微孔对单壁纳米碳管储氢性能的影响

用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率，发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时，单壁纳米碳管的管间孔也会成为有效的氢吸附位. 关键词： Monte Carlo方法 单壁纳米碳管 储氢 微孔     

辐照还原法制备Au掺杂MF气凝胶

利用辐照还原法在500 kGy辐照剂量下制备了Au掺杂MF有机气凝胶。通过X射线衍射（XRD）、能量色散光谱仪（EDX）和透射电子显微镜（TEM）测试证实了辐照法成功地制备出Au掺杂MF有机气凝胶复合物。EDX和TEM照片表明辐照处理后Au纳米颗粒均匀地分布在MF气凝胶骨架中,并且Au纳米颗粒的平均尺寸为5.8 nm。N2吸附数据分析表明掺入Au纳米颗粒后,MF气凝胶的比表面积、总孔体积、微孔体积和介孔体积都有所下降。     

碳纳米纤维吸附储氢性能分析

文中综合碳纳米纤维微观结构的表征结果以及氢吸脱附等温线的实验测量结果,对碳纳米纤维的吸附储氢性能进行了综合分析,分析发现:比表面积和中孔容积均与氢吸附量成线性关系;微孔容积对材料吸附性能影响较大,微孔容积与氢吸附量成抛物线关系;氢在常温左右以及77K下的吸附等温线呈现超临界气体的吸附特征,氢在273K和353K下的吸脱附等温线也基本重合,呈现的是物理吸附的特征。实验结果还说明:常温左右,甚至是77K下,碳纳米纤维均不适合于氢的吸附储存。     

氢在碳纳米纤维中的低温吸附储存特性

利用容积法测量了77K下氢在一种碳纳米纤维上的吸附等温线。采用分子模拟的方法模拟了77K下氢分子在平板状碳纳米纤维中的吸附,碳纳米纤维的石墨层层间距分别为0.335nm、0.6nm、0.9nm以及1.5nm。模拟结果表明:石墨层层间距为0.335nm的碳纳米纤维在77K下吸附储氢密度很难达到DOE的能量密度标准;当板间距为0.9nm时,系统吸附储氢的重量密度和体积密度均能达到最大,且在77K、1MPa下,能达到DOE的能量密度标准。     

功能纳米结构可控生长的新途径:非模板选择性自组装

文章介绍了一种非模板选择性自组装纳米结构的方法.从实验和理论上研究了两种有机分子在Ag单晶不同表面上的吸附行为,发现在Ag（775）基底上PTCDA分子会完全吸附在（111）台阶面上,而DMe-DCNQI分子则完全吸附在（221）台阶面上.该研究还阐明了PTCDA分子与基底原子之间的相互作用机制,提出了PTCDA与基底之间的相互作用是通过分子末端官能团的氧原子实现的,中心的π共轭区域与基底相排斥,理论模拟得到的氧原子的NIXSW相干长度以及碳原子的近边X射线吸收谱与实验结果符合得较好.     

甘氨酸在纳米碳管中的吸附及性质的分子模拟

采用分子力学、分子动力学方法模拟研究了甘氨酸分子在单壁纳米碳管中的吸附和扩散行为 ,并对甘氨酸分子在纳米碳管中的构象和能量进行了优化 .模拟计算结果表明 ,甘氨酸在纳米碳管中的构象发生了伸缩和扭转 ,这种构象的改变将会导致氨基酸生物性能的改变 ;纳米碳管对氨基酸分子具有较强的吸附作用 ,其中纳米碳管和甘氨酸分子之间的π -π相互作用增加了纳米碳管对氨基酸的吸附能 .模拟过程中氨基酸分子和纳米碳管之间的运动会保持很强的协同效应 ,使模拟体系构型在能量上处于最稳定的状态     

