【作者】 刘元；

【导师】 刘惠玲； 马军；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2010， 博士

【摘要】 电催化氧化法作为高级氧化技术（AOPs）的一种,用于处理水中难降解有机污染物,如酚类、芳胺类、芳烃类及农药等非常有效。开发高效稳定的电极以及提高电解体系的效率都是目前电化学技术最为关切的重点。硝基苯酚类化合物广泛存在于染料、石油、医药、农药和炸药等相关工业中,是一类难以生物降解的有害有机污染物。其降解和矿化一直以来都是研究的热点和难点。本文针对高效稳定的金属氧化物的开发、硝基苯酚类化合物的降解以及提高电解体系整体效率做了如下工作:制备了铋和钴等掺杂的改性二氧化铅电极。利用扫描电子显微镜（SEM）、原子力显微镜（AFM）和X射线衍射（XRD）等技术对改性二氧化铅电极的表面形貌和晶体结构进行了表征。通过极化曲线、循环伏安以及电化学阻抗等测试手段研究了改性二氧化铅电极的电化学性能。通过加速寿命试验得到了电极的使用寿命。研究了电解体系内氧化剂,比如羟基自由基、过氧化氢及次氯酸根等的生成情况。以邻硝基苯酚为目标有机物,考察了这些改性二氧化铅电极的电催化氧化性能。结果表明,铋掺杂二氧化铅电极（Ti/Bi-PbO₂电极）具有晶体尺寸较小、结构紧密的特点,并且表面比较粗糙。该电极的电催化活性以及电极稳定性要优于Ti/β-PbO₂电极以及另外改性的电极。此外,Ti/Bi-PbO₂电极的电流效率也是最高的。Ti/Bi-PbO₂电极不仅催化活性高而且能耗低,是一种理想的可以用来处理有机污染物的阳极材料。研究并分析了降解过程中有机物的矿化、动力学规律,定性、定量检测分析了Ti/Bi-PbO₂电极电催化氧化硝基苯酚类化合物（邻硝基苯酚o-NP、间硝基苯酚m-NP、对硝基苯酚p-NP、2, 4-二硝基苯酚2, 4-DNP、2, 5-二硝基苯酚2, 5-DNP、2, 6-二硝基苯酚2, 6-DNP和2, 4, 6-三硝基苯酚2, 4, 6-TNP）降解过程中的中间产物,并提出了硝基苯酚化合物可能的降解路径。通过循环伏安测试可以得知,硝基苯酚化合物在Ti/Bi-PbO₂电极上主要是通过间接氧化被降解的。Ti/Bi-PbO₂电极对硝基苯酚有很好的去除效果,有机物自身能够被完全去除,并且矿化度均超过了90%。七种硝基苯酚的降解快慢顺序如下:o-NP >m-NP >p-NP >2, 6-DNP >2, 5-DNP >2, 4-DNP >2, 4, 6-TNP。对硝基苯酚降解过程中的中间产物进行了检测、分析。发现到反应结束时,基本上所有的硝基都从苯环上脱落下来,并且最终主要以硝酸根的形式存在。通过液相色谱、质谱检测分析了中间产物的转化。检测结果表明在电催化氧化硝基苯酚的过程中,主要有三大类中间产物生成,分别为多羟基苯环类化合物、硝基苯酚的还原产物以及羧酸类物质。提出了硝基苯酚化合物可能的降解路径,主要包括三个步骤:第一,羟基取代硝基或取代氢原子而加成到苯环上;第二,芳香族化合物发生开环反应,生成羧酸类化合物;第三,羧酸类化合物进一步被氧化,最终转化成二氧化碳和水。通过对Ti/Ce-PbO₂电极制备工艺的优化,所制得的电极电荷传递电阻最小,催化活性最高。根据SEM、AFM和XRD的结果,发现与传统的二氧化铅电极（Ti/β-PbO₂）比较,Ti/Ce-PbO₂电极的晶体颗粒更加细小,表面更加粗糙,并且结构更加致密。Ti/Ce-PbO₂电极的使用寿命及耐腐性均优于Ti/β-PbO₂电极。Ti/Ce-PbO₂电极对邻硝基苯酚去除效果要优于Ti/β-PbO₂电极,降解速率是后者的2.29倍。并且能耗更小,与后者相比下降了18%。比较Ti/Ce-PbO₂电极使用前后性能测试结果,可知该电极具有很好的稳定性。铈的掺杂对提高二氧化铅电极的稳定性和催化活性有积极的作用。通过研究共存物质存在时,邻硝基苯酚的降解及矿化情况,可知当溶液中存在金属离子、醇类化合物、有机酸以及表面活性剂时,目标有机物的降解基本上没有受到影响,并且整个体系的矿化效果依然维持在较高的水平。本电催化氧化体系具有可靠的稳定性,能够抵御一定的外加负荷的冲击,这为本体系实际应用提供了依据。优化了三元复合的改性二氧化锡电极——Ce-Ru-SnO₂电极的制备工艺。与其他改性二氧化锡电极相比,该电极不仅电催化活性高,并且使用寿命长、能耗小。从SEM和XRD的结果来看,铈的掺杂能够减少电极表面的裂纹,提高电极的比表面积,还能减小二氧化锡的晶体颗粒尺寸,并使得晶体分布更加均匀。从加速寿命试验结果来看,Ce-Ru-SnO₂电极的加速寿命要明显长于传统的SnO₂-Sb2O5电极。从Ce-Ru-SnO₂电极使用前后性能研究来看,该电极在使用后没有发生明显的变化,表明该电极具有较好的稳定性。Ce-Ru-SnO₂电极对硝基苯酚类化合物有很好的去除效果。这些硝基苯酚的降解存在如下顺序:o-NP>p-NP>m-NP>2, 5-DNP>2, 4-DNP>2, 6-DNP>2, 4, 6-TNP。比较Ce-Ru-SnO₂电极与Ti/Bi-PbO₂电极可以发现,前者的电催化活性要优于后者,但是电极的使用寿命上则是后者好于前者。更多还原

【Abstract】 Electrocatalytic oxidation as one of the Advanced Oxidation Processes （AOPs） was effectively to treat some intractable organic pollutants, such as phenols, the aromatic amines, the aromatic hydrocarbons and the pesticides. Both the development of electrodes with high stability and enhancement of efficiency of electrochemical system are hot topics in the field of electrochemistry. Nitrophenols （NPs） represent a class of widely synthesized chemicals particularly involving in the manufactures of pesticides, dyes and pharmaceuticals, which are anthropogenic, toxic, inhibitory and bio-refractory organic compounds and are considered as hazardous substances and priority toxic pollutants. It is of significant importance to develop new treatment technologies for the destruction and mineralization of NPs in wastewater. In the present work, the following investigation have been carried out for the purpose of development of metal oxides electrodes with high stability, degradation of