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 CeO₂ 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 CeO₂/H₂O₂ systems. The formation of these oxidative species is strongly dependent on the pH value and the morphology of the CeO₂ 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. CeO₂ nanorods with excellent redox properties and higher concentration of Ce³⁺ and oxygen vacancies were more favorable for the generation of both HO˙ and peroxide-like intermediates than that of CeO₂ 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 H₂O₂.