Preparation Of Functional Nanomaterials By Pulsed Laser Ablation In Liquid

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.