Carbon nanotube purification: preparation and characterization of carbon nanotube paste electrodes

Paste electrodes have been constructed using single-wall carbon nanotubes mixed with mineral oil. The electrochemical behavior of such electrodes prepared with different percentages of carbon nanotubes has been compared with that of graphite paste electrodes and evaluated with respect to the electrochemistry of ferricyanide with cyclic voltammetry. Carbon nanotubes were purified by a treatment with concentrated nitric acid, then oxidized in air. In addition, electrochemical pretreatments were carried out to increase the selectivity of carbon nanotube electrodes. Performances of carbon nanotube paste and carbon paste electrodes were evaluated by studying such parameters as current peak, deltaEp, anodic and cathodic current ratio, and charge density toward several different electroactive molecules. Data interpretation based on the carbon nanotubes and carbon surface area is presented. Carbon nanotube paste and carbon paste electrodes were tested as H2O2 and NADH probes, and several analytical parameters were evaluated. The oxidative behavior of dopamine was examined at these electrodes. The two-electron oxidation of dopamine to dopaminequinone showed an excellent reversibility in cyclic voltammetry that was significantly better than that observed at carbon paste electrodes.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

Electrochemical properties and myocyte interaction of carbon nanotube microelectrodes

Arrays of carbon nanotube (CNT) microelectrodes (nominal geometric surface areas 20-200 μm(2)) were fabricated by photolithography with chemical vapor deposition of randomly oriented CNTs. Raman spectroscopy showed strong peak intensities in both G and D bands (G/D = 0.86), indicative of significant disorder in the graphitic layers of the randomly oriented CNTs. The impedance spectra of gold and CNT microelectrodes were compared using equivalent circuit models. Compared to planar gold surfaces, pristine nanotubes lowered the overall electrode impedance at 1 kHz by 75%, while nanotubes treated in O(2) plasma reduced the impedance by 95%. Cyclic voltammetry in potassium ferricyanide showed potential peak separations of 133 and 198 mV for gold and carbon nanotube electrodes, respectively. The interaction of cultured cardiac myocytes with randomly oriented and vertically aligned CNTs was investigated by the sectioning of myocytes using focused-ion-beam milling. Vertically aligned nanotubes deposited by plasma-enhanced chemical vapor deposition (PECVD) were observed to penetrate the membrane of neonatal-rat ventricular myocytes, while randomly oriented CNTs remained external to the cells. These results demonstrated that CNT electrodes can be leveraged to reduce impedance and enhance biological interfaces for microelectrodes of subcellular size.     

Carbon composite microelectrodes: charge percolation and electroanalytical performance

Microelectrodes based on two different epoxy-graphite composites (Araldite-M/HY5162 and Araldite-PY302-2/HY943) that are compatible with organic solvents have been developed and characterized. The variation in the bulk conductivity with graphite particle loading is described by percolation theory and indicates that the particles interact strongly with one another. The percolation threshold is 52% v/v loading of graphite, and this composite exhibits a bulk conductivity of 15 S m(-1). Microdisk electrodes of 25-microm diameter were produced by first etching a microcavity at the tip of a platinum microelectrode, which was then packed with a composite containing 60% v/v graphite so as to optimize both electrical conductivity and the electrode stability in acetonitrile and methanol solutions. Solution phase voltammetry of ferrocene is nearly ideal, and the responses are dominated by radial diffusion (slow scan rates) and semi-infinite linear diffusion (fast scan rates). The microelectrodes display high signal-to-noise ratios, good sensitivity, and low detection limits. The response times given by the product of the resistance, R, and capacitance, C, are 7.5 x 10(-4) and 1.4 x 10(-1) s for the Araldite M and PY302-2 composites, respectively. Although these response times are significantly slower than those associated with microelectrodes based on carbon fibers or metal wires, they are sufficient for time-resolved electroanalytical applications. The long response times arise from the large composite resistances, 3.1 x 10(11) and 8.3 x 10(11) Omega cm(-2) for Araldite M and PY302-2, respectively. Voltammetry of ferrocene in the absence of deliberately added supporting electrolyte is also reported. Significantly, indistinguishable slopes and intercepts for a calibration curve of peak current vs ferrocene concentration where 2 < [ferrocene] < 50 microM are obtained in the presence and absence of supporting electrolyte.     

