Intensifying Internal Electric Field on ZnO Nanoplates with Polar Surface Exposure and Cu Doping for Efficient Photocatalytic Methane Oxidation to Oxygenates

Abstract

Semiconductor photocatalysis has rendered a potential route for aerobic methane (CH₄) conversion to valued-added oxygenates under mild conditions, whereas suffering from low reaction efficiency caused by the high inertness of CH₄ molecules and the fast recombination of photogenerated charge carriers. Herein, Cu doped ZnO nanoplates with polar surface exposure are employed as an efficient photocatalyst for CH₄ oxidation in the presence of O₂, which exhibit the liquid C1 oxygenates yield of 4742.2 µmol g⁻¹ h⁻¹ with a selectivity of 99.6%, outperforming the counterparts with nonpolar surface exposure or without Cu doping. The detailed investigation elucidates that the activity enhancement is largely contributed by the intensified internal electric field, improving the separation of charge carriers and thus supplying sufficient electrons to drive surface redox reactions. More active/adsorption sites are also favorable to be created on Cu doped polar surface of ZnO, facilitating CH₄ conversion. Besides, the generation of ·OH radicals is proposed to follow a pathway of O₂ → ·OOH → H₂O₂ →·OH, wherein the doped Cu plays a significant role for O₂ reduction and H₂O₂ dissociation to ·OH, thereby enabling efficient CH₄ activation. This work offers new strategies for designing efficient photocatalysts to boost CH₄ oxidation under mild conditions.