Morphology- and pH-dependent peroxidase mimetic activity of nanoceria.

The peroxidase mimetic properties of nanoceria have attracted extensive attention in recent years. In this work, the peroxidase mimetic properties of CeO nanocrystals with different morphologies, namely, nanocubes and nanorods, were investigated. Two types of oxidative species, HO˙ radicals and peroxide-like intermediates, were identified in the CeO/HO systems. The formation of these oxidative species is strongly dependent on the pH value and the morphology of the CeO nanocrystals. The origin of the peroxidase mimetic activity of nanoceria was mainly ascribed to the presence of HO˙ under acidic conditions, whereas the peroxide-like species also played a major role under neutral and basic conditions. CeO nanorods with excellent redox properties and higher concentration of Ce and oxygen vacancies were more favorable for the generation of both HO˙ and peroxide-like intermediates than that of CeO nanocubes, exhibiting excellent peroxidase mimetic activity toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), methylene blue (MB), and congo red (CR) in the presence of HO.