Design And Application Of Electrochemical COD Sensor Based On ?-PbO₂

Electrochemical COD sensors can replace the time-consuming,laborious and environmental pollution of potassium dichromate oxidation method.The COD value of organic pollutants in water is given directly by electrical signals,which is the basis of on-line water quality monitoring.As the electrode material of COD sensor,it should have the characteristics of strong electrochemical oxidation ability(high oxygen evolution overpotential),good stability(good repeatability,long service life)and low price(easy to popularize).The ?-PbO2 electrode prepared by anodic oxidation method has the above characteristics.But in order to widely used,we still necessary to study ?-PbO2 electrode as follows:how to enhance adhesion and conductivity between the coating and the substrate;the influence of organic species for COD test;Optimization of determination conditions for electrochemical COD sensor.Based on the existing problems of electrochemical COD sensor,this paper will start from the following aspects:(1)graphite felts/?-PbO2,graphite sheet/?-PbO2,Ti/RuO2/?-PbO2,the different substrate of PbO2 electrode were prepared.SEM,XRD,LSV,and ·OH generation capability were test between three kinds of PbO2 electrodes.Finally,the graphite/?-PbO2 electrode was applied to the electrochemical COD detection.(2)In the aspect of electrochemical COD detection.Firstly,the best working potential of graphite/?-PbO2 electrode was determined to be 1.45 V,and then the best detection range of pH for graphite/?-PbO2 electrode was determined to be 4-11.Under this condition,we test the COD of single organic compounds(p-nitrophenol),using graphite/(3-PbO2 electrode,the anodic responding current intensity Iresp is well linear to the COD value of organics in the electrolyte(R2=0.99).By the same time,the graphite/?-PbO2 electrode was applied to the totally oxidation process of complex organic compounds(p-nitrophenol).(3)In the application of electrochemical COD detection,12 common organic compounds were selected for the detection of COD.The linear relationship between the COD value of 12 kinds of organic compounds and the anodic current were measured.Then,the deviation between the electrochemical determinationand the CODcr value of GB method was investigated.In order to reduce the error,the method of establelishing the working curve of the mixed water sample is put forward.Therefore,several methods are suggested to improve the accuracy of COD measurement through the anodic oxidation method.