方解石纳米孔隙内二氧化碳毛细凝聚的分子模拟

在二氧化碳地质封存、增产非常规油气以及孔隙材料表征测量方面,纳米孔隙中二氧化碳相态的准确预测具有重要意义。然而,由于纳米尺度下毛细力、分离压等作用力占据主导因素,流体在孔隙中的相行为与体相流体存在根本不同。已有实验和模拟表明,Kelvin毛细凝聚理论无法预测特征尺度10nm下的,孔隙内流体凝聚压力与体相饱和蒸气压的偏离程度。本文利用分子模拟方法,研究了孔径范围为0.83-8.0nm的方解石纳米孔隙中二氧化碳毛细凝聚。结果表明,微孔(小于2nm)中二氧化碳受吸附层影响,凝聚压力远低于体相饱和蒸气压,介孔(2?50nm)中二氧化碳受壁面影响,凝聚压力仍低于体相饱和蒸气压,且受孔径影响显著,并获得了纳米孔隙中二氧化碳相态随压力的变化规律。     

激光拉曼光谱研究苏丹红Ⅲ分子的吸附方式

用近红外傅里叶拉曼光谱研究了苏丹红Ⅲ分子在覆银纳米颗粒的抛光铝片表面上的吸附行为,得到了一系列高质量的增强拉曼散射（SERS）谱图。对苏丹红Ⅲ分子在银胶溶液、覆银滤纸、覆银粗糙铝片上的SERS谱进行比较,结果表明苏丹红Ⅲ分子在各基底上与银纳米颗粒表现出不同的吸附行为。在银胶溶液中,苏丹红Ⅲ分子主要是通过N=N双键吸附在银纳米颗粒上的;在沉积了银纳米颗粒的滤纸表面,同样地,主要是由N=N双键吸附;而在沉积了银纳米颗粒的抛光铝片表面,不仅N=N双键参与了吸附,苏丹红Ⅲ分子中的羟基与银颗粒有相互作用,并且铝片上的氧化铝颗粒也可能吸附了苏丹红Ⅲ分子。     

纳米结构Pt膜上CO吸附的异常红外效应机理研究

CO吸附在经方波电势处理后的纳米结构Pt金属膜电极上可观察到异常红外效应（AIREs）.在实验基础上用粒子间的相互作用和电子-空穴衰减机理分析、模拟了AIREs，表明Pt金属表面的纳米岛状结构增强了CO分子间及CO分子与纳米结构表面的相互作用，电子-空穴衰减引起的能量转移和粒子间相互作用的增强可以导致异常红外吸收谱线变化特征的出现. 关键词： 异常红外效应 粒子相互作用 电子-空穴衰减     

光纤聚合物探针在非均匀电磁场下的银纳米颗粒极化效应

介绍了光纤探针的制作流程及纳米颗粒的吸附方法,利用时域有限差分法对光纤探针的局域非均匀场下银纳米颗粒增强效应进行了数值模拟。首先,分析了不同形状的光纤聚合物探针尖端电场分布情况,为纳米颗粒的极化效应研究提供了参考;其次,模拟与仿真了纳米颗粒的半径、与探针间的距离对单个银纳米颗粒极化效应的影响;最后,以两个银纳米颗粒为例讨论了颗粒相对位置对极化效果的影响,并证明了光纤探针顶端以外的银纳米颗粒对电场的极化效应没有贡献。本文的仿真结果为光纤探针的制备以及其表面银纳米颗粒的吸附提供了理论支持。     

Ionic capillary evaporation in weakly charged nanopores

Using a variational field theory, we show that an electrolyte confined to a neutral cylindrical nanopore traversing a low dielectric membrane exhibits a first-order ionic liquid-vapor pseudo-phase-transition from an ionic-penetration "liquid" phase to an ionic-exclusion "vapor" phase, controlled by nanopore-modified ionic correlations and dielectric repulsion. For weakly charged nanopores, this pseudotransition survives and may shed light on the mechanism behind the rapid switching of nanopore conductivity observed in experiments.     

