Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni–C (graphitic) core–shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores of hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H_c = 138.4 O_e) and good ferromagnetism (M_r/M_s = 0.325).     

Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy

We introduce voltage-contrast scanning electron microscopy (VC-SEM) for visual characterization of the electronic properties of single-walled carbon nanotubes. VC-SEM involves tuning the electronic band structure and imaging the potential profi le along the length of the nanotube. The resultant secondary electron contrast allows to distinguish between metallic and semiconducting carbon nanotubes and to follow the switching of semiconducting nanotube devices, as confi rmed by in situ electrical transport measurements. We demonstrate that high-density arrays of individual nanotube devices can be rapidly and simultaneously characterized. A leakage current model in combination with fi nite element simulations of the device electrostatics is presented in order to explain the observed contrast evolution of the nanotube and surface electrodes. This work serves to fill a void in electronic characterization of molecular device architectures. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

海藻酸钠/碳纳米管复合凝胶球的制备及其吸附性能

提出一种安全简单污水处理的方法,以物理共混的方法利用海藻酸钠分散未经任何处理的原始多壁碳纳米管,得到均匀分散的海藻酸钠/碳纳米管(SA/MWNTs)水溶液,以CaCl2作为凝固浴,制备SA-Ca和SA/MWNTs-Ca复合凝胶球,利用凝胶球对甲基橙(MO)溶液进行吸附脱色研究。试验结果表明:海藻酸钠凝胶球对甲基橙去除率较低,随着碳纳米管含量的增加,当MWNTs增加到2.5g/L,SA/MWNTs-Ca凝胶球的吸附性能提高了3倍;并且随着凝胶球量的增加,去除率迅速增加,当凝胶球质量浓度从1～50g/L时,去除率有显著提高,增加近10倍;溶液pH值对吸附性能的研究还表明,溶液的pH值对SA/MWNTs-Ca凝胶球的吸附性能有较大的影响,pH值较低时有利于SA/MWNTs-Ca凝胶球对MO的吸附。     

利用碳纳米管吸附溶液中金属离子的研究进展

碳纳米管具有中空层状结构,大的比表面积和长径比,高的化学稳定性和热稳定性以及端帽、内腔、管壁容易被修饰等特点,是一种较为理想的吸附材料。综述了碳纳米管与吸附相关的结构和性质,分析了经硝酸氧化处理过的碳纳米管对溶液中金属离子的吸附作用原理,以及pH值、离子浓度对吸附作用的影响。讨论了将碳纳米管对金属离子的吸附作用与分离富集技术相联系,应用于元素分析测定,能够提高方法灵敏度,降低了元素检出限。在仪器分析方面将有巨大潜力。     

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Abstract

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH₄ molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH₄ molecule is preferentially adsorbed onto the CNT with a binding energy of ?2.84 kcal mol^?1. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of ?3.00 and ?1.44 kcal mol^?1 per adsorbed CH₄ molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.     

Scanning electron microscopy imaging of single-walled carbon nanotubes on substrates

Scanning electron microscopy (SEM) plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials.Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes (SWCNTs) are placed on a substrate.In this study,we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials.Substantial SEM observations are conducted at both high and low acceleration voltages,leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals,as well as the SEM imaging.This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.     

Physical properties of CVD boron-doped multiwalled carbon nanotubes

The effects of boron doping and electron correlation on the transport properties of CVD boron-doped multiwalled carbon nanotubes are reported. The boron-doped multiwalled carbon nanotubes were characterized by TEM as well as Raman spectroscopy using different laser excitations (viz. 488, 514.5 and 647 nm). The intensity of the D-band laser excitation line increased after the boron incorporation into the carbon nanotubes. The G-band width increased on increasing the boron concentration, indicating the decrease of graphitization with increasing boron concentration. Electrical conductivity of the undoped and boron-doped carbon nanotubes reveal a 3-dimensional variable-range-hopping conductivity over a wide range of temperature, viz. from room temperature down to 2 K. The electrical conductivity is not found to be changed significantly by the present levels of B-doping. Electron Paramagnetic Resonance (EPR) results for the highest B-doped samples showed similarities with previously reported EPR literature measurements, but the low concentration sample gives a very broad ESR resonance line.     

活性炭对正丁烷的吸附动力学研究

以木屑为原料、磷酸为活化剂,经过碳化、活化两步法制备的丁烷吸附炭,并考察了活性炭的吸附时间、正丁烷流量和吸附温度的变化对正丁烷吸附性能的影响;研究了活性炭在不同温度下的吸附动力学行为。实验证明,活性炭吸附正丁烷是一个吸附与解吸并存的快速物理吸附过程。正丁烷流量显著影响活性炭的吸附速率和吸附时间,但不影响活性炭的饱和吸附量(qe)。活性炭对正丁烷的饱和吸附量随着温度的升高而降低,表明正丁烷在活性炭上的吸附为放热反应。活性炭对正丁烷的吸附动力学行为遵循班厄姆动力学方程,其相关系数R2均>0.99,通过班厄姆方程计算得到的qe与实验得到的qe非常接近,通过拟合可以得到理想的吸附速率方程。     

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH₄ molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH₄ molecule is preferentially adsorbed onto the CNT with a binding energy of −2.84 kcal mol⁻¹. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of −3.00 and −1.44 kcal mol⁻¹ per adsorbed CH₄ molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.     

