超长碳纳米管的结构调控与制备：进展与挑战

碳纳米管由于其优异的性能和广泛的应用,在过去近三十年中引起了研究者广泛的研究兴趣。在众多不同类型的碳纳米管中,超长碳纳米管由于具有厘米级甚至分米级以上的宏观长度和相对完美的结构,展示出了优异的力学、电学、热学等多方面的优异性能,在透明显示、微电子产业、超强纤维、航空航天等领域具有广阔的应用前景。超长碳纳米管的结构控制制备是充分开发其优异性能并实现其实际应用的关键。在过去二十多年间,超长碳纳米管的研究取得了重要的进展。但同时,在结构控制与批量制备方面也面临巨大的挑战,还存在许多尚未解决的科学与技术难题,从而限制了其实际应用。本文对超长碳纳米管的生长机理、结构控制、选择性制备以及优异性能方面的进展及其背后的创新思想进行了系统的回顾;与此同时,讨论了超长碳纳米管近年来的研究进展、目前面临的挑战和未来的重点攻关方向。期望本文能为超长碳纳米管的可控合成、批量制备以及未来应用提供更多的启发和借鉴,为早日实现高质量超长碳纳米管的宏量制备和产业化起到一些推动作用。     

碳纳米管的宏量制备及产业化

作为纳米材料的代表之一,碳纳米管因其独特的一维结构具备了优异的力学、电学、热学、光学和反应性能,使其在能源存储与转化、复合材料、多相催化、环境保护及生物医药等领域具有大量的应用潜力.本文总结了多种类型碳纳米管宏量制备的化学及工程原理,并对多壁碳纳米管、单壁碳纳米管、双壁碳纳米管、定向碳纳米管、超顺排碳纳米管、水平超长碳纳米管、掺杂碳纳米管、螺旋碳纳米管、碳纳米管结及碳纳米管/石墨烯杂化物的宏量制备方法进行了评述.同时,对碳纳米管产业化中新的工程问题,如工业标准、环境评估以及产业化进展进行了分析.目前,碳纳米管已经具有成千吨的产能,并广泛应用于锂离子电池电极、导电复合材料、汽车配件和体育用品等领域.尽管如此,高性能的碳纳米管的宏量制备及其配套产业化技术仍有待深入开发,产品需要进一步丰富、市场需要进一步拓展,以望形成大规模纳米产业,促进社会的可持续发展.     

Novel conductive nanocomposites from perfluoropolyether waterborne polyurethanes and carbon nanotubes

The exceptional electrical conductivity of carbon nanotubes (CNTs) has been exploited for the preparation of conductive nanocomposites based on a large variety of insulating polymers. Among these, perfluoropolyether‐polyurethanes (PFPE‐PUs) represent a class of highly performing fluorinated materials with excellent water/oil repellency, chemical resistance, and substrate adhesion. The incorporation of highly conductive fillers to this class of highly performing materials allows them to be exploited in new technological and industrial fields where their unique properties need to be combined with the electrical conductivity or the electrostatic dissipation properties of carbon nanotubes. However, no studies have been presented so far on nanocomposites based on PFPE‐PUs and CNTs. In this work, polymer nanocomposites based on waterborne PFPE‐PUs and increasing amounts of carboxylated multiwall CNTs (COOH‐CNTs) were prepared and characterized for the first time. The effect of increasing concentration of COOH‐CNTs on the physical, mechanical, and surface properties of the nanocomposites was investigated by means of rheological measurements, dynamic mechanical analysis, thermal characterization, optical contact angle measurements, and scanning electron microscopy. In addition, electrical measurements showed that the highly insulating undoped PFPE‐PU system undergoes substantial modifications upon addition of COOH‐CNTs, leading to the formation of conductive nanocomposites with electrical conductivities as high as 1 S/cm. The results of this study demonstrate that the addition of COOH‐CNTs to PFPE‐PU systems represents a promising strategy to expand their possible use to technological applications where chemical stability, water/oil repellence and electrical conductivity are simultaneously required. Copyright © 2014 John Wiley & Sons, Ltd.     

