【作者】 胡胜亮；

【导师】 孙景； 杜希文；

【作者基本信息】 天津大学 ， 材料学， 2008， 博士

【摘要】 从传统碳材料(石墨、碳黑)转变成新型碳材料(纳米金刚石、纳米碳洋葱等)需要足够高的温度和压力,一般常规手段很难满足这样的要求。激光可通过瞬间高能量的输入产生碳材料相变的条件,因此可望成为一种有效合成新型纳米碳材料的方法。用高功率密度的短脉冲(纳秒)激光虽然可以产生足够高的温度和压力获得纳米金刚石(粒径为30～300 nm),但是它的有效工作的时间太短,合成效率低。本课题组提出了较低功率密度的长脉冲(毫秒)激光辐照循环石墨悬浮液的方法,获得了超细的纳米金刚石(粒径<10 nm)并且使产率得到了提高。本文结合两种不同类型激光产生的条件差异,从热力学和动力学两方面研究了毫秒脉冲激光获得超细纳米金刚石的原因。研究表明,金刚石稳定的平衡尺寸、较小的生长速率以及表面的混合杂化限制了较大颗粒金刚石的产生;在小尺寸下转变成金刚石结构的几率大,有助于产率的提高。首次在细小的纳米金刚石上发现了多重孪晶,研究了多重孪晶的形成过程,为金刚石晶粒的生长提供了重要的理论依据。通过理论计算和观察到的金刚石孪晶的中间结构,证明了多重孪晶是通过依次形成孪晶而产生的。用激光辐照悬浮在水中的碳黑,首次合成了亲水性的碳纳米洋葱,其具有良好的应用前景。通过各种分析手段表明碳纳米洋葱的亲水性主要是来自于表面的亲水基团。结合理论计算,研究了激光功率密度对碳纳米洋葱结构的影响:过高的激光功率密度会导致碳质量损失,使碳洋葱中心造成空洞;而过低的激光功率密度则使碳黑结构不能发生完全有序化。发光的碳纳米颗粒由于具有无毒、化学惰性以及良好的生物相容性的特点,在生物和医药领域具有重要的潜在应用价值,所以研究它的发光机制对提高其发光效率和控制荧光特征具有非常重要的意义。本文研究了化学修饰法获得的碳纳米颗粒发光的机制,并开发了激光下一步合成发光碳纳米颗粒的新工艺。碳纳米颗粒的发光主要来自于表面态,通过改变试剂可以获得不同特征的荧光发射。另外,实验中获得的碳纳米颗粒具有双光子激发荧光发射的特征。更多还原

【Abstract】 Laser irradiation for preparing nanomaterials has become one of the effective approaches and more and more impotrant with laser technique developing. The common technique hardly meets the high temperature and pressure required in phase transition from tranditional carbon materials (graphite and carbon black) to new carbon materials (nanodiamond and nanoonion et al.). However, pulsed laser can provide such conditions by imputing high energy enough in very short time. Thereby, laser irradiation will become a kind of method to synthesize new carbon materials.Although the larger nanodiamonds (30-300 nm in diameter) were formed in higher temperature and pressure produced by short-pulse-width (ns) laser with high laser power indensity, the yield was very low due to too short working time. Ultrafine nanodiamonds with sizes of smaller 10 nm were prepared by irradiating graphite suspension using long-pulse width (ms) laser at room temperature and normal pressure, and the yield was improved in our research group. The low power density and long pulse laser generated a lower temperature and a lower pressure, which determine the stable size of nanodiamonds. On the other hand, the low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limited the final size of nanodiamonds. Moreover, our study showed that the diamond-transition probabilties were high at the small size, which trended to improve the diamond yields.The multiply twinning structure (MTS) of nanodiamonds synthesized by pulsed-laser irradiation was firstly investigated theoretically and experimentally. The thermodynamic calculation shows MTS is more stable than single crystal in a certain size range and statistical results experimentally accords with the theory. A mechanism on the formation of MTS in nanodiamonds was proposed based on Transmission Electron Microscopy (TEM) observation, in which a single crystal successively grows into MTS through intermediate states, such as simple twin and triple twin.Hydrophilic carbon nanoonions were firstly synthesized by irradiating carbon black particles in water using pulsed laser, which exploited their application. All of analyzed techniques showed that the hydrophilic properties of carbon nanoonions orginated from hydrophilic ligands. Based on the theoretical calcaulation, the influences of laser power intensity on the structure of carbon nanoonions were studied in this paper: The higher laser power intensity could make the mass lose by carbon sublimation and resulted in the hole formation in the centre of carbon nanoonions; however, the lower laser power intensity could not produce carbon nanoonions due to lack of enough energy.Fluorescent carbon nanoparticles (CNPs) show high potential on the application of biology labelling and life science, because they own many advantages over the conventional quantum dots based on sulphides, selenides, or tellurides of zinc and cadmium, such as biocompatible, chemically inert, and can be surface-modified. Therefore, it is very important to study the luminescent mechanism. An effective method to synthesize fluorescent CNPs by laser irradiation of the suspension of carbon materials in organic solvent, the synthesis and surface modification of luminescent CNPs were believed to realize simultaneously. Compared with previous works, such a one-step process is simple and easy to be industrialized. Especially, by selecting organic solvents, the surface states could be modified conveniently to realize tuneable light emission. Based on the results of control experiments, the origin of the luminescence is proposed to be the surface states related to the ligands on the surface of CNPs. Especially, CNPs can emit visible light via two-photon excitation by using near-infrared light. The two-photon excitation makes photodynamic therapy harmless to health tissue adjacent to the diseased target tissue.更多还原