【作者】 谭德志；

【导师】 邱建荣；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2014， 博士

【摘要】 材料,能源以及信息被公认为现代文明的三大支柱,支撑着现代文明的发展。新材料的发现与制备不断推动着科学的发展,技术的进步以及人们生活水平的提高。纳米材料概念的提出和纳米技术的发展使得材料在人类文明的发展和人们的日常生活中发挥着越来越广泛而深远的影响。纳米材料研究中不断涌现的各种新奇的现象充实着人类知识的宝库。纳米材料的广泛使用使得各种科技和生活器件不断趋向于微型化便捷化多功能化。作为一种新型简便的制备纳米材料的方法,液相脉冲激光烧蚀法已被广泛用于制备各种功能纳米材料。本文主要系统研究了液相脉冲激光烧蚀法制备多种功能纳米材料的可能性。我们重点梳理并抓住了液相脉冲(主要是飞秒)激光烧蚀法的基本特点,即局部高温高压环境,快速冷却,以及纳米材料的同步修饰与复合。进而以此为基本的指导思路和依据进行实验设计,实现了多种功能纳米材料的制备。一,亚稳态功能纳米材料的制备一般亚稳相的制备都需要在高温高压条件下进行,并需要快速冷却,因此制备过程复杂,条件控制严格。由于脉冲激光(特别是飞秒激光)的脉宽很短,峰值功率极高,脉冲的能量可以在极短的时间内注入到材料内部。因此,液相脉冲激光烧蚀法可以在局部区域产生极端高温高压的条件,并产生等离子体。在这种局部的非平衡环境中,各种化学反应都可能发生,特别有利于产生亚稳态结构。同时周围液体的强烈的压缩和冷却作用可以使等离子体快速冷却下来,从而使亚稳相材料保存下来。通过控制溶液的性质以及脉冲光源,我们实现了不同亚稳态纳米材料的制备。我们使用液相飞秒与纳秒激光烧蚀法在氨水中分别成功制备了高温亚稳相-立方相二氧化锆和四方相二氧化锆。由于飞秒激光的峰值功率要比纳秒激光的高很多,所产生的温度和压强也更高。同时,等离子体的冷却速率也更高。所以我们认为飞秒激光比纳秒激光更有利于高温相的生成和稳定。二,表面修饰纳米材料的制备纳米材料的性质与其表面结构有着重要的关系。特别的,表面结构往往决定了其在不同环境中的相容性。同时特定的表面修饰还可以控制纳米材料的尺寸,提高纳米材料结构和性能的稳定性。一般制备表面修饰纳米材料都需要两步,即纳米材料的制备与修饰,反应条件控制往往较为严格。而在液相脉冲激光烧蚀法中,通过控制溶液的性质,即可一步实现纳米材料的制备与修饰。我们使用飞秒激光烧蚀法在1-已烯和丙烯酸／乙醇的混合溶液中分别制备了分散性很好的疏水性和亲水性硅纳米粒子。我们认为在液相飞秒激光烧蚀的极端环境中,活性很高的硅纳米粒子易与溶液的中不饱和有机物(1-已烯或者丙烯酸)发生加成反应,从而形成表明修饰。我们还发现,通过控制溶液的性质,不仅可以调控硅纳米粒子的表面结构与尺寸,还可以控制硅纳米粒子的光学性质。三,表面修饰亚稳态纳米材料的制备金刚石纳米粒子(碳纳米粒子的一种)具有优异的光学性质和生物相容性,但是其制备方法迄今仍然很有限。特别是,制备尺寸在5nm以下的金刚石纳米粒子仍然比较困难。金刚石属于碳的亚稳态结构,所以一般需要提供较高的温度才能形成。我们使用液相飞秒激光烧蚀法制备了金刚石纳米粒子。通过调控靶材和溶液,实现了对金刚石纳米粒子的尺寸,结构,表面性质和光学性质的调控。飞秒激光烧蚀分散在丙酮或者乙醇中的玻璃态碳、石墨粉末或者碳化甘蔗渣粉末制备出了不同尺寸,不同表面结构以及光学性质的金刚石纳米粒子。四,自组装纳米结构的制备作为一种新型的明星纳米材料,石墨烯具有独特的二维单层碳原子层结构,并表现出很多优异的性能。我们发现分散在乙醇溶液中的石墨烯经过飞秒激光烧蚀之后,可以转变成球状结构。这是第一次报道用飞秒激光诱导石墨烯组装形成球。通过控制飞秒激光的脉冲能量和照射时间,可以在很大范围内控制复合石墨烯球的尺寸。我们认为石墨烯在飞秒激光诱导下发生了逐层组装,形成球状结构。五,复合纳米材料的制备纳米材料的复合不仅可能保留原材料的性能,还可能带来原有性能的大幅度提升,甚至产生新的性能。目前已有很多制备不同复合材料的方法,但是制备含有超细纳米粒子的复合物方法却仍然不多。这主要是由于超细纳米粒子容易发生团聚。我们利用飞秒激光烧蚀法一步实现了氧化石墨烯的还原以及与超细纳米粒子的复合。我们制备了超细银纳米粒子-石墨烯复合物以及超细氧化锌纳米粒子-石墨烯复合物。银纳米粒子与氧化锌纳米粒子都是以单分散的状态生长在石墨烯上,其尺寸主要在3nm以下。我们认为大量的异质形核、超快冷却速率以及很小的热效应等因素限制了纳米粒子的尺寸,从而有利于形成超细纳米粒子。可以预测使用不同的前驱体,液相脉冲激光烧蚀法可以制备出更多的超细纳米粒子甚至是多功能复合纳米粒子与石墨烯的复合物。更多还原