Dielectrophoretically patterned carbon nanotubes to sort microparticles

This article compares the operation of a dielectrophoretic (DEP) platform before and after pattering carbon nanotubes (CNTs) between its microelectrodes. The diverse performance of the DEP system is assessed by separating 1 and 5 μm polystyrene particles. In the absence of CNTs, both particles can only be trapped by operating the system at low medium conductivities, (<10⁻³ S/m) and frequencies (<75 kHz). Alternatively, applying CNTs to the system, some CNTs coat the surface of particles and increase their overall conductivity and permittivity, whereas the rest of them are patterned between the microelectrodes and induce strong DEP forces at their free ends, which can effectively trap the coated particles. The first development extends the range of medium conductivities and frequencies at which the trapping of both particles is achievable, whereas the second development facilitates the selective deposition of particles along the surface of curved microelectrodes. Setting the medium conductivity to 2×10⁻³ S/m and the frequency to 20 MHz, most of 5 μm particles are trapped at the entry region of the first microelectrode pair, whereas most of 1 μm particles are trapped at the tips, and this distinction facilitates their separation. The trapping of 1 μm particles can be improved by decreasing the frequency to 1.5 MHz. This study demonstrates how the integration of CNTs into microfluidic systems enables them to operate beyond their capabilities.     

Parallelized continuous flow dielectrophoretic separation of DNA

Numerous microfluidic separation applications have been shown in the past years providing a fast analysis of biological samples like DNA or proteins. Microfluidic separation based on dielectrophoresis (DEP), that is the migration of a polarizable object in an inhomogeneous electric field, provides numerous advantages. However, the main drawback of DEP separation devices is that they are not sufficient for large-scale sample purification due to the lack of high sample throughput. In this work, we present for the first time a microfluidic device with two parallelized dielectrophoretic separations of (biological) samples smaller than 1 µm. The separation is carried out by means of insulator-based DEP, that is an insulating ridge reduced the flow through height and thus created a nanoslit at which the selective DEP forces occur. The device consists of a cross injector, two parallel operation regions and separate harvesting reservoirs where the samples are collected. Each DEP operation region contains an insulating ridge. We successfully demonstrate the separation of 100 and 40 nm beads and 10 and 5 kbp DNA with a separation purity of more than 80%. This states the proof-of-concept for up-scaling of dielectrophoretic separation by parallelization. As the present technique is virtually label-free, it offers a fast purification, for example in the production of gene vaccines.     

Nanographite impurities in carbon nanotubes: their influence on the oxidation of insulin, nitric oxide, and extracellular thiols

There has been growing interest in the use of modified-carbon-nanotube electrodes in applications such as the electrochemical detection of biologically significant compounds, owing to their apparent "electrocatalytic" properties and ability to enhance oxidative signals. In spite of their salient properties, little work has been done to further examine the reasons for these reported characteristics. In this report, we present clear evidence that the presence of nanographite impurities within carbon nanotubes (CNTs) is responsible for providing the previously reported enhanced electrochemical response. We have demonstrated this effect on homocysteine, N-acetyl-L-cysteine, nitric oxide, and insulin, which are important biological agents in the body. Moreover, we also showed that the influence of nanographite impurities on the electrochemistry of carbon nanotubes is prevalent among a variety of CNTs, such as single-walled CNTs, double-walled CNTs, and few-walled CNTs. Our findings will have a profound influence upon the biomedical applications of CNTs.     

Application of carbon nanotubes in extraction and chromatographic analysis: A review

Carbon nanotube (CNT), a well-known carbon-based nanomaterial has drawn much attention in many application fields including chemistry in the last few decades. Many researchers and scientists have shown huge interest to improve the extraction methodologies and adopt their applications in combination with chromatography technique. With respect to this, the exceptional applications of CNTs have been introduced as extraction sorbent due to their excellent inborn physical and chemical properties. In particular, CNTs have consistently been used as adsorbents in various techniques including solid-phase micro-extraction, solid-phase extraction, micro dispersive slid phase extraction, magnetic dispersive solid phase extraction, analytes enrichment, sample fractionation and clean-up as well as support for many derivatization reactions. Many research papers have discussed the successful use of CNTs to overcome the limitations of the extraction techniques due to their excellent sorbent capacity. In addition, considering the clear need to make chromatographic technique more successful, the applications of CNTs have been reported in the literatures in details as stationary and pseudo-stationary phases for the separation and extraction of challenging compounds. Because of the higher thermal and chemical stability, CNTs have been anticipated as stationary phase modifier for chromatographic applications to avoid bleeding of the columns and enable the analysis even at very high temperature (1200 °C). In liquid chromatography CNTs have primarily been used in combination with other packing materials (silica) and sometimes incorporated in a porous polymeric monolith. Therefore, the recent utilizations of CNTs as extraction materials and stationary phases have been illustrated in the current review and a table listing the details applications of CNTs in aforementioned field is provided as well. We believe that the review will help researcher to gain vast knowledge about application of carbon nanotubes in the field of separation chemistry.     

