碳纳米管催化苯酚湿式空气氧化性能研究

发布时间：2018-03-12 11:01

  本文选题：纳米碳材料　切入点：羧基官能团　出处：《华南理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：纳米碳材料因其拥有的独特电子结构和丰富表面官能团而成为广受关注的高性能材料,近年来,其作为无金属催化剂的应用引发了大范围关注。催化湿式空气氧化法作为一种有效的水处理技术,已被广泛应用于苯酚废水、含氰废水、农药废水等难降解有机废水的处理上。在含酚废水的催化湿式空气氧化中,寻找合适的绿色环保无二次污染的催化剂是该体系亟待突破的关键问题。本论文针对在工业废水中非常典型的含酚废水的催化湿式氧化处理,以易于制备的碳纳米管作为催化剂,探究碳纳米管氧化修饰和氮掺杂对其反应活性的影响,并在此基础上探索了反应机理。我们采用液相硝酸氧化修饰的方法在碳纳米管表面引入含氧基团,发现表面含氧基团,特别是羧基在催化苯酚湿式空气氧化反应中起到促进作用,羧基含量越高,反应活性越大。我们发现羧基在碳纳米管表面的存在方式与碳纳米管本身结构也对催化苯酚湿式空气氧化反应产生影响。对于管壁平行的普通CNT,其经硝酸氧化后的高反应活性主要来自于其表面包覆的羧基化碳碎片;而对于鱼骨状CNT,其特殊的结构使得其拥有大量边缘碳位点,连接在其侧壁的羧基与边缘碳协同作用为反应提供更高活性的氧活化位点。与普通CNT相比,掺氮的N-CNT具有较高的活性。对其进行相同的硝酸液相氧化处理,发现羧基的引入也能增大N-CNT的反应活性,但与此同时其表面的石墨氮位点也是反应的活性中心。虽然掺氮碳纳米管的活性不及经氧化修饰后的CNT,但HNO3氧化修饰步骤繁琐,且存在酸液污染的环境风险,因此研究无需氧化修饰的高活性碳材料具有重要意义。因此我们比较研究了5种不同前驱体和气氛下制备的掺氮碳纳米管对催化苯酚湿式空气氧化反应的活性。将不同的氮物种与反应活性进行关联,发现石墨氮含量与碳纳米管反应活性呈正相关,而其它氮物种与反应活性的关联并没有显示出规律性,因此我们认为石墨氮物种是掺氮碳纳米管催化湿式空气氧化苯酚反应的活性位。在此基础上我们优选出具有最佳活性的N-CNT(以苯胺为原料在NH3中制备)对其进行了反应条件的优化,实验发现当氧气分压为4MPa,温度为180℃,使用80mg催化剂,反应3.5 h后苯酚转化率能达到100%,TOC去除率高达75.6%。
[Abstract]:Nanocrystalline carbon materials have attracted much attention in recent years because of their unique electronic structure and rich surface functional groups. As an effective water treatment technology, catalytic wet air oxidation has been widely used in phenol wastewater and cyanide wastewater. Treatment of refractory organic wastewater such as pesticide wastewater. In catalytic wet air oxidation of phenolic wastewater, It is a key problem for the system to find a suitable catalyst for environmental protection without secondary pollution. In this paper, the catalytic wet air oxidation treatment of phenolic wastewater, which is typical in industrial wastewater, is studied. The effects of oxidation modification and nitrogen doping on the reaction activity of carbon nanotubes (CNTs) were investigated using carbon nanotubes (CNTs) as catalyst. On the basis of this, the reaction mechanism was explored. The oxygen-containing groups were introduced on the surface of carbon nanotubes by liquid phase nitric acid oxidation modification, and the oxygen-containing groups were found on the surface of carbon nanotubes. In particular, carboxyl groups play a catalytic role in catalyzing the wet air oxidation of phenol, and the higher the carboxyl group content is, It was found that the presence of carboxyl groups on the surface of carbon nanotubes and the structure of carbon nanotubes also had an effect on the catalytic wet air oxidation of phenol. For ordinary CNTs with parallel walls, the carbon nanotubes were oxidized by nitric acid. The high reactivity of carbon was mainly due to the carboxylated carbon fragments coated on its surface. For fishbone CNT, its special structure makes it have a large number of marginal carbon sites, and the synergistic effect of carboxyl and marginal carbon on its lateral wall provides a more active oxygen activation site for the reaction than ordinary CNT. N-CNT doped with nitrogen has high activity. It is found that the introduction of carboxyl groups can also increase the reaction activity of N-CNT by the same nitric acid liquid-phase oxidation treatment. Although the activity of nitrogen-doped carbon nanotubes is not as good as that of oxidized CNTs, the steps of HNO3 oxidation modification are cumbersome and the environmental risk of acid contamination exists. Therefore, it is important to study highly active carbon materials without oxidation modification. Therefore, we have compared the catalytic activity of nitrogen-doped carbon nanotubes (NCNTs) prepared under different precursors and atmospheres for the wet air oxidation of phenol. Different nitrogen species are associated with reactive activity, It was found that the content of graphite nitrogen was positively correlated with the reaction activity of carbon nanotubes, but the correlation between other nitrogen species and the reaction activity was not regular. Therefore, we think that the graphite nitrogen species is the active site of nitrogen-doped carbon nanotubes for the wet air oxidation of phenol. On this basis, we have selected the best active N-CNT (prepared from aniline in NH3). Optimization of reaction conditions, It was found that when the partial pressure of oxygen was 4MPa, the temperature was 180 鈩，

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