【作者】 李伟；

【导师】 肖玲；

【作者基本信息】 武汉大学 ， 环境科学， 2010， 博士

【摘要】 纳米科技是在20世纪90年代逐步发展起来的前沿、交叉性新兴学科领域。纳米材料是纳米科技发展的重要基础。它是指材料的几何尺寸达到纳米级尺度水平,并且具有特殊性能的材料。纳米材料由于比表面积大、表面反应活性高、表面原子配位不全等导致表面的活性位点增加,催化效率提高,吸附能力增强,可以有效的应用于分子的固定、信号的检测和吸附性能放大。壳聚糖是甲壳素N-脱乙酰基的产物,是自然界唯一大量存在的碱性多糖,具有良好的生物相容性、生物可降解性、无毒和抗菌性等特点,是一种环保的高分子原料。作为纳米复合材料的重要分支之一,壳聚糖基纳米复合材料的制备和应用得到了广泛的研究,主要目标是在保持壳聚糖所特有的优异性能的同时具有纳米材料的性能,开发出新功能纳米复合材料。进入21世纪,在环境污染的巨大压力下,应用于环境监测和治理的新材料成为科学研究的重要方向。本文根据电负性污染物检测和吸附的需要,从原料的选择及合成方法入手,通过合理的设计,制备了新型壳聚糖基纳米复合材料。采用傅里叶红外光谱、X射线衍射、扫描电镜、透射电镜、紫外-可见分光光度计、差热分析、电位测定、磁性能测试等分析手段表征了壳聚糖纳米材料的的结构、物理和化学性质,讨论了材料的形成过程机理。选取硝基苯、铬(Ⅵ)为对象,研究了制备的材料在电负性污染物的检测和吸附中的应用。主要研究内容和结论如下：1、壳聚糖季铵盐接枝多壁碳纳米管的合成、表征和应用为了在改善多碳管分散性的同时保持材料在宽pH范围内的电正性,通过共价键合法将2-羟丙基三甲基氯化铵壳聚糖(HACC)结合到多壁碳纳米管(MWCNT)上,制备了新的纳米复合材料HACC-g-MWCNT,傅里叶红外光谱(FTIR)测试表明HACC分子链的羟基和MWCNT的羧基形成了酯键,根据热失重曲线接枝在碳纳米管表面的HACC约占材料总质量的10.2%。通过TEM和SEM可以观察到HACC-g-MWCNT呈现清晰的核壳结构。HACC-g-MWCNT的Zeta电位在pH2-12范围内始终为正值。以电负性的Fe(CN)63-/4-作为研究对象的电化学实验结果表明,由于HACC接枝MWCNT使碳管间的团聚减少、厚度增加,从而增大了碳管的比表面积和电化学活性,与CS-g-MWCNT相比较,更多的阴离子富集到了修饰电极附近,其中有一定量的阴离子通过静电作用与修饰材料形成了较为牢固的结合。2、壳聚糖材料修饰电极的制备和应用以玻碳电极(GCE)为基础,制备了HACC-g-GCE、HACC-g-MWCNT/GCE和(carboxylated MWCNT/HACC-g-MWCNT)n/GCE三种新型的壳聚糖纳米材料修饰玻碳电极。以水体中电负性的硝基苯为研究对象,较系统的讨论了修饰玻碳电极的制备方法对其表面形貌和对电负性污染物硝基苯分析性能的影响。(1)通过共价键合法形成单分子修饰膜,得到的修饰电极在三类修饰电极中性能最为稳定、重现性最好。相对于裸玻碳电极和CS-g-GCE修饰电极,HACC-g-GCE修饰电极的氧化还原峰电流有较大的提高,在优化条件下对硝基苯的检测限是0.70mg·L-1；(2)采用滴涂法,使HACC-g-MWCNT、CS-g-MWCNT在电极表面形成一定厚度的修饰层,所制得修饰电极的稳定性和重现性较好,而且制备过程简易。相对于裸玻碳电极和CS-g-MWCNT/GCE, HACC-g-MWCNT/GCE的氧化还原峰电流有较大的提高,在优化条件下对硝基苯检测限是0.04mg·L-1；(3)通过层层白组装法制备了(carboxylated MWCNT/HACC-g-MWCNTn/GCE修饰电极,这个方法可以有效控制多层膜的形成和组成,在所研究的三类修饰电极中灵敏度最高,其中(carboxylated MWCNT/HACC-g-MWCNT)2/GCE修饰电极对硝基苯的检测限是18.4μg·L-1；(4)通过三类电极实验结果的比较分析,在相同的制备方法和测试条件下,壳聚糖季铵盐类修饰电极检测水体中硝基苯的灵敏度要高于壳聚糖类修饰电极。3、新型磁性壳聚糖纳米粒子的合成及性质利用壳聚糖对Fe2+、Fe3+离子的吸附能力控制磁流体的形成和粒子大小,根据原位共沉淀原理,设计了未见报道的一步合成法,制备出磁性壳聚糖纳米材料,分析比较了不同条件、方法制备的材料的性质、微观结构和形成机理。实验结果表明经过优化合成条件,一步合成法能够制备出平均粒径12nm、粒径分布窄的磁性壳聚糖纳米粒子。通过TEM照片,可以清晰的观察到纳米粒子的核壳结构,在颜色较深的内核外有一层均匀、厚度约为1nm-2nm的外壳,结合差热测试的结果综合分析,粒子的内核是由Fe3O4分散于壳聚糖分子链中形成。与传统的二步法相比,一步法制备的磁性壳聚糖纳米粒子的热稳定性明显增强,根据TGA-FTIR等实验结果,推测在粒子形成过程中Fe304粒子在壳聚糖分子内部和分子之间形成了梁架结构,这种通过金属或者金属离子的配位产生的桥梁作用增强了聚合物的热稳定性。4、磁性壳聚糖纳米粒子对水体中电负性污染物的吸附分别以水体中的有机物污染物硝基苯和无机物染物铬(Ⅵ)离子作为吸附对象,研究一步法合成的磁性壳聚糖纳米粒子对水体中电负性污染物的吸附。(1)磁性壳聚糖纳米粒子对硝基苯的饱和吸附量是活性炭的3.4倍,达到629mg/g,同时能够更快的达到吸附平衡。酸性条件下,磁性壳聚糖纳米粒子对硝基苯的吸附属于单分子层的化学吸附,可以用Langmuir吸附等温线较好的描述,吸附过程由表面反应控制,比较符合二级动力学模型。经过五次重复使用后吸附剂的吸附保留量是86%；(2)磁性壳聚糖纳米粒子对铬(Ⅵ)的饱和吸附量为34mg/g,根据所含壳聚糖的质量计算的饱和吸附量为322mg/g,高于文献报道的交联壳聚糖对铬(Ⅵ)的吸附能力215mg/g。酸性条件下,磁性壳聚糖纳米粒子对铬(Ⅵ)的吸附属于单分子层的化学吸附,可以用Langmuir吸附等温线较好的描述,吸附过程由表面反应控制,比较符合二级动力学模型。经过五次重复使用后吸附剂的吸附保留量是82%。更多还原

【Abstract】 Nanotechnology is one of the forefront cross-cutting disciplines which are gradually developed in the 1990s. The research of nanocomposites is an important foundation for nanotechnology. These materials are nano-scale level, with special properties such as high surface reactivity, catalytic efficiency and adsorption capacity as a result of the incomplete surface atoms, large surface area and active site. Chitosan is the N-deacylated chitin and only alkaline polysaccharide in nature, which has many desirable properties, including biocompatibility, biodegradability, nontoxicity, antimicrobial and so on. It is one of