高温退火一步非破坏性纯化碳纳米管

针对催化化学气相法合成的碳纳米管含有金属、金属氧化物和碳杂质, 且缺陷较多进行了非破坏性纯化研究. 基于碳纳米管与碳杂质间结构、性质的微小差异, 1800 ℃使粗制的碳纳米管高温退火3 h, 为避免碳纳米管氧化, 高温退火过程在氩气气氛中完成. 运用扫描电镜、透射电镜观察碳纳米管的形貌和结构, 发现高温退火后, 碳纳米管的端帽大部分被打开. 能谱检测显示, 粗制的碳纳米管中的杂质(Al, Si, Ni, Cu 质量分数w分别为4.67%, 0.27%, 40.12%和1.34%)退火后被除去. 拉曼分析表明, 退火前后石墨D, G峰面积S_D, S_G分别从1314900降至474921, 767157降至566292, 退火不仅有效地去除了样品中的碳杂质, 而且使碳纳米管的缺陷得到一定程度的修复, 石墨化度随之大大提高. 研究提出了一种简单的、非破坏性的、便于规模化的纯化方法.     

新型碳纳米管色谱固定相制备的研究进展

碳纳米管（CNTs）作为一种新型的功能材料,具有优异的物理、化学和机械性能,已经在分析化学领域得到了广泛的关注和应用。通过填充法或原位化学气相沉积法,可制备CNTs气相色谱固定相;将CNTs沉积在硅胶微球或有机聚合物基质微球表面,可制备填充式CNTs液相色谱固定相;通过包埋共聚法将CNTs嵌入聚合物整体柱内,可制备毛细管CNTs液相色谱整体柱。本文主要综述了近年来CNTs（单壁碳纳米管和多壁碳纳米管）用于色谱固定相制备的研究现状,包括气相色谱及液相色谱,并对该领域今后的发展进行展望。     

Dielectrophoretic separation of micron and submicron particles: A review

This paper provides an overview on separation of micron and submicron sized biological (cells, yeast, virus, bacteria, etc.) and nonbiological particles (latex, polystyrene, CNTs, metals, etc.) by dielectrophoresis (DEP), which finds wide applications in the field of medical and environmental science. Mathematical models to predict the electric field, flow profile, and concentration profiles of the particles under the influence of DEP force have also been covered in this review. In addition, advancements made primarily in the last decade, in the area of electrode design (shape and arrangement), new materials for electrode (carbon, silicon, polymers), and geometry of the microdevice, for efficient DEP separation of particles have been highlighted.     

Tuning periodicity of polymer-decorated carbon nanotubes

Carbon nanotube (CNT) is one of the most extensively investigated nanomaterials. Patterning soft matter such as liquid crystals and polymers on CNTs could potentially enable various applications for CNTs. We have demonstrated that controlled polymer crystallization using CNTs as the 1D nucleation sites can lead to periodically functionalized CNTs. Here we show that selected crystalline block copolymers can be periodically decorated along CNTs. This facile technique opens a gateway to periodic patterning on 1-D nanomaterials.     

