Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||韩永生, 李金兵|
银纳米材料在光学、电学、催化、医疗等多领域均表现出优异的应用前景，而纳米材料的性能与其形貌结构密切相关。前期工作中，人们通过改变反应温度和反应物浓度等实验参量，合成了不同形貌结构的银颗粒；但由于缺乏对银颗粒生长过程和控制机制的认识，银颗粒的可控合成和规模化制备仍然是一个挑战性问题。从化学工程角度看，材料的生长伴随着表界面的反应和传质过程。本课题组前期通过调控“反应-传质”过程定向合成了不同形貌的银颗粒，初步发现了表界面浓度场对银颗粒形貌的调控规律。本论文在组内前期工作基础之上，通过直接改变银离子局部浓度，进一步揭示表界面浓度场对银颗粒生长过程的调控规律和机制。主要研究发现如下：（1）采用电沉积法制备银颗粒，通过调节电位在反应溶液中生成氧化银胶体粒子副产物，通过外电场调控胶体粒子在溶液中的迁移速率，利用原位实验装置实时观测胶体粒子的迁移过程和银颗粒的生长过程，探索了表界面浓度场对银颗粒生长形貌的调控作用。研究发现随胶体粒子迁移速度增加，银离子传质增强，银颗粒生长前沿扩散层变薄，浓度梯度变大，银颗粒形貌由球状纳米晶依次变为团聚物、杂乱枝和枝晶结构。其中，银颗粒生长速度与银离子传质正相关，表明银颗粒生长过程是传质受限过程。最后结合格子Boltzmann模拟，验证了表界面浓度场对银颗粒形貌演化的调控机制。（2）为了进一步揭示表界面浓度场对银颗粒生长过程的调控作用，通过定向调控界面浓度场，以期观察到银颗粒生长方向的改变。采用置换法制备银颗粒，利用原位实验装置实时观测银棒的生长过程，通过外加电场控制银离子的迁移速率和方向，研究了表界面浓度场对银棒生长方向的调控作用。研究发现受表界面浓度场驱动银棒出现放射式多方向生长，失去以往只沿一个方向生长的趋势；随银离子电迁移速率增加，生长方向两侧浓度场的非均匀分布增强，银棒偏向高浓度场的侧枝获得优势生长。通过在生长方向正前方增强银离子传输，银棒长成十字架，并向多个方向生长。;Sliver nanomaterials have shown potential applications in many fields including optics, electricity, catalysis and medical treatment. Owe to the strong dependence of silver morphology on the properties of particles, silver particles with different structures were synthesized by regulating reaction temperature, chemical concentration and other experimental parameters. However, the rational synthesis and scale up of silver particles remain a challenge due to the lack of the understanding on their growth process and the control mechanism. From the view of chemical engineering, the growth of materials is accompanied by the reaction and mass transfer process at the interface. In the previous studies of our group, silver particles with different morphologies were largely synthesized by controlling the reaction and mass transfer process, finding the role of the interface concentration field on the morphology evolution of silver particles. On the basis of previous studies, this paper further investigated the role of the interface concentration field on the growth process of silver particles by directly regulating the local concentration of silver ions. The main findings are as follows: (1) In the process of synthesizing silver particles through electrodeposition method, the in-situ experimental device was used to observe the growth of silver particles. By controlling the potential applied to the synthesis, silver oxides as by-products were produced in the solution. They migrated to the growth front of crystal, which is driven by the electric field. It was found that the mass transfer of silver ions was promoted with the increase of migration speed of colloid particles. The diffusion layer became thinner and the concentration gradient became sharper at the growth front of silver particles. The morphology of silver particles changed from spherical nanocrystals to aggregates, disordered branches and dendritic structures with the increase of migration speed of colloid particles. Among them, the growth rate of silver particles is positively correlated with the mass transfer of silver ions, which indicated that the formation of silver crystal is limited by the mass transfer. The role of interface concentration field on the evolution of silver particle morphology was confirmed by the Lattice Boltzmann simulation and the regulation mechanism was discussed. (2) To further discover the role of interface concentration on the growth of silver particles, the change of interface concentration was regulated in special directions, in which the growth direction of silver particles was expected to change with the interface concentration. The replacement reaction method was employed to generate silver rods. The in-situ experimental device was used to observe the growth process of silver rods in a real time. It was found that the silver rods grew from single direction growth at first to multiple directions as a result of the enhancement of the mass transfer. When there was an anisotropic distribution of silver ions, silver rods tended to grow to the rich sides of silver ions. Furthermore, silver cross was formed with the enhancement of silver ions diffusion at front of growth.
|胥永辉. 表界面浓度场对银颗粒生长过程的调控作用[D]. 中国科学院大学,2020.|
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