X-ray Absorption Fine-Structure Spectroscopy Study of Photocatalyzed, Heterogeneous As(III) Oxidation on Kaolin and Anatase

Abstract

We have used X-ray absorption fine-structure spectroscopy (XAFS) to investigate As(III) adsorption on bulk Georgia kaolin (KGa-1b), Wyoming smectite (SWy-2), anatase (TiO2), gibbsite [Al(OH)3], and amorphous silica (am-SiO2) with the goal of identifying the oxidants responsible for As(III) oxidation in KGa-1b. After 30 h of reaction, ≥30% of the added As(III) was oxidized to As(V) in KGa-1b and anatase experiments, whereas only ≈10% of the added As(III) was oxidized in experiments using bulk SWy-2 and gibbsite. As(III) oxidation was negligible in experiments using am-SiO2. The proportion of As(III) oxidized by KGa-1b increased with increasing equilibration time, decreased significantly with increasing pH (up to pH 8), and decreased slightly with increasing ionic strength. Although Mn has been proposed as the potential oxidant of As(III) in KGa-1b, it can account for only ≈2% of the As(V) produced under the conditions of our experiments because of its low concentration in this material (3 ppm). Proof that ...