【Abstract】 Materials, energy, and information are recognized as the three pillars of modern civilization, supporting the development of modern civilization. Discovery and preparation of new materials promote the development of science, technology and people’s living standards. The development of nanomaterials and nanotechnology makes the material having an increasingly profound and significant impact on the development of human civilization and people’s daily life. Various new emerging phenomena and novel properties of nanomaterials enrich our knowledge about nature and science. Widespread use of nanomaterials makes a variety of devices in technology and life smaller, faster, smarter and multi-functional. As a simple method for preparing novel nanomaterials, pulsed laser ablation in liquid has been widely adopted to fabricate functional nanomaterials.This disertation systematically exploited the possibility of preparing a wide range of functional nanomaterials by pulsed laser ablation in liquid. We focused on the basic characteristics of pulsed laser (mainly femtosecond laser) ablation in liquid, such as the local high temperature and high pressure conditions, rapid cooling, as well as in situ functionalization and hybridization of nanomaterials. Guided by these basic characteristics, we conceived, designed and carried out the experiments to prepare functiononal nanomaterials.1. Prepraration of metastable functional nanomaterialsPreparation of metastable phased nanomaterials is generally performed under high temperature and pressure conditions, and requires rapid cooling, and therefore the manufacturing processes are usually complicated. Since the pulse width of the pulsed laser (especially femtosecond laser) is very short, the peak power intensity is very high and the energy can be injected to the ablated materials in a short period of time. Therefore, extreme conditions with high temperature and high pressure are created in the local area, and a plasma plume is also produced. Under such local nonequilibrium environments, many chemical reactions may occur, particularly conducive to produce metastable structures. Furthermore, the rapid cooling and the compression effect casued by the surrounding liquid cool the plasma down quickly, and thereby the generated metastable nanomaterials are frozen. By controlling the nature of the liquid and the pulsed lasers, we prepared different metastable nanomaterials. Cubic and tetragonal zirconia were successfully fabricated by femtosecond and nanosecond laser ablation in ammonia, respectively. Due to the peak power of the femtosecond laser was much higher than that of the nanosecond laser, the resulting temperature and pressure was higher using the femtosecond laser. Also, the cooling rate was higher. Therefore, we suggested that femtosecond laser was more conducive to the formation and stabilization of high-temperature phased nanomaterials.2. Preparation of surface functionalized nanomaterialsThe surface structure of nanomaterials has a significant impact on their properties. In particular, the surface structure often determines the solubility and compatibility of nanomaterials under different environments. Furthermore, the surface modification can also control the size of nanomaterials to improve the stabilization of their structure and properties. Preparation of surface functionalized nanomaterials usually needs two steps, including the preparation and functionalization processes, which is often complicated and stringent. Whereas, by controlling the nature of the solutions, preparation of specific surface functionlized nanomaterials can be achieved by using pulsed laser alation in liquid in one step. In this case, well dispersed hydrophobic and hydrophilic silicon nanoparticles (NPs) were prepared by femtosecond laser ablation in1-hexene and a mixed solution of acrylic acid and ethanol, respectively. We proposed that under extreme environments created by femtosecond laser ablation in liquid, silicon NPs generated by ablation were highly active and easily reacted with the unsaturated organic compounds (1-hexene or acrylic acid) through addition reactions, thereby forming surface functionalized silicon NPs. We found that not only the size and surface structures, the optical properties were also regulated.3. Preparation of surface functionalized metastable nanomaterialsNanodiamonds (a kind of carbon NPs) exhibit excellent optical properties and biocompatibility. Unfortunately, there are no many methods for preparing nanodiamonds. In particular, preparing nanodiamonds with size smaller than5nm is still quite difficult. Diamond is a kind of metastable carbon structure, which is usually generated under high temperature conditions. We prepared nanodiamonds by using femtosecond laser ablation in liquid. Nanodiamonds with different sizes, surface states and optical properties were fabricated by femtosecond laser ablation of glassy carbon, graphite or carbonizated sugarcane bagasse powders dispersed in ethanol or acetone.4. Prepare of nanostructures through femtosecond laser induced self-assembly As a new kind of carbon materials, graphene, a two-dimensional monolayer of carbon structure, exhibits many superior properties. We found that graphene dispersed in the ethanol was converted into spheres after femtosecond laser ablation. This is the first time to report on femtosecond laser induced self-assembly of graphene to generate spheres. By changing the pulse energy and irradiation time, the size of grapene spheres was tuned in a wide range. We proposed that the layer-by-layer assembly of graphene is responsible for the conversion of graphene into spheres.5. Preparation of hybrid nanomaterialsHybrid nanomaterials may not only retain the initial properties of each component, but also exhibit enhanced performance and new properties. Currently, there are many methods for preparing hybrid nanomaterials. However, fabrication of hybrid nanomaterials containing ultrafine NPs is difficult, and this is mainly due to the aggregation of ultrafine NPs. The reduction of graphene oxide and generation of ultrafine NPs-graphene hybrids were realized simultaniously. We prepared ultrafine Ag NPs-graphene hybrids and ultrafine ZnO NPs-graphene hybrids. Ag and ZnO NPs with the size smaller than3nm were monodispersed on the graphene. We suggested the heterogeneous nucleation, fast cooling rate and small thermal effects hindered the growth of NPs, thus contributing to the formation of ultrafine NPs. Our results implied that using different precursors, femtosecond laser ablation in solution would be a general mthod to prepare ultrafine NPs-graphene hybrids, and even multifunctional hybrids.更多还原