【作者】 马传军；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境工程， 2011， 博士

【摘要】 化学需氧量(COD)是水污染监测中的重要参数,同时也是我国“十二五“期间总量减排的四项约束性指标之一。COD的标准测量方法是重铬酸钾法,以该方法为基础开发的在线式设备结构复杂,产生二次污染。近年来发展起来的电化学测量方法,克服了标准方法的诸多不足。本文在课题组前期工作的基础上,以器件化的BDD膜电极为核心传感器,搭建了COD在线式分析仪。另外,研究制备了Ti/BDD/PbO2和Ti/Sb-SnO2/PbO2两种复合电极,提高了电化学方法测定COD的检测限,以期适应轻度污染水体的监测。本文围绕以上内容开展的研究工作主要包括以下几个方面：(1)利用微波等离子体气相化学沉积设备,控制氢气流量89sccm,甲烷流量1sccm,硼烷流量10sccm,微波功率2000 W,反应压强4000-6000 Pa,基体温度600-800℃,可以制备出棱角分明、刻面清晰的微米级BDD膜；XRD谱图可观察到(111)和(220)晶面的衍射峰,Raman光谱中出现了位于1334 cm-1处的尖峰,显示制备的BDD膜具有良好的形貌和晶形。电化学测试表明BDD膜电极的电势窗口大于3.5 V,阳极析氧电位大于2.3 V,是作为COD传感器的良好电极材料。将BDD膜进行器件化组装,器件化的电极具有良好的密封性,不同电极对100 mg/L的葡萄糖水样测定的相对标准偏差小于10%,显示了良好的平行性,为在仪器中的使用奠定了基础。(2)以器件化的BDD膜电极为核心传感器,开发了与之配套的在线式监测方法和仪器。探讨了样机的开发框架、主要配件、测量流程、标准曲线模型等问题。优化的相关参数分别为：硼碳比10000 ppm、电极直径8 mm、清洗电位4 V、清洗时间90s。在优化条件下,样机的检测范围为30-10000 mg/L,可以在较大的范围内对污染源进行监测；对不同COD浓度的葡萄糖水样进行测定的相对标准偏差均小于5%,显示出良好的稳定性。与标准方法相比,基于BDD膜电极的COD在线样机的检测时间大为缩短(测量周期5-8 min,其中响应时间为2 min),无二次污染问题,进一步完善后有望进行市场化运作。(3)采用微波等离子体气相化学沉积和电沉积两步法制备了Ti/BDD/PbO2复合电极,利用电化学方法进行COD测定研究。该方法的最优测量电位为1.45 V,线性范围为0.5-175 mg/L,检测限为0.3 mg/L(S/N=3)。对实际废水的测定结果表明,该方法与标准方法之间的相对误差小于10%,具有较好的一致性。与现有电化学测量方法相比,该方法的检测限大为提高,在低浓度污水的监测方面具有良好的应用前景。(4)采用热分解与电沉积结合的方法制备了Ti/Sb-SnO2/PbO2复合电极,并将其用于COD测定研究。实验优化的测量电位为1.4 V,pH值为3-9,Na2SO4浓度为25 mM。在此优化的条件下,建立的COD浓度与响应电流之间的关系为inet=2.059 COD+0.3762,线性范围为0.5-200 mg/L,对应的检测限为0.3 mg/L。对包括地表水在内的实际水样的测定结果表明,该方法与标准方法之间的最大相对误差小于12%。该方法同时具有不使用有毒有害试剂,易实现在线测定等优势,不但可以用于污染源排放的控制领域,而且有望在轻微污染水体的有机物污染监测方面加以应用。综上所述,以器件化的BDD膜电极为COD传感器搭建的在线式分析仪,具有结构简单、测量周期短,检测范围宽等优点,且不使用有毒化学试剂,有效的解决了二次污染问题。同时,本文研究制备的Ti/BDD/PbO2和Ti/Sb-Sn02/PbO2两种复合电极的灵敏度大为提高,很好的适应了污染源监测的需求,有助于促进电化学测量方法在COD测定领域的应用与发展。更多还原

【Abstract】 Chemical oxygen demand (COD) is an important parameter for the evaluation of water quality and it is also one of the four reduction indicators during the twelfth five-year plan. The most common COD determination method is dichromate titration. The on-line COD analyzer based on dichromate method results in secondary pollution and the structure of this kind of analyzer is also complex. The electrochemical method developed in recent years can avoid many disadvantages involved in the conventional method. In the past research, the environmentally friendly material, boron doped diamond (BDD), was used as a sensor to determine COD under manual operating condition. In this dissertation, a practical BDD film electrode is fabricated and applied to a homemade on-line COD analyzer, and then the relative measurement parameters are optimized. Additionally, two kinds of composite electrode materials, Ti/BDD/PbO2 and Ti/Sb-SnO2/PbO2, are prepared, enhancing the detection limit of COD measurement by electrochemical method. The application of both electrodes would be extremely attractive in the field of COD determination for surface water or other clean waters with low COD values. Around what mentioned above, the following work has been done:(1) A microwave plasma chemical vapor deposition system (MPCVD) was used to prepare BDD films. The source gas (flow rate 100 sccm) with a mixture of methane (1 sccm), hydrogen (89 sccm), and B2H6 (10 sccm) was employed as the reagents. Temperature