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Investigating the Mechanism of Hydrogen Peroxide Photoproduction by Humic Substances.
MedLine Citation:
PMID:  23046212     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The mechanism(s) by which hydrogen peroxide (H2O2) is photo-produced by humic substances (HS) and chromophoric dissolved organic matter (CDOM) was probed by examining the dependence of the initial H2O2 photo-production rate (RH2O2) and apparent H2O2 quantum yields on dioxygen concentration for both untreated and borohydride-reduced samples. Although borohydride reduction substantially reduced light absorption, the RH2O2 were largely unaffected. Apparent monochromatic and polychromatic quantum yields thus increased following reduction. The results indicate that light absorption by charge-transfer (CT) states or by (aromatic) ketone/ aldehydes does not lead to significant H2O2 photo-production. High concentrations of triplet quenchers relative to dioxygen produced only small decreases (sorbic acid) or small increases (Cl-, Br-) in RH2O2, indicating that neither 1O2 nor excited triplet states of quinones contribute significantly to H2O2 photo-production. The dependence of RH2O2 on [O2] provides evidence that the intermediate(s) reacting with O2 to produce superoxide (O2 ) are relatively long-lived (~tens of microseconds or more). Evidence for the photochemical formation of O2-reducing intermediates under anaerobic conditions was also obtained; these reducing intermediates appeared to be relatively stable in the absence of O2. Our data suggest that these O2-reducing intermediates are generated by intramolecular electron transfer from short-lived excited states of electron donors to ground-state acceptors.
Authors:
Yi Zhang; Rossana Del Vecchio; Neil V Blough
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-10
Journal Detail:
Title:  Environmental science & technology     Volume:  -     ISSN:  1520-5851     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-10     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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