Catalytic Decomposition of Hypochlorite Anions by Ceria Nanoparticles Visualized by Spectroscopic Techniques

Hypochlorous acid (HOCl) and hypochlorite anions (−OCl) are nonselective oxidants produced by activated neutrophils and monocytes and play an important role in the formation of immune response of a living organism. At the same time, because of the strong oxidative properties of hypochlorites, their concentrations in cells need to be under strict control. In this paper, cerium oxide nanoparticles (nanoceria) were used for spectroscopically controlled catalytic decomposition of hypochlorite anions. The processes of scavenging of hypochlorite anions by ceria nanoparticles and regeneration of nanoceria were monitored using the changes in hypochlorite absorption and 5d → 4f luminescence of Ce3+ ions during oxidation–reduction cycles. The high oxygen deficiency of ceria nanoparticles provides sufficient mobility of oxygen ions, leading to the involvement of both surface and bulk Ce3+ ions into oxidation, whereas the recovery of initial Ce3+/Ce4+ ratio is terminated by the slow diffusion of oxygen out of ceria nanoparticles.