Noble Metal-Free FeOOH/Li_0.1WO₃ Core-Shell Nanorods for Selective Oxidation of Methane to Methanol with Visible-NIR...

Hydroxyl radicals (^•OH) generated in the photocatalytic process are crucial to the conversion of methane (CH₄) to value-added methanol (CH₃OH) at room temperature. However, utilizing noble metal-free catalysts and low-energy photons of solar light, such as visible and near-infrared light (vis-NIR), is difficult to provide more electron states to form ^•OH radicals. Here, we developed FeOOH/Li_0.1WO₃ core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO₃): (1) lithium ions intercalating into the hexagonal tunnels of h-WO₃ to form Li_0.1WO₃ nanorods and (2) using FeOOH-wrapped Li_0.1WO₃ to obtain FeOOH/Li_0.1WO₃ core-shell nanorods. Introduction of lithium induces polaron transition in Li_0.1WO₃, enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when H₂O₂ is selected as an oxidant favors the generation of more ^•OH radicals available for CH₄ oxidation to CH₃OH. Meanwhile, FeOOH with Fe^III as an "electron sink" highly improves the separation of photoinduced electrons and holes in Li_0.1WO₃. Eventually, efficient selective formation of CH₄OH is achieved with remarkable generation rates up to ∼342 and ∼160 μmol g^-1 at visible light (420-700 nm) and NIR light (≥800 nm), respectively. Our finding opens up new possibilities for developing noble metal-free catalysts for solar energy-driven CH₄ conversion to CH₃OH under ambient conditions.