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脉冲激光制备发光碳纳米颗粒 总被引:2,自引:0,他引:2
利用毫秒脉冲激光辐照石墨悬浮液制备了超细碳纳米颗粒, 经过有机聚合物PEG 2000N的表面修饰, 碳纳米颗粒发出了较强的可见光, 并具有双光子激发的特征. 利用硫酸奎宁作参比, 测得碳纳米颗粒的荧光量子产率为6.3%. 石墨颗粒通过吸收激光能量快速升温并升华, 形成了大量的碳蒸气; 在周围液体介质的冷却下, 通过凝聚形成了碳纳米颗粒. 由于尺寸量子限制效应, 经过有机聚合物修饰后, 碳纳米颗粒表面产生了能量势阱, 导致了碳纳米颗粒的可见光发射. 发光的碳纳米颗粒具有无毒、化学惰性和良好的生物相容性, 在生物医药领域具有重要的应用价值. 相似文献
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纳米金刚石解团聚的一种新方法——石墨化-氧化法 总被引:2,自引:0,他引:2
用炸药爆炸法制备的纳米金刚石(ND)是由直径为4~6 nm的金刚石微晶粒组成,但这种纳米晶粒相互团聚,形成尺寸大得多的团聚体,至今尚未找到很有效的解团聚方法.该文提出了一种可用于这种纳米金刚石解团聚的新方法——石墨化-氧化法.将纳米金刚石粉在氮气中1 000 ℃加热1 h,这时纳米颗粒表面和界面上生成石墨层,再用在空气中450 ℃氧化的方法,将界面上的石墨层除去.将经过这样处理后的样品放入水中用超声波分散后,超过50%(质量百分数)的金刚石颗粒可以被分散到直径小于50 nm.可见这种方法对纳米金刚石的解团聚有一定的效果.但是同时也生成了一部分尺寸更大的团聚体,认为可能是生成了颗粒间的C-O-C键,需要进一步用适当的化学方法进行解离.对这一过程的机理进行了初步讨论. 相似文献
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以超支化聚合物囊泡为模板制备了贵金属纳米颗粒表面功能化的杂化囊泡.模板囊泡通过多巴胺修饰的超支化聚醚HSP-DA在水中自组装形成.在碱性条件下,囊泡表面的多巴胺自聚合生成聚多巴胺,实现囊泡的交联.由于聚多巴胺具有强黏附特性,因此可以将HSP-PDA交联囊泡分别与Au纳米溶胶、Ag纳米溶胶直接混合,得到Au纳米颗粒或Ag纳米颗粒功能化的杂化囊泡.分别测定了2种杂化囊泡的拉曼光谱,发现杂化囊泡产生了明显的表面增强的拉曼光谱(SERS)信号,清晰显示了对应于囊泡模板分子的拉曼信号,表明可以通过SERS来原位检测囊泡的组成.Ag纳米颗粒杂化囊泡展示出更高的SERS灵敏度,可进一步作为探针检测水中浓度为10-7mol/L罗丹明6G分子,得到了显著增强的拉曼光谱,证明所制备的Ag纳米颗粒杂化囊泡可用于目标分子的痕量检测. 相似文献
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以强σ键连接的sp2和sp3杂化碳饱和簇模型,即金刚石和石墨两相和团簇模型为研究对象,通过分子结构、电荷分布、能带结构、电子态密度和分子轨道的第一性原理计算和分析,研究了类金刚石薄膜中sp2-sp3轨道杂化的空间结构稳定性的成键特性等.结果表明,成键过程中由于微扰作用破坏了原子内部"吸引"与"排斥"的平衡关系,使电子云重新分布,而键能大小和电子云的重叠密切相关,因而两相共存对电荷分布和结构均有影响.能带结构分析发现sp2杂化C原子将π键引入,产生π和π*能带使带隙变窄,说明类金刚石薄膜的半导体本质.电子态密度计算结果中费米能级附近出现杂质峰,说明存在中间杂化和/或π态和σ态的转化. 相似文献
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<正>新型低维碳材料的探索与制备是纳米碳材料领域的重要挑战。石墨炔(Graphyne)是一种二维(2D)碳的同素异形体材料1,由sp和sp2两种杂化态的碳原子共同构成,在二维平面内具有均一分布的孔洞结构,因此具有与富勒烯(0D),碳纳米管(1D)和石墨烯(2D)完全不同的电子结构和骨架结 相似文献
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Since their discovery in 1990, the study of sp2 bonded carbon nanotubes has grown into a field of research in it's own right; however the development of the sp3 analog, diamond nanowires, has been slow. A number of theoretical models have been proposed to compare the relative stability of diamond and graphite at the nanoscale; and more recently, to compare nanodiamonds and fullerenes. Presented here is a study of the phase stability of nanocarbon in one-dimension. The structural energies of carbon nanotubes and diamond nanowires have been calculated using density functional theory within the generalized gradient approximation, and used to determine the atomic heat of formation as a function of size. 相似文献
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The dynamics of structure evolution of nanodiamonds ranging from 22 to 318 atoms of various shapes is studied by density functional tight-binding molecular dynamics. The spherical and cubic nanodiamonds can be transformed into fullerene-like structures upon heating. A number of the transformed fullerenes consist of pentagons and hexagons only. Others contain squares, heptagons, and octagons. One simulated fullerene is an isomer of C(60). The temperature of the transformation depends on the size, shape, and orientation of initial cluster. To be transformed into onion-like fullerenes, the spherical nanodiamonds should have 200 atoms or more, while the cubic ones require 302 atoms or more. The time-resolved energy profiles of all the transformations clearly reveal three-stage transformation character. During the first stage, the energy reduces quickly due to converting sp(3) carbon with dangling bond at the surface into sp(2) one, and the formation of partial sp(2) envelope wrapping the cluster. For the second stage, energy decreases slowly. The remaining interior carbon atoms come to the surface through the hole in the sp(2) envelope, and similar amount of sp(3) and sp(2) atoms coexist. The third stage involves the closure of holes, accompanied by the detachment of C(2) molecules and carbon chains from the edges. The energy decreases relatively fast in this stage. The proposed three-stage transformation pathway holds for all the simulations performed in this work, including those with the instant heating. 相似文献
