Electrocatalytic Oxidation Processes for Treatment of Halogenated Organic Pollutants in Aqueous Solution: A Critical Review

Abstract

Halogenated organic pollutants (HOPs) are a class of organic substances that are difficult to degrade, easily bioaccumulate, and are stable in the environment. Compared with biological, physical, and chemical methods, electrocatalytic oxidation technology has the advantages of a strong oxidation ability, high efficiency, mild reaction conditions, and high automation. The direct and indirect electrochemical oxidation mechanisms in electrocatalytic oxidation processes are discussed. The generation processes and properties of oxidative species in indirect electrochemical oxidation processes, including hydroxyl radicals, active chlorine, sulfate radicals, O 3 , H 2 O 2 , carbonate radicals, and 1 O 2 , are summarized. The cell designs involved in the flow-by, flow-through, and three-dimensional configurations are outlined. The removal ratios, intermediate products, and electrocatalytic oxidation mechanisms of halogenated pollutants, including perfluorinated, polyfluorinated, chlorinated, brominated, and iodinated organic compounds, are reviewed. The oxidative and mineralization ability, detoxification ability, and energy consumptions of electrocatalytic oxidation compared with other technologies are comprehensively evaluated. This Review are intended to introduce some effective strategies for lowering energy consumption in electrocatalytic oxidation processes. Finally, the current deficiencies and development trends in electrocatalytic oxidation are discussed.

Recent Advancements in Electrochemical Hydrogen Production via Hybrid Water Splitting

“…[82][83][84][85][86] Comparatively, direct or indirect electrochemical oxidation of contaminants for wastewater remediation is becoming a research hotspot, benefiting from significant merits of widespread applicability, environmental compatibility, and appreciable cost-effectiveness. [87,88] Equally importantly, many organic pollutants are more prone to deep oxidation to produce CO and CO 2 than water, so in addition to the hydrazine, urea, ammonia mentioned before, methylene blue, phenol, and formaldehyde could also be used as the suitable anodic sacrificial agents. [27][28][29][30][31] As a result, combining the organic pollutant degradation and electrochemical H 2 preparation is a promising strategy.…”

Enhanced Mineralization of Organic Pollutants through Atomic Hydrogen-Mediated Alternative Transformation Pathways

“…In recent years, hydroxyl radical ( · OH)-mediated anodic oxidation technology has emerged as a promising approach for removing diverse organic contaminants from wastewater. Its advantages over established wastewater treatment technologies lie in its ability to produce · OH in situ through modular cell construction, which reacts nonselectively with various contaminants, such as phenol, aniline, organosulfur compounds, and deprotonated amines. − However, the efficiency of · OH-mediated oxidation process may diminish when treating organics with electron-withdrawing groups, including olefins, unactivated hydrocarbons, and halogenated organic compounds. , The oxidation of these antioxidant pollutants requires a higher potential than the redox potential of · OH at E ° = 2.73 V vs SHE, thus necessitating extended treatment duration and increased electrical consumption for their mineralization. − For example, carbon–halogen bonds of halogenated contaminants generally remain intact during · OH-oxidation due to the high dissociation energy of 222–456 kJ/mol. ,− Consequently, low removal efficiencies for compounds like 4-chloroaniline were observed in a dual photoelectrode photoelectrochemical system . Additionally, insufficient 4-nitrophenol removal of 51% and total organic carbon (TOC) of 20% after 300 min anodic oxidation treatment were observed .…”

In situ Raman monitoring of electroreductive dehalogenation of aryl halides at an Ag/aqueous solution interface

“…Unfortunately, halogenated hydrocarbons are not easy to degrade in the natural environment and can accumulate in the body due to their good physical and chemical stability and acid resistance. 1,2 This results in widespread distribution of halogenated organic pollutants (HOPs), posing a threat to the environment and biological health. Therefore, many technologies have been developed to destroy the strong C-X bonds (X = F, Cl, Br, I), such as biodegradation, 3,4 chemical treatment, 5 ionizing radiation, 6 and photochemistry.…”

“…7,8 Recently, an electrochemical strategy that uses electrons as a clean reactant provides an efficient and green tool for the reductive dehalogenation of HOPs, and has attracted increasing attention over the past decade. 1,2 Meanwhile, continuous efforts have been made to elucidate the electroreductive dehalogenation mechanisms. [9][10][11][12] Various techniques, such as cyclic voltammetry, 13 nuclear magnetic resonance 14 and gas chromatography-mass spectrometry, 15 have been employed to investigate the electron transfer coefficient and reaction intermediates.…”