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

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 cm² 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