【作者】 于洪斌；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 掺硼金刚石（BDD）作为电极材料具有众多优点,如电势窗口宽、析氧电位高、背景电流低、抗腐蚀、化学性质稳定等,从而被广泛应用于电化学水处理和污染物的电分析。在水污染监测中,COD,即化学需氧量,是衡量水体有机污染的重要指标。标准测量方法为重铬酸钾法,但此法存在很多内在缺点,而且很难实现自动测量和在线测量。近年来发展的电化学COD测量方法,克服了很多传统方法的不足,但缺乏合适的电极材料,阻碍了此方法在实际中的广泛应用。为此,本文尝试以环境友好的BDD材料为电极,采用电化学安培法进行COD的测定,并对COD的流动注射分析方法进行了探索。另外,TiO₂光催化技术是水处理研究中的热点之一,但由于光生电荷载流子的快速复合而导致量子效率较低,使得该技术还难于应用到实际当中。在解决此问题的方法中,利用异质结材料作为光催化剂被认为是一个很好的途径,因为异质结内建电场可以有效地减少光生电荷载流子的复合。所以,本论文利用具有p型半导体性质的BDD为基底,将其与n型TiO₂复合制备TiO₂-BDD异质结光催化剂,以期得到更高的光催化能力。围绕以上内容所开展的工作主要包括以下几个方面:（1）采用热丝化学气相沉积设备,在金属钛基底上制备了BDD膜。通过扫描电镜、拉曼光谱仪和X射线衍射仪对样品进行表征,显示所制备的BDD膜均匀、致密、连续,晶粒尺寸在1-1.5μm;膜中金刚石拉曼特征峰明显;XRD谱图中可以观察到金刚石的（111）、（220）和（311）晶面衍射峰。另外,通过循环伏安技术的研究,表明BDD膜电极具有很宽的电化学电势窗口、高的析氧电位和很低的背景电流,而且电化学稳定性良好。因此,所制备BDD膜是比较理想的电极材料。（2）以BDD膜为电极,利用电化学安培法进行了COD测试研究。优化的pH值和测量电位分别为2和2.5V（vs.SCE）。本研究方法的线性范围与检测限分别为20-9000mg·L^-1和7.5 mg·L^-1COD（S/N=3）。经过20天,共超过400次的测量使用,BDD膜电极性能依然保持稳定。在优化的测试条件下,本研究方法可以很好地用于模拟水样和实际废水COD的测定。与传统铬法相比,此方法操作简易,耗时短（＜5min）,且所采用的电极为环境友好的BDD材料,测试中不使用有毒物质,因此可以有效避免二次污染。（3）以BDD膜电极为检测元件,结合流动注射自动进样设备,组建成COD的流动注射分析（FIA）系统。优化的测试条件分别为,测量电位2.8V（vs.Ag/AgCl）、载液流速2.5 mL·min^-1,电解质0.25MNa₂SO₄,pH6.5。在优化条件下,利用此FIA系统,可以很好地完成模拟水样和实际废水COD的测定。FIA系统测定COD的线性范围为2-150mg·L^-1,检测限为1.0 mg·L^-1（S/N=3）。经过25天,共超过600次的测量使用,FIA系统仍运行稳定。通过与传统铬法在模拟水样和实际废水COD测定中的比较,表明二者之间具有较好的一致性。与传统铬法相比,FIA系统可以大大缩短分析时间,降低试剂用量,测定结果具有更好的重现性。另外,FIA系统中采用的电极材料为环境友好的BDD,且测试过程不使用有毒物质,所以不产生二次污染问题。更重要的是,FIA系统初步实现了COD的自动化测量,促进了环保、原位、在线型COD测试系统的发展。（4）采用两步化学气相沉积方法,制备出TiO₂-BDD复合材料,即先用热丝化学气相沉积系统制备BDD基底,再利用金属有机化学气相沉积方法于BDD基底上沉积TiO₂薄膜。通过扫描电镜、透射电镜、Raman光谱仪和X射线衍射仪对样品进行了结构表征,表明所制备的TiO₂-BDD复合材料表面均匀、连续,TiO₂为锐钛矿型;另外,采用半导体参数测试仪对样品进行了电学性质表征,证明TiO₂薄膜与BDD基底之间形成了异质结;光电压特性测量中,TiO₂-BDD异质结与化学气相沉积于钛片上的TiO₂膜（TiO₂-Ti）相比,具有更高的响应,表明异质结促进了光生电子与空穴的分离。在光催化实验中,选择偶氮染料活性黄15（RY15）与Cr（Ⅵ）作为目标物,分别以TiO₂-Ti和TiO₂-BDD为光催化剂,相同实验条件下,对比考察了二者的光催化能力。结果显示无论单独处理RY15或Cr（Ⅵ）,还是同时光催化氧化RY15和光催化还原Cr（Ⅵ）,TiO₂-BDD异质结光催化剂都表现出更高的光催化能力,这可能主要缘于异质结内建电场促进了光生电荷载流子的分离。另外,在同时光催化氧化和光催化还原反应中,观察到了明显的协同效应。这种双向促进作用使污染物可以被更有效地降解。实验中还对pH值和曝气条件进行了考察,结果表明偏酸性条件有利于RY15和Cr（Ⅵ）的光催化降解;氧气的连续曝入,对RY15的光催化氧化与Cr（Ⅵ）的光催化还原都有一定的促进作用。最后简要探讨了TiO₂-BDD异质结的光催化机珲。更多还原

【Abstract】 As a versatile electrode material,boron-doped diamond（BDD）possesses many advantages such as wide electrochemical window,low voltammetric background current,high level of mechanical strength arid corrosion resistance.Therefore,BDD has been investigated widely in the fields of electrochemical wastewater treatments and the electroanalysis of pollutants.As for water pollution,chemical oxygen demand（COD）is an important measure of organic pollution in water.Unfortunately,the conventional dichromate method for COD tests includes several inherent drawbacks.More importantly,the conventional method is difficult to be conducted automatically.The electrochemical method developed in recent years could overcome many disadvantages involved in the conventional method.However, the lack of proper electrode materials might limit the widespread application of this method in practice.Considering what mentioned above,the environmentally