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The stable superhydrophobic surface of the ZrO2 substrate could be conveniently and rapidly prepared by KrF laser irradiation. With different laser energy density, the static water contact angle (CA) increased from 72° to approximately 151°. It was found that the formation of micro–nano fluctuant geometry surface structure was the dominant factor to the hydrophobic property after laser irradiation. When the laser‐irradiated sample annealed at O2 atmosphere, formation of oxygen‐related defects with high surface free energy could make the CA decrease abruptly at the beginning. After being stored at ambient atmosphere, the CA would reconvert to the value of the freshly irradiated sample gradually. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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A. P. Koshcheev P. V. Gorokhov M. D. Gromov A. A. Perov U. Ott 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(10):1708-1714
The influence of standard chemical treatment used to extract interstellar nanodiamonds from meteorites on the chemical composition of the surface of synthetic nanodiamonds with substantially different properties was studied by thermal desorption mass spectrometry and IR spectroscopy. The chemistry of the surface of nanodiamonds after treatment was substantially different from that of initial particles. The suggestion was made that the chemical structure of the surface of diamond particles in the interstellar space could be reconstructed from the data on meteorite diamonds. Mass spectrometric studies also gave information about possible mechanisms of the release of noble gases from meteorite diamonds at various temperatures. 相似文献
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The intrinsic mechanism of graphitization occurring on the (111) surface of nanodiamonds (NDs) during the transformation from NDs into bucky diamonds are explored using density functional theory (DFT) computations in conjunction with density functional based tight-binding simulations. The DFT results indicate that dangling bonds (DBs) on the ND surfaces play an important role in the graphitization process, and the orientation of the DBs on different ND surfaces determines whether there will be a graphitization process or not. Moreover, a criterion is proposed to estimate rupturing of the C-C bonds between different layers on the [111] direction in the NDs and is verified to be applicable to illustrate the phase transformation from sp(3) into sp(2) bonding structures. The energy contributions of the four-coordinated carbon atoms located at different positions on the (111) surface are exhibited for the first time and discussed in detail to gain a clear picture for the transition from NDs into bucky diamonds. The outcome may provide a deeper understanding on the influence of DBs upon the transformation from sp(3) into sp(2) bonding structures. 相似文献
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Copper deposition patterns on graphite electrodes were analyzed by scanning electron microscopy. The deposition patterns correlate very well with the electrochemical activity of different graphites. The results indicate that treatment of graphite by electroactivation, laser irradiation of polishing on 600-grit silicon carbide paper produces active sites on the surface. The density of the sites directly reflects the electrochemical reactivity of the surface. 相似文献
