Unveiling Hydroxyl Radical Mediated Anaerobic Photocatalytic Dehydrogenation of HMF via Sulfur-Vacancy-Engineered Fe2O3/ Sv-CdIn2S4 Nanostructured S-Scheme Heterojunction

Abstract

Selective photocatalytic oxidation of biomass-derived platform molecules demands precise control over reactive oxygen species to suppress nonselective overoxidation pathways. Herein, we report hierarchically nanostructured sulfur vacancy-engineered Fe2O3/Sv-CdIn2S4 S-scheme heterojunction that achieves 88% DFF yield with 99% selectivity upon visible-light irradiation under anaerobic conditions in aqueous medium. Systematic sulfur vacancy engineering increases DFF yield from 17% for bulk CdIn2S4 to 65.5% for Sv-CdIn2S4 and selectivity from 75% to 99%. Furthermore, coupling with Fe2O3 nanocubes to construct a well-defined nanoscale heterointerface creates highly active nanocatalytic center which boosts performance via an internal electric field that directs nanoscale interfacial charge transfer and enhances charge separation efficiency. Radical scavenging and EPR studies reveal that anaerobic conditions enable •OH-mediated oxidation derived from interfacial water. While pristine Sv-CdIn2S4 operates via surface-confined •OH species and direct hole transfer, coupling with Fe2O3 establishes nanoscale S-scheme architecture that preserves highly oxidative holes for bulk water oxidation to •OH radicals. This upgraded pathway selectively terminates at the aldehyde stage, whereas molecular oxygen introduces competing •O2– species that promote overoxidation to carboxylic acids. This finding challenges the conventional requirement for molecular oxygen in photocatalytic oxidation, demonstrating that water-derived •OH radicals are sufficient and superior for selective alcohol-to-aldehyde transformations. This anaerobic photocatalytic approach extends to other important biomass-derived alcohols, offering an oxidant-free pathway for selective aldehyde production that advances green biomass upgrading and circular chemical synthesis. Collectively, this work establishes design principles for noble metal-free nanocatalysis by demonstrating that engineering sulfur vacancies as electronic modulators within nanostructured S-scheme pathways enables anaerobic operation to suppress nonselective radical chemistry, facilitating the efficient valorisation of biomass-derived platform chemicals under extremely mild, oxidant-free conditions.