【作者】 董新义；

【导师】 杨文胜； 迟力峰；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 近年来,贵金属纳米材料由于其独特的光学、电学性质,在生物医用检测、催化、非线性光学等领域受到了广泛的关注。银纳米粒子作为贵金属纳米材料中的重要一类,也逐渐地被深入研究,特别在尺寸、形貌的可控性制备以及表面性质研究等方面。柠檬酸钠还原法是制备贵金属纳米材料的常用方法之一,其在银纳米粒子的合成方面的应用也备受关注。本论文在传统柠檬酸钠还原法制备银纳米粒子的基础上,通过对粒子形成过程系统、定量的研究,采用改变体系pH值、引入成核剂和使用两种还原剂等方法实现了银纳米粒子成核-生长平衡,从而制备了单分散、尺寸/形貌可控的球形和三角形片状柠檬酸钠修饰的银纳米粒子。在两步法的基础上,引入强还原剂快速诱导成核以解决柠檬酸钠弱的还原能力在成核过程中的缺陷,用柠檬酸钠作为粒子生长过程的还原剂,获得了一系列尺寸的柠檬酸钠修饰的球形银纳米粒子。吸收光谱监测表明,柠檬酸钠还原阶段是银纳米粒子逐渐生长过程,此反应过程不存在二次成核现象。TEM表征表明,通过改变NaBH4的用量可以有效调控球形纳米粒子的尺寸。在低浓度的反应体系中,采用共还原的热化学方法合成了三角形片状银纳米粒子。对该热化学方法中三角形银纳米粒子的形成过程进行深入研究,提出了三角形片状银纳米粒子的转化机制。确定了影响球形银纳米粒子到三角形片状纳米粒子转化的主要影响因素。该转化过程中,小尺寸球形粒子的浓度与溶液中残余银离子浓度达到平衡是三角形片状结构得以转化的重要条件。通过调节还原剂硼氢化钠和柠檬酸钠的加入比例,可以调控节平衡,控制银纳米粒子的边长,获得了一系列不同尺寸的柠檬酸钠修饰的三角形片状银纳米粒子。更多还原

【Abstract】 Noble metal nanoparticles have attracted a great deal of attention during the past decades due to their unique electronic and optical properties and good chemical stabilities. The synthesis of noble metal nanparitcles and the utility of them as building block for bio-sensor and other devices are major subject of nanotechnology researches today.Silver nanoparticles, as an important member of the noble metal nano-materials, have also been in-depth studied. Great efforts have been devoted to control over the size and shape of silver nanoparticles since it is well documented that their properties are both size- and shape-dependent. Though various shapes and sizes of silver nanoparticles could be well synthesized in nonaqueous solution, the synthesis in aqueous system is still a tremendous challenge. From a green chemistry standpoint, synthesis of silver nanoparticles in aqueous solution is necessary. Synthesis of silver nanoparticles by citrate reduction is an ideal model system, this method had been widely investigated and developed since it was first invented by Turchevich because the citrate is well consistent with the bio-molecules. On the other hand, citrate is a weak ligand, and it is facile to be exchanged with other ligands. Synthesis of gold nanoparticles by the citrate reduction method has been well developed, while the synthesis on silver nanoparticles is still under exploring.In this dissertation, we selected the citrate reduction of silver nitride method as a model system. The kinetic factors which affecting the particle growth were studied in details. New synthesis strategy has been designed according to the nucleation-growth-ripening theory, and shape/size-controlled citrate caped silver nanoparticles were obtained.This dissertation includes three parts:1. we first did research on the following factors, such as reductant concentration, pH value, and reaction temperature, which affect the reaction rate and final shape\size of nanoparticles. Ultimately, we demonstrated that pH value played a crucial role in controlling the reaction rate and the final particle shape and size. We also identified there reaction steps of this synthesis, which are nucleation, growth and particle ripening. pH value can affect the redox rate of this system and through which affect the nucleation and growth rate. According to the well-known LaMer model, a stepwise reduction method, in which the nucleation and growth stages were carried out at high and low pH, respectively, is proposed. The shape control over the spherical silver nanoparticles is improved greatly due to the improved balance between nucleation and growth stages in the stepwise method.2. Encouraged by the stepwise reduction method, we adopted NaBH4 to control over the nucleation stage of reaction, and using sodium citrate as a reducing agent in the growth process. The particle size was decreased with the increasing of NaBH4 concentration due to the increasing concentration of silver nuclei reduced by NaBH4. By adjusting the molar ratio of the two reducing agents, the silver particles with various sizes (from 20 nm to 50 nm) were obtained. TEM images showed that the size distribution of the silver nanoparticles was also improved to around 6%.3. Using a co-reduction of NaBH4 and citrate under the lower AgNO3 concentration of 1×10-4 M, we prepared triangular silver nanoprisms with uniform thickness and various edge lengths. Through the study of thermo synthesis method, we proposed triangular sheet transmission mechanism. Also, we ascertained the two decisive factors that impact the transformation from spherical silver nanoparticles transforming into triangular nanoprisms: spherical particle size and the residual silver precursor. The transformation started when the concentration of AgNO3 was about 40% left, and kept 5×10-6 M for all through the transformation process during the 20 to 50 hours. Meaning an inter-particle Ostwald ripening process took place. Further investigation shows that the triangular silver nanoprisms could be synthesized only in the range of the NaBH4 concentration of 5×10-7 M to 5×10-5 M. Moreover, by adjusting the ratio of reductant, we could control the side length of triangular silver nanoparticles, and obtain a series of triangular silver nanoparticles with various sizes.更多还原