Recently, PNAS (Proceedings of the National Academy of Sciences of the United States of America) published online the latest findings in green advanced oxidation technology by Professor Peng Chuang's research group from WHU’s School of Resource and Environmental Sciences. This study achieved radical-based advanced oxidation using only air and electricity, offering a new route for pollution control based on green chemistry.
The paper is entitled Sustainable and Feasible Reagent-free Electro-Fenton via Sequential Dual-cathode Electrocatalysis. Wang Jiabei, a graduate student of 2018 from the School of Resource and Environmental Sciences, is the first author. The paper was independently completed by Peng Chuang's research group, and Wuhan University is the sole institution for this paper.
Fenton reagent achieves non-selective degradation of organic pollutants, with strong oxidizing hydroxyl radicals that exist for a very short time, thereby avoiding secondary pollution caused by oxidants. However, conventional Fenton technology costs a large amount of hydrogen peroxide (H2O2) and ferrous iron, which is not only costly but also needs additional processes to remove the residual iron agent. Electro-Fenton technology can produce H2O2 by in situ electrocatalytic reduction of oxygen, or realize the regeneration of ferrous ions to reduce its dosage. Previous studies have shown that H2O2 can also be electro-catalytically converted into hydroxyl radicals by one-electron reduction. However, this reaction and the two-electron reduction of oxygen have different requirements for electrode materials and reaction potential. Therefore, it is not practical to obtain hydroxyl radicals with a one-step oxygen reduction at the same electrode.
Based on previous studies, electrochemical deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) electro-deposited on carbon cloth as a cathode can achieve an efficient generation of H2O2 with an electron transfer number up to about 2.5 and a current efficiency of 88.7 %. The H2O2 solution with a concentration of 243.1 mg / L is obtained in two hours with an energy consumption of only 4.7 kWh / kg H2O2. The generated H2O2 can be further electro-reduced to produce hydroxyl radicals on a stainless-steel–mesh cathode. The source of hydroxyl radicals is verified by electron paramagnetic resonance and fluorescence spectroscopy. The degradation experiment shows that the hydroxyl radicals generated by this method could simultaneously realize the decolorization of organic dyes and total organic carbon (TOC) removal.
The process substitutes catalysis for chemicals, running solely on air and electricity to realize the degradation of pollutants, which is in line with the principle of green chemistry. In addition, the practical application of this process is promising as its electrode mature commercial materials are cheap and suitable for mass production, which ensures strong long-term operation reliability. Its energy consumption is equivalent to that of the existing electro-Fenton technology. It can realize the removal of tetracycline hydrochloride and bisphenol A, which are difficult to degrade organic pollutants, without the dissolution of metal ions. The generated hydrogen peroxide can also be used for UV-based photo-Fenton advanced oxidation.
The paper also reflects the authors' view on the philosophy of science. They formally propose the logical fallacy of 'appeal to nanotechnology', and express concern about its negative impact on research in related fields.
Link to the paper: https://www.pnas.org/content/118/34/e2108573118
Rewritten by Shen Shutian
Edited by Zhang Ruoxi & Zou Xiaohan
