TiO₂-Photocatalyzed As(III) Oxidation in a Fixed-Bed, Flow-Through Reactor

Abstract

SECTION S.1. ADDENDUM TO MATERIALS AND METHODS SEM sample preparation. In preparation for examining coating thickness, beads were immobilized in epoxy, ground down to expose cross sections (Buehler Ecomet 3, 1 µM grinding size), and coated with a 9 nm layer of carbon (Cressington Turbo Carbon Evaporater 208c). To assess surface morphology, beads were immobilized with carbon tape and coated with a 4 nm iridium layer (Cressington Sputter Coater 208 HR). Sample preparation for LC-ICP-MS analysis. Samples collected from runs with influent As(III) concentrations of 2.6 µM and 8.3 µM were diluted 3-fold and 10-fold in water. Standards (0.033-1.33 µM, PlasmaCal) were prepared in the same matrix as the samples being analyzed (i.e. 5 mM NaNO 3 or synthetic groundwater). The LC injection volume was 50 µL. An anion exchange column (Agilent speciation column with guard column) with an eluent solution of 3.4 mM phosphate, 0.26 mM EDTA, and 2% methanol (pH 6.0) was used to separate As(III) and As(V) peaks, resulting in respective retention times of 2.4 and 7.3 min at a flow rate of 0.9 mL min-1 .

Permanganate oxidation of arsenic(III): Reaction stoichiometry and the characterization of solid product

“…The mechanisms and the effectiveness of As(III) oxidation by varying oxidants have been extensively studied because complete oxidation of As(III) to As(V) is imperative for the enhancement of As removal efficiency (Driehaus et al, 1995;USEPA, 2001;Lee and Choi, 2002;Dodd et al, 2006;Ferguson and Hering, 2006). Accordingly, the removal processes of As from drinking water conventionally utilize the pre-oxidation of As(III) to As(V), followed by a process of coprecipitation or adsorption (USEPA, 2003).…”

Photocatalytical removal of inorganic and organic arsenic species from aqueous solution using zinc oxide semiconductor

“…This behavior was in agreement with previous reports on a TiO 2 surface where the photocatalytic oxidation of [As(III)] was extremely fast, involving oxidation of the arsenic atom to the pentavalent oxidation state. 10,36–40 By using TiO 2 , the As(V) concentration that was formed as a by-product increased up to 4.9 mg As L −1 in the first 2 h and remained constant thereafter. The observed difference between TiO 2 and sol–gel ZnO semiconductors was due to the excellent adsorption capability of sol–gel ZnO semiconductor shown for [As(V)], thus the [As(V)] concentration in the treated solution was largely decreased in spite of the continuous generation of [As(V)] by the oxidation of [As(III)].…”

Perspectives and Advances in Photocatalysis

“…Basically, the element arsenic exists in four oxidation states: the + 5 oxidation state or arsenate, the + 3 known as the arsenite, the 0 oxidation state popularly known as the arsenic and the − 3 oxidation state referred to as arsine. The arsenite and the arsenate are common in natural waters-the arsenite (As 3+ ) include As(OH) 3 , As(OH) The photocatalytic oxidation of the hazardous As +3 has recently been demonstrated (Yang et al 1999;Ferguson and Hering 2006;Li et al 2009;Pena et al 2005;Bissen et al 2001). When arsenite is oxidised to arsenate, the toxicity of the original trivalent cation is drastically reduced.…”