Determination of chemical oxygen demand in mixed organic solution by Ti/TiO2 nanotube array electrode method

Chemical oxygen demand (COD) is a significant parameter for analyzing water quality. However, the detection methods still suffer from the problems of secondary pollution, use of harmful substances, complicated operations, etc. To trace these problems, a Ti/TiO2 nanotube array (NTA) electrode was successfully prepared in this work by the secondary anodic oxidation method. The prepared electrode was used to determine the COD of single- and multi-component solutions (including aniline, rhodamine B, and potassium hydrogen phthalate). The Ti/TiO2 NTA electrode exhibited higher electrochemical oxidation efficiency than the neat Ti one. The electrocatalytic reactions of the target organics on the electrode surface were confirmed to conform to the first-order kinetic process. Within a COD range of 5–150 mg/L, COD value was not only proportional to the anodizing current but also related to organic matter itself. The activation energies of electro-oxidation reaction of different substances differed from each other (An: 14.25 kJ/mol, RhB: 18.56 kJ/mol, and KHP: 35.32 kJ/mol), indicating the differences in their dynamic behaviors on the electrode surface. The related bias obtained for all successive measurements was below ± 5.8%. Therefore, we report a fast, effective, accurate, and well reproducible COD detection method that is feasible for both single-component and multiple-component organic solutions.