Engineering ultra-small nanoceria with antioxidant and UV-shielding properties as functional nanomaterials in composite coatings for complex surface protection

The development of advanced catalytic shields against UV-induced and oxidative degradation phenomena is critical to address multifaceted deterioration processes. The maximization of the surface-to-volume ratio in ultra-small cerium oxide nanoparticles (CeO2 NPs) favors the Ce(III)/Ce(IV) exchange on the surface and the formation of oxygen vacancies, creating an ideal platform to target entangled degradation issues. Here, we design a microwave-assisted scalable process to obtain highly stable CeO2 NPs (2 nm), and we demonstrate the redox cycling of the nanocatalyst by means of environmental XPS. Thereafter, we develop a polymer nanocomposite formulation in which the biopolymer and the catalytic nanomaterial work synergistically to provide a protective action without hindering the active sites present at the surface of the NPs. We test the protective action of the coating in the challenging context of cultural heritage, investigating its performance on ancient frescoes. Their surfaces are often subjected to pigment degradation, triggered by a combination of light, salts, and high relative humidity. We verify how, thanks to the joint action of the biopolymer and the NPs, the CeO2 NP-based coating effectively mitigates complex deterioration mechanisms.