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

Tran Van Cong; Nguyen Duc Hung; Ngoc Dung Tran Thi; Nguyen Van Hoang; Surya Veerendra Prabhakar Vattikuti; Nam Nguyen Dang

doi:10.1021/acsomega.1c03487

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

ACS Omega. 2021 Sep 29;6(40):26329-26337. doi: 10.1021/acsomega.1c03487. eCollection 2021 Oct 12.

Authors

Tran Van Cong¹, Nguyen Duc Hung², Ngoc Dung Tran Thi², Nguyen Van Hoang¹, Surya Veerendra Prabhakar Vattikuti³, Nam Nguyen Dang^{4

5}

Affiliations

¹ Institute of New Technology, 17 Hoang Sam Street, Cau Giay District, Hanoi 100000, Vietnam.
² Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet Street, Cau Giay District, Hanoi 100000, Vietnam.
³ School of Mechanical Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea.
⁴ Future Materials & Devices Lab., Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City 700000, Vietnam.
⁵ The Faculty of Environmental and Chemical Engineering, Duy Tan University, Danang 550000, Vietnam.

Abstract

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.