爆轰制备纳米石墨片的微观形成过程研究

 石墨的层状结构使外来物质可进入层间,形成插入层;插入层在爆轰条件下分解后可将石墨层片推开,形成纳米石墨薄片。通过建立石墨层间化合物有限元模型,利用γ拟合法获取层间化合物的相关参数,基于Thomas-Fermi方程推导出相邻石墨层片分离时的层间作用力与层间距的函数关系;通过LS-DYNA模拟了石墨层片的分离过程,并给出石墨层间距随时间的变化关系,从而阐明薄片状无粘连纳米石墨的形成过程。     

碳同素异形体中的正电子理论

在密度函数理论的基础上,采用中性原子叠加模型和有限差分方法(SNA-FD)计算了石墨,金刚石和C60这三种碳的同素异形体中的正电子分布和湮没情况. 计算表明,在片层结构的石墨晶体中,正电子主要在石墨层间的空隙中湮没,计算出的石墨中的正电子寿命为208ps,与文献中的实验结果210ps符合很好. 在金刚石单晶中,正电子主要在碳原子之间的空隙中存在并发生湮没,计算出的金刚石中的正电子寿命为1159ps,与文献中的实验结果110ps相符合;在面心立方结构的C60晶体中,正电子主要在C60分子球壳内外侧及分子之 关键词： 石墨 金刚石 C60 正电子寿命     

Langmuir-Blodgett 膜中分子聚集行为的偶极作用模型

基于经典静电场理论，描述了Langmuir-Blodgett (LB)膜中棒状分子聚集行为的偶极作用模型，给出了LB膜结构与光谱性质的关系. 讨论了X型或Z型膜中分子间距、层间距、分子取向、膜层数等结构参数对分子聚集行为的影响. 理论结果与实验值符合较好. 关键词： Langmuir-Blodgett膜 聚集体 偶极相互作用 半花菁     

水二聚体分子间相互作用势

利用超分子二阶到四阶多体微扰理论和扩展的相关一致基组(aug-cc-pVTZ)结合有效的中点键函数(3s3p2d1f1g)计算水二聚物的平衡结构和分子间相互作用势,并用平衡方法修正基组重叠误差.在MP2/aug-cc-pVTZ理论级别优化水二聚物几何构型.与正常优化的结果相比,平衡修正优化得到的RO-O和α值分别轻微的增加0.002 nm和0.19°,同时,θ值减小0.013°.在MP2水平利用扩展的相关一致基组结合有效键函数,预言了RO-O和ΔECP值分别为0.0923 nm和-4.86 kcal/mol,计算结果与实验值符合得很好.用exp-4.2势函数拟合分子间相互作用能的离散点,拟合结果与从头算计算的结果一致.     

2-吡啶甲醇红外光谱的密度泛函理论研究

利用密度泛函理论(density functional theory,DFT) 在B3LYP/6-311G(d,p)水平上对2-吡啶甲醇分子进行了结构优化和频率计算,得到了该分子的稳定构型和全部振动模式。通过与吡啶分子的结构参数以及相关文献数据的对比,发现理论值与实验值相吻合。理论计算和实验测得的红外光谱数据的比较分析表明,理论计算与实验测量结果符合得较好, 并对2-吡啶甲醇分子的振动模式进行了归属。     

原子簇La8-xBaxCuO6的原子磁矩和自旋极化的电子结构研究

利用MS-Xα方法研究了化合物La2-yBayCuO4的原子磁矩和自旋极化的电子结构.理论计算得到母相氧化物La2CuO4的Cu原子磁矩为0.37μB,与实验值0.48±0.15μB基本一致. 研究结果显示, 由于Ba原子对部分La的替代,使构成化合物的基本原子簇La8-xBaxCuO6的点群对称性降低,分子轨道简并度解除,轨道杂化效应增强,减弱了氧化物的(准)二维特性,导致Cu-O层与其近邻原子层的耦合增强,因此影响了原子层间的电荷迁移方向,对Cu-O层中载流子的性质有重要影响. 由于Ba掺杂在化合物中产生的空穴,不仅进入O格点,也同时进入Cu格点,对Cu-O层上Cu和O原子价态、磁矩以及电子态密度分布有重要影响. 研究结果认为,由于掺杂产生的空穴对化合物超导电性的影响具有两面性:初期掺杂有利于产生超导电性;当掺杂较多时抑制超导电性. 这是导致La214体系的超导转变温度Tc随掺杂量y的变化(即Tc-y拱形曲线)的一个重要原因.     