Direct identification of metallic and semiconducting single-walled carbon nanotubes in scanning electron microscopy

Because of their excellent electrical and optical properties, carbon nanotubes have been regarded as extremely promising candidates for high-performance electronic and optoelectronic applications. However, effective and efficient distinction and separation of metallic and semiconducting single-walled carbon nanotubes are always challenges for their practical applications. Here we show that metallic and semiconducting single-walled carbon nanotubes on SiO(2) can have obviously different contrast in scanning electron microscopy due to their conductivity difference and thus can be effectively and efficiently identified. The correlation between conductivity and contrast difference has been confirmed by using voltage-contrast scanning electron microcopy, peak force tunneling atom force microscopy, and field effect transistor testing. This phenomenon can be understood via a proposed mechanism involving the e-beam-induced surface potential of insulators and the conductivity difference between metallic and semiconducting SWCNTs. This method demonstrates great promise to achieve rapid and large-scale distinguishing between metallic and semiconducting single-walled carbon nanotubes, adding a new function to conventional SEM.     

Comparative experimental study of methane adsorption on multi-walled carbon nanotubes and granular activated carbons

In this study, methane storage capacity of granular activated carbons (GACs) and two types of multi-walled carbon nanotubes (MWCNTs) was investigated and compared. An experimental apparatus consisting a dual adsorption vessel was set up for measurement of equilibrium adsorption of methane on adsorbents using volumetric technique at pressure range of 0–50?bar at different temperatures. The first type of MWCNs has shown lower methane uptake (4.5?mmol?g^?1) compared to GACs (6.5?mmol?g^?1) at the temperature of 283.15?K and the pressure of 50?bar, while 33?mmol?g^?1 of methane storage capacity was achieved using the second type of MWCNTs that is much higher than methane storage on GACs at the same operating conditions. The superior uptake performance for the second type of MWCNTs can be attributed to its specific characteristics such as smaller pore size and higher pore volume. The experimental data of adsorption were almost equally well described by Langmuir, Freundlich and Sips equations to determine the model isotherms. The isosteric heat of methane adsorption on the adsorbent was calculated based on Clausius–Clapeyron and the Sips isotherm model using the experimental data at different temperatures. Results revealed that the isosteric heat of methane adsorption on MWCNTs was lower than the heat of methane adsorption on GACs. Low values obtained for isosteric heats of adsorption indicated dominance of physisorption mechanism for all adsorbents. In general, the obtained data indicated that some well-structured MWCNTs with uniform and narrow size distribution as well as higher pore volume are potential materials for methane storage and deserve further study.     

载Mn活性炭纤维的制备及性能研究

采用化学活化法制备载Mn活性炭纤维(ACF-Mn),考察了活化剂的浓度、活化时间对吸附性能的影响,利用XRD、SEM、EDX等手段描述了晶体结构,表面形貌和元素组成.结果表明,制备ACF-Mn的最佳工艺条件为:活化剂浓度2%,活化温度700℃,活化时间80min,ACF-Mn的碘吸附值和碱性官能团含量分别为905mg·g-1和83mmol·g-1,得率为88%,担载Mn的质量百分比为2.26%,原子百分比为0.28%.ACF-Mn为乱层石墨微晶结构,微晶尺寸较小,有利于微孔形成,处理后的纤维表面粗糙度和碱性官能团含量明显增大,提高了ACF的吸附性能.     

Synthesis and field electron emission properties of hybrid carbon nanotubes and nanoparticles

Hybrid ZnO-carbon nanotubes as well as nanodiamond-carbon nanotubes were synthesized via a straightforward process of plasma enhanced chemical vapor deposition. For the former, ZnO nanoparticles were instantly coated on the tube surface in the final growing process of carbon nanotubes, while for the latter diamond nanoparticles were grown using pretreatment of a silicon substrate with Ni(NO(3))(2)·6H(2)O/Mg(NO(3))(2)·6H(2)O alcohol solution prior to deposition and a high H(2)/CH(4) gas flow ratio in the deposition process. The morphology and microstructure of the obtained hybrid materials were characterized by transmission electron microscopy. Both hybrid ZnO-carbon nanotubes and nanodiamond-carbon nanotubes exhibited excellent field emission properties.     