of the substrate was 800℃and pressure of the reacting chamber was in the range of 4000-6000 Pa. The fabricated BDD film was composed of well faceted diamond crystals in the micron range. The characteristic peak of diamond in Raman spectrum appeared clearly at 1334 cm-1 and the diffraction peaks of diamond (111) and (220) in XRD pattern were observed, indicating that the quality of the BDD film was perfect. Then the BDD film was assemble into a practical BDD film electrode with good sealing performance. The assembled BDD film electrode would be an important part of the homemade on-line COD analyzer.(2) Based on the assembled BDD film electrode, a homemade on-line COD analyzer was developed. The factors such as the instrument framework, the main components, the measurement process and the model of the calibration were discussed. The optimum B/C ratio was 10000 ppm, the diameter of electrode was 8 mm, the cleaning applied potential was 4 V and the cleaning time was 90 s. Under the optimized conditions, the analyzer was successfully employed to determine the COD values of glucose samples with different concentration and the resulting relative standard deviation (RSD) was below 5%. As compared with the standard method, the homemade analyzer could be carried out rapidly and overcome the shortage of secondary pollution. Therefore, the analyzer was promising to realize market operation.(3) A novel Ti/BDD/PbO2 composite electrode was prepared for COD determination via chemical vapor deposition (CVD) combined with electrodepositition method. Under the potential of 1.45 V, a linear range of 0.5-175 mg/L and a detection limit of 0.3 mg/L were achieved. The real samples from sewage plant, food and dyeing factories were applied to test the feasibility. The results measured by Ti/BDD/PbO2 composite electrode agreed well with those determined by the standard method. The proposed method with lower detection limit showed a respect in COD detection of slight polluted water.(4) A Ti/Sb-SnO2/PbO2 electrode was fabricated and applied in the area of COD determination. The optimum applied potential, pH range and electrolyte were 1.4 V,3-9 and 25 mM Na2SO4. Under the optimized testing conditions, the relationship between the net current and COD,inet=2.059COD+0.3762, was obtained. The linear range and the detection limit were 0.5-200 mg/L and 0.3 mg/L (S/N=3), respectively. The COD measurements for real water samples from reservoir, municipal sewage plants, and dyeing factories could be well completed and the resulting largest RSD was lower than 12%. So the proposed method would promote the development of a fast, in situ and on-line COD analysis.In conclusion, the structure of the on-line COD analyzer based on the BDD film electrode was simple and the measurement range is wide. More importantly, the analyzer could be carried out rapidly and overcome the shortage of secondary pollution. Meanwhile, the prepared Ti/BDD/PbO2 and Ti/Sb-SnO2/PbO2 composite electrode were sensitive enough to meet the requirement of pollution monitoring, which was hoped to promote the development of COD determination by electrochemical method.更多还原