Photocatalytic Oxidation of Small Molecular Hydrocarbons over ZnO Nanostructures: The Difference between Methane and Ethylene and the Impact of Polar and Nonpolar Facets

The development of efficient photocatalysts to oxidize small molecular hydrocarbons under atmospheric conditions is of great significance. In our previous study, it was found that nanosized ZnO can fulfill this purpose with unprecedented activity. However, the difference between the hydrocarbons and the impact of polar and nonpolar facets of ZnO are far from understood. Herein, by the successful synthesis of facet-dependent ZnO photocatalysts with predominantly (0001)- and (011̅0)-facets-exposed single-crystalline nanosheets and nanorods, it was observed that the photocatalytic reaction of CH4 over ZnO surface follows quasi-first-order kinetics, while the photocatalytic reaction of C2H4 on the highly active ZnO nanosheets surface followed two-stage linear fitting kinetics. By exploring the band edge potentials, photoelectric response in combination with Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR), the differences between methane and ethylene photo-oxidation and the impact of polar and nonpolar facets are systematically discussed.