| As a kind of advanced oxidation process(AOPs),electrochemical water treatment technology has received extensive attention due to its high efficiency,multi-functionality and environmental friendliness.Among them,the emerging three-dimensional(3D)electrode technology has received special attention,which is developed on the basis of filling some conductive particles(called particle electrodes)in traditional two-dimensional(2D)electrode devices.After turning on power,these conductive particles are polarized under the action of electrostatic induction to form a large number of microelectrodes,which not only increases the specific surface area of the electrode,but also shortens the migration distance of the reactants,and improves the current efficiency and processing capacity.Under the same conditions,the system has higher degradation efficiency and lower energy consumption than the 2D electrode system.However,most of these three dimensional electrode systems fail to achieve significant improvements in catalytic efficiency,only by less than 30%.Such problems as high energy consumption and strong dependence on the main electrode limit its practical application.In order to overcome these shortcomings,it is necessary to explore novel catalytic systems with high catalytic activity.In this study,a new type of electrochemical advanced oxidation system namely the bipolar electrode system was prepared,its degradation mechanism and the influence of different operating parameters on its degradation of pollutants were studied,and the bipolar electrode system was applied to the degradation of ammonia nitrogen.The bipolar electrode system can overcome the defects of the three-dimensional electrode system and has low power consumption.The main contents are as follows:(1)TiO2/C composites were successfully prepared by sol-gel method.The electrochemical properties of TiO2/C composites were characterized by electrochemical cyclic voltammetry test.The results show that oxygen reduction occurs at the cathode of TiO2/C composites under applied voltage,and the reduction peak is located at-0.35V vs.Ag/AgCl.The oxygen reduction peak still exists after 1000 cycles of cyclic voltammetry scanning,which proves that the prepared TiO2/C cathode has superior stability.In the process of preparing bipolar electrodes,appropriate addition of Na2SO4 is beneficial to increase the specific surface area of the bipolar electrode and greatly improve its electrocatalytic activity.The best ratio of catalytic material,Na2SO4 and photosensitive resin binder is 8:1:2.Under this ratio,the bipolar electrode has the largest hardness and the highest catalytic activity.By laser confocal electron microscopy,we observed that the surface of the bipolar electrode with good performance was rough and uneven with a large number of fine pores(2)The electrochemical process happened in the BPE system was investigated in detail based on the theories of bipolar electrochemistry.Three pathways were proposed for the generation of ·OH in the BPE system:H2O2 generated on the cathode of driving electrode,which decomposed on the cathode of BPE to·OH;·OH generated on the anode of BPE directly and O2 reacted directly with TiO2 to generate·OH.The BPE system could provide 26.80 mg/L·OH for 1 hour at driving potential of 2.0 V.The optimal operation parameters for driving potential,pH and temperature were 2.0 V,pH 3.0 and 298K,respectively.Especially,the electricity consumption of the BPE system is calculated to be 54%lower than that of the 3D system.In addition,BPE has better reusability and durability compared with 3D electrodes.The analysis on degradation kinetics and thermodynamics exhibits that MB degradation is an endothermic reaction.The endothermic process mainly happened during the electrocatalytic reaction of TiO2/C composites towards·OH generation(3)Ammonia nitrogen can be degraded successfully by using bipolar electrode system.The optimal operating parameters of degradation are pH=11.0,driving voltage 2 V,T=308 K,respectively.Under this reaction condition,the degradation efficiency of ammonia nitrogen was about 70.91%for 1 h.When pH=3.0,ammonia nitrogen mainly exists in the form of NH4+,and when pH=10.0,ammonia nitrogen mainly exists in the form of NH3 molecule.Among them,·OH can oxidize free NH3 molecules,but it is difficult to oxidize NH4+.Isopropanol is used as a masking agent for ·OH to verify that the main reason for the degradation of ammonia nitrogen in the bipolar electrode system is that the ·OH attack and destroy ammonia nitrogen. |
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