Promotion and inhibition of oxidase-like nanoceria and peroxidase-like iron oxide by arsenate and arsenite

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Nanoparticles are massively discharged into the aquatic environment leading to adverse health effects. Considering their adsorption of small molecules and polymers, it is important to study the effect of aqueous system composition on NPs’ behavior and toxicity. Nanomaterials with enzyme-like activities have caught a lot of recent research interest. Since nanozyme reactions take place on the surface of nanomaterials, their catalytic activities often show significant influence by adsorption of small molecules and polymers. CeO2 and Fe3O4 nanoparticles are two classic nanozymes, showing oxidase and peroxidase like activities, respectively. Inorganic arsenic species are critical for environmental and catalytic research. In this study, we used 3,3′,5,5′-tetramethylbenzidine (TMB) as a model substrate to examine the effect of inorganic arsenic species (As(III) and As(V)) on the activity of CeO2 and Fe3O4. The oxidation capacity of nanoceria was decreased to one third with the addition of 1 mM As(III), but was improved by 3-fold in the presence of 0.1 mM As(V). The former is mainly due to the reducing power of As(III), while the latter is attributable to the adsorption of As(V) on the nanoceria surface decreasing the electrostatic repulsion between nanoceria and TMB. For Fe3O4, its activity was first promoted and later inhibited by both As(III) and As(V). Therefore, nanomaterials not only affect arsenic species through redox chemistry and adsorption, but in turn arsenic can affect the catalytic activity of nanomaterials.