Study On Determination Of COD By Ti/TiO₂ Electrode And Its Reaction Kinetics

Chemical oxygen demand(COD)is an important organic pollution parameter.How to detect COD simply and quickly is of great significance for pollution prevention.The catalytic oxidation method of the electrode is a promising online detection technology for COD analysis because of its advantages of being fast,simple,and easy to automate.However,due to the wide variety of organic pollutants in water,whether these methods can oxidize various organic compounds in a short time without any difference,the reliability of COD determination by catalytic oxidation method is not satisfactory in practical applications.Therefore,as a relatively new COD analysis and detection technology,catalytic oxidation still needs to do a lot of work in electrode research and development,electrode reaction mechanism.In this paper,two kinds of Ti/TiO2 electrodes,Ti/TiO2 thin film electrodes and Ti/TiO2 nanotube array electrodes were prepared by anodic oxidation.The SEM,XRD,cyclic voltammetry and linear scanning voltammetry of the two prepared electrodes were characterized,and they were applied to the determination of COD by electro-catalytic oxidation and the surface dynamics of the electrodes during electro-catalytic oxidation were studied.Ti/TiO2 electrode with nanotube array structure of anatase phase and inner diameter of 100 nm and wall thickness of 20 nm was prepared by the secondary anodization method,and the porous needle-like mesh Ti/TiO2 thin film electrode with rutile phase was prepared by the primary anodization method.The electrochemical performance test showed that the reaction of Ti/TiO2 electrode was irreversible,and the oxygen evolution overpotential of Ti/TiO2 nanotube electrode was higher than that of Ti/TiO2 thin film electrode,which had higher electrocatalytic oxidation capability.With rhodamine B(RhB),phenol(PhOH),aniline(An),methyl orange(MO),methylene blue(MB)and potassium hydrogen phthalate(KHP)as the target pollutants,the COD concentration of the single-component organic solution determined by two electrode electrochemical methods is proportional to the anodic oxidation current I in the linear range of 5-120 mg/L,and the determination result of COD in the mixed-component organic solution is also valid in this linear range.The same COD concentration and different oxidation currents of different organic substances indicate different electrocatalytic kinetic behaviors of organic substances on the surface of Ti/TiO2 electrode.With MO,MB and KHP as the target pollutants,the kinetic behavior of organic matter on the surface of Ti/TiO2 nanotube array electrode was studied by chronoamperometry.The electro-catalytic reaction was in accordance with the first-order kinetic process.The activation energy Ea of different organic compounds was obtained by reaction rate constant k at different temperature,MO was 38.82 kJ/mol,MB was 13.80 kJ/mol and KHP was 35.55 kJ/mol.The kinetic behavior of different organic substances on the electrode surface is different,which proves that the oxidation current is not only linearly related to the COD concentration of organic substances,but also related to the type of organic substances.In addition,the Pearson correlation coefficient is 0.985 through repeated experiments of potassium hydrogen phthalate simulated wastewater.The values obtained by the electrochemical COD test method and the standard COD test method have high consistency.The Ti/TiO2 electrode test system has good reproducibility and stability.