静电势能模型对类水滑石结构与性能的理论研究

采用晶体学理论建立类水滑石静电势能模型,对由20层且每层2107个阴离子组成的镁铝类水滑石超分子体系中层间阴离子所受的静电势能进行理论计算．研究结果表明,调变层板金属离子摩尔比影响层板电荷密度与层间阴离子间距,计算得到的阴离子静电势能值与其热稳定性相一致:插层阴离子的电荷与尺寸不同直接影响阴离子的势能大小．     

Y型Langmuir-Blodgett膜中分子聚集行为的偶极作用模型

利用经典静电场理论，描述了Y型Langmuir-Blodgett (LB) 膜中棒状分子聚集行为的偶极作用模型，给出了Y型LB膜结构与光谱性质的关系.讨论了Y型膜中分子间距、层间距、分子取向、膜层数等结构参数对分子聚集行为的影响，并在此基础上比较了Y型膜和Z型膜分子聚集行为的异同.理论结果与实验规律符合较好.     

石墨烯纳米孔道内受限水介电常数影响因素的分子动力学模拟

受限水的介电特性对于石墨烯电容器的储能效率有着重大的影响.因此本文使用分子动力模方法,研究了不同石墨烯纳米孔道宽度(0.812～10 nm)下内受限水介电常数的分布及其影响因素.结果表明,在石墨烯纳米孔道内部受限水双电层结构可分为空隙层、界面层和体相层三个部分.其整体的介电常数随孔道大小的降低而线性减少.这是由内部体相层的宽度的降低而导致的.此外电极电压大小和石墨烯-水相互作用参数ε_CO的强弱也会显著改变电极表面的双电层(Electric Double Layers, EDLs)结构.其中电压的增大使得介电常数分布的震荡的程度也随之增加,最终导致了整体介电常数的减小.与之类似,亲水态的石墨烯表面(高ε_CO)下受限水分布的震荡程度也显著增加,这导致了整体介电常数的降低.     

长链烷烃和醇在石墨表面吸附的扫描隧道显微镜研究

用扫描隧道显微镜（STM）研究了室温下十八醇（1-C18H37OH）和十四烷（C14H30）在石墨表面的吸附行为.十八醇在石墨表面自组装形成条状结构.实验发现了十八醇分子在石墨表面的两种不同的密排方式，它们形成并列的不同宽度的条状结构.还发现，由于溶剂（正十四烷C14H30）的完全蒸发，留下的十八醇分子在石墨表面吸附的自组装结构与固液界面中十八醇分子在石墨表面的吸附形成的结构在分子方向、表面分子晶体的晶格常数及条状结构宽度等方面有很大的不同.此外，实验中也发现溶剂十四烷在某种情况下也能在石墨表面吸附形成可供STM观察的有较长时间稳定性的条状周期结构.实验观察到的十四烷在石墨表面形成的晶体结构与固液界面中观察到的有序结构的晶体结构常数和分子排列方向也是不同的.根据STM图像，提出了十八醇和十四烷在石墨表面吸附的结构模型. 关键词： 十四烷 十八醇 石墨 扫描隧道显微镜     

Hydrothermal method for the production of reduced graphene oxide

Reduced graphene oxide, RGO (also called chemically modified graphene, CMG) was synthesized by a simple hydrothermal method, with graphite oxide (GO), prepared by the modified Hummers method, served as the raw material. Structural and morphological studies indicate the degree of reduction is dependent on the temperature, which is also verified by Raman analysis. The variation in interlayer distance and the intensity ratio of the D to G Raman modes (I_D/I_G) indicates higher reaction temperature can accelerate the reduction of GO. The conductivity also varies with the degree of reduction, as verified by electrochemical analyzer. Moreover, the reaction process affects organic functional groups, the mechanism during the reaction process is discussed.     

Intercalation compounds of fluorographite and graphite oxide with spin probes

Electron spin resonance technique was used to study the structure of intercalation compounds of fluorographite and graphite oxide containing stable nitroxyl radicals. Depending on the introduced score concentration the paramagnetic molecules in the interlayer space were found to exist as isolated ordered species or to form magnetoconcentrated phases. The angular distribution of isolated molecules of 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl in the interlayer space of fluorographite and graphite oxide were determined. The capability of nitroxyl radicals to react with the C-F bonds of fluorographite at 298 K was found.     

