Ionic Radii and Concentration Dependency of RE3+ (Eu3+, Nd3+, Pr3+, and La3+)-Doped Cerium Oxide Nanoparticles for Enhanced Multienzyme-Mimetic and Hydroxyl Radical Scavenging Activity

The antioxidant activity of cerium oxide nanoparticles (CNPs) depends on the concentration of oxygen vacancies and Ce3+ active sites. In the present work, we report the impact of 5 mol % trivalent rare-earth-doped (RE3+ = Eu3+, Nd3+, Pr3+, and La3+) CNPs on the oxidation state modulation and antioxidant property with respect to ionic radii. An increase in the lattice parameter, strain, and oxygen vacancy concentration was observed as a function of ionic radii. Among the various dopants in CNPs, La3+ with higher ionic radii having smaller crystallite size (7.9 nm) and higher vacancy displayed better peroxidase, oxidase, and hydroxyl radical (HO•) scavenging activities. The kinetic parameters for the peroxidase and oxidase activities were found to be superior with Km = 0.217 and 0.261 mM, respectively, for 5 mol % La3+-doped CNPs. To divulge the role of dopant concentration on the structural properties, we also explored using 10 and 20 mol % La3+ doping in CNPs. Because of the smaller crystallite size (6.7 nm) and higher defect level (3.12 × 1021 cm–3), 20% La3+ doping showed superior peroxidase and oxidase activities, as shown by the low Km values. CNPs exhibit both peroxidase and oxidase activities in a concentration-dependent manner. Moreover, CNPs exhibit concentration-dependent peroxidase and oxidase activities that can be selectively activated for various theranostic applications. Thus, our results demonstrate the crucial role of ionic radii and the concentration of RE3+ dopants on defect formation in CNPs for improved antioxidant properties of ceria.