Core–Shell MIL-125-NH2@FeOOH Nanocomposites for Highly Selective Photocatalytic Oxidation of Methane to Formaldehyde in Water Vapor

Formaldehyde (HCHO), a crucial industrial chemical, finds extensive applications across diverse sectors, including household products, commercial materials, aviation, and medical supplies. Methane (CH4), as an abundant C1 resource, presents a promising feedstock for HCHO synthesis. However, the direct conversion of CH4 to HCHO remains challenging due to its inherent chemical inertness, characterized by low polarizability and high C–H bond dissociation energy (439 kJ mol–1), coupled with the high reactivity of intermediate products. The development of efficient strategies for selective CH4 oxidation to high-value HCHO under mild conditions is therefore of significant practical importance. In this study, we developed a series of MIL-125-NH2@FeOOH-x heterostructured photocatalysts (FM-x) through the controlled deposition of FeOOH nanoparticles on MIL-125-NH2 surfaces. Comprehensive characterization and photocatalytic evaluations reveal that the optimized FM-1 catalyst facilitates in situ H2O2 generation and subsequent decomposition into hydroxyl radicals (•OH), enabling efficient CH4 photooxidation. Remarkably, the FM-1 catalyst achieves an exceptional HCHO production rate of 197.79 μmol·gcat–1 with >99.99% selectivity in water vapor, significantly outperforming both pristine FeOOH and MIL-125-NH2 components. This work presents a promising photocatalytic system for selective CH4 conversion, offering new insights into the design of efficient catalysts for C1 chemistry.