共查询到20条相似文献，搜索用时 546 毫秒
1.
WZ Li SS Xie LX Qian BH Chang BS Zou WY Zhou RA Zhao G Wang 《Science (New York, N.Y.)》1996,274(5293):1701-1703
Large-scale synthesis of aligned carbon nanotubes was achieved by using a method based on chemical vapor deposition catalyzed by iron nanoparticles embedded in mesoporous silica. Scanning electron microscope images show that the nanotubes are approximately perpendicular to the surface of the silica and form an aligned array of isolated tubes with spacings between the tubes of about 100 nanometers. The tubes are up to about 50 micrometers long and well graphitized. The growth direction of the nanotubes may be controlled by the pores from which the nanotubes grow. 相似文献
2.
Hinds BJ Chopra N Rantell T Andrews R Gavalas V Bachas LG 《Science (New York, N.Y.)》2004,303(5654):62-65
An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing. 相似文献
3.
Fast mass transport through sub-2-nanometer carbon nanotubes 总被引：1，自引：0，他引：1
Holt JK Park HG Wang Y Stadermann M Artyukhin AB Grigoropoulos CP Noy A Bakajin O 《Science (New York, N.Y.)》2006,312(5776):1034-1037
We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are several orders of magnitude higher than those of commercial polycarbonate membranes, despite having pore sizes an order of magnitude smaller. These membranes enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration. 相似文献
4.
Carbon nanotubes display either metallic or semiconducting properties. Both large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or "ropes" of aligned single-walled nanotubes (SWNTs), are complex composite conductors that incorporate many weakly coupled nanotubes that each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the different shells. By choosing among the shells, we can convert a MWNT into either a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity allows us to generate entire arrays of nanoscale field-effect transistors based solely on the fraction of semiconducting SWNTs. 相似文献
5.
Deheer WA Bacsa WS Châtelain A Gerfin T Humphrey-Baker R Forro L Ugarte D 《Science (New York, N.Y.)》1995,268(5212):845-847
Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties. 相似文献
6.
目的 研究多壁碳纳米管(MWCNTs)做固相萃取吸附剂对水中的16种有机磷农药残留的吸附富集效果.方法 MWCNTs SPE柱采用水相净化体系,有机磷农药采用双柱双检测器GC/FPD法测定.结果 优化的净化条件为:水样采用HAc-NaAc缓冲溶液调节pH=5.0,MWCNTs SPE柱用5 mL甲醇和5 mL HAc-... 相似文献
7.
Hata K Futaba DN Mizuno K Namai T Yumura M Iijima S 《Science (New York, N.Y.)》2004,306(5700):1362-1364
We demonstrate the efficient chemical vapor deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis. 相似文献
8.
A simple technique is described here that produces aligned arrays of carbon nanotubes. The alignment method is based on cutting thin slices (50 to 200 nanometers) of a nanotube-polymer composite. With this parallel and well-separated configuration of nanotubes it should be possible to measure individual tube properties and to demonstrate applications. The results demonstrate the nature of rheology, on nanometer scales, in composite media and flow-induced anisotropy produced by the cutting process. The fact that nanotubes do not break and are straightened after the cutting process also suggests that they have excellent mechanical properties. 相似文献
9.
Stephan O Ajayan PM Colliex C Redlich P Lambert JM Bernier P Lefin P 《Science (New York, N.Y.)》1994,266(5191):1683-1685
Composite sheets and nanotubes of different morphologies containing carbon, boron, and nitrogen were grown in the electric arc discharge between graphite cathodes and amorphous boron-filled graphite anodes in a nitrogen atmosphere. Concentration profiles derived from electron energy-loss line spectra show that boron and nitrogen are correlated in a one-to-one ratio; core energy-loss fine structures reveal small differences compared to pure hexagonal boron nitride. Boron and carbon are anticorrelated, suggesting the substitution of boron and nitrogen into the carbon network. Results indicate that singlephaase CyBxNx as well as separated domains (nanosize) of boron nitride in carbon networks may exist. 相似文献
10.
Ericson LM Fan H Peng H Davis VA Zhou W Sulpizio J Wang Y Booker R Vavro J Guthy C Parra-Vasquez AN Kim MJ Ramesh S Saini RK Kittrell C Lavin G Schmidt H Adams WW Billups WE Pasquali M Hwang WF Hauge RH Fischer JE Smalley RE 《Science (New York, N.Y.)》2004,305(5689):1447-1450
Well-aligned macroscopic fibers composed solely of single-walled carbon nanotubes (SWNTs) were produced by conventional spinning. Fuming sulfuric acid charges SWNTs and promotes their ordering into an aligned phase of individual mobile SWNTs surrounded by acid anions. This ordered dispersion was extruded via solution spinning into continuous lengths of macroscopic neat SWNT fibers. Such fibers possess interesting structural composition and physical properties. 相似文献
11.
Cao A Dickrell PL Sawyer WG Ghasemi-Nejhad MN Ajayan PM 《Science (New York, N.Y.)》2005,310(5752):1307-1310
We report that freestanding films of vertically aligned carbon nanotubes exhibit super-compressible foamlike behavior. Under compression, the nanotubes collectively form zigzag buckles that can fully unfold to their original length upon load release. Compared with conventional low-density flexible foams, the nanotube films show much higher compressive strength, recovery rate, and sag factor, and the open-cell nature of the nanotube arrays gives excellent breathability. The nanotube films present a class of open-cell foam structures, consisting of well-arranged one-dimensional units (nanotube struts). The lightweight, highly resilient nanotube films may be useful as compliant and energy-absorbing coatings. 相似文献
12.
