Electrochemical Plasma for Treating 2,4,5-Trichlorophenoxyacetic Acid in a Water Environment Using Iron Electrodes.

Herbicide compounds containing aromatic rings and chlorine atoms, such as 2,4,5-trichlorophenoxyacetic (2,4,5-T), cause serious environmental pollution. Furthermore, these compounds are very difficult to decompose by chemical, physical, and biological techniques. Fortunately, the high-voltage direct current electrochemical technique can be controlled to form a plasma on metallic electrodes. It creates active species, such as H2, O2, and H2O2, and free radicals, such as H•, O•, and OH•. Free radicals that have a high oxidation potential (e.g., OH•) are highly effective in oxidizing benzene-oring compounds. Iron electrodes are used in the study to combine the dissolving process of the iron anode electrode to create Fe2+ ions and the electrochemical Fenton reaction. In addition, the flocculation process by Fe(OH)2 also occurs and the plasma appears with a voltage of 5 kV on the iron electrode in a solution of 30 mg L-1 of 2,4,5-T. After a period of time of the reaction, the aromatic-oring compounds containing chlorine were effectively treated, and the electric conductivity of the solution increased due to the amount of Cl- ions released in the solution and the decrease in the pH value. The degradable products of 2,4,5-T were qualitatively characterized by gas chromatography-mass spectrometry (GC-MS), and it was determined that straight-chain carboxylic acids are formed in the solution. These compounds are easy to oxidize thoroughly under appropriate conditions in a solution via OH• free radicals. Moreover, 2,4,5-T was also quantitatively analyzed using a calibration curve from GC-MS and high-performance liquid chromatography (HPLC). Furthermore, this work also suggests that the performance of the treatment process can be optimized by controlling the technological factors, such as the input voltage, the distance between anodic and cathodic electrodes, the initial concentration of 2,4,5-T, and flowing air through the solution that represents an approximately 99.83% degradable efficiency. Finally, the work demonstrates a potential technology for treating the 2,4,5-T compound, particularly for environmental pollution treatments.