Study On Methyl Red Degradation In A Novel Gas Diffusion Electrode System

With the fast development of dyes industry, the wastewater produced by dyes industry becomes one of the main sources of water pollution. Due to the variety of dyes, the dyes wastewater is characteristic of high concentration, COD and color as well as its poor biodegradation, the treatment of dyes wastewater is still the problem of industrial wastewater treatment. In recent years, advanced oxidation processes (AOPs) have attracted a lot of interest for degrading non-biodegradable wastewater. Among them, electrochemical oxidation method is a green technology because the reaction condition is mild and the hydroxyl radicals are produced through direct or indirect method by the reaction of a catalytic electrode without adding chemical reagents.Recently many researchers have done much research on cathodic materials, however, there still exist some problems. For example, the current efficiency of H₂O₂ production on gas diffusion electrode is not high, gas diffusion electrode is not sufficiently discussed in degrading organics in the environment. Because of the shortage of cathode materials, a cathode with a high production of H₂O₂ was studied in order to increase the current efficiency and H₂O₂ production, therefore in this study the foUowings will be discussed exhaustly:1 , The gas diffusion electrode made of graphite is used as working electrode, pH and cathodic potential are important factors influencing H₂O₂ production, so the influences of pH and cathodic potential are especially studied. The results showed that in the undivided system H₂O₂ production and current efficiency were high at different pH values, H₂O₂ could reach 45 mg/L, H₂O₂ current efficiency kept above 60%. When cathodic potential was -0.55 V vs. SCE, H₂O₂ concentration was higher than other potentials. 2, Methyl red degradation was studied by different electrochemical methods usingcathodic production of H₂O₂ in the undivided system.(1) In the presence of Na₂SO₄, methyl red was degraded by cathodic production of H₂O₂. When Na₂SO₄ concentration was 0.1 M, pH =3, cothodic potential was-0.55 V vs. SCE, methyl red removal was 60%. When Fe2+ was added into the system, electro-Fenton reaction took place, which produced ?OH. When Fe2+ was added, methyl red was decolored in 5 min, its removal reached 63% and removal rate was greatly improved. After 30 min, its removal could reach 80%.(2) Methyl red was degraded by the coupling of Fe anode and gas diffusion electrode. Methyl red was quickly removed in 5 min, its removal could reach 78% and its catalytic property was better than the above two technology. When the cell voltage was 3.5 V, pH=2.5, methyl red removal reached 86%. In the presence of NaCl, CI" was oxidized into HCIO, oxygen was reduced to H2O2 and organics was degraded by the coupling of anodic oxidation and cathodic reduction. It was found that methyl red was almost removed in 30 min, the optimized reaction condition was 0.15 M NaCl, pH=4, -0.7 V vs. SCE.3 > Methyl red removal was compared in the above electrochemical methods. UV-vis spectra changes were analyzed and the kinetics of methyl red degradation by different electrochemical methods was analyzed. The above methods are good for degrading dyes wastewater, they are expected tobe applicable for practical wastewater treatment.