碳纳米管对羟基磷灰石基复合材料力学性能的影响

将力学性能优良的碳纳米管(CNTs)与羟基磷灰石(HA)生物陶瓷相复合,发展CNTs/HA复合材料来应用于骨组织修复领域,有望解决HA生物陶瓷力学性能的不足.通过3种不同的制备方法,即通过表面活性剂将CNTs分散在HA基体中、通过酸碱中和反应将CNTs与HA共沉淀以及通过体外浸泡在CNTs上矿化生长HA等方法来获得CNTs/HA复合材料.深入研究CNTs的表面结构和分散状态对CNTs/HA复合材料力学性能的影响.结果表明,CNTs的添加改变了HA的脆性,导致复合材料抗压力学性能得到提高.但是,由于复合材料制备方法的不同,导致CNTs在HA基体中的分散状态、表面结构的完整性以及与HA的界面结合情况不同,导致其抗压力学性能不同.其中,通过表面活性剂将CNTs分散在HA基体中而获得复合材料的抗压力学性能表现最好,而CNTs与HA通过共沉淀法所获得复合材料的抗压力学性能表现最差.     

Functionalized carbon nanotubes and nanofibers for biosensing applications

This review summarizes recent advances in electrochemical biosensors based on carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with an emphasis on applications of CNTs. CNTs and CNFs have unique electric, electrocatalytic and mechanical properties, which make them efficient materials for developing electrochemical biosensors.We discuss functionalizing CNTs for biosensors. We review electrochemical biosensors based on CNTs and their various applications (e.g., measurement of small biological molecules and environmental pollutants, detection of DNA, and immunosensing of disease biomarkers). Moreover, we outline the development of electrochemical biosensors based on CNFs and their applications. Finally, we discuss some future applications of CNTs.     

碳纳米管可控制备的过去、现在和未来

碳纳米管独特的几何和电子结构使其具有丰富优异的性质,因此在过去的二十余年备受研究者的关注。然而,碳纳米管结构的多样性成为其从实验室走到产业化的最大阻碍,结构决定性质,制备决定未来,完善的结构控制制备技术将成为碳纳米管基础研究和产业化应用中至关重要的一环。本文首先对碳纳米管的结构进行描述,然后综述了碳纳米管的结构可控制备方法和溶液纯化分离技术,提出未来理想的碳纳米管制备之路是将碳纳米管精细结构控制方法与宏量制备技术相结合,在降低碳纳米管生产成本的同时,提高其纯度,并建立碳纳米管产品的标准。最后,展望了碳纳米管的杀手锏级应用和该领域的机遇和挑战。     

碳纳米管对羟基磷灰石基复合材料力学性能的影响

将力学性能优良的碳纳米管(CNTs)与羟基磷灰石(HA)生物陶瓷相复合,发展CNTs/HA复合材料来应用于骨组织修复领域,有望解决HA生物陶瓷力学性能的不足。通过3种不同的制备方法,即通过表面活性剂将CNTs分散在HA基体中、通过酸碱中和反应将CNTs与HA共沉淀以及通过体外浸泡在CNTs上矿化生长HA等方法来获得CNTs/HA复合材料。深入研究CNTs的表面结构和分散状态对CNTs/HA复合材料力学性能的影响。结果表明,CNTs的添加改变了HA的脆性,导致复合材料抗压力学性能得到提高。但是,由于复合材料制备方法的不同,导致CNTs在HA基体中的分散状态、表面结构的完整性以及与HA的界面结合情况不同,导致其抗压力学性能不同。其中,通过表面活性剂将CNTs分散在HA基体中而获得复合材料的抗压力学性能表现最好,而CNTs与HA通过共沉淀法所获得复合材料的抗压力学性能表现最差。     

Effect of nano‐size nodular structure induced by CNT‐promoted phase separation on the fabrication of superhydrophobic polyvinyl chloride films

The nonsolvent‐induced phase separation (NIPS) method was employed to fabricate the porous films based on polyvinyl chloride loaded with carbon nanotubes (CNTs). The combinational addition of CNTs and a proper nonsolvent (ethanol) resulted in a porous surface layer with the nano‐size nodular structure possessing an exact superhydrophobic behavior (water contact angle [WCA] = 157° and sliding angle [SA] <5°). The size of PVC nodules at the surface layer varies in the range of 200 to 800 nm depending on the nonsolvent concentrations, and polymer molecular weight. The effects of various nonsolvent concentrations as well as PVC molecular weight on the surface properties of the films were also investigated. Morphological and roughness analyses revealed the pronounced role of PVC molecular weight on the size of nodules, and the structural uniformity of the surface morphology based on the thermodynamic parameters such as relaxation time and dynamic of polymer chains. The concurrent use of CNTs and nonsolvent led to promote the NIPS process due to the nucleating role of CNTs, which were localized within the polymer‐rich phase leading to an ultra‐fine and packed nodular surface structure. Transmission electron microscopy results also proved the very well dispersion quality of CNTs. Glass transition temperature of PVC was also assessed, and the results were correlated to the associating ability of CNTs with polymer chains during the phase separation process. Overall, the promising potential of CNT/ethanol combination on the surface porosity and hydrophobicity of PVC nanocomposite films was revealed in this study, which could further extend its application window.     

