Formulation of Antioxidant Composites by Controlled Heteroaggregation of Cerium Oxide and Manganese Oxide Nanozymes

Antioxidant composites based on nanozymes [manganese oxide microflakes (MnO₂ MFs) and cerium oxide nanoparticles (CeO₂ NPs)] were formulated by controlled heteroaggregation. The interparticle attraction via electrostatic forces was systematically tuned with surface functionalization by the poly(diallyldimethyl chloride) (PDADMAC) polyelectrolyte. The PDADMAC-coated MnO₂ MFs (PMn) were heteroaggregated with oppositely charged CeO₂ NPs to generate the Ce-PMn composite, while the PDADMAC-functionalized CeO₂ NPs (PCe) were immobilized onto bare MnO₂ MFs, resulting in the Mn-PCe composite. Both the adsorption of PDADMAC and the self-assembly of oppositely charged particles resulted in charge neutralization and charge reversal at appropriately high doses. The interparticle force regimes, the aggregation states, and the physicochemical properties of the relevant dispersions were also highly dependent on the dose of PDADMAC, as well as that of PDADMAC-functionalized metal oxides (PMO) enabling the fine-tuning and control of colloidal stability. The individual enzyme-like activity of either metal oxide was not compromised by PDADMAC adsorption and/or heteroaggregation, leading to the formation of broad-spectrum antioxidant composites exhibiting multiple enzyme-like activities such as superoxide dismutase, oxidase, and peroxidase-type functions. The low cost and ease of preparation, as well as controllable colloidal properties render such composites potential enzyme mimicking agents in various industrial fields, where processable antioxidant systems are needed.