水合亮氨酸构型的系统寻找与研究

同时考虑亮氨酸可能的水分子络合方式及亮氨酸分子的所有内轴转动,对亮氨酸与1～3个水分子的复合结构Leu-(H₂O)_n进行了系统寻找．分别用BHandHLYP/6-31+G*和BHandHLYP/6-311++G**方法对结构进行了优化和单点能计算．发现亮氨酸水合结构与孤立亮氨酸有着很好的对应关系,且亮氨酸的水合结构可以可靠地通过对亮氨酸的结构直接加水得到．对中性、双电性亮氨酸水合结构的红外计算光谱与溶液中亮氨酸实验光谱进行了比较与分析,发现双电性Leu-(H₂O)₃的红外光谱与实验符合得最好,表明溶质在气相中与适量的水分子络合便能较好地模拟溶质在溶液中的红外光谱．     

Temperature effects on the diffusion of water and monovalent counterions in the hydrated montmorillonite

We investigate here the effect of temperature on the diffusion of water and cations in the Wyoming-type montmorillonite clay. The considered cations are monovalent compensating ions, such as Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ in one-, two- and three-hydration states. For this purpose, molecular dynamics simulations have been performed to obtain the dynamic behaviour regarding the interlayer ions and water molecules under a temperature range between 260 and 400 K. The diffusion coefficient of water and cations in different hydrated clays increases with temperature. The influence of temperature on the diffusion of water is much greater than that of cations in one-, two- or three-hydrated clay. The degree of hydration plays an important role on the diffusion behaviour of water and counterions. We found that the effect of temperature is negligible in weakly hydrated clay, whereas it became significant in highly hydrated one. Besides, the size and mass of cations’ hydrate also affect the diffusion behaviour of water and cations in the interlayer space of hydrated clay.     

Different modes and consequences of electron transfer in intercalation compounds

Intercalation reactions form one of the most versatile types of solid-state reactions known. Considering the layered host lattices they form an interesting access to artificial multilayers of very different properties. Many of these reactions are connected with redox processes. After a very short and general overview on the intercalation chemistry in layered host lattices, three different types of charge transfer accompanied with intercalation will be considered in detail and the consequence for the properties of the products will be discussed: (a) by means of electrointercalation into conducting host lattices (e.g. 2H-TaS₂) electrons are transferred to the conduction band of the host accompanied with the simultaneous uptake of cations (here organic cations like methylene blue, methylviologen) in the interlayer space. Potential vs. time curves give valuable information about two-phase regions, homogeneity ranges and deviations from equilibrium. The consequence for the superconducting properties is shown; (b) treating the graphite intercalation compound C₂₄(HSO₄)(H₂SO₄) with strong oxidants leads to graphite oxide (GO). The oxidant is directly attached to the carbon network forming C–OH and C–O–C functions. Applying ¹³C MAS NMR of GO (and derivatives) we could identify the ether function as epoxide groups. This result has strong implications for the chemical behaviour of GO and could lead to new carbon networks; (c) clay minerals containing iron in the octahedral layers can undergo changes of the oxidation state of Fe-ions. We have found in vermiculites from Spain that Fe²⁺ can be oxidized completely to Fe³⁺, whereas the degree of reduction of the Fe³⁺ is rather restricted but varies with the composition of the clay. However, the extent of reduction can be strongly increased by heating the reduced samples.     

Graphene oxide thin film coated quartz crystal microbalance for humidity detection

In this paper, we demonstrated that chemically derived graphene oxide (GO) thin film as a humidity sensitive coating deposited on quartz crystal microbalances (QCMs) for humidity detection. By exposing GO thin film coated QCMs to various relative humidity (RH) environments at room temperature, the humidity sensing characteristics of the QCMs such as sensitivity and linearity, response and recovery, humidity hysteresis were investigated. The experiment results show that GO thin film coated QCMs exhibit an excellent humidity sensing performance. Moreover, the possible humidity sensing mechanism of GO thin film coated QCMs was also investigated by monitoring the crystal's motional resistance change. It is suggested that the frequency response of the QCMs is dependent on water molecules adsorbed/desorbed masses on GO thin film in the low RH range, and on both water molecules adsorbed/desorbed masses on GO thin film and variations in interlayer expansion stress of GO thin film derived from swelling effect in the high RH range.     

