrier transfer. The SV–BiSA sites act as electron (e–) traps, lowering the O–O bond cleavage barrier of H2O2 to generate •OH. Concurrently, the CdUS sites serve as hole (h+) traps (strong Lewis acid sites), selectively adsorbing the terminal –OH of GLY to trigger dehydrogenation and generate the key carbon-centered radical (C•) intermediate. This surface-confined C• radical then undergoes radical–radical cross-coupling with •OH to yield GLA without detectable C–C bond cleavage. This spatially separated e–/h+ trap mechanism enables efficient charge separation and a dual-pathway redox cascade, providing a rational design for atom-precise photocatalysts.