Performance Evaluation Of Boron Doped Diamond Electrode In Toxicity Control Of Wastewater And Detection Of Pollutants

Boron doped diamond (BDD), as a kind of environmentally friendly electrode material, possesses low background current, wide potential window, stable physicochemical properties and good biological compatibility. Therefore, BDD shows good application prospects in electrochemical detection and water treatment of pollutants. However, the application of traditional BDD electrode in environmental detection and water pollution control has been hindered by poor reaction selectivity and limited reaction interface. In this thesis, the toxicity control in wastewater treatment based on BDD electrode and the modifications of BDD electrodes has been explored for the application of BDD electrode in wastewater treatment, the construction of selective reaction interface and the enhancement of reaction interface area on BDD electrodes. The main works and results are listed as follows:(1) A series of BDD electrodes were prepared on silicon substrate with different proportions of CH4 as carbon source by MWPCVD systems. The effects of different proportions of CH4 to potential window were investigated by cyclic voltammogram. The results showed that the stable potential windows of the BDD electrodes increased from 1.9 V to 3.5 V when the proportion of CH4 decreased from 20% to 1%. Meanwhile, the grain size of BDD increased from 100 nm to 2-3 μm and the crystallinity of BDD improved significantly. Moreover, the electron transfer properties of the BDD electrode prepared with 1% CH4 was analyzed by electrochemical impedance spectroscopy (EIS), and the results showed that the kinetics of the REDOX reaction on BDD surface was controlled by the diffusion process, the mass transfer process was the main limited step.(2) The BDD electrode was applied in the EAOPs as the anode for the treatment of actual dyeing wastewater effluent, and the efficiency was investigated using COD, TOC, acute toxicity and genotoxicity as evaluation indicators. After 4 h treatment, the removal rates of COD and TOC were 89.7% and 49.5%, respectively. The bioassays revealed that the mortality rate of zebrafish exposed to the water samples for 96 h decreased from 93% to 0. The genotoxicity of dyeing wastewater effluent at 75% dilution was reduced more than 50%. The results illuminated that the EAOP based on BDD anode realized effective treatment of dyeing wastewater by the mineralization decomposition of organic pollutants to reduce the COD, TOC and acute toxicity as well as genotoxicity.(3) The MIPs modified BDD (MIPs/BDD) electrode was prepared by in situ electro-polymerization of pyrrole on BDD electrode in the presence of SMX. The electrochemical detection method with good selectivity to SMX was presented based on the specific recognition of MIPs to template molecule. This approach provided a linear rang of 0.1-100 mmol/L with a LOD of 25.5 nmol/L (S/N=3). The proposed method provided precise and reliable results for the analysis of SMX in lake water, the spiked recoveries were 96.0-106.2%. The signal current to SMX which was much greater than those to three other kinds of sulfa drugs showed good selectivity for SMX. After more than 50 times used in 30 days, the signal current to 50 μmol/L SMX remained 96.7% of the initial value.(4) The vertical columnar array diamond and the three-dimensional porous diamond were fabricated by MWPCVD technology and phase transform ation, respectively. The characterization results showed that the diamond columns of the columnar-diamond with the uniform size (Rxh:8|μm×12 μm) was parallel to each other and perpendicular to the basal plane and the diamond crystals was preferential growth by (111) crystal plane with good crystallinity, as well as very low content of non diamond phase. Meanwhile, the three-dimensional porous diamond with similar microstructure with precursor showed the interplanar spacing (d=2.1 A) and XRD diffraction peak of diamond (111) crystal plane, as well as interplanar spacing (d=3.4 A) and XRD diffraction peak of graphite (002) crystal plane. This suggests that columnar-diamond prepared was possessed of higher crystallinity, and phase transformation efficiency of non diamond to diamond was needed improved.(5) The electrochemical performances of the vertical columnar BDD array electrode prepared by above MWPCVD method was tested, and the results showed larger electrochemical reaction interface which was 1.6 times to traditional BDD electrode. Furthermore, the electrochemical detection of COD with high sensitivity was presented based on the array electrode. The larger electrochemical reaction interface enhanced the current response to COD (9.70 μA/(mg·L-1)), nearly 4 times of it on traditional BDD electrode. This approach provided a linear rang of 9.6-1000.0 mg/L with a LOD of 3.1 mg/L. The signal electrical response was tested to be 96.8% of the initial value after 30 days, as well as being tested for more than 100 times,which confirmed the stability. The error of the determination COD value in the industrial wastewater effluent between this approach and the conventional dichromate method was within 10.0%.The above results illuminate that the EAOP based on BDD anode is an effective way for the removal of organic pollutants and biological toxicity in wastewater. Meanwhile, it is also indicated that the reasonable modification and structure design are able to effectively improve the corresponding electrochemical properties of BDD electrode and achieve the purposes like selective detection or response signal enhancement. In this thesis, the application in water treatment, the modification of BDD and its application in pollution detection were explored, which provides theoretical bases for the application and development in the detection and control of environmental pollution.