Synthesis of nitrogen doped graphite oxide and its electrochemical properties

We herein report a synthesis nitrogen-doped graphite oxide (N-doped GO) by heat treatment with melamine. The N-doped GO contains 4 at % of nitrogen, incurring the oxygen reduction reaction by nitrogen functional groups. Two kinds of aqueous electrolytes are used for finding the electrocatalytic activities, resulting in symmetric oxygen reduction reaction peaks at −0.8 and 0 V in 6 M KOH and 1 M H₂SO₄ electrolytes, respectively. The N-doped GO is more activated in the acid electrolyte compared to thermally reduced graphite oxide (TrGO). Specific volumetric capacitance of N-doped GO in 1.8 M tetraethylmethylammonium tetrafluoroborate electrolyte is 57.4 F cc⁻¹ which is higher than 30.5 F cc⁻¹ of the TrGO, demonstrating positive effects of the nitrogen doping in the organic electrolytes for the energy storage devices.     

双酚A在氧化石墨烯表面吸附的分子动力学模拟

双酚A(bisphenol A,BPA)是一种内分泌干扰物,会对机体多方面产生不良影响,包括生殖系统、神经系统、胚胎发育等.因此,在水环境中如何检测和去除BPA显得尤为重要.实验研究表明,氧化石墨烯(graphene oxide,GO)对BPA具有优异的吸附去除性能,但在分子层面的吸附机制尚不清楚.分子动力学模拟,能提供BPA在GO表面的动态吸附过程以及吸附构象等详细信息,可以弥补实验的不足.本文利用GROMACS分子动力学模拟软件,系统模拟了BPA在含GO的水溶液中的吸附过程,并计算了吸附自由能.结果显示:所有的BPA均被吸附在GO两侧,通过分析BPA的吸附构象以及与GO的相互作用,发现π-π疏水作用对吸附起主导作用,且显示出很好的稳定性,而静电和氢键作用增加了GO的吸附能力.通过自由能计算,BPA在GO表面的结合能达30 k J/mol,远大于水分子的5 k J/mol.这些结果进一步证实GO对BPA具有很强的吸附能力以及GO作为吸附剂在水溶液中去除BPA的可行性.     

Fabrication of ultrasound-mediated tunable graphene oxide nanoscrolls

In this work, a cost-effective and facile method was adopted for the fabrication of graphene oxide nanoscrolls (GONS) by low frequency (20 kHz) ultrasonication with tunable dimensions. The graphene oxide (GO) was synthesized by modified Hummer’s method using synthetic graphite as a base material. Later, GO suspension (0.05 g L⁻¹) were made using methanol as solvent and subjected to different ultrasonication conditions. It was found that GO sheets curls themselves into nanoscrolls by overcoming the energy barrier for scrolling with the help of bubble cavitation energy provided by ultrasonication. Also, the effect of ultrasonication power (100–150 W) for irradiation time (0.5–3 h) over the GONS dimensions were investigated. The spiral wounded GONS structures were shown using electron microscopy. Raman Spectroscopy, Thin-film X-Ray Diffraction, Energy Dispersive X-Ray, FT Infrared Spectroscopic analysis were also done to endorse GONS formation. Factors affecting GONS formation such as sonication power and solvent selection were studied as scrolling of GO sheets are strongly dependent on sonication parameters and solvent characteristics. It was found that GONS length varies inversely with irradiation time for identical power density. Also, a solvent with relatively large Hansen solubility parameter, lower dipole movement and less negative value of zeta potential support GONS formation of longer length. Raman analysis overlays the rapid oxygen-defect site cleavage mechanism. The obtained GONS unlocks further developments in various engineering applications like adsorption, drug delivery and filtration membrane.     

Infrared and Raman spectra of aquamolybdenum (VI) oxide hydrate (MoO3·2H2O)

The infrared and Raman spectra of MoO₃·2H₂O are recorded and analysed on the basis of vibrations due to MoO₆ octahedra and H₂O molecules. Considerable changes in the frequencies of the octahedra have been observed due to strong distortion in the octahedral arrangement. The inactivev ₆ vibration of O _h symmetry became active in the Raman spectrum. Co-ordinated (aquated) and hydrated (interlayer) water molecules give rise to different frequencies.