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To have a clear insight into the diamond nucleation upon the hydrothermal synthesis and the reduction of carbide (HSRC), we performed the thermodynamic approach on the nanoscale to elucidate the diamond nucleation taking place in HSRC supercritical-fluid systems taking into account the capillary effect of the nanosized curvature of the diamond critical nuclei, based on the carbon thermodynamic equilibrium phase diagram. These theoretical analyses showed that the nanosize-induced interior pressure of diamond nuclei could drive the metastable phase region of the diamond nucleation in HSRC into the new stable phase region of diamond in the carbon phase diagram. Accordingly, the diamond nucleation is preferable to the graphite phase formation in the competing growth between diamond and graphite upon HSRC. Meanwhile, we predicted that 400 MPa should be the threshold pressure for the diamond synthesis by HSRC in the metastable phase region of diamond, based on the proposed thermodynamic nucleation on the nanoscale. 相似文献
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The basic steps of researches for the synthesis of diamond from the gas phase is reviewed. The experimental results obtained on the thermal activation of a medium by using diamond powders as nucleation centers are considered. It has been established that the diamond rate from hydrocarbons exceeds that of graphite. Fractionation of the stable carbon isotopes is observed. The presence of hydrogen influences differently the growth of diamond and that of graphite.
The method of periodical pulse supersaturations is described, enabling one to obtain epitaxial films and isometrical diamond crystals. The method of activation of the gas medium by using an electric discharge allowed to obtain polycrystalline diamond films on the surface of metals and semiconductors. A possibility of the homogeneous formation of diamond in the gas phase has been established. The possibility of realization of this process in the cosmic space is discussed. 相似文献
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The present paper discusses the synthesis of diamond in its metastable region from carbonaceous gases, in particular methane. The diamond synthesis on seed crystals is made possible owing to the orientation effect of surface forces on the formation of a new phase. Discussed is also the joint crystallization of diamond and graphite. The basic experiments were made on highly dispersed diamond powders. The growth of diamond in kinetic and diffusion regions has been studied. Presented are results of studying the fractionation of stable carbon isotopes when growing a diamond. 相似文献
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Chong KF Loh KP Vedula SR Lim CT Sternschulte H Steinmüller D Sheu FS Zhong YL 《Langmuir : the ACS journal of surfaces and colloids》2007,23(10):5615-5621
The biocompatibility of diamond was investigated with a view toward correlating surface chemistry and topography with cellular adhesion and growth. The adhesion properties of normal human dermal fibroblast (NHDF) cells on microcrystalline and ultrananocrystalline diamond (UNCD) surfaces were measured using atomic force microscopy. Cell adhesion forces increased by several times on the hydrogenated diamond surfaces after UV irradiation of the surfaces in air or after functionalization with undecylenic acid. A direct correlation between initial cell adhesion forces and the subsequent cell growth was observed. Cell adhesion forces were observed to be strongest on UV-treated UNCD, and cell growth experiments showed that UNCD was intrinsically more biocompatible than microcrystalline diamond surfaces. The surface carboxylic acid groups on the functionalized diamond surface provide tethering sites for laminin to support the growth of neuron cells. Finally, using capillary injection, a surface gradient of polyethylene glycol could be assembled on top of the diamond surface for the construction of a cell gradient. 相似文献