Oxygen vacancy engineering of cerium oxide for the selective photocatalytic oxidation of aromatic pollutants.

The engineering of oxygen vacancies in CeO2 nanoparticles (NPs) allows the specific fine-tuning of their oxidation power, and this can be used to rationally control their activity and selectivity in the photocatalytic oxidation (PCO) of aromatic pollutants. In the current study, a facile strategy for generating exceptionally stable oxygen vacancies in CeO2 NPs through simple acid (CeO2-A) or base (CeO2-B) treatment was developed. The selective (or mild) PCO activities of CeO2-A and CeO2-B in the degradation of a variety of aromatic substrates in water were successfully demonstrated. CeO2-B has more oxygen vacancies and exhibits superior photocatalytic performance compared to CeO2-A. Control of oxygen vacancies in CeO2 facilitates the adsorption and reduction of dissolved O2 due to their high oxygen-storage ability. The oxygen vacancies in CeO2-B as active sites for oxygen-mediated reactions act as (i) adsorption and reduction reaction sites for dissolved O2, and (ii) photogenerated electron scavenging sites that promote the formation of H2O2 by multi-electron transfer. The oxygen vacancies in CeO2-B are particularly stable and can be used repeatedly over 30 h without losing activity. The selective PCOs of organic substrates were studied systematically, revealing that the operating mechanisms for UV-illuminated CeO2-B are very different from those for conventional TiO2 photocatalysts. Thus, the present study provides new insights into the design of defect-engineered metal oxides for the development of novel photocatalysts.