Degradation Of The Organic Pollutants Using Electro-fenton-like System

With the fast development of industry,all kinds of synthesized organic pollutants which are difficult to degrade have become one of the major sources of pollution.Although the traditional electric-Fenton process have overcome some disadvantages of Fenton treatment method,such as on-site production of H₂O₂,it still has some strawbacks including sludge production,narrow pH range and limited production of hydrogen peroxide.Composite activated carbon fiber?ACF?cathode Mn₃O₄/ACF,which was prepared using a cyclic voltammetry method,was employed in a heterogeneous Electro-Fenton-like system for the degradation of a model dye,methylene blue?MB?,with no other reagents added.The decolorization ratio and the mineralization of MB in the different pH were investigated and the active oxygen species involved in the system were also detected.The experiment results showed that when solution pH was set as 3.0,5.0 and 7.0,the decolorization ratio reached to 97.26%,99.97% and 99.88%,respectively,and TOC removal achieved to 69.79%,88.55% and 76.86%,indicating the extensive feasibility of the system in broad pH range.The results of detection of the active oxygen species demonstrated that H₂O₂ was electro-produced at the surface of cathode,and the hydroxyl free radical ?OH generated by the Fenton-like reaction of Mn₃O₄ with H₂O₂ was responsible to the degradation of MB.The superoxide radical O₂^-was also proved playing important role in decolorization of MB.The mechanism of degradation of contaminants by this heterogeneous Electro-Fenton-like system was preliminarily discussed.Fe?III?-Alg catalysts were prepared by complexing of ferric ions with sodium,which was used in an electro-Fenton system with ACF cathode to degrade a dye MB.The preparation condition for the catalysts and the electrolysis condition for degradation of MB were optimized.The Fe?III?-Alg catalysts were analyzed by SEM?FI-IRand XPS.The oxidizing agents generated by reducing dissolved oxygen in the system were determined and the degradation mechanism of MB was discussed.The experiment results showed that this electro-fenton system has efficient removal effect for MB that the removal rate reached 97.33%.Comparing with the soluable catalysts,Fe?III?-Alg was easier to be removed,and the removal rate for MB kept at relative high level in pH range of 3.0 7.0.Bi₂?MoO₄?₃ was synthesized using sol-gel method,and the morphology,structure and constitutes were verified usi?ng SEM,XRD,FTIR and XPS.Bi₂?MoO₄?₃/Ti electrode was then prepared by coating the synthesized a-Bi₂?MoO₄?₃ at the surface of Ti mesh,was employed in a Electro-Fenton system for the degradation of acid orange II?AOII?.and the catalysis of Bi₂?MoO₄?₃ for the electro-reduction of oxygen to produce hydrogen peroxide was investigated using cyclic voltametry?CV?,electrochemical impedance spectroscopy?EIS?and constant current bulk electrolysis.The results showed that Bi₂?MoO₄?₃/Ti has obvious catalytic action for the production of hydrogen peroxide through two different pathways,and a dual catalysis including a direct electrochemical catalysis and an indirect Bi0 mediated chemical catalysis was proposed.Both two catalytic pathways play important role in making more hydrogen peroxide.each of them makes varied contribution on different conditions of current density in constant current bulk electrolysis of AOII.When the current density was 0.9 mA.cm-2,the removal rate of AOII reached 94.80%.