TiO2 nanotubes: Self-organized electrochemical formation, properties and applications

The present paper gives an overview and review on self-organized TiO₂ nanotube layers and other transition metal oxide tubular structures grown by controlled anodic oxidation of a metal substrate. We describe mechanistic aspects of the tube growth and discuss the electrochemical conditions that need to be fulfilled in order to synthesize these layers. Key properties of these highly ordered, high aspect ratio tubular layers are discussed. In the past few years, a wide range of functional applications of the layers have been explored ranging from photocatalysis, solar energy conversion, electrochromic effects over using the material as a template or catalyst support to applications in the biomedical field. A comprehensive view on state of the art is provided.     

含钾羟基磷灰石粉体的制备及其吸附性能研究?

采用化学沉淀法制备出 Ca3(PO4)2粉体,经过高温煅烧得到α-Ca3(PO4)2粉体.将粉体投入到KOH 溶液中,在120℃温度下水化不同时间,制备出含钾羟基磷灰石粉体,利用 X 射线衍射,透射电子显微镜进行分析表征.再将含钾羟基磷灰石粉体投入到NaF溶液中,研究粉体对 F－的吸附性.实验结果表明,含钾羟基磷灰石粉体对氟离子的吸附采用Lagerg-ren拟二级反应动力学方程拟合效果较好,吸附速率较快,吸附机制主要是通过离子交换作用.将吸附过程通过 Langmuir/Freundlich 吸附等温模型拟合,采用Langmuir模型拟合效果较好,静态吸附饱和量为31．55 mg/g.     

Water vapor adsorption properties of amorphous cefditoren pivoxil evaluated by adsorption isotherms and microcalorimetry

Water vapor adsorption of ground cefditoren pivoxil was studied. The amount of water adsorbed increased with a decrease in the crystallinity of cefditoren pivoxil. It was found from the microcalorimetric measurements that the differential heat of water vapor adsorption at 1.5% adsorbed water increased with decreasing crystallinity of cefditoren pivoxil, suggesting that hygroscopicity of cefditoren pivoxil was enhanced by grinding. These results indicated that hydrophilic adsorption sites in cefditoren pivoxil increased through the grinding process. The results of infrared (IR) spectra examination suggested that the increment of hydrophilic adsorption sites through the grinding process resulted from the change of the environment of the carbonyl groups in two esters and amide.     

沙柳基磁性多孔炭的制备及其吸附亚甲基蓝性能研究

采用水热法原位改性沙柳生物炭制备磁性多孔炭复合材料,利用SEM、XRD、FT-IR、XPS和BET分别对多孔炭的形貌、结构表征,并研究磁性多孔炭吸附去除废水中亚甲基蓝性能.系列表征分析结果表明磁性复合材料表面疏松多孔,比表面积为63.01 m2/g,含有-COOH、-OH等丰富的官能团.在亚甲基蓝初始质量浓度为50 m...     

Physical and chemical properties and adsorption type of activated carbon prepared from plum kernels by NaOH activation

Activated carbon was prepared from plum kernels by NaOH activation at six different NaOH/char ratios. The physical properties including the BET surface area, the total pore volume, the micropore ratio, the pore diameter, the burn-off, and the scanning electron microscope (SEM) observation as well as the chemical properties, namely elemental analysis and temperature programmed desorption (TPD), were measured. The results revealed a two-stage activation process: stage 1 activated carbons were obtained at NaOH/char ratios of 0-1, surface pyrolysis being the main reaction; stage 2 activated carbons were obtained at NaOH/char ratios of 2-4, etching and swelling being the main reactions. The physical properties of stage 2 activated carbons were similar, and specific area was from 1478 to 1887m(2)g(-1). The results of reaction mechanism of NaOH activation revealed that it was apparently because of the loss ratio of elements C, H, and O in the activated carbon, and the variations in the surface functional groups and the physical properties. The adsorption of the above activated carbons on phenol and three kinds of dyes (MB, BB1, and AB74) were used for an isotherm equilibrium adsorption study. The data fitted the Langmuir isotherm equation. Various kinds of adsorbents showed different adsorption types; separation factor (R(L)) was used to determine the level of favorability of the adsorption type. In this work, activated carbons prepared by NaOH activation were evaluated in terms of their physical properties, chemical properties, and adsorption type; and activated carbon PKN2 was found to have most application potential.     

Molecular dynamics simulation studies of structural and mechanical properties of single-walled carbon nanotubes

Structural and mechanical properties of armchair, zig-zag and chiral single-walled carbon nanotubes are computed by employing Molecular Dynamics simulation technique using Discover code with Compass force field via Materials Studio program developed by the Accelrys. Consistent with the literature, we find that the armchair SWCNT is energetically favored over zig-zag and chiral nanotubes. Predicted structural parameters agree well with experimental observations. Observed radial distribution functions show that the single-walled carbon nanotubes remain crystalline after exposing them to 300 K. The predicted Young's and the Shear moduli were in reasonable agreement with other reports. Our predictions show that the Young's modulus of the tubes increases as the diameter of the tube decreases.