Fabrication and characterization of magnetic nanoporous zeolite templated carbon

The effects of heat-treatment and guest adsorption on the structure and electronic/magnetic properties were investigated for zeolite templated carbon (ZTC) by using potassium, bromine, and helium as guest species. ZTC consists of a curved graphene network, which has regularly arranged nanopores with a periodicity of 1.4 nm. X-ray diffraction and Raman spectra reveal that the regular nanopore structure is preserved during vacuum heat-treatment (<380 °C) and potassium adsorption process. On the other hand, bromine adsorption is found to destroy the nanopore structure. Helium atoms adsorbed in the nanospace participate in the energy dissipation of the radical spins in ZTC through collisions with the spins.     

Nanobubbles in solid-state nanopores

From conductance and noise studies, we infer that nanometer-sized gaseous bubbles (nanobubbles) are the dominant noise source in solid-state nanopores. We study the ionic conductance through solid-state nanopores as they are moved through the focus of an infrared laser beam. The resulting conductance profiles show strong variations in both the magnitude of the conductance and in the low-frequency noise when a single nanopore is measured multiple times. Differences up to 5 orders of magnitude are found in the current power spectral density. In addition, we measure an unexpected double-peak ionic conductance profile. A simple model of a cylindrical nanopore that contains a nanobubble explains the measured profile and accounts for the observed variations in the magnitude of the conductance.     

Density functional theory study on ion adsorption and electroosmotic flow in a membrane with charged cylindrical pores†

ABSTRACT

Ion adsorption and electroosmotic flow induced by an external electric field have a variety of practical applications, especially for membrane technology. In this work, a partially perturbative density functional theory (DFT) based on the modified fundamental measure theory was applied to investigate the ion density distributions and partitions in a charged cylindrical pore. Different types of electrolyte solutions, including both charge symmetric and asymmetric, were examined using the proposed theory with various pore diameters, bulk densities, ion valencies and surface charge densities. The ion concentration profiles calculated with the theory exhibit good agreements with the results of the Monte Carlo simulations, while the results of the Poisson–Boltzmann equation deviate greatly especially for the high valence electrolytes in narrow cylindrical pores. Some interesting phenomena discovered in both experiments and simulations, such as the reverse distribution of the ions and charge inversion, can be well reproduced with the DFT. Based on the ion concentration distributions obtained from the DFT, the transient velocity profiles of the electroosmotic flow in the charged cylindrical nanopores were calculated with the Navier–Stokes (NS) equation. The characteristics of the electroosmotic flow were discussed under the different bulk electrolyte concentrations and thickness of the electric double layer inside the nanopore. The enhancement of the velocity near the pore wall, which cannot be described by the traditional theory, was well characterised by the DFT combined with the NS equation.     

Study on Fluorescence Characteristic of Quercetin–Nanoporous Anodic Aluminum Oxide Composites

Nanoporous Anodic Aluminum Oxide (AAO), its average diameters of porous were 50 nm, was obtained by two-step electrochemical anodization aluminum process. Highly ordered luminescence arrays formed by filling AAO nanopores with quercetin molecules has been studied by fluorescent spectroscopy in this work. AAO showed stronger adsorption capability of quercetin than Al³⁺-quercetin complex. The mechanism may be physical and chemical adsorption all together. Meanwhile, red shift of the maximum fluorescence peak of quercetin in AAO was observed. The molecular assemblies in the nanopore array are highly ordered and the fluorescence polarization dependence indicates a preferred molecular orientation along the pore axis. This maybe explains the mechanism of molecular luminescence depending on its environment.     

DNA in nanopores: counterion condensation and coion depletion

Molecular dynamics simulations are used to study the equilibrium distribution of monovalent ions in a nanopore connecting two water reservoirs separated by a membrane, both for the empty pore and that with a single stranded DNA molecule inside. In the presence of DNA, the counterions condense on the stretched macromolecule effectively neutralizing it, and nearly complete depletion of coions from the pore is observed. The implications of our results for experiments on DNA translocation through alpha-hemolysin nanopores are discussed.     

