【作者】 张静；

【导师】 马军；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2010， 博士

【摘要】 随着工业的迅速发展,人类面临的水资源危机越来越严重,传统的水处理工艺难以去除水中有毒有害有机物。高级氧化工艺具有反应迅速、适用范围广、高稳定难降解有机物去除效率高等优点,得到研究者的广泛研究。TiO2除了作为光催化剂外,在臭氧催化氧化领域也表现出良好的催化活性。本论文中利用溶胶凝胶法制备了纳米级的金红石型TiO2并对TiO2进行了金属掺杂改性研究。分别以硝基苯和草酸作为目标物,筛选出掺杂效果最好的催化剂并优化了制备条件。本研究对催化剂的表面性质进行了表征,推测了臭氧催化氧化机理。本文采用溶胶凝胶法制备了纳米级的TiO2,以硝基苯为目标物进行臭氧催化氧化试验。结果表明,不同晶型的TiO2具有不同的催化性能,锐钛矿型的TiO2几乎没有催化臭氧的能力,金红石型TiO2具有良好的催化性能。在金红石型TiO2催化臭氧的反应中,随着催化剂投量、臭氧浓度、反应温度提高,硝基苯去除率也随之增加;随着溶液pH升高,硝基苯的去除率也随之升高,在溶液pH值为10时具有最高的去除率,随后降低;不同的水质本底对硝基苯去除率的基本没有影响。金红石型TiO2催化臭氧工艺中羟基自由基的形成是主导的反应机理,该工艺过程中有机物降解生成的中间产物与单独臭氧工艺也基本相同:羧酸类、醛酮类、酚类。选择了钴、铁、镍、锰及锌五种过渡态的金属离子对TiO2进行掺杂改性研究。制备的Mn/TiO2、Ni/TiO2、Co/TiO2、Fe/TiO2、Zn/TiO2这五种催化剂相对单独臭氧氧化工艺均大幅地提高了硝基苯的去除率,但与金红石型的纯TiO2催化效果相差并不大,掺杂并没有能提高臭氧催化分解硝基苯的效果。监测结果表明,在臭氧催化氧化过程中有微量金属离子溶出,但均远远低于国家标准。Mn/TiO2和Co/TiO2这两种掺杂催化剂能够大幅度地提高体系中TOC的去除率,通过对中间产物的分析,Mn/TiO2和Co/TiO2能够进一步催化臭氧氧化硝基苯的中间产物,比如难以被臭氧分子直接氧化的草酸。以草酸作为目标物,分别研究了各催化剂对臭氧催化氧化的活性。结果发现,Mn/TiO2和Co/TiO2具有良好的催化能力,可以明显提高臭氧去除草酸的效率,TiO2、Ni/TiO2、Fe/TiO2、Zn/TiO2催化臭氧氧化过程中对草酸的去除率不高。分别对催化剂煅烧温度和金属离子掺杂比例的制备条件进行了优化,改变煅烧温度和离子掺杂比例对Ni/TiO2、Fe/TiO2、Zn/TiO2催化臭氧分解草酸效率的提高基本没有效果;Mn/TiO2最优的煅烧温度为500℃,锰和钛的最佳摩尔掺杂比例1/20,为锐钛矿和金红石相的混合晶相;Co/TiO2最优的煅烧温度为500℃,钴和钛的最佳摩尔掺杂比例为1/30,锐钛矿和金红石混合晶相。分别研究了Mn/TiO2和Co/TiO2催化臭氧分解草酸过程的影响因素:在本实验所考察的臭氧流量范围内,臭氧投量的变化对草酸去除率基本没有影响;随草酸初始浓度的升高,草酸的去除率降低;随着催化剂投量、水体温度升高,草酸去除率也随之升高,但反应30min后不同反应条件下的草酸均已基本被去除;在反应温度为10℃条件下草酸的去除率远低于在20℃、30℃、40℃反应温度下的去除率;pH值影响着Mn/TiO2表面所带的电荷正负性和草酸的电离程度,溶液pH值对草酸去除率影响显著,在较低初始pH值条件下,臭氧催化氧化对草酸具有更好的去除效果。通过XRD表征发现,锰和钴的掺杂使得TiO2锐钛矿向金红石结构的相变温度升高,并且粉末的粒径增大。对实验制备的Mn/TiO2和Co/TiO2进行XRF、XPS表征,发现锰和钴元素在催化剂表面的比例高于内部比例,分别以MnO2和TiCoO3的形式存在。锰和钴的掺杂使得催化剂表面的钛出现正三价,导致出现氧空位,造成了TiO2晶格缺陷,在催化剂表面Ti主要以正四价的形式存在,约占70%。在利用Mn/TiO2和Co/TiO2催化臭氧分解草酸过程中草酸直接矿化为二氧化碳和水没有中间产物的生成。通过投加叔丁醇和利用ESR试验证明了在这两种反应体系中有羟基自由基生成并参与了草酸的氧化反应,但羟基自由基并不是唯一的氧化剂。推测草酸首先被吸附或者络合于催化剂表面,然后被羟基自由基和臭氧分子氧化,草酸的吸附是整个反应的制约步骤。更多还原

