【作者】 高磊；

【导师】 陈乾旺；

【作者基本信息】 中国科学技术大学 ， 材料物理与化学， 2014， 博士

【摘要】 废弃塑料产生的“白色污染”已经成为最严重的污染之一。这些废弃塑料不仅对环境造成了潜在的危害,还不利于人们的身心健康。对废弃塑料进行回收再利用,并将其转化为附加值更高的材料,不仅有利于缓解日益严重的环境压力,还可节约大量的能源和原材料。另一方面禽类羽毛如鸡毛等废弃角蛋白也日益危害着环境,如何处理和利用也成为一个亟待解决的棘手问题。现需要开发一种有效的工艺可以同时处理这些不同类型的废弃物,并制备出高附加值的功能材料。在本论文中,笔者将超临界二氧化碳(scCO2)体系用于处理这些不同类型的废弃物,制备出几种碳纳米材料,并探讨其在超疏水、催化等领域的应用。禽类羽毛是可再生的、廉价的、丰富的。如果它们能够转化为价值更高的功能材料,则具有巨大的商业价值。本文研究揭示1克鸡毛(包括羽柄和羽片)在超临界二氧化碳体系中600℃的温度下热解3小时,能形成0.25克形貌较好的直径为1-5微米的碳微球和0.26克碳酸氢铵(一种化肥)。在产物形成的过程中,反应温度至关重要。低于600℃时,则没有碳酸氢铵生成,且也只有少量碳产物出现。生成的碳微球具有很高的氮含量,大约为12.8wt%。在这个工艺中,鸡毛中大约30.6wt%的氮被转化为碳酸氢铵中的氮,大约21.1wt%的氮被掺杂到含氮的碳微球中。随后我们将制备出来的碳微球和退火后的碳微球作为原料应用到超疏水纺织涂层上来,其接触角可达到153.2±1.7和165.2士2.5°。这个工艺最大的优势是能够同时将鸡毛转化为两种价值更高的产物。笔者也研究了将鸡毛制备成碳纳米管的工艺技术,发现在上述体系中加入醋酸镍就能够得到碳-Ni3S2同轴纳米纤维(Ni3S2@C),然后经酸处理能将其进一步转化为氮掺杂的碳纳米管(N-CNTs)。在这个工艺中,鸡毛中大约34.0wt%的氮被转化为碳酸氢铵肥料中的氮,大约9.5wt%的氮被掺杂到碳纳米管中。鸡毛中大约86.6%的硫元素被转化为Ni3S2,这样有利于减少硫化氢二氧化硫等有害气体的排放。在硼氢化钠提供氢气的对硝基苯酚向对氨基苯酚转化的还原反应,Ni3S2@C和N-CNTs样品都有很高的催化活性,,其初次的速率常数分别为0.9×10-3s-1和2.1×10-3s-1。经过6次循环后,仍然具有较高的催化活性,且催化剂很容易离心分离。氮掺杂碳纳米管的催化活性要高于氮掺杂石墨烯的催化活性,且和Pd等一些贵金属催化剂活性相当。氮掺杂碳纳米管中的氮含量达到了6.43wt%,这保证了其卓越的催化性能。这是个有效的低成本的回收利用废弃鸡毛的方法,同时展示了氮掺杂碳纳米管材料的一个新的应用领域。使用废弃PET和Si02微球为原料,先在超临界二氧化碳体系中,在650℃的温度下保持3小时,之后在1500℃真空下退火4小时,成功制备出立方3C碳化硅纳米线。制备出的碳化硅纳米线有十几微米长,直径为30-150纳米。这些碳化硅纳米线形成主要发生在PET形成的碳微球内部。因此,生成的碳化硅纳米线均被碳微球所包裹,只有在空气中加热去除外部多余的碳后,这些碳化硅纳米线才能被SEM和TEM所观察到。在大气环境下,聚烯烃类废弃物需要上百年才能降解完全,以聚乙烯废弃物为碳源,以四水合醋酸镍为催化剂在超临界二氧化碳体系中制备出了碳纳米管-镍复合材料。制备出来的碳纳米管有十几个微米长,直径为100纳米左右,且包含20wt%直径为100纳米的镍纳米颗粒在其表面。用它来催化对硝基苯酚向对氨基苯酚转化的还原反应,碳纳米管-镍复合材料具有很好的催化活性。这不仅提供了一种处理废弃塑料的方法,还展示了一种新的直接由废弃塑料制备纳米催化剂材料的方法。更多还原

