Abstract
The direct and selective transformation of naturally abundant methane (CH4) into high-value-added oxygenates, e.g., methanol, ethanol, and formic acid, is one of the "Holy Grails" in chemistry and chemical productions. However, complex mixtures of products, often due to over-oxidations, make such transformations highly challenging. Herein, gallium nitride (GaN), a methane-active semiconductor, catalyzes the photooxidation of methane and empowers the fine-controlling of chemoselectivity toward methanol and formic acids, simply by regulating the O2 content in water. In contrast to previous methods, no overoxidation products (CO2 and CO) were observed in this process. Mechanistic investigations and the corresponding quantitative experiments indicated that the controllable generation of moderately reactive oxygen radicals (•OOH and •OH) in combination with the direct methane activation triggered by GaN is responsible for the highly selective reactivity and tunability through a photo-generated radical process.