浸入式中空纤维膜元件的优化设计

在浸入式中空纤维膜元件纯净水测试实验基础上,研究了膜通量的分布情况,提出了膜元件的优化参数——单位产水膜成本,讨论了膜丝尺寸、出水方式、成本构成、应用场合等对膜元件的优化设计的影响,建立了一种中空纤维膜元件优化设计的方法.     

Fabrication and characterization of recyclable carbon nanotube/polyvinyl butyral composite fiber

A surface-draw method to fabricate recyclable carbon nanotube/polyvinyl butyral (CNT/PVB) composite fibers is reported. This method is effective for both single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube. The CNT mass content of CNT/PVB composite fibers can vary from 0 to 80 wt.%, which is higher than most CNT/polymer composites reported to date. The diameter of the composite fibers can be controlled in the range of 10-100 μm, with essentially unlimited draw length. The composite fibers with 7.4 wt.% SWCNTs showed optimal tensile properties. Compared with pure PVB fibers, the tensile strength, failure strain, and elastic modulus of the composite fiber have improved about 127%, 27%, and 73%, respectively. In addition, SWCNT/PVB composites with 66.7 wt.% SWCNTs have the highest conductivity of 42.9 S m⁻¹. More importantly, the major benefit is the “greenness” of the method, which involves environment friendly ethanol-water solvent with no functionalization of the nanotube required, and only simple apparatus are needed. The CNT/PVB composite fibers obtained can be dissolved in ethanol solution and reformed with the surface draw method without any additional treatment; and the material properties after recycle is comparable to those fabricated in the first round.     

Carbon nanotube arrays for optical design of amorphous silicon solar cells

Effective light trapping is essential for the conversion efficiency increase in thin film solar cells. Vertically aligned multiwalled carbon nanotubes (MWNTs) arrays with proper spacing form an ideal light trapping structure. In this work, we have demonstrated feasibility of the incorporation of MWNTs as back contact into amorphous silicon solar cells. Intrinsic amorphous silicon films were uniformly deposited onto vertically aligned MWNTs arrays. Scanning Electron Microscopy (SEM) was used to investigate the surface morphology of our films. The film surface area exposed to light was found to be increased dramatically due to the high-aspect ratio of MWNTs. Our findings open up a new way of managing light in thin film silicon solar cells by controlling the nano-geometry of MWNTs on substrates.     

Carbon nanotube-modified carbon fiber microelectrodes for in vivo voltammetric measurement of ascorbic acid in rat brain

This study demonstrates a new electrochemical method for in vivo measurements of ascorbic acid (AA) in rat brain with multiwalled carbon nanotube (MWNT)-modified carbon fiber microelectrodes (CFMEs) based on the electrochemical property of MWNTs for facilitating AA oxidation. Cyclic voltammetry results indicate that the prepared MWNT-modified CFMEs possess a marked electrocatalytic activity toward AA oxidation and can be used for its selective measurement in the presence of other kinds of electroactive species coexisting in rat brain, such as 3,4-dihydroxyphenylacetic acid, uric acid, and 5-hydroxytryptamine. The selectivity of the MWNT-modified CFMEs toward AA measurement is further studied in vivo by exogenously infusing ascorbate oxidase into the brain, and the results confirm that the prepared electrodes are selective and can thus be used for reliable in vivo measurements of AA in rat brain, combined with their good stability during in vivo measurements. The basal level of striatum AA is determined to be 0.20 +/- 0.05 mM (n = 3). The application of the voltammetric method with the MWNT-modified CFMEs is preliminarily demonstrated for in vivo observation of homeostatic regulation of striatum AA with exogenous infusion of AA into the brain.     

Parameter control, characterization, and optimization in the fabrication of optical fiber near-field probes

Tip diameter and transmission efficiency of a visible-wavelength near-field optic probe determine both the lateral spatial resolution and experimental utility of the near-field scanning optical microscope. The commonly used tip fabrication technique, laser-heated pulling of fused-silica optical fiber followed by aperture formation through aluminization, is a complex process governed by a large number of parameters. An extensive study of the pulling parameter space has revealed a time-dependent functionality between the various pulling parameters dominated by a photon-based heating mechanism. The photon-based heat source results in a temperature and viscosity dependence that is a complex function of time and fiber diameter. Changing the taper of the optical probe can affect transmission efficiency by an order of magnitude or more.     

