From charge equilibrium to catalytic performance: Engineering the Fe2O3-TiO2 interface for optimal S-scheme VOC abatement

Abstract

In this research, Fe2O3-TiO2 S-scheme heterojunction photocatalysts (x-FeT, where x is the molar % of Fe2O3) have been developed and employed for efficient abatement of gaseous toluene. Among the series, 0.25-FeT emerges as the optimal system, exhibiting superior photophysical properties: prolonged carrier lifetime (0.78 ns), narrowed bandgap (3.07 eV), high photocurrent density (27.4 μA cm−2), and low charge-transfer resistance (9.49 Ω). The composite achieves 76.1% toluene degradation with an apparent quantum yield of 3.39 × 10-2 % under optimal conditions (1 ppm toluene, dry air, 100 mL min−1, and 352 nm UV). Key to its performance is the deliberate engineering of the interfacial energetics: UPS and in situ XPS analysis reveal a strong internal electric field (IEF) and band bending characteristic of a robust S-scheme. In situ EPR confirms that the IEF promotes the selective recombination while preserving high-energy electrons in Fe2O3 (−0.34 V vs. NHE) and holes in TiO2 (+3.08 V vs. NHE), enabling prolific generation of •O2- and •OH radicals. In-situ DRIFTS, GC-MS, and DFT simulations elucidate the degradation pathway: hydrogen abstraction forms a benzyl radical, followed by oxidation, culminating in ring-opening and mineralization to CO2 and H2O. Precise control of the Fe2O3:TiO2 ratio tunes the Fermi-level alignment and IEF strength, thereby optimizing the S-scheme charge dynamics for efficient VOC oxidation. The 0.25-FeT heterojunction is thus recommended as a highly effective and rationally designed photocatalytic medium for the abatement of recalcitrant VOCs in air.