Water Science and Technology (Aug 2021)
Determination of chemical oxygen demand in mixed organic solution by Ti/TiO2 nanotube array electrode method
Abstract
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. HIGHLIGHTS A Ti/TiO2 nanotube array electrode was prepared by a secondary anodic oxidation method, a simple and rapid technique.; The Ti/TiO2 electrode exhibited high electrochemical performance. Its electro-oxidation kinetics conformed to first-order kinetics.; For COD determination by the Ti/TiO2 electrode, net current was affected by temperature, and types and ratios of organics, due to functional groups in the organics.;
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