Carbon nanotube based transparent conductive films: progress,challenges, and perspectives

Developments in the manufacturing technology of low-cost, high-quality carbon nanotubes (CNTs) are leading to increased industrial applications for this remarkable material. One of the most promising applications, CNT based transparent conductive films (TCFs), are an alternative technology in future electronics to replace traditional TCFs, which use indium tin oxide. Despite significant price competition among various TCFs, CNT-based TCFs have good potential for use in emerging flexible, stretchable and wearable optoelectronics. In this review, we summarize the recent progress in the fabrication, properties, stability and applications of CNT-based TCFs. The challenges of current CNT-based TCFs for industrial use, in comparison with other TCFs, are considered. We also discuss the potential of CNT-based TCFs, and give some possible strategies to reduce the production cost and improve their conductivity and transparency.     

Carbon nanotube T junctions: formation and properties

The formation of carbon nanotube T junctions (CNTJs) and their transport properties are reviewed. The CNTJs were formed by coupling chemically functionalized nanotubes with linker molecules. Both end-to-side and end-to-end intermolecular junctions can be assembled by reacting chloride terminated nanotubes with aliphatic diamines. The functionalized nanotube mats were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The incorporation of functional groups into nanotubes is indicated by the pronounced shift of tangential vibration modes in Raman spectra and of carbon is binding energy in X-ray photoelectron spectra. For transport measurements the functionalized nanotubes were adsorbed on Si substrates, and subsequent electrodes were painted on top of the selected T junctions by lithography and lift-off techniques. The bar of the "T" is used as the transistor channel and the stem of the "T" is used as the gate. In this configuration, the active area is confined to a few nanometers in all three dimensions.     

碳纳米管及其研究进展

本文综述了碳纳米管的发展背景、制备方法、形成机理、性能和应用 ,并对今后碳纳米管研究存在的问题作了扼要的论述     

谐振式光纤陀螺的数字检测方案及其优化设计

提出了一种基于 DSP 芯片实现的双频率数字调制谐振式光纤陀螺系统的闭环检测方案。在此方案中,利用带通滤波器从探测器的输出光强信号中提取其基波频率的正弦信号,通过相关检测原理去掉干扰的噪声,并利用低通滤波器提取与探测器输出光强幅度直接成正比的直流信号,将其转换成相应的谐振频差,利用此频差即可求得陀螺的旋转角速度。此方案检测线路简单,操作方便,基于 DSP 芯片的实现则大大提高了系统处理速度。同时,还利用 Matlab 软件对检测系统中的滤波器参数进行了优化设计,提高了系统的检测精度。     

Synthesis and characterization of vertically aligned carbon nanotube forest for solid state fiber spinning

Continuous carbon nanotubes (CNT) fibers were directly spun from a vertically aligned CNT forest grown by a plasma-enhanced chemical vapor deposition (PECVD) process. The correlation of the CNT structure with Fe catalyst coarsening, reaction time, and the CNTs bundling phenomenon was investigated. We controlled the diameters and walls of the CNTs and minimized the amorphous carbon deposition on the CNTs for favorable bundling and spinning of the CNT fibers. The CNT fibers were fabricated with an as-grown vertically aligned CNT forest by a PECVD process using nanocatalyst an Al2O3 buffer layer, followed by a dry spinning process. Well-aligned CNT fibers were successfully manufactured using a dry spinning process and a surface tension-based densification process by ethanol. The mechanical properties were characterized for the CNT fibers spun from different lengths of a vertically aligned CNT forest. Highly oriented CNT fibers from the dry spinning process were characterized with high strength, high modulus, and high electrical as well as thermal conductivities for possible application as ultralight, highly strong structural materials. Examples of structural materials include space elevator cables, artificial muscle, and armor material, while multifunctional materials include E-textile, touch panels, biosensors, and super capacitors.     

