Fabrication Of TiO₂ Nanotube-based Chemical Oxygen Demand?COD? Sensor And Its Sensing Performance

Analytical determination of the quantity of organic matter in water is crucial for water quality assessment and pollution control. The quantity of drainage system can be expressed by COD value to judge the level of organic pollutant. The traditional COD detection methods usually have several unavoidable drawbacks, including secondary environmental pollution, complicated operation and serious Clinterference. Hence, it is urgent to develop a new COD detection method to avoid all above-mentioned drawbacks. In this thesis, TiO₂ nanotube array was prepared by an anodic oxidation method and used as a photoelectrocatalytic COD sensor for detecting several kinds of typical organic pollutants.Firstly, to prepare TiO₂ nanotube array with well-defined nanostructure, high crystallinity and excellent photoelectrocatalytic performance, the experimental parameters such as electro-oxidation voltage, electro-oxidation time and calcination temperature were optimized primarily. The results clearly showed that the optimum conditions are as follows: oxidation voltage is 40 V, oxidation time is 4 h, calcination temperature is 550 oC and electrolyte is 0.25 wt% NH4F-0.75wt% H2 OEG. Secondly, the photoelectrocatalytic performance of TiO₂ nanotube array was optimized by adjusting the external applied bias potential and the amount of oxygen supplied. According to the photoelectrocatalytic mechanism of TiO₂, external bias potential can be applied to promote the separation of photogenerated holes and electrons. Afterwards, photogenerated holes and electrons can be captured by superficial O2 or H2 O to form active oxygen radicals with sufficient oxidative ability to destroy organics adsorbed on the TiO₂ surface. Thus, the concentration of organic matter can be reflected by photocurrent of photoelectrocatalytic reaction. Experimental results showed that excellent photoelectrocatalytic activity of TiO₂ nanotubes can be achieved at the 1.0 V applied bias potential and oxygen saturation. Finally, the photocurrent response of different organic matters at TiO₂ nanotube array was tested through chronoamperometry in a three-electrode electrochemical cell in which a Ag/Ag Cl electrode was used as the reference electrode, a platinum foil was used as counter electrodes and the prepared TiO₂ nanotube array as the working electrode. The results revealed that Inet increased linearly with increment of log Cm, and the COD value determined by this photoelectrocatalytic mechanism of TiO₂ array was well consistent with theoretical COD values, indicating that the proposed COD sensor in this thesis can be used for the detection of COD values of different organic matter with high accuracy.In brief, TiO₂ array based photoelectrocatalytic COD sensor of this thesis has many advantages such as wide linear range, good reproducibility, lower detection limit and environmental friend as compared with the standard method, endowing it to be a promising candidate for real-time detection of COD.