Environmental electrochemistry: Remediation of halogenated organic pollutants

Four electrochemical studies have been undertaken that employ cyclic voltammetry, differential pulse voltammetry, and controlled-potential electrolysis and that entail remediation of environmental pollutants via the reductive cleavage of carbon-halogen bonds predominantly at silver cathodes. Numerous studies have shown silver cathodes, when compared to inert electrodes (such as carbon), shift reduction potentials needed for scission of carbon-halogen bonds to more positive values. First, electrochemical stripping analysis has been employed for the determination of trihalomethanes in water, where submicromolar concentration levels were able to be measured in a moderate time scale. Then a study of the effect of organic and aqueous-organic media on the reduction of (1R,2r,3S,4 R,5r,6S)-hexachlorocyclohexane (Lindane) at a silver cathode was undertaken, giving evidence to more effective reduction of Lindane when water is present. Also, intermediates in the reduction of Lindane at a silver electrode were identified, which could not be detected for electrolyses with a carbon cathode. Third, electrochemical remediation of decabromodiphenyl ether was investigated at carbon or silver cathodes in both dimethylformamide and dimethyl sulfoxide. This flame retardant was effectively debrominated in dimethylformamide to form diphenyl ether, dibenzofuran, phenol, benzene, and a mixture of congeners of dibromodiphenyl ether. Finally, the reduction of 5-chloro-2-(2,4-dichloro-phenoxy)phenol (triclosan) at silver along with its methyl derivative, (2,4-dichloro-1-(4-chloro-2-methoxyphenoxy)benzene) at silver and carbon was studied in the hope of understanding their reduction mechanisms. It appears that, once the alcohol group is modified to a methoxy functionality, the electrolysis can occur more favorably. Identification and quantitation of products and reaction intermediates have been accomplished with the aid of gas chromatography and mass spectrometry.