核壳型功能材料的设计组装及性能研究

发布时间：2018-01-10 22:18

本文关键词：核壳型功能材料的设计组装及性能研究　出处：《大连工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：近年来,贵金属纳米粒子因自身具有的特殊物理和化学性质而成为最具发展前景的催化剂之一。尺寸的可控性、形貌的特殊性和高的比表面积使其在许多液相反应中表现出较高的催化活性和选择性。其中,Ag纳米粒子(Ag NPs)因相对其他贵金属的价格相对便宜而成为研究焦点。但是,纳米粒子因较小的尺寸,在实际应用中普遍面临易团聚、难分离回收的问题。能够有效解决该难题的一种方法是将其稳定到具有不同形貌、不同尺寸、不同组成的各类载体上。其中,日益兴起的磁性核壳结构复合纳米球,如机械和化学稳定的Fe3O4@SiO2核壳结构材料,因具有大的比表面积和可磁控分离能力,能够将活性组分分散到其表面,增大催化剂的有效活性面积,且能够实现催化剂的快速高效分离和回收,因此已被广泛用做贵金属纳米粒子的前景支撑材料。此外,在纳米金属粒子的制备过程中常常会用到NaBH4、水合肼等有毒有害的还原剂,对环境和生物体不利。为了遵循“绿色化学”的发展理念,越来越多的研究人员开始采用生物相容性的高聚物或植物根、茎、叶的提取液来绿色还原和有效稳定纳米金属粒子。其中,壳聚糖(CS),一种天然产生、生物可降解、生物相容、非毒性的多糖,因含有大量的羟基和氨基活性功能基团而使其成为一种有效的吸附剂和稳定剂以及贵金属离子的还原剂,且作为基质材料已受到广泛关注。于是,我们选择壳聚糖的水溶液来绿色还原和稳定Ag NPs,且过程中不需要添加额外的有毒还原剂和溶剂。但是,如何将磁性核壳结构材料Fe3O4@SiO2与壳聚糖结合成为一个整体是问题的关键。考虑到氨基修饰的Fe3O4@SiO2(Fe3O4@SN)的表面和壳聚糖均带有正电荷,于是我们首先选择磷钨酸(HPW),一种典型的多聚含氧阴离子,作为Fe3O4@SN和壳聚糖之间的桥连剂,通过静电和氢键相互作用将二者有效结合。此外,为了增强引入壳聚糖层的机械强度,我们选择戊二醛(GLA)作为壳聚糖层的有效交联剂。然后,用已制备的强健载体来原位还原和稳定Ag NPs。并用NaBH4还原对硝基苯酚(4-NP)的反应作为模型反应体系系统考察了已制备磁性核壳型催化剂Fe3O4@SN/HPW@CG-Ag的催化性能。结果表明,在最佳的制备条件下,如HPW、GLA的加入量和AgNO3的初始浓度均最佳时,该多功能复合催化剂表现出了良好的催化活性(反应7 min完成)和稳定性(至少重复使用10次)。且因磁性铁核Fe3O4的存在,能够在外加磁场的作用下实现催化剂的快速分离和回收。此外,对不同制备阶段的产品也进行了系统的表征。鉴于戊二醛对壳聚糖的交联是通过壳聚糖中的氨基和戊二醛中的醛基发生席夫碱反应完成的,又考虑到Fe3O4@SN的表面也含有氨基,于是想要采用戊二醛替代HPW作为桥连剂,通过共价相互作用实现Fe3O4@SN和壳聚糖的结合。和上个实验方案相比,该方案的制备过程和产物组成更加简单,更加经济。我们也将新制备的载体Fe3O4@SN/GLA@CS用做绿色还原剂和稳定剂来原位制备Ag基纳米催化剂。并在上个实验的基础上,进一步探讨了反应时间、反应温度对壳聚糖的还原能力和Ag NPs尺寸、尺寸分布和催化性能的影响。且也将最佳的催化剂应用到了4-NP的催化还原反应中。更重要的是该催化剂因含有较小尺寸的Ag NPs,表现出了更好的催化性能(反应3 min即可完成),且具有良好的可重复使用性(至少重复使用6次)和易回收性。结合以上两个实验的表征结果,我们推测在Ag NPs的制备过程中,起还原作用的是壳聚糖中的氨基。又考虑到Fe3O4@SN的表面也含有氨基,于是我们想要证明Fe3O4@SN表面的氨基能否在上述探讨的最佳条件下直接还原和制备Ag NPs。结果表明,在Fe3O4@SN的表面确实有均一的小尺寸Ag NPs产生。相对于上两个实验,由于没有了壳聚糖层的存在,反应物更容易接近活性位点,催化剂的饱和磁化强度更强,因此在4-NP的还原反应中表现出了更好的催化活性(反应2 min即可完成)和磁响应能力。在本研究课题中,通过采用不同的作用机理和方法已成功制备了具有不同壳的磁性核壳结构载体。之后,又将这一系列载体用做绿色的还原剂和稳定剂制备了具有良好催化性能、稳定性、可重复使用性以及易回收性的Ag基磁性核壳型纳米催化剂。因此,本文中多功能磁性核壳结构载体和催化剂的设计理念为制备长期稳定、易分离回收、经济、绿色的载体和催化剂体系提供了借鉴意义。
[Abstract]:In recent years, the special physical and chemical properties of noble metal nanoparticles by itself has become one of the most promising catalyst. The controllable size, morphology of special and high specific surface area which shows high catalytic activity and selectivity in many liquid reactions. Among them, Ag nanoparticles (Ag NPs) becomes the focus of research because relative to other precious metals prices relatively cheap. However, due to the smaller size of nanoparticles, generally face agglomerate in the practical application, difficult separation and recovery problems. An effective method to solve this problem is the stability with different shapes, different sizes, different types of carrier the composition. Among them, the magnetic core-shell structure composite nanoparticles growing, such as mechanical and chemical stability of Fe3O4@SiO2 core-shell structure materials, because of its large surface area and magnetic separation ability, can be Dispersion of active component to the surface of the active area increasing catalyst, fast and efficient and can achieve the separation and recovery of catalyst, therefore it has been widely used as the noble metal nanoparticles the prospect of supporting materials. In addition, the nano metal particle preparation process often used in NaBH4, hydrazine hydrate and other toxic reducing agents, detrimental to the environment and organisms. In order to follow the development of the concept of "green chemistry", more and more researchers begin to use biocompatible polymer or plant root, stem, leaf extract to green reduction and effective stability of nano metal particles. The chitosan (CS), a kind of natural, biodegradable. The biocompatibility, non toxicity of polysaccharide, containing hydroxyl and amino functional groups of the reducing agent is an effective adsorbent and stabilizer and metal ions, and as The matrix material has attracted widespread attention. Therefore, we choose the solution of chitosan to green reduction and stability of Ag NPs, and the process does not need to add additional toxic