| The treatment of reduced nitrogen wastewater has always been the focus of environmental protection.Electrocatalytic technology has been favored by researchers in the treatment of nitrogen-containing wastewater due to its advantages of no secondary pollution and low reaction condition requirements.However,the application of electrocatalytic technology is hindered by the problems such as easy corrosion,poor denitrification effect,poor economy efficiency,and unclear denitrification mechanism.In this paper,palladium（Pd）,tin（Sn）and manganese（Mn）are used to modify ruthenium（Ru）-iridium（Ir）electrode to improve the performance of the electrode.The prepared electrode is used as the working electrode,and inorganic reducing nitrogen（ammonia nitrogen）,straight-chain organic reduced nitrogen（acrylonitrile）and cyclic organic nitrogen（sulbactam sodium）are selected as the research objects.The degradation law,kinetics,and mechanism of electrocatalytic oxidation of wastewater containing chlorine and nitrogen are intensively studied.The main conclusions are as follows:（1）Ru-Ir solid solution electrodes with different molar ratios of Ru-Ir are synthesized by thermal oxidation.Scanning electron microscope（SEM）,Transmission electron microscope（TEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）show that the mole ratio of Ru-Ir affected the formation and microstructure of Ru-Ir solid solution,and then affected the performance of chlorine evolution and electrical conductivity of Ru-Ir electrode.The optimum molar ratio of Ru-Ir for preparing Ru-Ir solid solution electrodes is 2:1,and the chlorine evolution potential of Ru-Ir electrode is 1.0690 V（vs SCE）.The crystal structure of Ru-Ir solid solution is rutile,and the crystal arrangement is uniform.（2）Pd was used to enhance the corrosion resistance of Ru-Ir electrode,Sn improved the electrocatalytic performance of Ru-Ir electrode,and the corrosion resistance and chlorine evolution performance of Ru-Ir electrode were enhanced.The Pd-Sn modified Ru-Ir electrode was successfully prepared,and then the denitrification law and kinetics of the treatment of chlorine-containing inorganic nitrogen（ammonia nitrogen）wastewater with this electrode were studied.SEM,TEM,XRD,and XPS explain that the molar ratio of Pd-Sn affects the microstructure,crystallinity and binding energy of the Ru-Ir electrode material,and then affects the chlorine evolution performance and corrosion resistance of the electrode.When the molar ratio of Pd-Sn is 3:1,the modified Ru-Ir electrode showed the best chlorine-evolution performance and corrosion resistance.The chlorine-evolution potential and corrosion current density were 1.064 V（vs SCE）and 6.52×10-4 A·cm-2,respectively.The optimum conditions for the synthesis of the Pd-Sn modified Ru-Ir electrode were as follows:the molar ratio of Ru-Ir is 2:1,the molar ratio of Pd-Sn is 3:1,in which the mass of Pd and Sn is 1.5%of the total mass of elements,the calcination time is 4.0 h,the calcination temperature is 500℃,and the solvent is water.The denitrification process of ammonia-nitrogen conforms to the zero-order kinetic equation and the apparent activation energy is 14.089 k J/mol.The electrocatalytic oxidation technology mainly relies on indirect oxidation to remove ammonia-nitrogen,that is,under the action of the"oxidant"chloride ion,ammonia-nitrogen is eventually converted to nitrogen.According to Response Surface Methodology（RSM）,the optimal reaction conditions for the electrocatalytic treatment of 200 m L of high-chloride ammonia-nitrogen wastewater with chloride ion concentration of 5000 mg/L and ammonia-nitrogen content of 50 mg/L were as follows:the p H was 7.07,the reaction time was 37.98 min and the current was 0.99 A.（3）The Mn-Sn modified Ru-Ir electrode was successfully prepared by utilizing the diversity and organophilicity of Mn oxides and combining with the good electrocatalytic performance of Sn,and then the law,kinetics and denitrification process of treating chlorine-containing straight-chain organic nitrogen（acrylonitrile）wastewater with this electrode were studied.SEM,TEM,XRD and XPS declared that the molar ratio of Mn-Sn affected the microstructure,crystallinity and type of manganese oxide of the modified Ru-Ir electrode materials,thus improving the electrocatalytic performance of the modified electrode materials.When the molar ratio of Mn-Sn is 1:1,the modified Ru-Ir electrode has the best electrocatalytic performance with oxygen-evolution potential of1.303V and voltammetric charge of 1.51C·cm-2,respectively.The optimum synthesis conditions of Mn-Sn modified Ru-Ir electrode were as follows:the mass of the two elements of Mn-Sn accounts for 1.5%of the total mass of the elements,the molar ratio of Ru-Ir is 2:1,the molar ratio of Mn-Sn is 1:1,the calcination time is 4.0 h,the calcination temperature is 450℃,and the solvent is water.Mn-Sn modified Ru-Ir electrode can realize high-efficiency removal and denitrification of acrylonitrile,which is the result of direct oxidation and indirect oxidation.200 m L of acrylonitrile wastewater with acrylonitrile content of 1000 mg/L and chloride ion concentration of 5000 mg/L was treated by electrocatalysis,and the removal rate of acrylonitrile can reach 100%under the reaction conditions of 1.0 A and reaction time of 50 min.However,the denitrification rate is only 85.9%because acrylonitrile will be partially converted into other organic nitrogen in the solution.（4）The electrocatalytic technology could be used as the pretreatment technology of sulbactam sodium wastewater,and the removal rate of sulbactam sodium could reach90%.Denitrification process of sulbactam sodium wastewater by electrocatalytic oxidation is mainly done by indirect oxidation.Under the action of"oxidant"chloride ion,the removal rate of total nitrogen can reach 71.9%,but the mineralization rate of organic matter is only 33.6%,indicating that after the electrocatalytic treatment of sulbactam sodium wastewater,the biochemical unit is needed to carry out the mineralization of organic matter. |
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