Non-radical pathway dominated catalytic oxidation of As(III) with stoichiometric H2O2 over nanoceria

Heterogeneous catalysis is a promising approach to achieve efficient As(III) oxidation by H 2 O 2 at circumneutral pH. However, radical-attack pathways dominated catalytic As(III) oxidation over most metal oxides is undesirably associated with low utilization of H 2 O 2 induced by rapid self-quenching of radicals. In this study, we developed a non-radical catalytic route to improve H 2 O 2 utilization efficiency for catalytic As(III) oxidation based on nanoceria. The performance and mechanism of As(III) oxidation by H 2 O 2 was investigated by employing four types of nanoceria with different crystallite sizes (9.1–80.6 nm). At the H 2 O 2 /As(III) molar ratio of 2.0, nanoceria exhibited crystallite size-dependent catalytic activity for oxidation of As(III) over a wide pH range (5–9). Based on comprehensive study including scavenging, enzymatic, and pretreatment experiments and miscellaneous spectroscopy techniques, the catalytic As(III) oxidation over nanoceria was proved to be mainly mediated by the non-radical Ce-hydroperoxo surface complexes, whilst the surface hydroperoxyl radical served as a minor oxidant. In contrast, the roles of dissolved oxygen, homogeneous H 2 O 2 , and OH radical were all negligible. No obvious interconversion of Ce(III)/Ce(IV) was observed by XPS for the catalytic process. Such non-radical pathway enabled a stoichiometric reaction with high H 2 O 2 utilization efficiency (90.5%–122%). Moreover, nanoceria could be recycled for five consecutive runs without desorption/regeneration treatment. This study sheds new light on the development of nanoceria-based catalytic processes for efficient oxidation of As(III).