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.