Multifunctional antioxidant and UV-shielding coating based on highly engineered ultra small CeO2 NPs for complex surface protection

Surface protection is a shared concern of different fields, since the exposed facets of different substrates are most commonly subjected to a variety of deteriorating environmental factors. The issue calls for novel coating strategies, able to counteract complex mechanisms and withstand interaction with different agents. With this in mind, we designed a multifunctional biopolymer nanocomposite based on cerium oxide nanoparticles (CeO2 NPs) and we tested it in a challenging case study. First, we engineered the NPs to achieve ultra-small sizes, resulting in a maximization of the surface-to-volume ratio and finally increasing the number of available active sites on the surface. Then, we deeply studied their catalytic activity and we linked it to the Ce(III)/Ce(IV) redox cycling established at their surface. We investigated the interaction of the NPs with different factors (i.e., O2 atmosphere, H2O2 solution, UV light, and high temperature) by means of Environmental XPS, proving the potential of the nanocatalyst for long-lasting protection. To fully exploit the functionality of the NPs, we incorporated them in an optimized chitosan formulation taking care to guarantee the active sites on the surface of the NPs are not hindered by the matrix. We demonstrated that the synergistic action of CeO2 NPs and chitosan gives rise to optimal UV-shielding and antioxidant action, by testing the coating in the context of pigments degradation. Both redox and UV-induced mechanisms, induced by simultaneous presence of UV light, chlorine-based salts and high relative humidity, are efficiently limited thanks to the barrier effect of the coating.