【作者】 吴梦洁；

【导师】 方云；

【作者基本信息】 江南大学 ， 化学工艺， 2011， 硕士

【摘要】 纳米银作为金属银的一种特殊形态,具有粒径小、比表面积大、催化活性高、熔点低的特点,同时保留了金属银的导电性好、导热系数高、抗菌性能好的优点,在催化、信息存储、生物标记、抗菌以及表面增强拉曼光谱等领域具有潜在的应用价值而得到科学工作者的密切关注。纳米银的性质取决于其大小、形状、组成、结晶度以及结构（实心与空心）。原则上,调节以上性能参数的任何一项就能细微的调控纳米银的性质。在众多纳米银材料的制备方法中,其中多元醇法相对于其它方法来说无需借助其它设备而具有简便、廉价和产率高的优点,在制备特殊形貌的纳米材料中备受关注。本文以多元醇法为原型,在常温水相中,在不加晶种的条件下,利用表面活性剂和大分子作为软模板制备银纳米粒子,不仅绿色无有机物污染,还具有产率高,能耗少的优点。以表面活性剂和大分子作为软模板由来已久,因其对纳米粒子保护充分,对纳米粒子形貌调控显著的优点而被广泛应用。表面活性剂和大分子之间存在相互作用,在一定表面活性剂浓度范围内,表面活性剂和大分子软团簇结构会发生胶束结构的改变,即存在双临界胶束浓度特性。在第一临界浓度c₁以前,大分子和表面活性剂分子之间无相互作用;在c₁和c₂之间,表面活性剂分子吸附在大分子链上形成束缚胶束,在c₂以后,大分子链上的束缚胶束达到饱和,溶液中开始形成自由胶束。PVP是一种常见的水溶性大分子,SDS是一个典型的阴离子表面活性剂,两者的混合水溶液也具有上述特征,且加入银氨络离子这种双临界胶束浓度特性不会改变。PVP-SDS混合水溶液作为纳米制备的软模板具有特殊的意义,它具备二级模板作用,可以二次调控纳米粒子的生长。在反应初期,SDS束缚胶束吸附溶液中的银氨络离子,在反应进行的过程被富集的银氨离子在SDS束缚胶束周围还原形成原级纳米晶粒,即辅助均相成核过程,此为一级模板作用。随着原级纳米晶粒的进一步增多,依附在大分子链上的原级纳米银晶粒由于大分子链的牵引而彼此靠近融合生长得到进一步的纳米结构物,此为二级模板作用。此外PVP分子还兼具有定向吸附和弱还原功能,PVP分子链可以定向吸附在纳米银的某些晶面上,利于银纳米粒子的定向生长;在适当的条件下PVP链还具有微弱的还原作用,能够充当弱还原剂还原银氨离子。本文在常温、水相、无需加入晶种和有机溶剂的条件下,以PVP-SDS为软模板,用葡萄糖还原银氨络离子制得五重孪晶银纳米粒子。该纳米银的等离子共振吸收峰在441 nm处,XRD表明其为面心立方体,在（111）晶面有最强吸收;通过HRTEM观察到纳米银颗粒的晶格条纹和孪晶面证实其为多重孪晶（MTP）,选区电子衍射（SAED）证实了其五重孪晶结构。该纳米粒子具有很高的生长活性,可以进一步生长得到棒状纳米银。实验考察了模板的作用机理,在银纳米棒生长的第一阶段,SDS束缚胶束起主要模板作用,得到直径约为5-10 nm的原级纳米银晶粒。在第二生长阶段,PVP大分子链起主要模板作用,得到的直径约为50±5 nm的次级纳米银颗粒;在第三生长阶段,五重孪晶的晶体生长规律占居主导地位,通过Ostwald熟化生长,合成了直径为40 nm,最大长度为700 nm的银纳米棒,软模板仅通过选择性吸附起到辅助晶体生长的作用。采用自晶种法制备片状银纳米粒子,在PVP-SDS软模板保护下以硼氢化钠为还原剂快速还原银氨络离子制得银晶种,在后续反应中高浓度的PVP链充当弱还原剂,缓慢还原银氨络离子得到银,在PVP-SDS软模板中调控SDS浓度、PVP浓度以及pH改变纳米银的形貌,制得三角片状、圆盘状以及截角三角片状纳米银。通过组装得到树枝状纳米银结构。更多还原