nitrophenols and enhancement of efficiency of entire electrochemical system.A set of modified PbO₂ anodes doped with the oxides of Bismuth and Cobalt were prepared by the means of electrodeposition in nitrate solutions. Scanning electronic microscopy （SEM）, Atomic force microscopy （AFM） and X-ray diffraction （XRD） were used to characterize the morphology and crystal structure of modified PbO₂ anodes. The electrochemical properties of these modified PbO₂ anodes were studied by means of linear sweep, cyclic voltammetry and electrochemical impedance spectroscopy （EIS）, respectively. The service lives of modified anodes were obtained in terms with accelerated life tests. Oxidants such as hydroxyl radical, hydrogen peroxide and hypochlorite ion were determined. Electrocatalytic oxidation of o-nitrophenol （o-NP） was conducted by using these electrodes as anode and stainless steel sheet as cathode. The results indicated that Bismuth doped PbO₂ electrode （Ti/Bi-PbO₂） was characterized of smaller crystal size, compact structure and rough surface. This anode displayed a better electrocatalytic activity and higher stability than those of Ti/β-PbO₂ anode, as well as other modified anodes. In addition, the current efficiency of Ti/Bi-PbO₂ was the highest of all PbO₂ anodes. Ti/Bi-PbO₂ anode had the highest electrocatalytic activities and the lowest energy consumption. The Ti/Bi-PbO₂ anode was a promising anode for the treatment of organic pollutants.The electrocatalytic oxidation of o-nitrophenol （o-NP）, m-nitrophenol （m-NP） and p-nitrophenol （p-NP）, 2, 4-dinitrophenol （2, 4-DNP）, 2, 5-dinitrophenol （2, 5-DNP）, 2, 6-dinitrophenol （2, 6-DNP） and 2, 4, 6-trinitrophenol （2, 4, 6-TNP） has been studied on Bi-doped lead dioxide anodes in acid medium by cyclic voltammetry and bulk electrolysis. The mineralization and kinetics of organic compounds were studied in the course of electrolysis. The intermediates accumulated during the electrolysis were analyzed qualitatively and quantitatively. Furthermore, possible degradation pathways of nitrophenols were proposed. The results of voltammetric studies indicated that these nitrophenols were indirectly oxidized by·OH radical in the solutions. Within the present experimental conditions used, almost complete elimination of nitrophenols and more than 90% mineralization were achieved. The electrocatalytic oxidation of NPs lay in the order: o-NP >m-NP >p-NP >2, 6-DNP >2, 5-DNP >2, 4-DNP >2, 4, 6-TNP. The intermediates generated during the electrolysis of nitrophenols were determined and analyzed. Nitrate ion is identified as the major nitrogen final reaction product during the NPs oxidation, while a minor amount of ammonia is left at the end of electrolysis, which indicated that almost all the nitro groups detached from aromatic rings. The results of LC / MS and HPLC suggest that three kinds of intermediates are generated, i.e. polyhydroxylated intermediates, reduction products of NPs and carboxylic acids. In the long run, polyhydroxylated intermediates and reduction products of NPs were eventually oxidized to micromolecular carboxylic acids, such as maleic acid, oxalic acid, acetic acid and formic acid, etc. The