Optimizing The Operation Condition Of COD On-line Monitoring Instrument Based On Boron Doped Diamond Electrode

Boron-doped diamond (BDD) possesses many advantages such as wide electrochemical window, low voltammetric background current, high level of mechanical strength and corrosion resistance. Therefore, the environmentally friendly material BDD was adopted as an electrode to determine COD by amperometric method with the self-made COD on-line monitoring instrument. Meanwhile, test conditions of the self-made COD on-line monitoring instrument were optimized. The main work is summarized as following:(1) The BDD film was prepared on a titaninm pillar in a microwave plasma chemieal vapour deposition (MW-PCVD) reactor. The characterization of SEM, Raman spectrum and XRD demonstrated that the BDD film was uniform, continuous, and compact. The characteristic peak of diamond in Raman spectrum appeared clearly and the diffraction peaks of different crystal plane diamond in XRD pattern were observed. Therefore, the BDD film was high quality. The electrochemical characteristics of BDD film were analyzed in cyclic voltammetry. The results indicated that the BDD film possessed low voltammetric background current, wide electrochemical window, good electrochemical stability and reversibility It was believed that the BDD film was a good electrode material.(2) The BDD film was packaged as an electrode. The COD of glucose simulated wastewater were determined in self-made COD on-line monitoring instrument by using a BDD electrode. In the early experiments, the determination of COD was not stable. It was positive that the outside temperature and BDD film wrer not the main factors. The main factor was applied voltage. It was more suitable that applied voltage was 2.3V. According to optimizing the test conditions of the self-made COD on- line monitoring instrument, we can conclude that the optimized conditions of the instrument were:applied voltage was 2.33V, electrolyte concentration was 0.25M sodium sulfate solution. pH range was wide, the instrument could accurately measured in the range of our study (pH=2-11). Regeneration concentration must be greater than 0.3M. Dilution ratio was 1:5.(3) The interference of the chloride ion has been studied. The result indicated that the interference began to produce when the chloride ions concentration was greater than 200mg/L, and the degree of interference varied with the concentration of chloride ions increased. (4) The COD of other organic simulated wastewater were online determined. The COD response values for the small molecule organic were greater. However, for the macromolecular organic matter, the COD values could be detected when the COD was greater than 200mg/L.