Anodic Oxidation For Degradation Of Dyeing Wastewater In Eleochemical Systems With Titanium Suboxide Anode

Electrochemical advanced oxidation processes(EC-AOPs) have been widespread concern in biorefractory organic wastewater treatment, because of its high-effect, low-consumption, no secondary pollution superiority. The percentage of abatement and the effciency of EC-AOPs depend to a great extent on the nature of the anode material, and thus, its properselection is extremely important.The electrode must have the properties of enough electrical conductivity high catalytic activity, high physical and chemical stability, being resistant to erosion, corrosion, low cost and long service life. Titanium oxides have unique crystal and electron structure, which result in good electrical conductivity and excellent corrosion resistance. Among the series of titanium oxides, the Ti4O7 has the highest conductivity. Herein, the monolithic porous Ti4O7 electrode is fabricated, and for decolorization of Methylene Blue(MB, used as a model azo dye) compared with traditional carbon cloth in a two chamber electrochemical oxidation system, and also investigated for electrochemical tertiary treatment of refractory industrial dyeing and finishing wastewater(DFWW).Electrochemical Impedance Spectroscopy(EIS), Tafel behavior, Cyclic Voltammetry(CV), Chrono Potentiometry and Accelerated lifetime tests were measured to investigate the electrochemical properties of MB on carbon cloth anode and Ti4O7 anode. EIS demonstrated that the Ti4O7 anode behaves good electrical conductivity approaching that of carbon cloth, what’more, charge transfer resistance(Rct) of Ti4O7 anode was much lower than that of carbon cloth anode, in addition, the exchange current density for Ti4O7 abode was two orders of magnitude higher than that for carbon cloth suggesting that the Ti4O7 anode was more favourable for electrons transfer from the anode to MB. Cyclic Voltammetry demonstrated that the oxidation peak current of Ti4O7 anode is 7.4 times higher than that of carbon cloth anode. What’more, for Ti4O7, the potential for water oxidation should be 2.5 V(vs. SCE). Thus, Ti4O7 owned higher electro-oxidation activity compared with carbon cloth and promoted the mass transport process as the larger active surface area of porous Ti4O7. Furthermore the CV curves of Ti4O7 showed barely changed after test for 200 cycles, on the contrary, carbon cloth has a significantly decreased after running 200 cycles., the chrono potentiometry curves showed which result could reduce the undesirable OER occurs. The result of accelerated life test showed that the working life time of electrode at a defined current density could be approximately 30 years for Ti4O7 anode, by contrast to 7 years for carbon cloth anode. Thus, Ti4O7 anode has good conductivity, brilliant stability, excellent electrochemical stability, large electrochemical window and long service life time.The electrochemical oxidation system with carbon cloth anode and Ti4O7 anode were usde to analyzed the the performance of different anodes on MB degradation. The MB degradation efficiency with Ti4O7 anode achieved 99.6% within 105 min, while the carbon cloth anode was only 76.2%. At the end of the reaction, the mineralization rate with Ti4O7 anode achieved 83.6%, while the carbon cloth anode was only 43.2%. A possible cathodic reaction mechanism for the degradation of MB was suggested based on the electrochemical combustion: the MB was completely mineralized to H2 O, CO2, and inorganicions on the surface of Ti4O7 anode by physisorbed ·OH.We also analyzed the key factors affecting MB degradation, mineralization and performance of the electrochemical oxidation system with Ti4O7 anode. It turned out that when the initial concentration of MB keeped below 100 mg/L, 1.13 m A/cm2 was the optimal current density, 3.01 was the optimal anolyte p H for electrochemical oxidation system to fulfill higher efficiency of degradation and mineralization, lower power consumption and higher Coulombic efficiency.Thereafter, the performances of Ti4O7 was examined and assessed for electrochemical tertiary treatment of refractory industrial dyeing and finishing wastewater(DFWW). At current density of 8 m A/cm2 after 2 h reaction, the concentration of s COD was met the discharge standard issued by Environment Protection Agency of China. Last, the possible mechanisms for electrochemical decomposition of organic pollutants by Ti4O7 were analyzed and discussed based on the change of chloride ion concentration, p H and the removal efficiency of s COD during the recation. As a result, the oxidation of DFWW by electrogenerated active chlorine could coexist with the direct oxidation at the electrode surface, as well as with the reaction with hydroxyl, chloro, and oxychloro radicals.