Reactions of Ultrasonically Generated Hydroxyl Radicals with Arsenic in Aqueous Environments

Motamedi, Sahar; Cai, Yong; Ο'Shea, Kevin Ε.

doi:10.1021/bk-2003-0835.ch007

Cited by 3 publications

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“…Our results using gamma radiolysis to selectively generate O 2 -• /HO 2 • showed minimal conversion of As(III) to As(V) . The addition of superoxide dismutase (SOD) to solutions subjected to ultrasonic irradiation (under O 2 -• or • OH generating conditions) showed no effect on the oxidation of As(III) to As(V), while • OH scavengers had a dramatic effect, indicating • OH-mediated oxidation. , In contrast recent reports indicate that superoxide anion radical is responsible for the conversion of As(III) during TiO 2 photocatalysis.…”

Section: Resultsmentioning

confidence: 95%

“…As(III) and As(V) were determined by a PS Analytical Millenium Excalibur Atomic Fluorescence System, AFS (PSA 10.055) coupled to a HPLC (anion exchange column, PRP X-100, 250 mm × 4.6 mm × 10 μm). Details of the analytical procedures used are described elsewhere …”

Section: Methodsmentioning

confidence: 99%

“…The conversion of As(III) to As(V) in UV-irradiated TiO 2 suspension has been reported by a number of groups. − Most of these studies assess the conversion of As(III) during TiO 2 photocatalysis by monitoring the As(III) concentrations in solution (typically a minor fraction of the arsenic species) and do not specifically address the extent and conversion of As(III) and As(V) adsorbed (often > 90%) onto the TiO 2 . While it was reported that O 2 -• is the main oxidant in the conversion of As(III) to As(V) during TiO 2 PCO, , radiolysis and sonolysis studies indicate that O 2 -• /HO 2 • do not appreciably convert As(III) to As(V). , A number of reports also suggest hydroxyl radical or valence band hole plays a key role in the TiO 2 PCO of As(III). , Given the conflict surrounding the role of superoxide anion radical and hydroxyl radicals during advanced oxidative treatment and TiO 2 PCO of As(III), we have conducted detailed mechanistic studies in an attempt to resolve the roles of the different reactive species formed at the surface of TiO 2 during photocatalysis. Radiolysis and competitive kinetic studies were used to access the reaction of O 2 -• with As(III).…”

Section: Introductionmentioning

confidence: 99%

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Mechanistic Evaluation of Arsenite Oxidation in TiO₂Assisted Photocatalysis

Kamat

Ο'Shea

2005

J. Phys. Chem. A

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We report herein a detailed assessment of the roles of O2, H2O2, *OH, and O2-* in the TiO2 assisted photocatalytic oxidation (PCO) of arsenite. Although both arsenite, As(III), and arsenate, As(V), adsorb extensively onto the surface of TiO2, past studies relied primarily on the analysis of the arsenic species in solution, neglecting those adsorbed onto the surface of TiO2. We used extraction and analyses of the arsenic species adsorbed onto the surface of the TiO2 to illustrate that the oxidation of As(III) to As(V) occurs in an adsorbed state during TiO2 PCO. The TiO2 photocatalytic oxidation (PCO) of surface adsorbed As(III) in deoxygenated solutions with electron scavengers, Cu2+, and polyoxometalates (POM) yields oxidation rates that are comparable to those observed under oxygen saturation, implying the primary role of oxygen is as a scavenger of the conduction band electron. Pulse radiolysis and competition kinetics were employed to determine a rate constant of 3.6 x 10(6) M(-1) s(-1) for the reaction of As(III) with O2-*. Transient absorption studies of adsorbed hydroxyl radicals, generated by subjecting colloidal TiO2 to radiolytic conditions, provide convincing evidence that the adsorbed hydroxyl radical (TiO2+*OH) plays the central role in the oxidation with As(III) during TiO2 assisted photocatalysis. Our results suggest the reaction of superoxide anion radical does not contribute in the conversion of As(III) when compared to the reaction of As(III) with *OH radical during TiO2 PCO.

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Section: Resultsmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanistic Evaluation of Arsenite Oxidation in TiO₂Assisted Photocatalysis

Kamat

Ο'Shea

2005

J. Phys. Chem. A

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“…Fe ( The proposed reactions below can explain and summarize the mechanisms of the photochemical redox transformation (Stumm et al, 1996;Motamedi et al, 2003;Baumanis et al, 2011). As(V) reduction was observed.…”

Section: The Effect Of Hematite Particle Size On Arsenite and Arsenatmentioning

confidence: 99%

The Effect of Iron Oxide Nanoparticles on the Fate and Transformation of Arsenic in Aquatic Environments

Dickson¹

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A variety of dispersion techniques were investigated to disperse bare commercial IONPs. Vortex was able to disperse commercial hematite nanoparticles into unstable dispersions with particles in the micrometer size range while probe ultrasonication dispersed the particles into stable dispersions of nanometer size ranges for a prolonged period of time. Using probe ultrasonication and vortex to prepare IONPs suspensions of different particle sizes, the adsorption of arsenite and arsenate to bare hematite nanoparticles and hematite aggregates were investigated. To understand the difference in the adsorptive behavior, adsorption kinetics and isotherm parameters were determined.Both arsenite and arsenate were capable of adsorbing to hematite nanoparticles and vii hematite aggregates but the rate and capacity of adsorption is dependent upon the hematite particle size, the stability of the dispersion and the type of sorbed arsenic species.Once arsenic was adsorbed onto the hematite surface, both iron and arsenic can undergo redox transformation both microbially and photochemically and these processes can be intertwined. Arsenic speciation studies in the presence of hematite particles were performed and the effect of light on the redox process was preliminary quantified. The redox behavior of arsenite and arsenate were different depending on the hematite particle size, the stability of the suspension and the presence of environmental factors such as microbes and light. The results from this study are important and have significant environmental implications as arsenic mobility and bioavailability can be affected by its adsorption to hematite particles and by its surface mediated redox transformation.Moreover, this study furthers our understanding on how the particle size influences the interactions between IONPs and arsenic thereby clarifying the role of IONPs in the biogeochemical cycling of arsenic.

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