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Citation
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HERO ID
90579
Reference Type
Journal Article
Title
Photocatalytic oxidation of arsenite on TiO2: understanding the controversial oxidation mechanism involving superoxides and the effect of alternative electron acceptors
Author(s)
Ryu, J; Choi, W
Year
2006
Is Peer Reviewed?
1
Journal
Environmental Science & Technology
ISSN:
0013-936X
EISSN:
1520-5851
Volume
40
Issue
22
Page Numbers
7034-7039
Language
English
PMID
17154013
DOI
10.1021/es0612403
Web of Science Id
WOS:000241941700029
URL
http://pubs.acs.org/doi/abs/10.1021/es0612403
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Abstract
#Previously we have reported that superoxide plays the primary role as oxidant of As(III) in the UV/TiO2 system, however, since then there has been a controversy over the true identity of the major As(III) oxidant. This study aims to establish a comprehensive understanding of the oxidative mechanism which satisfactorily explains all of the observed results during the photocatalytic oxidation (PCO) of As(III). The key step that has masked the true oxidative mechanism is related to the fact that the adsorbed As(III) on TiO2 serves as an external charge-recombination center where the reaction of As(III) with an OH radical (or hole) is immediately followed by an electron transfer to make a null cycle. This was confirmed by the observation that the photoanodic current obtained with a TiO2 electrode immediately decreased upon spiking with As(III), portraying the superoxide-mediated PCO as the dominant pathway. The degradation of competitive substrates (benzoic acid and formic acid) was delayed until As(III) was fully converted into As(V) since the normal PCO mechanism that is based on the action of adsorbed OH radicals (or holes) is not working as long as As(III) is present on the TiO2 surface. However, the As(III) PCO mechanism is entirely altered when alternative electron acceptors (Ag+, Cu2+, polyoxometalate) are present. When these alternative electron acceptors are more efficient than O2 they are able to intercept the CB electron, impeding the recombination pathway and enabling an anoxic oxidation mechanism in which OH radicals and holes play the role of main As(III) oxidant. In the presence of polyoxometalate or Cu2+, the above-mentioned photoanodic current immediately increases upon spiking As(III), indicating that the PCO mechanism has changed in the presence of more efficient electron acceptors. Comprehensive mechanisms of As(III) PCO and experimental factors that alter the mechanism are discussed.
Tags
IRIS
•
Arsenic Hazard ID
1. Initial Lit Search
PubMed
ToxNet
4. Considered through Oct 2015
6. Cluster Filter through Oct 2015
•
Arsenic (Inorganic)
1. Literature
PubMed
Toxline, TSCATS, & DART
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