possible degradation pathways of NPs were proposed, including three major steps: 1) the denitration and substitution by hydroxyl radicals on aromatic rings seem to be the first stage; 2) aromatic ring-opening reactions took place to generate carboxylic acids; 3) carboxylic acids were further oxidized into CO₂ and H2O.Cerium doped lead dioxide anode, i.e. Ti/Ce-PbO₂, was prepared by electrodeposition. After the optimization of preparation technique, a Ti/Ce-PbO₂ anode with lower charge transfer resistance and higher electrocatalytic activity was obtained. SEM, AFM, XRD and X-ray photoelectron spectrometry （XPS） were used to characterize the morphology, crystal structure and elements states of modified anode. The results of SEM, AFM and XRD showed that the crystal size of Ti/Ce-PbO₂ anode was smaller than undoped PbO₂ （Ti/β-PbO₂） and no diffraction peaks corresponding to CeO₂ formed. The result of accelerated life test implied that Ti/Ce-PbO₂ anode had favorable electrochemical stability. The electrochemical oxidation of o-NP on Ti/Ce-PbO₂ anode displayed a faster degradation rate and higher mineralization efficiency than Ti/β-PbO₂ anode （the degradation rate of former was 2.29 times higher than that of latter）. In addition, Ti/Ce-PbO₂ anode had higher current efficiency and lower energy consumption （the energy consumption of former decreased by 18% compared with latter）. Comparing the properties of Ti/Ce-PbO₂ anode before and after use, this modified lead dioxide electrode displayed benign stability. The results indicated that the incorporation of Cerium fascinated to improve the stability and electrocatalytic activity of lead dioxide anode. The investigations on the effect of co-exsting substances on electrochemical oxidation of o-NP came into the following conclusions. The degradation of o-NP was nearly not impacted in the presence of metal ions, alcohols, organic acids and surfactant. The present electrochemical system displayed a reliable stability and resistance to impact of additional load.The preparation parameters for the Cerium doped ternary SnO₂ based oxides anode were optimized. When the molar percentages of Cerium and Ruthenium were 1% and 5%, the prepared anode had high electrocatalytic activity and stability. The results of SEM and XRD revealed that the incorporation of Cerium could decrease the cracks of anode surface, enhance the specific surface area and diminish the crystal size of modified SnO₂ anode, as well as cause a better dispersion of oxides. The results of accelerated life test indicated that the service life of Ce-Ru-SnO₂ anode was longer than that of traditional SnO₂-Sb2O5 anode. Comparing the properties of Ce-Ru-SnO₂ anode before and after use, almost no evident difference was observed, which demonstrated that this anode had benign stability. Nitrophenols could be effectively eliminated on Ce-Ru-SnO₂ anode. The degradation of NPs lies in the order: o-NP>p-NP>m-NP>2, 5-DNP>2, 4-DNP>2, 6-DNP>2, 4, 6-TNP. The comparison of Ce-Ru-SnO₂ anode with Ti/Bi-PbO₂ anode indicated that the electrocatalytic activity of former was superior to that of latter. Nevertheless, the service life of latter was longer.更多还原