environmental-friendly polymer materials. As an important branch of nanocomposites, the preparation and application of chitosan-based nanocomposites have been widely studied. The main objective of these researches is to find new functional nanocomposite which maintain the useful properties of chitosan.In the 21st century, the new materials used in environmental monitoring and treatment become an important direction of scientific research, under the enormous pressure of environmental pollution. In this study, a series of chitosan-based nanocomposites are prepared based on the needs of detection and adsorption of electronegative pollutants. The synthetic methods have been discussed comprehensively. Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), thermogravimetric analysis(TGA) and so on, were used to characterize the structures, physical and chemical properties of chitosan-based nanocomposites. The chitosan-based nanocomposites were used in the detection and adsorption of electronegative pollutants, selecting nitrobenzene and chromium(Ⅵ) as the objects. The main study contents and conclusions are as follows.1. Synthesis and relevant electrochemical properties of 2-hydroxypropyltrimethyl ammonium chloride chitosan-grafted multiwalled carbon nanotubes.A 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC)-grafted multiwalled carbon nanotubes (MWCNT) composite (HACC-MWCNT) was prepared through grafting HACC onto the surfaces of MWCNT. The differences in the FTIR and TGA curves between the materials indicated the existence of a strong link between HACC and MWCNT in the structure. This result was further confirmed by TEM and SEM images that the shell structure and extra phase of HACC on the surface of MWCNT were observed. The HACC-MWCNT maintained positive charge through the range of pH value (1-12). These effects were attributed to the function groups of HACC. It was very different from chitosan-modified composites whose positive charge was mainly due to protonated amine groups in aqueous acidic solution. The cyclic voltammetry of the negatively charged redox probe, Fe(CN)63-/4-, showed that the electrochemically active area of MWCNT was increased greatly after grafting HACC. The negatively charged ions were retained in the HACC-MWCNT film by the electrostatic interactions. The retention of negatively charged ions has consequences when used as sensors for the negatively charged molecules. Further applicated this material to supercapacitors and sensors are expected and currently under inverstigation.2. Preparation and application of chitosan materials-modified electrodes.The preparation and properties of the chitosan materials-modified electrodes were discussed systematicly, including three new modified electrode (HACC-g-GCE, HACC-g-MWCNT/GCE and (carboxylated MWCNT/HACC-g-MWCNT)n/GCE). The electrochemical behaviors of nitrobenzene on the modified electrodes were studied. The single-molecule-membrane modified electrodes which were obtained through covalent modification were most stable and reproducible in the three types of discussed electrodes. Compared with bare GCE and CS-g-GCE, the redox peak currents of nitrobenzene on HACC-g-GCE were greatly improved under