Interfacial Triplet-Energy Funneling Directs Energy-Transfer-Mediated Singlet Oxygen Generation for Deep Toluene Mineralization

Abstract

Photocatalytic oxidation is a promising strategy for volatile organic compounds (VOCs) abatement, but incomplete mineralization and carbonaceous intermediate accumulation remain major challenges, especially when conventional charge-transfer pathways generate nonselective radical reactive oxygen species. Selective activation of molecular oxygen toward singlet oxygen (1O2) offers a potential route to controlled oxidation, yet efficient energy-transfer-mediated 1O2 generation in solid-state photocatalysts remains difficult to achieve. Herein, a strongly coupled In(OH)3/ZnGa2O4 heterojunction with an electronic structure consistent with an S-scheme configuration is constructed to investigate interfacial excited-state regulation. Spectroscopic measurements indicate modified excited-state relaxation and a reduced effective singlet–triplet energy separation, which may favor singlet-to-triplet conversion. Combined spectroscopic analyses, quenching experiments, and density functional theory calculations support a proposed interfacial triplet-energy-funneling pathway involving ZnGa2O4-related/interfacial triplet-related states and subsequent energy transfer to adsorbed O2 for 1O2 generation. As a result, the optimized In(OH)3/ZnGa2O4 photocatalyst achieves 98.3% toluene removal and 92.4% mineralization in a continuous-flow gas-phase reactor, together with excellent cycling stability and humidity tolerance. Mechanistic results further suggest that a pathway involving 1O2 contributes to methyl oxidation and the subsequent conversion of oxygenated intermediates, potentially limiting carbonaceous residue accumulation. This work provides an excited-state-engineering strategy for selective molecular oxygen activation and offers a promising route toward efficient, durable, and deeply mineralizing photocatalytic VOCs abatement.