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

Hydroxyl radicals (OH) generated in the photocatalytic process are crucial to the conversion of methane (CH) to value-added methanol (CHOH) 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/LiWO core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO): (1) lithium ions intercalating into the hexagonal tunnels of h-WO to form LiWO nanorods and (2) using FeOOH-wrapped LiWO to obtain FeOOH/LiWO core-shell nanorods. Introduction of lithium induces polaron transition in LiWO, enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when HO is selected as an oxidant favors the generation of more OH radicals available for CH oxidation to CHOH. Meanwhile, FeOOH with Fe as an "electron sink" highly improves the separation of photoinduced electrons and holes in LiWO. Eventually, efficient selective formation of CHOH is achieved with remarkable generation rates up to ∼342 and ∼160 μmol g 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 CH conversion to CHOH under ambient conditions.