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  本文關(guān)鍵詞：核殼型功能材料的設(shè)計組裝及性能研究　出處：《大連工業(yè)大學》2015年碩士論文　論文類型：學位論文

  更多相關(guān)文章： 核-殼結(jié)構(gòu) 綠色還原 Ag納米顆粒 多相催化 磁控分離

【摘要】：近年來,貴金屬納米粒子因自身具有的特殊物理和化學性質(zhì)而成為最具發(fā)展前景的催化劑之一。尺寸的可控性、形貌的特殊性和高的比表面積使其在許多液相反應(yīng)中表現(xiàn)出較高的催化活性和選擇性。其中,Ag納米粒子(Ag NPs)因相對其他貴金屬的價格相對便宜而成為研究焦點。但是,納米粒子因較小的尺寸,在實際應(yīng)用中普遍面臨易團聚、難分離回收的問題。能夠有效解決該難題的一種方法是將其穩(wěn)定到具有不同形貌、不同尺寸、不同組成的各類載體上。其中,日益興起的磁性核殼結(jié)構(gòu)復合納米球,如機械和化學穩(wěn)定的Fe3O4@SiO2核殼結(jié)構(gòu)材料,因具有大的比表面積和可磁控分離能力,能夠?qū)⒒钚越M分分散到其表面,增大催化劑的有效活性面積,且能夠?qū)崿F(xiàn)催化劑的快速高效分離和回收,因此已被廣泛用做貴金屬納米粒子的前景支撐材料。此外,在納米金屬粒子的制備過程中常常會用到NaBH4、水合肼等有毒有害的還原劑,對環(huán)境和生物體不利。為了遵循“綠色化學”的發(fā)展理念,越來越多的研究人員開始采用生物相容性的高聚物或植物根、莖、葉的提取液來綠色還原和有效穩(wěn)定納米金屬粒子。其中,殼聚糖(CS),一種天然產(chǎn)生、生物可降解、生物相容、非毒性的多糖,因含有大量的羥基和氨基活性功能基團而使其成為一種有效的吸附劑和穩(wěn)定劑以及貴金屬離子的還原劑,且作為基質(zhì)材料已受到廣泛關(guān)注。于是,我們選擇殼聚糖的水溶液來綠色還原和穩(wěn)定Ag NPs,且過程中不需要添加額外的有毒還原劑和溶劑。但是,如何將磁性核殼結(jié)構(gòu)材料Fe3O4@SiO2與殼聚糖結(jié)合成為一個整體是問題的關(guān)鍵�？紤]到氨基修飾的Fe3O4@SiO2(Fe3O4@SN)的表面和殼聚糖均帶有正電荷,于是我們首先選擇磷鎢酸(HPW),一種典型的多聚含氧陰離子,作為Fe3O4@SN和殼聚糖之間的橋連劑,通過靜電和氫鍵相互作用將二者有效結(jié)合。此外,為了增強引入殼聚糖層的機械強度,我們選擇戊二醛(GLA)作為殼聚糖層的有效交聯(lián)劑。然后,用已制備的強健載體來原位還原和穩(wěn)定Ag NPs。并用NaBH4還原對硝基苯酚(4-NP)的反應(yīng)作為模型反應(yīng)體系系統(tǒng)考察了已制備磁性核殼型催化劑Fe3O4@SN/HPW@CG-Ag的催化性能。結(jié)果表明,在最佳的制備條件下,如HPW、GLA的加入量和AgNO3的初始濃度均最佳時,該多功能復合催化劑表現(xiàn)出了良好的催化活性(反應(yīng)7 min完成)和穩(wěn)定性(至少重復使用10次)。且因磁性鐵核Fe3O4的存在,能夠在外加磁場的作用下實現(xiàn)催化劑的快速分離和回收。此外,對不同制備階段的產(chǎn)品也進行了系統(tǒng)的表征。鑒于戊二醛對殼聚糖的交聯(lián)是通過殼聚糖中的氨基和戊二醛中的醛基發(fā)生席夫堿反應(yīng)完成的,又考慮到Fe3O4@SN的表面也含有氨基,于是想要采用戊二醛替代HPW作為橋連劑,通過共價相互作用實現(xiàn)Fe3O4@SN和殼聚糖的結(jié)合。和上個實驗方案相比,該方案的制備過程和產(chǎn)物組成更加簡單,更加經(jīng)濟。我們也將新制備的載體Fe3O4@SN/GLA@CS用做綠色還原劑和穩(wěn)定劑來原位制備Ag基納米催化劑。并在上個實驗的基礎(chǔ)上,進一步探討了反應(yīng)時間、反應(yīng)溫度對殼聚糖的還原能力和Ag NPs尺寸、尺寸分布和催化性能的影響。且也將最佳的催化劑應(yīng)用到了4-NP的催化還原反應(yīng)中。更重要的是該催化劑因含有較小尺寸的Ag NPs,表現(xiàn)出了更好的催化性能(反應(yīng)3 min即可完成),且具有良好的可重復使用性(至少重復使用6次)和易回收性。結(jié)合以上兩個實驗的表征結(jié)果,我們推測在Ag NPs的制備過程中,起還原作用的是殼聚糖中的氨基。又考慮到Fe3O4@SN的表面也含有氨基,于是我們想要證明Fe3O4@SN表面的氨基能否在上述探討的最佳條件下直接還原和制備Ag NPs。結(jié)果表明,在Fe3O4@SN的表面確實有均一的小尺寸Ag NPs產(chǎn)生。相對于上兩個實驗,由于沒有了殼聚糖層的存在,反應(yīng)物更容易接近活性位點,催化劑的飽和磁化強度更強,因此在4-NP的還原反應(yīng)中表現(xiàn)出了更好的催化活性(反應(yīng)2 min即可完成)和磁響應(yīng)能力。在本研究課題中,通過采用不同的作用機理和方法已成功制備了具有不同殼的磁性核殼結(jié)構(gòu)載體。之后,又將這一系列載體用做綠色的還原劑和穩(wěn)定劑制備了具有良好催化性能、穩(wěn)定性、可重復使用性以及易回收性的Ag基磁性核殼型納米催化劑。因此,本文中多功能磁性核殼結(jié)構(gòu)載體和催化劑的設(shè)計理念為制備長期穩(wěn)定、易分離回收、經(jīng)濟、綠色的載體和催化劑體系提供了借鑒意義。
[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.

【學位授予單位】：大連工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：O643.36;TB383.1

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