Tandem Hydroperoxyl-Alkylperoxyl Radical Quenching by an Engineered Nanoporous Cerium Oxide Nanoparticle...

The use of nanomaterials as inhibitors of the autoxidation of organic materials is attracting tremendous interest in petrochemistry, food storage, and biomedical applications. Metal oxide materials and CeO₂ in particular represent one of the most investigated inorganic materials with promising radical trapping and antioxidant abilities. However, despite the importance, examples of the CeO₂ material's ability to retard the autoxidation of organic substrates are still lacking, together with a plausible chemical mechanism for radical trapping. Herein, we report the synthesis of a new CeO₂-derived nanoporous material (NCeONP) with excellent autoxidation inhibiting properties due to its ability to catalyze the cross-dismutation of alkyl peroxyl (ROO^•) and hydroperoxyl (HOO^•) radicals, generated in the system by the addition of the pro-aromatic hydrocarbon γ-terpinene. The antioxidant ability of NCeONP is superior to that of other nanosized metal oxides, including TiO₂, ZnO, ZrO₂, and pristine CeO₂ nanoparticles. Studies of the reaction with a sacrificial reductant allowed us to propose a mechanism of inhibition consisting of H atom transfer from HOO^• to the metal oxides (MO + HOO^• → MO-H^• + O₂), followed by the release of the H atom to an ROO^• radical (MO-H^• + ROO^• → MO + ROOH). Besides identifying NCeONP as a promising material for developing effective antioxidants, our study provides the first evidence of a radical mechanism that can be exploited to develop novel solid-state autoxidation inhibitors.