optimized conditions, with the detection limit of 0.7mg·L-1. By drop coating method which could form a certain thickness of layer on the electrode surface, the modified electrodes were prepared simply with good stability and reproducibility. Compared with bare GCE and CS-g-MWCNT/GCE, the redox peak currents of nitrobenzene on HACC-g-MWCNT/GCE were greatly improved under optimized conditions, with the detection limit of 0.04mg·L-1. Through layer-by-layer self-assembly method, the formation and composition of multilayers of the modified electrodes could be precisely controled. These modified electrodes were most stable and reproducible in the three kinds of discussed electrodes. In the studied modified electrode (carboxylated MWCNT/HACC-g-MWCNT)2/GCE showed the highest sensitivity with the detection limit of 18.4μg·L-1. By comparison of three types of electrodes, the HACC-modified electrodes had higher sensitivity to nitrobenzene than chitosan-modified electrodes. 3. Preparation and characterizaton of chitosan-Fe3O4 nanoparticles synthesized via a novel one-step modifying process.A novel modifying process was designed to prepare ultrasmall magnetic chitosan nanoparticles which exhibited unique thermal stability and decomposition mechanism. The results revealed that this approach eliminated the aggregation among nanoparticles. The magnetic analysis indicates that the particles are superparamagnetic with a saturation magnetization of 73.5emu/g. Fe3O4-chitosan could be separated rapidly from the aqueous solution by permanent magnet. A shell of chitosan with a thickness found to be lnm-2nm, was coated evenly on the magnetic chitosan with good dispersibility and new thermal property. To further study the decomposition process, the combined TGA-FTIR technique was used to the analysis of the evolution with the temperature of the gas products evolved in the degradation of the magnetic chitosan. The phenomena were observed directly from TGA-FTIR stack plots. From the measurements data, it suggested that the unusal thermal behaviors of chitosan might be attributed to the additional bridging through metal oxide.4. Adsorption of nitrobenzene and chromium(Ⅵ) on magnetic Fe3O4-chitosan nanoparticles.Fe3O4-chitosan nanoparticles were prepared and used as adsorbents for nitrobenzene and chromium(Ⅵ) removal. The capacity of adsorption for nitrobenzene species decreased with the increase of the solution pH values. The equilibrium data followed Langmuir isotherm model with maximum capacities of 629mg/g. The adsorption process could be described by the pseudo-second-order model. Regeneration tests revealed that the capacity of the prepared sorbent through five cycles was found to be 86% of the fresh one for nitrobenzene removal. The capacity of adsorption for chromium(VI) species decreased with the increase of the solution pH values. The equilibrium data followed Langmuir isotherm model with maximum capacities of 322mg/g based on the weight of chitosan. The adsorption process could be described by the pseudo-second-order model. Regeneration tests revealed that the capacity of the prepared sorbent through five cycles was found to be 82% of the fresh one for chromium(Ⅵ) removal.更多还原