friendly material,BDD, was adopted as an electrode to determine COD by amperometric method.Meanwhile,a flow injection COD testing system was also emplored.Additionally,the photocatalytic technique with TiO₂ as a photocatalyst has been studied frequently in wastewater treatments because TiO₂ is easily available,nontoxic,inexpensive and chemically stable.However,TiO₂ also suffers severe constraints in practical applications due to the bottleneck of poor quantum yield that is normally caused by the rapid recombination of photogenerated electrons and holes. Among the ways to settle this problem,the application of heterojunction materials as photocatalysts is a good method because the internal electrostatic field of heterojunctions can provide a potential driving force to reduce the recombination of photogenerated charge carriers.Consequently,the p type material of BDD was tried combining with the n type material of TiO₂ to form a heterojunction.Higher photocatalytic ability can be expected when this heterojunction is used as a photocatalyst.In this dissertation,some works were carried out as follows:（1）The BDD film was prepared on a titanium sheet in a hot filament chemical vapor deposition（HF CVD）reactor.The characterization of SEM,.Raman spectrum and XRD demonstrated that the BDD film was compact,continuous,and uniform.The crystallites were about 0.5-1.5μm with no evident cracks or extensive pitting.The characteristic peak of diamond in Raman spectrum appeared clearly and the diffraction peaks of diamond（111）, （220）and（311）in XRD pattern were observed.Additionally,the results investigated in cyclic voltammetry indicated that the BDD electrode was electrochemically stable with a wide electrochemical potential window and a low voltammetric background current.It was believed that the BDD film was a good electrode material.（2）The amperometric determination of COD was conducted by using a BDD electrode. The optimum pH value and applied potential were 2 and 2.5 V（vs.SCE）,respectively.The linear range was 20-9000 mg·L^-1and the detection limit was 7.5 mg·L^-1COD（S/N=3）.The performance of the BDD electrode still kept stable after over 400 COD tests during a period of 20 days.Under the optimized testing conditions,the proposed method was successfully employed to determine the COD of synthetic water samples and real samples.As compared with the conventional dichromate method,the amperometric method presented here could be carried out easily and rapidly（＜5 min）.Moreover,the electrode material of BDD was environmentally friedly and no toxic chemicals were used in COD tests.Consequently,the problem of secondary pollution could be avoided efficiently.