Engineered interface coverage and precise cocatalyst placement in MOF-derived heterojunction photocatalysts for selective methane oxidation

While the rational fabrication of heterojunction photocatalysts with tunable interfaces and precise location control of cocatalysts holds great promise for enhanced photocatalysis, the synergistic integration of these parameters remains a substantial challenge. Herein, a series of metal–organic framework (MOF) composites with compact interfaces and customizable interface coverage are designed by epitaxial growth of ZIF-8 on the surface of MIL-125-NH₂, yielding ZIF-8_m/MIL-125-NH₂ (m = 21, 35, 65, representing the coverage percentage of ZIF-8 on the MIL-125-NH₂ surface). These composites are then converted into ZnO/TiO_x heterojunctions through a two-step thermal treatment, termed ZTO-m, for photocatalytic CH₄ oxidation. The results reveal that the interface coverage in ZTO-m plays critical roles in charge separation, where ZTO-65 gives the best activity. With ZTO-65 as a basis, the cocatalysts, Au clusters and CoO_x species, are respectively positioned onto TiO_x and ZnO. The targeted positioning of cocatalysts not only improves charge separation but also facilitates O₂ activation. As a result, the resulting Au-Co-ZTO demonstrates excellent activity toward liquid oxygenate production, achieving 1723.5 μmol g⁻¹ h⁻¹ with a selectivity of 99%, in photocatalytic CH₄ oxidation.