Preparation, optimization, and characterization of topotecan loaded PEGylated liposomes using factorial design

This study reports the development of liposomal system for a potent antitumor drug, topotecan. To achieve this goal conventional and PEGylated liposomes were prepared according to a factorial design by hydration method followed by extrusion. Parameters such as type of lipid, percentage of cholesterol, percentage of phosphatidylglycerols, percentage of polyethylene glycol (PEG)-lipids, and drug to lipid molar ratio were considered as important factors for the optimizing the entrapment and retention of topotecan inside the liposomes. The size and zeta-potential of the PEGylated and conventional liposomes were measured by particle size analyzer and zeta-potentiometer, respectively. The stability and release characteristics of PEGylated liposome loaded topotecan were compared with conventional liposomes and free topotecan. The optimized PEGylated [distearoyl phosphatidylcholine (DSPC)/cholesterol/ distearoyl phosphatidylglycerol (DSPG)/ distearoyl phosphatidylethanolamine-PEG(2000) (DSPE-PEG(2000)); 7:7:3:1.28] and related conventional [DSPC/cholesterol/DSPG; 7:7:3] liposomes showed a narrow size distribution with a polydipersity index of 0.15 and 0.10, an average diameter of 103.0 +/- 13.1 and 95.2 +/- 11.10 nm, and with drug loading of 11.44 and 6.21%, respectively. Zeta-potential was -10 +/- 2.3 and -22 +/- 2.8 mV for PEGylated and conventional liposomes, respectively. The results of stability evaluation showed that the lactone ring of topotecan was notably preserved upon liposome encapsulation. PEGylated liposomes containing topotecan showed a significant decrease (P < 0.001) in release rate in comparison with conventional leptosomes. These results indicate the suitability of PEGylated liposomes in controlling topotecan release. The prepared liposomes (especially PEGylated liposomes) as those described here may be clinically useful to stabilize and deliver topotecan for the treatment of cancer.     

牛肌腱胶原纤维提取条件优化及其结构表征

以牛肌腱为原料,通过酸-酶结合法提取胶原纤维,比较不同时间、pH值、酶用量下的胶原纤维提取率以及可溶性胶原含量,从而得到提取胶原纤维最优工艺,并用SDS-PAGE电泳、DSC、IR、SEM、AFM对胶原纤维进行了结构表征.研究结果表明,在4℃下,酸-酶结合法水解的最佳条件为,时间40h、pH值为2.5、酶用量1.0％.该条件下所得胶原纤维提取率较高,红外特征峰明显,分子量大且分布窄,变性温度为66.7℃;SEM显示胶原纤维呈现孔隙均匀的三维网状结构,孔径约为100～300μm;AFM观察到胶原纤维以单根原纤维、纤维束等形式存在,明暗相间的横纹间距为60.35nm.综合认为制备得到了具有天然三股螺旋结构的胶原纤维.     

Carbon nanotube electron sources and applications

In this review we give an overview of the present status of research on carbon nanotube (CNT) field emitters and their applications. Several different construction principles of field-emission devices with CNTs are summarized. The emission mechanism is introduced and a detailed overview is given of the measured emission properties and related topics of CNT electron sources. We give also several examples of field-emission devices with CNT electron emitters that are presently being investigated in the academic world as well as in industry. Carbon nanotube electron sources clearly have interesting properties, such as low voltage operation, good stability, long lifetime and high brightness. The most promising applications are the field-emission display and high-resolution electron-beam instruments. But several hurdles remain, such as the manufacture of an electron source or an array of electron sources with exactly the desired properties in a reproducible manner.     

碳纳米管:可控制备决定未来（英文）

在过去几十年中,碳纳米管由于其优异的物理和化学性质而备受关注,被认为是一个强有力的未来明星材料.尽管基于碳纳米管的诸多产品及应用实例相继浮现,但是碳纳米管所呈现出的实际性质与理论值之间依然存在较大差异,无法达到研究者的预期,这源自于目前尚未成熟的控制制备技术.碳纳米管的可控制备技术包括结构的精细控制方法和样品的宏量制备技术,这在很大程度上决定了碳纳米管的未来发展前景.基于此,本文概述了近几十年来研究者们在碳纳米管的精细结构控制、聚合状态设计和样品宏量制备等方面的主要进展,进一步指出了碳纳米管未来的可控制备技术必须与特定化的应用紧密结合,以迎接即将来临的产业化时代.