【Abstract】 As a special form of silver, the nano-silver not only has advantages of small particle size, large surface area, high catalytic activity and low melting point, but also maintains good characteristics of metal silver, such as high electrical conductivity, high thermal conductivity and good performance in anti-bacterial. Since then it has been widely used in catalysis, information storage, biological labeling, anti-bacterial and surface enhanced Raman scattering （SERS）. The properties of the nano-silver are mainly determined by its size, shape, composition, crystallinity and morphology （solid versus hollow）. In principle, one could control any of these parameters to fine-tune the properties of the nano-silver.Compared with other preparation of the nano-silver, polyol process has been increasing popular, which has various advantages, such as simple, inexpensive, high yield and without needing the help of machine. In this paper, based on the prototype of polyol process, the nano-silver were synthesized by using surfactants and macromolecules as soft templates in normal temperature, but without adding seed or organic solvent. This method was totally green, and has many significant advantages such as without organic solvent pollution, high yield and low energy consumption.It was a long time to use surfactants and macromolecules as soft templates, since they can fully cap nanoparticles and significantly control the morphology of nanoparticles. The interaction between surfactants and macromolecules has been confirmed. At a certain range of surfactants concentration, the micelle structures of the soft clusters which consist of surfactants and macromolecules were changed with the change of surfactants concentration, which showed the characteristic of two critical concentrations.Before the first critical micelle concentration c₁, there is no interaction between surfactants and macromolecules; between c₁ and the second critical micelle concentration c₂, surfactants adsorb on macromolecules chain to form bound micelles; after c₂, the bound micelle has been saturated and the free micelles begin to form. In our research, since PVP is a common water-soluble macromolecule and SDS is a typical anionic surfactant, the complex of PVP-SDS aqueous solution can provide the above characteristics. Simultaneously, by adding silver ammonia complex ion in solution the two critical micelle concentrations remain the same.The complex of PVP-SDS aqueous solution as soft templates to prepare nano-silver has special meanings. It has two-level template effect, which can control the growth of nanoparticles twice. In the initial stage, silver ammonia ion was adsorbed to the SDS bound micelles. With the reduction of silver ammonia ion, the amount of Ag was enriched by SDS bound micelles and finally nano-crystals were formed. This stage was the process of assisting homogeneous nucleation. This is the first level of template effect. Then with the number of nano-crystals increasing, more and more nano-crystals attached on the chains of polymers, which made nano-crystals close to each other and grow to nanostructures in the end. This is the second level of template effect. Meanwhile, PVP chains acted as oriented adsorption and a weak reducer. PVP chains can be absorbed to a certain crystal face of silver nanoparticles, which was benefit to oriented growth of silver nanoparticles. Besides, PVP chains also have a weak effect of reduction in the appropriate condition, which can act as a weak reducer to reduce silver ammonia ions.Multiply twinned particles （MTP） of nanosilver were synthesized from ammoniacal silver ion reduced by glucose in aqueous solution of polyvinylpyrrolidone （PVP） and sodium dodecyl sulfate （SDS） aggregations. In this method, there was normal temperature, water phase, without adding seeds and on organic solvents. The Plasma resonance absorption of MTP was at 441 nm, the size was 50±5 nm in diameter. The XRD diffraction pattern shows the face centric structure （fcc） of MTP with the strongest diffraction peak at （111） lattice plane. The lattice fringes and twin planes were observed by the high-resolution transmission electron microscopy （HRTEM） and the quintuple twinned structure of silver nanoparticles was further validated by selected area electron diffraction （SAED）. The as-prepared MTP of nanosilver with high growth activity could further grow into silver nanorods by the inducing of the template. We present an explanation to the growth mechanism of soft template. In the first stage, SDS bound micelles played a major role of the template to get the original silver nano-crystals of 5-10 nm in diameter. Second, PVP chains play a major role of the template, got 50±5 nm in diameter of the secondary silver nanoparticles. Third, the five-twinned crystal self growth became dominance, finally 40 nm in diameter and 700 nm in length of silver nanorods were synthesized by Ostwald ripening, the soft template only play a supporting role by selective adsorption in crystal growth.Flake-like silver nanoparticles was prepared by self-seeding in the PVP-SDS aqueous solution. In this method, sodium borohydride was used to fast reducer to obtain silver seed, in the subsequent of reaction, high concentration of PVP chains acted as weak reduction agent to slowly reduce of silver ammonia complex ion. Modified the pH and the concentration of SDS or PVP, the morphology of silver nanoparticles were changed. By this means, we obtained triangular, flakes and truncated triangular of nanosilver. We also got dendritic silver nano-structure through base assemble.更多还原