On the origin of the oxidizing ability of ceria nanoparticles

Abstract

To better understand the oxidizing ability of ceria nanoparticles (nanoceria), the influences of protons, dissolved oxygen (DO), superoxide dismutase (SOD) and catalase on the oxidation of organic dyes in an aqueous suspension of rod-like nanoceria were investigated in detail. The strong oxidizing ability of nanoceria was verified. Electron paramagnetic resonance (EPR) results revealed the existence of superoxide anion radicals (˙O₂⁻) and hydroxyl radicals (˙OH) in the nanoceria suspension without additional hydrogen peroxide (H₂O₂). A reasonable origin of the oxidizing ability of nanoceria was hypothesized: the adsorbed ˙O₂⁻ on the nanoceria surface can dismutate to H₂O₂ via the SOD-mimetic activity of nanoceria, and then, the ˙OH are produced through a Fenton-like reaction. This process is inherent and pH-dependent. The regeneration of ˙O₂⁻ and persistent production of ˙OH can be realized by including DO in an aqueous solution. Moreover, we found that the Ce⁴⁺ in nanoceria could also directly act as an oxidant at low pH values.