solvent and reducing agent. However, how will the magnetic core-shell structure material Fe3O4@SiO2 and combined with chitosan as a whole to consider is the key to the problem. The amino modified Fe3O4@SiO2 (Fe3O4@SN) on the surface of chitosan with positive charge, so we first select the phosphotungstic acid (HPW), a typical poly oxygen anion, as between Fe3O4@SN and chitosan bridging agent, effectively combined with electrostatic interaction and hydrogen bonding of the two. In addition, in order to enhance the mechanical strength of chitosan layer, we choose glutaraldehyde (GLA) as crosslinking agent of chitosan layer. Then, with a strong carrier prepared in situ reduction and stability of Ag NPs. and NaBH4 reduction of p-nitrophenol (4-NP As the reaction system) model reaction system was investigated have catalytic properties of preparation of magnetic core-shell Fe3O4@SN/HPW@CG-Ag catalyst. The results showed that the optimum preparation conditions, such as HPW, dosage and initial concentration of AgNO3 GLA were the best, the multifunctional composite catalyst showed good catalytic activity (7 min reaction completion) and stability (at least 10 times of repeated use). And because of the existence of Fe3O4 nuclear magnetic iron, can realize catalyst under magnetic field the rapid separation and recovery. In addition, the influence of preparation phase of the products were characterized. Due to crosslinking with glutaraldehyde on chitosan is completed the aldehyde group in chitosan and glutaraldehyde in the amino Schiff reaction, and considering the surface of Fe3O4@SN also contain amino groups, and then want to replace HPW using glutaraldehyde as a bridging agent through covalent interactions. The combination of Fe3O4@SN and chitosan. Compared with the experiment plans, preparation process and product of the architecture is simpler, more economical. We will also support Fe3O4@SN/GLA@CS new preparation for green reducing agent and stabilizer for preparation of Ag based nano catalyst in situ. And on the basis of experiments. To further explore the reaction time, reaction temperature on the chitosan and Ag reduction ability of NPs size, influence the distribution of catalytic performance and size. And also the best catalysts to the selective catalytic reduction of 4-NP reaction. It is more important because of the small size of the catalyst containing Ag NPs showed better catalytic performance (3 min reaction can be completed), and has good reusability (at least 6 times of repeated use) and recyclability. The characterization results combined with the above two experiments, we speculate that Ag NPs in the preparation process, reducing work The chitosan amino. And considering the Fe3O4@SN surface also contains amino, so we want to prove that the Fe3O4@SN surface can amino optimal conditions during the discussion of the direct reduction and preparation of Ag NPs. showed that the small size Ag NPs does have a uniform on the surface of the Fe3O4@SN. Compared to the two experiment no, because the chitosan layer, the reaction is more accessible to the active site, the stronger the saturation magnetization of the catalyst, so the reduction reaction of 4-NP showed better catalytic activity (2 min to complete the reaction) and magnetic response capability. In this research, the mechanism and by different methods have been successfully fabricated by magnetic core-shell structure with different carrier shell. After this, and a series of carriers for green reducing agent and stabilizer system has good catalytic properties, the preparation of a stable, heavy The Ag based magnetic core shell type nanocerst is versatile and recyclable. Therefore, the design concept of multi-functional magnetic core shell structure carrier and catalyst provides reference for preparing long-term stability, easy separation and recycling, economy, green carrier and catalyst system.

【学位授予单位】：大连工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TB383.1

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