Boosting Water Vapor-Assisted Methane Photooxidation Over S-Scheme MIL-125-NH₂(Ti)/WO₃ Heterojunction Photocatalysts

Abstract

The photocatalytic conversion of methane (CH₄) into value-added oxygenates without overoxidation under mild conditions remains a significant challenge in heterogeneous catalysis. Here, we rationally designed a series of S-scheme MIL-125-NH₂(Ti)/WO₃-x (MW-x) heterostructures via electrostatic self-assembly for efficient CH₄ photooxidation. The direct S-scheme charge transfer mechanism at the MIL-125-NH₂(Ti)/WO₃ interface enhances spatial separation of photogenerated electron-hole pairs, thereby optimizing redox efficiency. The WO₃ nanosheets, with their strong oxidative capacity, promote in situ H₂O₂ generation from water, whereas the Ti³⁺/Ti⁴⁺ redox centers in MIL-125-NH₂(Ti) catalyze H₂O₂ decomposition into hydroxyl radicals (·OH). These ·OH species efficiently activate the C–H bonds of adsorbed CH₄, yielding methyl radicals (·CH₃). The concurrent generation and coupling of ·OH and ·CH₃ radicals drive selective formation of C₁ oxygenates. Notably, the optimized MW-3 catalyst exhibits exceptional performance, achieving a total C₁ oxygenate yield of 502.17 μmol·g_cat⁻¹ under ambient conditions, surpassing most reported photocatalysts for CH₄ conversion.

Keywords

C₁ liquid products / methane / photooxidation / S-scheme heterojunction

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