Mechanism of Persulfate Activation by Phenols

The activation of persulfate by phenols was investigated to further the understanding of persulfate chemistry for in situ chemical oxidation (ISCO). Phenol (pK a = 10.0) activated persulfate at pH 12 but not at pH 8, suggesting activation occurred only via the phenoxide form. Evaluation of the pheno...

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Bibliographic Details
Published in:Environmental science & technology 2013-06, Vol.47 (11), p.5864-5871
Main Authors: Ahmad, Mushtaque, Teel, Amy L, Watts, Richard J
Format: Article
Language:English
Subjects:
Applied sciences
Decontamination. Miscellaneous
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Groundwaters
Hydrogen peroxide
Hydrogen Peroxide - chemistry
Hydrogen-Ion Concentration
Natural water pollution
Oxidation
Pentachlorophenol - chemistry
Phenols
Phenols - chemistry
Pollution
Pollution, environment geology
Soil and sediments pollution
Soil Pollutants - chemistry
Structure-Activity Relationship
Sulfates - chemistry
Toxicity
Water treatment and pollution
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Summary:The activation of persulfate by phenols was investigated to further the understanding of persulfate chemistry for in situ chemical oxidation (ISCO). Phenol (pK a = 10.0) activated persulfate at pH 12 but not at pH 8, suggesting activation occurred only via the phenoxide form. Evaluation of the phenoxide activation mechanism was complicated by the concurrent activation of persulfate by hydroperoxide anion, which is generated by the base catalyzed hydrolysis of persulfate. Therefore, phenoxide activation was investigated using pentachlorophenoxide at pH 8.3, midway between the pK a of pentachlorophenol (pK a = 4.8) and that of hydrogen peroxide (pK a = 11.8). Of the two possible mechanisms for phenoxide activation of persulfate (reduction or nucleophilic attack) the results were consistent with reduction of persulfate by phenoxide with oxidation of the phenoxide. The concentration of phenoxide required for maximum persulfate activation was low (1 mM). The results of this research document that phenoxides activate persulfate via reduction; phenolic moieties ubiquitous to soil organic matter in the subsurface may have a significant role in the activation of persulfate during its injection into the subsurface for ISCO. Furthermore, the results provide the foundation for activation of persulfate by other organic anions without the toxicity of phenols, such as keto acids.
ISSN:0013-936X
1520-5851
DOI:10.1021/es400728c