【作者】 田飞；

【导师】 孙景； 杜希文；

【作者基本信息】 天津大学 ， 材料学， 2009， 博士

【摘要】 高能激光可以把物质瞬间蒸发并形成等离子体。等离子体在随后的冷却过程中发生凝聚从而生长为纳米材料。目前多数使用的纳秒激光虽然功率密度大,能制备多种纳米材料,但是由于其脉宽较短(纳秒),有效作用时间短,不利于创造稳定的纳米材料生长条件。相比较而言,长脉宽激光(毫秒),由于其脉宽是纳米激光的近百万倍,因而对于提供纳米材料稳定的生长条件以及提高制备效率具有重要的意义。本文介绍利用长脉宽(毫秒)激光器,通过改变激光器脉宽、炭材料状态、引入催化剂等工艺手段,利用传统炭材料(石墨、炭黑)制备出了多种新型炭材料(纳米金刚石、碳纳米管、碳纳米洋葱、石墨烯、发光碳纳米颗粒)。本文对比分析了纳秒和毫秒激光烧蚀制备纳米金刚石的条件以及金刚石生长的物理化学过程,利用热力学和动力学计算了金刚石的平衡尺寸以及生长尺寸。计算结果很好地解释了纳秒和毫秒激光制备的不同尺寸纳米金刚石的形成原因。根据超细纳米金刚石的热力学计算结果以及高分辨透射电镜照片推测了其多重孪晶生长过程,提出了纳米金刚石的生长理论。通过低能量激光束烧蚀炭黑制备出了亲水性碳纳米洋葱。实验结果分析表明碳纳米洋葱表面的亲水基团是造成其具有良好亲水特性的原因。利用石墨和纳米镍混合物,制备出了具有单层或多层膜结构的石墨烯。利用炭黑和微米镍粉混合物,制备出了碳纳米管。激光烧蚀炭黑或石墨的有机悬浮液制备出了具有生物相容性的发光碳纳米颗粒,通过变化有机溶剂的种类实现了发光碳纳米颗粒的发光峰位调控。利用分子动力学模拟证明激光将炭材料转变为碳原子,在冷却过程中能出现sp1、sp2、sp3杂化碳原子,当遇到适宜的沉积条件,可以分别形成纳米金刚石、碳纳米管、石墨烯等。激光烧蚀金属镍靶制备出了NiO纳米立方体,激光产生的极端非平衡条件是其形成的最重要因素。激光烧蚀金属钛靶制备出了金红石和锐钛矿混合的TiO2纳米球。光催化性能测试结果表明TiO2纳米球是一种具有高催化效率的纳米材料。激光烧蚀不同液体介质中的金属靶材有望用于制备形貌、成分、结构可控的纳米材料。更多还原

【Abstract】 High energy laser could result in the vaporation of materials and the formation of plasma plume with high temperature and high pressure. When the temperature and pressure of the plasma plume start to drop down, the condensation of the plasma would result in the formation of nanomaterials. Although most of the widely used nanosecond pulsed lasers could output laser beam with high power density to facilitate the synthesis of nanomaterials, the short pulse width (nanosecond) also means the madly short effective acting time that is not conducive to productivity. The long-pulse-width laser (millisecond) has a pulse width million times longer than the nanosecond laser, which is much of meaningful for the growth and yield of nanomaterials.This paper focuses on the preparation of new carbon materials (nanodiamodns, carbon nanotubes, carbon onions, graphene, and fluorescent carbon nanoparticles) by the change of pulse width and starting materials (graphite and carbon black), introduction of catalyst using millisecond laser. Not only the physical and chemical conditions generated by laser with different pulse width and the growth process of nanodiamonds were comparative analyzed, but the equilibrium sizes and growth sizes of nanodiamonds were calculated by combing the thermodynamics and dynamics. Theortical calculations were in good agreement with experimental results and gave reasonable explanation on the formation of nanodiamonds with different sizes. According to the thermodynamics and high resolution transmission electron microscope results, we proposed the formation of multiply twining strtuture (MTS) of nanodiamonds and the corresponding growth theory. Carbon onions with hydrophilic characteristics were synthesized through irradiating carbon black suspension using millisecond pulsed laser at room temperature. Laser energy absorption resulted in the structure transformation of carbon black and the formation of hydrophilic groups on the surface of carbon onion. Carbon onions with hollow cores and the incomplete graphitic shells were produced from the starting materials under high and low laser power density, respectively. All the experimental results showed that the hydrophilic properties of carbon nanoonions orginated from surface hydrophilic ligands. Graphene with single or multiply layer structure were prepared using graphte/nanosized nickel powder as starting material by laser ablation. Carbon nanotubes were synthesized using carbon black/microsized nickel powder by laser ablation. Biocompatible fluorescent carbon nanoparticles (CNPs) were prepared by laser ablating carbon black or graphite suspended in the organic solvents, the tunable of peak in the PL spectrum was realized by adjusting the solvents. Carbon material molecular dynamics simulation results showed that the laser lead to the formation of carbon atoms immediately after laser ablation, the sp1、sp2、sp3 hybridized carbon atoms could exist during the cooling process, the nanodiamonds, carbon nanotubes, graphene could be formed under different environmental conditions.The NiO nanocubes were prepared by laser ablating a nickel target immered in water, the extreme nonequilibrium condition was responsible for the formation of NiO nanocubes generated by laser ablation. Mixed-phase (rutile and anatase) titania nanospheres (MTNs) were prepared by long-pulse-width laser ablation of a bulk titanium target in water. We proposed a mechanism of the formation of MTNs, where thermal dynamics and the long lifetime of plasma plume were responsible for the co-existence of rutile and anatase phases. The photocatalytic properties of MTNs exhibit significant improvement compared with the commercial titania powder. The ablation of metal target immersed in different liquid is promising for the synthsis of nanomaterials with controllable morphology, composition and structure.更多还原