离子浓度及表面结构对岩石孔隙内水流动特性的影响

酸性环境引发的岩石孔隙表面溶解增加了孔隙内水溶液的盐离子浓度,破坏了孔隙的表面结构.本文采用分子动力学模拟的方法研究了纳米级岩石孔隙内水溶液的流动特性,分析了盐离子浓度和孔隙表面结构对水流速度分布的影响及原因.研究结果表明:纳米级岩石孔隙内的水溶液流动符合泊肃叶流动特性,流速呈"抛物线"分布;随盐离子浓度增加,水溶液内部氢键网络变得更为致密,水黏度随其呈线性增长;水溶液中离子浓度越大,孔隙表面对水流动的阻力越大,最大流速越小,速度分布的"抛物线"曲率半径越大;岩石孔隙表面结构的破坏改变了流动表面的粗糙程度,增加了孔隙表面对H2O分子的吸引力.随表面结构破坏程度的增大,水溶液在近壁区域的密度增大,流速降低;当表面破坏程度达到50%时,水溶液在近壁区域出现了明显的负边界滑移现象.     

Water wettability in nanoconfined environment

Water confined in nanoscale space behaves quite differently from that in the bulk.For example,in biological aquaporins and in carbon nanotubes,the traversing water molecules form a single file configuration.Water would stay in vapor state in extremely hydrophobic narrow nanopores owing to the physicochemical interactions between the water molecules and the surface of the nanopore.A spontaneous wet-dry transition has been identified in both biological and artificial nanopores.The nanopore is either fulfilled with liquid water or completely empty.Based on this mechanism,the wetting and dewetting processes inside nanopores have been further developed into highly efficient nanofluidic gates that can be switched by external stimuli,such as light irradiation,electric potential,temperature,and mechanical pressure.This review briefly covers the recent progress in the special wettability in nanoconfined environment,water transportation through biological or artificial nanochannels,as well as the smart nanofluidic gating system controlled by the water wettability.     

超快贝塞尔光束在硫化锌晶体表面制备纳米孔

硫化锌(ZnS)晶体是重要的宽光谱红外窗口材料,高深径比纳米孔的超快激光制造技术为中红外波导傅立叶变换光谱仪等光子器件的实现提供了重要的技术途径。本文采用中心波长为1030 nm、重复频率为100 kHz、脉冲宽度为223 fs~20 ps可调的Yb:KGW激光光源,用石英锥镜产生高斯-贝塞尔光束,并用4f系统构建了40倍缩束的超快激光直写系统。在能量为36~63μJ,脉宽为12.5~20 ps的情况下,在ZnS晶体上成功刻写了直径为80~320 nm的纳米孔结构。通过聚焦离子束(FIB)剥蚀和扫描电子显微镜(SEM)成像确定了纳米孔隙表面形貌、直径及深度信息。研究了激光脉冲能量、脉冲宽度对纳米孔隙的影响。结果表明,在20 ps脉冲宽度、48μJ脉冲能量的激光参数下,纳米孔隙的深度约为270μm。     

CARS diagnostics of fluid adsorption and condensation in small mesopores

Coherent anti‐Stokes Raman scattering (CARS) spectroscopy is applied to diagnostics of phase behavior of a fluid in pores of nanoporous glasses. Samples with mean pore radii of 2 and 3.5 nm were filled with compressed carbon dioxide at near‐room temperatures. CARS spectra of the 1388 cm⁻¹ Q‐branch were measured at isothermal compressing in a wide pressure range including the transition from gaseous to condensed state. The spectra show specific transformations caused by fluid adsorption and condensation in nanopores. We have carried out calculations of the spectral profiles based on the phase behavior of carbon dioxide in cylindrical glass nanopores. Phase behavior modeling was performed using thermodynamic concepts of surface adsorption and capillary condensation. A good agreement between experimental spectra and calculations was obtained. The potential of CARS technique for the diagnostics of fluid phase behavior in pores and for the characterization of nanoporous host structure is discussed. Copyright © 2011 John Wiley & Sons, Ltd.