To find use in electronics, single-walled carbon nanotubes need to be efficiently separated by electronic type and aligned to ensure optimal and reproducible electronic properties. We report the fabrication of single-walled carbon nanotube (SWNT) network field-effect transistors, deposited from solution, possessing controllable topology and an on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs are tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network in which nanotube chirality separation and simultaneous control of density and alignment occur in one step during device fabrication. Micro-Raman experiments corroborate device results as a function of surface chemistry, indicating enrichment of the specific SWNT electronic type absorbed onto the modified dielectric. 相似文献
13.
Process improvements in silica membrane fabrication, especially the use of clean-room techniques, resulted in silica membranes without detectable mesoscopic defects, resulting in significantly improved transport properties. Supported membranes calcined at 400 degreesC were 30 nanometers in thickness, showed a H2 permeance at 200 degreesC of 2 x 10(-6) moles per square meter per second per Pascal (mol m-2 s-1 Pa-1), and had a CH4 permeance more than 500 times smaller. Molecules larger than CH4 were completely blocked. Silica membranes calcined at 600 degreesC showed no detectable CH4 flux, with a H2 permeance of 5 x 10(-7) (mol m-2 s-1 Pa-1) at 200 degreesC. These results signify an important step toward the industrial application of these membranes such as purification of H2 and natural gas as well as the selective removal of CO2. 相似文献
14.
In the processes that are used to produce single-walled nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of nanotubes assemble continuously from arrays of nanotubes, which are intrinsically long. 相似文献
15.
LC Venema JWG Wildoer JW Janssen SJ Tans HLJT Tuinstra LP Kouwenhoven C Dekker 《Science (New York, N.Y.)》1999,283(5398):52-55
Carbon nanotubes provide a unique system for studying one-dimensional quantization phenomena. Scanning tunneling microscopy was used to observe the electronic wave functions that correspond to quantized energy levels in short metallic carbon nanotubes. Discrete electron waves were apparent from periodic oscillations in the differential conductance as a function of the position along the tube axis, with a period that differed from that of the atomic lattice. Wave functions could be observed for several electron states at adjacent discrete energies. The measured wavelengths are in good agreement with the calculated Fermi wavelength for armchair nanotubes. 相似文献
16.
Cu/CuO改性碳纳米管对亚甲基蓝的吸附特征 总被引：1，自引：1，他引：0
为探讨Cu/CuO改性碳纳米管对亚甲基蓝的吸附特征,采用Cu/CuO对碳纳米管进行了改性,通过SEM、XRD和比表面积-孔径分析仪对改性前后碳纳米管进行表征。以改性前后碳纳米管为吸附剂,研究了改性前后碳纳米管对亚甲基蓝的吸附动力学和吸附等温线,并且分析了环境因素包括温度、pH和离子强度对吸附的影响。结果表明:改性前后碳纳米管对亚甲基蓝的吸附过程符合准二级动力学方程,且在2 h左右达到吸附平衡,吸附等温线符合Freundlich模型,改性之后碳纳米管对亚甲基蓝的吸附能力增强。改性前后碳纳米管对亚甲基蓝的吸附量随温度的增加而降低,随pH和离子强度的增大而增大。研究表明,Cu/CuO改性碳纳米管对亚甲基蓝的吸附效果优于原始碳纳米管,Cu/CuO改性碳纳米管去除溶液中的亚甲基蓝主要通过疏水性相互作用、静电相互作用和铜与亚甲基蓝之间的络合作用。 相似文献
17.
Bockrath M Liang W Bozovic D Hafner JH Lieber CM Tinkham M Park H 《Science (New York, N.Y.)》2001,291(5502):283-285
We report the characterization of defects in individual metallic single-walled carbon nanotubes by transport measurements and scanned gate microscopy. A sizable fraction of metallic nanotubes grown by chemical vapor deposition exhibits strongly gate voltage-dependent resistance at room temperature. Scanned gate measurements reveal that this behavior originates from resonant electron scattering by defects in the nanotube as the Fermi level is varied by the gate voltage. The reflection coefficient at the peak of a scattering resonance was determined to be about 0.5 at room temperature. An intratube quantum dot device formed by two defects is demonstrated by low-temperature transport measurements. 相似文献
18.
随着对纳米碳管研究的不断深入,对碳纳米管的应用研究越来越受到人们的重视。本文主要对应用碳纳米管萃取环境中有机污染物的研究进展作一综述,并对其在此领域的应用前景进行了展望。 相似文献
19.
A reduction-pyrolysis-catalysis synthesis of diamond 总被引：2，自引：0，他引：2
Diamond powder was synthesized through a metallic reduction-pyrolysis-catalysis route with the reaction of carbon tetrachloride and sodium at 700 degreesC, in which the sodium was used as reductant and flux. This temperature is much lower than that of traditional methods. The x-ray powder diffraction patterns showed three strong peaks of diamond. The Raman spectrum showed a sharp peak at 1332 inverse centimeters, which is characteristic of diamond. Although the yield was only 2 percent, this method is a simple means of forming diamond. 相似文献
20.
T Ishikawa S Kajii K Matsunaga T Hogami Y Kohtoku T Nagasawa 《Science (New York, N.Y.)》1998,282(5392):1295-1297
A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), fibrous fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC). 相似文献