| Abstract
| - We report herein a detailed assessment of the roles of O2, H2O2, •OH, and O2-• in the TiO2 assistedphotocatalytic oxidation (PCO) of arsenite. Although both arsenite, As(III), and arsenate, As(V), adsorbextensively onto the surface of TiO2, past studies relied primarily on the analysis of the arsenic species insolution, neglecting those adsorbed onto the surface of TiO2. We used extraction and analyses of the arsenicspecies adsorbed onto the surface of the TiO2 to illustrate that the oxidation of As(III) to As(V) occurs in anadsorbed state during TiO2 PCO. The TiO2 photocatalytic oxidation (PCO) of surface adsorbed As(III) indeoxygenated solutions with electron scavengers, Cu2+, and polyoxometalates (POM) yields oxidation ratesthat are comparable to those observed under oxygen saturation, implying the primary role of oxygen is as ascavenger of the conduction band electron. Pulse radiolysis and competition kinetics were employed todetermine a rate constant of 3.6 × 106 M-1 s-1 for the reaction of As(III) with O2-•. Transient absorptionstudies of adsorbed hydroxyl radicals, generated by subjecting colloidal TiO2 to radiolytic conditions, provideconvincing evidence that the adsorbed hydroxyl radical (TiO2+•OH) plays the central role in the oxidationwith As(III) during TiO2 assisted photocatalysis. Our results suggest the reaction of superoxide anion radicaldoes not contribute in the conversion of As(III) when compared to the reaction of As(III) with •OH radicalduring TiO2 PCO.
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