【Abstract】 White pollution caused by waste plastic has become one of the most serious problems facing mankind. The waste plastic not only has potential harm to the environment, but also is not beneficial for physical and mental health. Recycling of waste plastic or converting to higher value-added products will be help to reduce the environment pressure and save a lot of energy and raw materials. On the other hand, the keratin wastes such as chicken feathers have also become harm to the environment increasingly, and how to deal with these wastes becomes a difficult problem to be solved. Now a general approach which is compatible with these different kinds of waste and converts them to value-added products needs to be developed. Here in this dissertation, supercritical carbon dioxide (scCO2) is used to treat these different types of waste into carbon materials, and their applications in the field of superhydrophobicity and catalysis have been explored.Poultry feathers are renewable, inexpensive and abundantly available. They hold great business potentials if they can be converted to valuable functional materials. Pyrolysis of1g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (SC-CO2) system at600℃for3h leads to the formation of0.25g well-shaped carbon microspheres(CMS) with diameters of1-5μm and0.26g ammonium bicarbonate ((NH4)HCO3). Reaction temperature plays a critical role in the product formation. Below600℃, no (NH4)HCO3and little carbon product could be generated. The CMS product has very high nitrogen content (12.8wt.%). Using this strategy, ca.30.6wt.%of the nitrogen content in the chicken feathers is transferred to (NH4)HCO3and ca.21.1wt.%is transferred into nitrogen-containing CMS product. Furthermore, we developed a simple coating strategy to prepare super-hydrophobic fabric materials using CMS and annealed CMS products, and the water contact angle can reach153.2±1.7and165.2±2.5°. The biggest advantage of this strategy is that the whole chicken feather (quills and barbs) can be converted to two valuable materials at the same time. Furthermore, other nitrogen-containing materials (such as nylon-6) can also be converted to carbon microspheres and (NH4)HCO3highly efficiently, suggesting the generality of this process.We have also developed a strategy for the catalytic conversion of chicken feather waste to carbon-Ni3S2coaxial nanofibers (Ni3S2@C) which can be further converted to nitrogen doped carbon nanotubes (N-CNTs). Using this strategy, ca.34.0wt.%of the nitrogen content in the chicken feathers is transferred to (NH4)HCO3fertilizer and ca.9.5wt.%is transferred into the outer nitrogen-containing carbon nanotubes. About86.6wt.%S of element in the chicken feathers is converted into Ni3S2, which is beneficial to reduce the emissions of harmful gas, such as H2S or SO2. Both Ni3S2@C and N-CNTs exhibit high catalytic activity and good reusability in reduction of4-nitrophenol (4-NP) to4-aminophenol (4-AP) by NaBH4with the first order rate constant (k) of0.9×10-3s-1and2.1×10-3s-1, respectively. Moreover, the catalyst can be easily recycled by centrifugation and maintain the catalytic activity even after6cycles. The catalytic activity of N-CNTs is better than that of N-doped graphene and comparable to commonly used noble metal catalyst. The N content in N-CNTs reaches as high as6.43wt.%, which is responsible for the excellent catalytic performance. This strategy provides an efficient and low-cost method for the comprehensive utilization of chicken feathers. Moreover, this study provides a new application direction for the N-CNTs materials.3C-SiC nanowires have been synthesized by reaction of Polyethylene terephthalate (PET) waste with SiO2microspheres in a supercritical carbon dioxide system at650℃for3h, followed by vacuum annealing at1500℃for4h. The3C-SiC nanowires are tens of microns in length and30-150nm in diameter. It is found that the reaction forming3C-SiC nanowires take place in the inner of the carbon microspheres generated from PET. Therefore,3C-SiC nanowires are embedded in carbon microsphere. After removing the external superfluous carbons by heating in air, the nanowires appear and can be observed by SEM and TEM.Polyethylene-based waste plastics need hundreds of years to degrade in atmospheric conditions. As such, innovative treatment methods are highly desired. Herein, carbon nanotubes with Ni nanopaticles encapsulation are synthesized using polyethylene waste as carbon source and nickel acetate tetrahydrate as catalyst in supercritical carbon dioxide system at650℃for3h. The carbon nanotubes are tens of microns in length and about100nm in diameter, containing20wt%of Ni nanoparticles with diameter of about100nm. About60.7wt%carbon in the polyethylene waste is converted to carbon nanotubes. The carbon nanotubes with Ni nanopaticles encapsulation display a high catalytic activity for the reduction of4-nitrophenol to4-aminophenol. This not only provides an alternative strategy to treat plastic waste, but also demonstrates a new direction for the applications of the carbonaceous materials generated from the plastic waste.更多还原