Bismaleimide/carbon nanotube hybrids for potential aerospace application: I. Static and dynamic mechanical properties

Two kinds of hybrids based on diallyl bisphenol A modified bismaleimide (BMI‐BA) and carbon nanotubes (CNTs) or aminated carbon nanotubes (A‐CNTs) were prepared, their static and dynamic mechanical properties were investigated in detail by using impact and flexural measurements as well as dynamic mechanical analysis (DMA). Results show that these mechanical properties of hybrids greatly depended on the nature (or the functional groups on CNTs) and loading in BMI‐BA matrix of hybrids. For example, the BMI‐BA/A‐CNT hybrid with a desirable amount of A‐CNTs has a higher impact strength than the original BMI‐BA resin, while all BMI‐BA/CNT hybrids have lower impact strength than the original BMI‐BA resin. DMA test shows that all hybrids have somewhat lower storage modulus and glass transition temperature than a pure polymer, which maybe attributed to the fact that both CNTs and A‐CNTs shift the curing peak to a higher temperature range and thus decrease the crosslinking density of networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Probing the Electronic Effect of Carbon Nanotubes in Catalysis: NH3 Synthesis with Ru Nanoparticles

Carbon nanotubes (CNTs) have been shown to modify some properties of nanomaterials and to modify chemical reactions confined inside their channels, which are formed by curved graphene layers. Here we studied ammonia synthesis over Ru as a probe reaction to understand the effect of the electron structure of CNTs on the confined metal particles and their catalytic activity. The catalyst with Ru nanoparticles dispersed almost exclusively on the exterior nanotube surface exhibits a higher activity than the CNT‐confined Ru, although both have a similar metal particle size. Characterization with TEM, N₂ physisorption, H₂ chemisorption, temperature‐programmed reduction, CO adsorption microcalorimetry, and first‐principles calculations suggests that the outside Ru exhibits a higher electron density than the inside Ru. As a result, the dissociative adsorption of N₂, which is an electrophilic process and the rate‐determining step of ammonia synthesis, is more facile over the outside Ru than that over the inside one.     

A review of dielectrophoretic separation and classification of non-biological particles

Dielectrophoresis (DEP) is a selective electrokinetic particle manipulation technology that is applied for almost 100 years and currently finds most applications in biomedical research using microfluidic devices operating at moderate to low throughput. This paper reviews DEP separators capable of high-throughput operation and research addressing separation and analysis of non-biological particle systems. Apart from discussing particle polarization mechanisms, this review summarizes the early applications of DEP for dielectric sorting of minerals and lists contemporary applications in solid/liquid, liquid/liquid, and solid/air separation, for example, DEP filtration or airborne fiber length classification; the review also summarizes developments in DEP fouling suppression, gives a brief overview of electrocoalescence and addresses current problems in high-throughput DEP separation. We aim to provide inspiration for DEP application schemes outside of the biomedical sector, for example, for the recovery of precious metal from scrap or for extraction of metal from low-grade ore.     

Carbon nanotubes,science and technology part (I) structure,synthesis and characterisation

Since their discovery in 1991 by the Japanese scientist “Sumio Iijima”, carbon nanotubes have been of great interest, both from a fundamental point of view and for future applications. Different types of carbon nanotubes can be produced in various ways. Economically feasible large-scale production and purification techniques are still under development. Carbon nanotubes are discussed in this review in terms of history, types, structure, synthesis and characterisation methods. Carbon nanotubes have attracted the fancy of many scientists worldwide. The unique and unusual properties of these structures make them a unique material with a whole range of promising applications.