（3）A flow injection analysis（FIA）system for COD measurements was established successfully based on a flow injection apparatus with BDD as an electrode.The optimum applied potential,flow rate of carrier,electrolyte and pH value were 2.8 V（vs.Ag/AgCl）,2.5 mL·min^-1,0.25 M Na₂SO₄ and 6.5,respectively.Under the optimized testing conditions,the COD measurements for synthetic water samples and real wastewater samples could be well completed by using the proposed FIA System.The linear range and the detection limit were 2-150 and 1.0 mg·L^-1（S/N=3）,respectively.The FIA system still performed stably after over 600 COD tests during a period of 25 days.In addition,the proposed method and the conventional method consisted well with each other in terms of the COD tests for both synthetic and real samples.The application of FIA system could not only shorten the analysis period but also cut down the dosage of reagents.Meanwhile,a better reproducibility could be obtained.Furthermore,the electrode material adopted in the FIA system was environmentally friendly,and no toxic chemicals were used in the process of COD determination,which was undoubtedly beneficial to the avoidance of secondary pollution.More importantly,the COD measurement could be conducted automatically,which would promot the development of an environmentally friendly,in situ,and on-line COD testing system.（4）A TiO₂-BDD heterojunction photocatalyst was fabricated via two phase of CVD processes.That is,this heterojunction material was prepared first by depositing a BDD film on a titanium sheet in a HF CVD reactor,followed by covering a layer of TiO₂ in a metal-organic CVD system.The morphology and structure were characterized by using SEM, TEM,and Raman spectrum and XRD,respectively.The results demonstrated that the composite of TiO₂-BDD appeared to be continuous and uniform,and the crystal phase of TiO₂ was anatase.Besides,theⅠ-Ⅴplot detected by a semiconductor characterization system indicated that a heterojunction was formed between the BDD substrate and TiO₂.In the measurement of surface photovoltage（SPV）,the response of the heterojunction in UV region was stronger than that of TiO₂ deposited on a titanium sheet（TiO₂-Ti）,suggesting that the heterojuncti0n could facilitate the separation of photogenerated electrons and holes.An azo dye C.I.reactive yellow 15（RY15）and Cr（Ⅵ）were selectedto investigate the photocatalytic ability of TiO₂-Ti and TiO₂-BDD heterojunction.The results indicated that the heterojunction photocatalyst exhibited higher photocatalytic ability than TiO₂-Ti in the degradation of systhetic wastewater samples either containing only RY15 or only Cr（Ⅵ）or both pollutants. This good photocatalytic ability might be benefited from the reduced recombination of photogenerated charge carriers due to the existence of heterojunction.At the same time,a distinct synergic effect was observed in the simultaneous oxidation of RY15 and reduction of Cr（Ⅵ）.This mutual promoting effect could faciliated the efficient degradation of pollutants. Additionally,the effects of pH and gas sparging on photocatalysis were also studied.An acidic condition was beneficial to the photocatalytic oxidation of RY15 and the photocatalytic reduction of Cr（Ⅵ）.Oxygen sparging promoted more or less the reactions of both photocatalytic oxidation and reduction.At last,the possible photocatalytic mechanism was discussed.更多还原