Spatially confined TiO2@MIL-101-Fe S-scheme heterojunctions enable efficient and selective visible-light oxidation of cyclohexane

Construct TiO 2 @MIL-101-Fe S-scheme via impregnation in situ hydrolysis. • Hierarchically distributed TiO 2 maximizes interfacial contact. • Achieves 13.91% cyclohexane conversion and retains high activity after five cycles. • Interfacial fields drive spatial charge separation and preserve redox potentials. • Hierarchical confinement and pore-mouth anchoring enable selective C H activation. The selective photocatalytic oxidation of cyclohexane is a sustainable and environmentally friendly route for KA-oil production, yet it remains limited by low conversion, moderate selectivity, and inefficient charge utilization. This study employed an in-situ TBOT hydrolysis strategy to synthesize a TiO 2 @MIL-101-Fe S-scheme heterojunction with hierarchically distributed TiO 2 nanodomains within the MOF pores, at pore mouths, and on the external surface. This spatially engineered heterostructure enhances photogenerated carrier separation, stabilizes the interface, and improves cyclohexane oxidation efficiency and KA-oil selectivity. The optimized 50 wt% composite material achieved a cyclohexane conversion rate of 14.3%, which was 2.17 times that of the original MIL-101-Fe material. Meanwhile, it still maintained a cyclohexane conversion rate of up to 13.9% and excellent catalytic activity after five cycles. Steady-state and time-resolved photoluminescence, electrochemical impedance, and transient photocurrent measurements reveal accelerated charge separation and prolonged carrier lifetime, enabled by an S-scheme heterojunction with a built-in interfacial electric field. Radical trapping and ESR studies indicate that photogenerated holes and electrons dominate C H activation, with reactive oxygen species contributing synergistically. DFT calculations confirm directional electron transfer and preserved high redox potentials. This work highlights spatially confined S-scheme heterojunctions as a general strategy to enhance photocatalytic efficiency, selectivity, and stability, offering a promising avenue for solar-driven hydrocarbon oxidation. Graphical abstract Download: Download high-res image (215KB) Download: Download full-size image