Redox enzyme-mimicking activities of CeO2 nanostructures: Intrinsic influence of exposed facets

CeO₂ nanoparticles (NPs) have been well demonstrated as an antioxidant in protecting against oxidative stress-induced cellular damages and a potential therapeutic agent for various diseases thanks to their redox enzyme-mimicking activities. The Ce³⁺/Ce⁴⁺ ratio and oxygen vacancies on the surface have been considered as the major originations responsible for the redox enzyme-mimicking activities of CeO₂ NPs. Herein, CeO₂ nanostructures (nanocubes and nanorods) exposed different facets were synthesized via a facile hydrothermal method. The characterizations by X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy show that the Ce³⁺/Ce⁴⁺ ratio and oxygen vacancy content on the surfaces of as-synthesized CeO₂ nanostructures are nearly at the same levels. Meanwhile, the enzymatic activity measurements indicate that the redox enzyme-mimicking activities of as-synthesized CeO₂ nanostructures are greatly dependent on their exposed facets. CeO₂ nanocubes with exposed {100} facets exhibit a higher peroxidase but lower superoxide dismutase activity than those of the CeO₂ nanorods with exposed {110} facets. Our results provide new insights into the redox enzyme-mimicking activities of CeO₂ nanostructures, as well as the design and synthesis of inorganic nanomaterials-based artificial enzymes.