Determination Of COD In Mixed Solution By Ti/TiO₂ Nanotube Electrode

Chemical oxygen demand(COD)refers to the amount of oxidant consumed when water samples are oxidized with strong oxidant under certain conditions.COD is the measurement of the concentration of organic and inorganic oxides in water,reflecting the extent to which water was contaminated by reducing substances.So it is an important index of water quality evaluation.The determination of COD by electrochemical method is to oxidize the organic matter in the water by electrolysis or electrocatalysis.The amount of organic matter in the water was calculated by the current(Amperage)or electricity(Coulomb)consumption in the oxidation process.The COD value obtained by this method is also called electrochemical oxygen demand.In this paper,the Ti/TiO2 nanotube array electrode was prepared by anodizing method.The prepared electrode was characterized by SEM and XRD.The electrode surface dynamic behavior during electrocatalytic oxidation was studied and applied to the determination of COD by electrochemical method.The Ti/TiO2 nanotube array electrode was prepared by secondary anodizing method with inner diameter of 100 nm,wall thickness of 20 nm.It has stable electrocatalytic oxidation performance.By aniline,Rhodamine B and potassium hydrogen phthalate are used as the target pollutants,the kinetic behavior of organic compounds on the surface of Ti/TiO2 nanotube array electrode was studied by chronoamperometric method,the electrocatalytic reaction was in accordance with the first-order kinetic process.The activation energy Ea of electrode reaction of different organic compounds was obtained by the reaction rate constant k at different temperatures.The activation energy Ea of Aniline,rhodamine B,and potassium hydrogen phthalate were 18.56 kJ/mol,14.25 kJ/mol and 35.32 kJ/mol,respectively.It shows that the kinetic behavior of different organic substances on the electrode surface was different,so the oxidation current was related to the type of organic matters when the electrocatalytic reaction proceeds.In addition,the parameters of Ti/TiO2 nanotube array electrode catalytic organics was studied.The results show that the catalytic degradation efficiency decreases with the increase of initial concentration of organic matter,and the influence of plate spacing on catalytic degradation was not significant.By aniline(an),Rhodamine B(RhB)and potassium hydrogen phthalate(KHP)are used as the target pollutants,the COD of single component organic solution,twocomponent mixed organic solution and three-component mixed organic solution in the linear range of 5-150 mg/L were measured by Ti/TiO2 nanotube array electrode electrochemical method,and the working electrode potential was controlled at 2-3.5 v(vs.sce).The experimental results show that the COD value are directly proportional to the anodic oxidation current I,and when the COD concentration is the same,the different organic matters exhibit different oxidation currents I,indicating that the electrocatalytic kinetic behavior of organic substances on the surface of Ti/TiO2 electrode are different.