Chlorinated Byproduct Formation during the Electrochemical Advanced Oxidation Process at Magnéli Phase Ti₄O₇ Electrodes

Abstract

This research investigated chlorinated byproduct formation at Ti4O7 anodes. Resorcinol was used as a model organic compound representative of reactive phenolic groups in natural organic matter and industrial phenolic contaminants and was oxidized in the presence of NaCl (05 mM). Resorcinol mineralization was >68% in the presence and absence of NaCl at 3.1 V/SHE (residence time = 13 s). Results indicated that ∼4.3% of the initial chloride was converted to inorganic byproducts (free Cl2, ClO2 –, ClO3 –) in the absence of resorcinol, and this value decreased to <0.8% in the presence of resorcinol. Perchlorate formation rates from chlorate oxidation were 115371 mol m–2 h–1, approximately two orders of magnitude lower than reported values for boron-doped diamond anodes. Liquid chromatography–mass spectroscopy detected two chlorinated organic products. Multichlorinated alcohol compounds (C3H2Cl4O and C3H4Cl4O) at 2.5 V/SHE and a monochlorinated phenolic compound (C8H7O4Cl) at 3.1 V/SHE were proposed as possible structures. Density functional theory calculations estimated that the proposed alcohol products were resistant to direct oxidation at 2.5 V/SHE, and the C8H7O4Cl compound was likely a transient intermediate. Chlorinated byproducts should be carefully monitored during electrochemical advanced oxidation processes, and multibarrier treatment approaches are likely necessary to prevent halogenated byproducts in the treated water.

On-Demand Atomic Hydrogen Provision by Exposing Electron-Rich Cobalt Sites in an Open-Framework Structure toward Superior Electrocatalytic Nitrate Conversion to Dinitrogen

“…The electrochemical process is regarded as next-generation technology for water treatment owing to its considerable effectiveness for multiple contaminants and the potential to be powered by renewable energy. − However, challenges including high energy consumption and toxic byproduct formation need to be overcome for its widespread implementation. − During the electrocatalytic nitrate reduction process, unpleasant nitrite and/or ammonia could be released to the treated effluent due to H* provision–utilization mismatch (Scheme a). Conventionally, prolonged electrolysis or enhanced current density may further reduce nitrite to N 2 , at the expense of higher energy consumption.…”

Nitrate Removal in an Electrically Charged Granular-Activated Carbon Column

“…Besides the lower energy consumption, in this electrically charged GAC reaction system, there is no N 2 O yield, whereas in the catalytic reactive electrochemical system, over 40% of nitrate was electrically transformed into N 2 O. In addition, the formation of chlorate and perchlorate (a result of chloride oxidation) has been raised as a concern in electrochemical water treatment systems . In our experiments, chlorate and perchlorate were not detected in the column effluent under any of the conditions tested (detection limit of 10 μg/L).…”

“…In addition, the formation of chlorate and perchlorate (a result of chloride oxidation) has been raised as a concern in electrochemical water treatment systems. 61 In our experiments, chlorate and perchlorate were not detected in the column effluent under any of the conditions tested (detection limit of 10 μg/L). Thus, this process is promising for the treatment of nitrate-contaminated groundwater at multiple scales.…”

Electrochemical Aging and Halogen Oxides Formation on Multiwalled Carbon Nanotubes and Fe3O4@g-C3N4 Coated Conductive Membranes

“…The generation of chlorine related byproducts during electrochemical membrane filtration is initiated by the oxidation of chloride at the anode surface, which follows the general oxidation pathway as shown in Figure c (Cl – → Cl· → HOCl/OCl – → ClO 2 – → ClO 3 – → ClO 4 – ). − However, halogen oxides byproduct generation highly depends on the electrode materials . The halogenated byproduct formation on the two presented composite conductive membranes has not been reported elsewhere.…”