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Environmental science & technology

Rotating Ring-Disk Electrode and Quantum-Chemical Study of the Electrochemical Reduction of Monoiodoacetic Acid and Iodoform.


PMID 26496660

Abstract

This study examined the electrochemical (EC) reduction of monoiodoacetic acid (MIAA) and iodoform (CHI3), which are typical iodine-containing disinfection byproducts (I-DBPs). Experiments carried out using the method of a rotating ring-disk electrode (RRDE) with a gold working electrode showed that the reduction of CHI3 and MIAA is diffusion-controlled. The MIAA diffusion coefficient was determined to be (1.86 ± 0.24)·10(-5) cm(2) s(-1). The yield of the iodide ion formed as a result of MIAA or CHI3 reduction was affected by the presence of dissolved organic matter (DOM) and resorcinol. Increasing concentrations of DOM or resorcinol did not affect the EC reduction of the examined I-DBPs, but the formation of iodide was suppressed. This indicated that free iodine, ·I, was formed as a result of the first step in the EC reduction of MIAA and CHI3. This also indicated that the pathway of the EC reduction of MIAA and CHI3 was different from that typical for the reduction of Br- and Cl-containing DBPs, in which case Br(-) or Cl(-) tend to be formed as a result of the electron transfer. Quantum-chemical (QC) calculations confirmed the thermodynamic likelihood of and possible preference to the formation of free iodine species as a result of the EC reduction of MIAA, CHI3, and other I-DBPs.