【Abstract】 With the rapid development of industry, the human being are facing ever increasing problem of water crisis. The traditional water treatment process is difficult to remove toxic organic compounds from water. Having many advantages, such as: quick response, high efficiency for the degardation of stabel organic pollutants, advanced oxidation processes are widely investigated. In addition to being used as a photocatalyst, TiO2 also showed good catalytic activity in the field of catalytic ozonation. In this paper, nanosized rutile TiO2 and metal doped TiO2 were prepared by sol-gel method, and investigated for their effectiveness in degrading organic pollutants in catalytic ozonation.The best way of catalyst doping were selected and the preparation conditions were optimized, using nitrobenzene and oxalic acid as the target respectively. The surface properties of the catalysts were characterized. The mechanism of catalytic ozonation was speculated.In this paper, nano-sized TiO2 was propared by sol-gel method, and nitrobenzene was used as the target for catalytic ozonation experiment. Different crystal structure of TiO2 have different catalytic properties. Anatase TiO2 almost has no ability for catalytic ozonation, while rutile TiO2 has good catalytic properties. In the rutile-type TiO2 catalytic ozonation reaction, the nitrobenzene removal rate increases respectively with the increase in the amount of catalyst, ozone concentration, reaction temperature. The removal rate of nitrobenzene increases with the increase of solution pH. When the solution pH value is 10, the degradation rate of nitobenzene is highest. In different water background, the removal rate of nitrobenzene were almost the same. Rutile TiO2 catalyzed ozonation is the dominant reaction mechanism of hydroxyl radical. Degradation intermediates of nitrobenenze generated during catalytic ozonation is basically the same with those generated in ozonation alone: That is: carboxylic acids, aldehydes and ketones, phenols.Cobalt, iron, nickel, manganese and zinc were chosen for doping TiO2. The presence of Mn/TiO2、Ni/TiO2、Co/TiO2、Fe/TiO2、Zn/TiO2 are significantly increased the removal rate of nitrobenzene by ozonation comparing with the case of ozone oxidation alone. Rutile TiO2 catalytic effect is not significantly different from the five types of catalyst. Doping is not able to increase the effect of catalytic ozonation of nitrobenzene. Trace metal ion was released from the catalyst, but the concentrations of metal ion dissolved are far below the national standards.The presence of Mn/TiO2 and Co/TiO2 significantly improved the removal rate of TOC. By the analysis of intermediate products, Mn/TiO2 and Co/TiO2 can further oxidize nitrobenzene intermediates, such as oxalic acid which is difficult to be directly oxidized by ozone molecules.Using oxalic acid as a target, the catalytic activity of catalysts were examined. Mn/TiO2 and Co/TiO2 have good catalytic ability, and can significantly enhance the ability of ozone to remove oxalic acid. TiO2、Ni/TiO2、Fe/TiO2、Zn/TiO2 have poor capacity to remove oxalic acid by catalytic ozonation. The calcination temperature and ratio of metal ion doping were optimized. Changing the calcination temperature and doping ratio almost had no effect on Ni/TiO2、Fe/TiO2、Zn/TiO2 for improving the catalytic activity. The optimal calcination temperature of Mn/TiO2 is 500℃, with a mixed phase of anatase and rutile. The best molar doping ratio of Mn/TiO2 is 1/20. The optimal calcination temperature of Co/TiO2 is 500℃, with a mixed phase of anatase and rutile. The best molar doping ratio of Co/TiO2 is 1/30.The influencing factors on the degradation of oxalic acid in catalytic ozonation process were studied respectively with Mn/TiO2 and Co/TiO2 as the catalyst. Within the ozone flux in this experiment, the changing of ozone flux almost had no effect on oxalic acid removal rate. Oxalic acid removal rate decreased with the increase of initial concentration of oxalic acid. Oxalic acid removal rate increased with the increase of the amount of catalyst used and the water temperature respectively, and almost reached completely removal. The removal rate of oxalic acid reacting at 10℃, was much lower than those achieved at 20℃, 30℃, 40℃. The charge of positive and negative values of Mn/TiO2 surface is affected by pH value, and the ionization degree of oxalic acid and by pH values. The pH value significantly affected the removal rate of oxalic acid. At lower initial pH values, oxalic acid removal rate is faster.Measured by XRD, the doping of Mn and Co make the transition temperature of anatase to rutile phase increase, and the size of catalyst increases. Obeserved by means of XRF and XPS, the proportion of Mn and Co on the catalyst surface is higher than the proportion of internal side of the catalyst. Mn and Co were combined with the titanium and went into the TiO2 lattice. Mn and Co in the catalyst were in the form of MnO2 and TiCoO3. There were Ti3+ in the surface of the catalyst, and oxygen vacancy and lattice defects were formed. In the catalyst surface, Ti mainly exists in the form of Ti4+. In the catalytic ozonation, oxalic acid was mineralizad and converted directly into CO2 and H2O. Tert-butyl alcohol addition and ESR experiments showed the generation of hydroxyl radical in catalytic ozonation. Hydroxyl radical is the oxidant formed in this reaction, but not the only oxidant. It is speculated that oxalic acid was absorbed or complexed in the catalyst surface in the first step. Oxalic acid in the surface of catalyst was oxidized by hydroxyl radical and ozone molecule. The adsorption of oxalic acid is the control steps in the whole reaction.更多还原