Electrochemical Determination of Chemical Oxygen Demand Using Ti/TiO2 Electrode

To overcome the shortcomings of the conventional potassium dichromate method (PDM) for monitoring chemical oxygen demand (COD) of waters, many efforts have been made on developing quick and environment-friendly techniques. Among all alternatives, electrochemical (EC) techniques are very competitive due to their relatively simple devices and quickness. A number of electrodes have been fabricated to investigate electrochemical determination of COD. However, little work has been reported on TiO2 based electrode for this purpose. In the present work, Ti/TiO2 electrode was simply prepared by anodic oxidation of pure titanium. Aqueous solutions of potassium hydrogen phthalate and phenol were electrolyzed by chronocoulometry in a three-electrode system with Ti/TiO2 as working electrode (anode). Organic compounds were electrochemically oxidized on Ti/TiO2 electrode by hydroxyl radicals and the released electrons were recorded and transferred to currents. The electric currents were proportional to the COD values of the water samples being investigated. Based on data of COD values and corresponding currents, a linear regression equation was obtained for a certain kind of waste water. With the regression equation, current of an unknown water sample was transferred to its COD value. Conditions for the presented EC method were set up as cell voltage 2.0V v.s. SCE and pH 7.0. The linear range of COD was of about 25 similar to 30 mg/L. COD values of real waste water samples were measured by Ti/TiO2 electrode and the relative errors were all in the range of +/- 8% compared with data determined by conventional PDM. The electrochemicalmethodology was successfully applied to evaluate COD in waste water.