Photocatalytic oxidation mechanism of arsenite on tungsten trioxide under visible light
By Jaesung Kim and Gun-hee Moon and Seungdo Kim and Jungwon Kim
Published in Journal of Photochemistry and Photobiology A: Chemistry
2015
Abstract
The oxidation of arsenite (As(III)) to arsenate (As(V)) and the involved oxidants on tungsten trioxide (WO3) under visible light were mechanically investigated. Three oxidant species, valence-band hole (hvb+), hydrogen peroxide (H2O2), and hydroxyl radical (OH), can be generated on \WO3\ under visible light. However, As(III) was not oxidized to As(V) in the presence of H2O2. In addition, the oxidation rate of As(III) to As(V) was not reduced in the presence of \OH\ scavenger. These results indicate that the oxidation of As(III) to As(V) is primarily initiated by hole, but both \OH\ and \H2O2\ are little involved in As(III) oxidation to As(V). This hole-mediated oxidation of As(III) to As(V) on \WO3\ was further confirmed by X-ray photoelectron spectroscopy (XPS) analysis (i.e., the adsorption of As(III) on WO3) and photoelectrochemical measurement (i.e., the enhanced photocurrent by As(III) addition). Although \OH\ is little involved in As(III) oxidation to As(V), the production of \OH\ was reduced in the presence of As(III). This behavior implies that As(III) on \WO3\ acts as an external charge recombination center, where the oxidation of As(III) to intermediate As(IV) species by hole or \OH\ is immediately followed by the reduction of As(IV) to As(III) by conduction-band electron (ecb