Ionotronics Based on Horizontally Aligned Carbon Nanotubes

Controlled ion transport through ion channels of cell membranes regulates signal transduction processes in biological systems and has also inspired the thriving development of ionic electronics (ionotronics or iontronics) and biocomputing. However, for constructing highly integrated ionic electronic circuits, the integration of natural membrane‐spanning ion channel proteins or artificial nanomembrane‐based ionic diodes into planar chips is still challenging due to the vertically arranged architecture of conventional nanomembrane‐based artificial ionic diodes. Here, a new design of ionic diode is reported, which allows chip‐scale integration of ionotronics, based on horizontally aligned nanochannels made from multiwalled carbon nanotubes (MWCNTs). The rectification of ion transport through the MWCNT nanochannels is enabled by decoration of oppositely charged polyelectrolytes on the channel entrances. Advanced ionic electronic circuits including ionic logic gates, ionic current rectifiers, and ionic bipolar junction transistors (IBJT) are demonstrated on planar nanofluidic chips by stacking a series of ionic diodes fabricated from the same bundles of MWCNTs. The horizontal arrangement and facile chip‐scale fabrication of the MWCNT ionic diodes may enable new designs of complex but monolithic ionotronic systems. The MWCNT ionic diode may also prove to be an excellent platform for investigation of electrokinetic ion transport in 1D carbon materials.     

Bifunctional Carbon Nanotubes by Sidewall Protection

A vertically aligned array of multiwalled carbon nanotubes (MWCNTs) impregnated with polystyrene is utilized to independently functionalize each end of the MWCNTs. The presence of the polystyrene matrix prevents sidewall oxidation of the CNTs, resulting in carboxylate derivatization at the CNT tips during processing via plasma oxidation. The membrane is subsequently dissolved in toluene, resulting in a suspension of CNTs with carboxylate‐derivatized tips. The CNT tips are further functionalized using carbodiimide‐mediated linking of carboxylate at the CNT tips with an amine of 2‐aminoethanethiol. This treatment results in thiol functionality and Fourier‐transform infrared (FT‐IR) studies confirm amide‐bond formation. Gold nanoparticles that are readily observed using transmisison electron microscopy (TEM) are then covalently linked to the thiol functional groups. Estimates of the average nanoparticle density are observed to decrease from ～ 526 particles μm^–1 near the CNT tips to negligible values (< 7 particles μm^–1) at locations beyond 700 nm from the CNT tips. This is consistent with a membrane geometry where CNTs tips are above the polystyrene surface owing to differing oxidation rates. Bifunctional CNTs (with different chemical functionality at either end of each CNT) is achieved by thiol functionalization on only one side of the oxidized CNT membrane floating on top of a 2‐aminoethanethiol functionalization reaction solution. After dissolution of the polystyrene matrix, TEM analysis shows gold‐nanoparticle decoration at the thiol‐functionalized end of the CNT.     

碳纳米管的制备、修饰及其应用

简要介绍了碳纳米管的制备及其纯化技术，以及近年来碳纳米管修饰、管内填充方面的研究，并概述了碳纳米管在复合材料、发光材料、纳米器件方面的应用及其在固体基片上的定向组装。     

Multiwalled Carbon Nanotubes Induced Hypotension by Regulating the Central Nervous System

Cardiovascular disease is the leading cause of death worldwide. Normal blood pressure is very important for overall well‐being and unexpected decrease in blood pressure may cause many detrimental consequences. The attractive properties of multiwalled carbon nanotubes (MWCNTs) entice their usage in many cutting edge brain‐specific therapies. However, the effects of MWCNTs to the central nervous system are not fully understood. In this work, the authors report that carbon nanotubes can significantly cause blood pressure to fall down when introduced into the brain at very low dosage. It is found that MWCNTs induce increased expression of neuronal nitric oxide synthase in the medulla cardiovascular center, which consequently attenuate sympathetic nerve activity and cause decrease in blood pressure and heart rate. In addition, MWCNTs promote acetylation and nuclear translocation of nuclear factor‐κB in brain cells. This work illustrates how CNTs can potentially change blood pressure by interrupting the central nervous system and is significant to the biomedical applications of CNTs.     

Platinum Nanoparticle Clusters Immobilized on Multiwalled Carbon Nanotubes: Electrodeposition and Enhanced Electrocatalytic Activity for Methanol Oxidation

3D flowerlike Pt nanoparticle clusters are electrodeposited onto multiwalled carbon nanotubes (MWCNTs) by using a three‐step protocol, which is all‐electrochemical and involves a key, second step of a potential pulse sequence. This 3D fractal morphology is in marked contrast to the 2D uniform nanoparticle dispersion of MWCNTs, which is achieved when the second step adopts cyclic voltammetry instead of a potential‐step method. The former is found to exhibit significantly higher electrocatalytic activity and better stability than the latter for oxidation of methanol. These attractive features are attributable to the unique 3D flowerlike structure of Pt nanoparticle clusters on MWCNTs with much higher electrochemically active surface areas. Our work points to a new path for the preparation of 3D Pt/MWCNT nanocomposites, which are promising as electrocatalysts in direct methanol fuel cells.     

粒子轰击对碳纳米管微结构和场发射性能的影响

研究了粒子轰击对碳纳米管膜微结构和场电子发射性能的影响。研究结果表明．采用多种等离子体处理碳纳米管能改变其微结构．并显著提高场发射点密度．从而改善场发射性能。随着粒子轰击时间的延长,发射电流先降低,然后又增加甚至超过原始碳纳米管膜的发射电流。我们认为发射性能的变化归功于不同的发射机理：粒子轰击处理后．电子由纳米管尖端发射逐渐变为主要从管体上的纳米瘤发射,致使发射点密度显著增加。     

On the Synthesis of Carbon Nanofibers and Nanotubes by Microwave Irradiation: Parameters,Catalysts, and Substrates

The microwave (MW)‐assisted synthesis of one dimensional carbon systems is introduced as a promising approach to improve the speed and cost‐effectiveness of the fabrication process. Improved reaction conditions are generated by direct MW heating and synthesis under advanced reaction conditions. The influence of the reaction conditions is investigated and the importance of individual process parameters on the synthesis is discussed. Temperature and pressure data recorded during the irradiation process are analyzed in detail and allow the determination of essential process parameters. This leads to improved reaction conditions, better control of the one‐dimensional carbon nanosystems by tuning the catalyst materials, and allows expanding this approach to initiate the synthesis on a variety of different substrates, such as quartz glass and mica.     

Hydroxyapatite Modified with Carbon‐Nanotube‐Reinforced Poly(methyl methacrylate): A Nanocomposite Material for Biomedical Applications

The paper reports on a freeze‐granulation technique to prepare a novel nanocomposite of poly(methyl methacrylate) (PMMA)‐modified hydroxyapatite (HA) with multiwalled carbon nanotubes (MWCNTs) as reinforcement for a new generation biomedical bone cement and implant coatings. By using this technique it is possible to increase material homogeneity and also enhance the dispersion of MWCNTs in the composite matrix. The phase composition and the surface morphology of the nanocomposite material were studied using X‐ray diffraction, field‐emission scanning electron microscopy, and micro‐Raman spectroscopy. Additionally, nanomechanical properties of different concentrations of MWCNT‐reinforced nanocomposite were performed by a nanoindentation technique, which indicates that a concentration of 0.1 wt % MWCNTs in the PMMA/HA nanocomposite material gives the best mechanical properties.     

Preparation,Characterization, and Application of L‐Cysteine Functionalized Multiwalled Carbon Nanotubes as a Selective Sorbent for Separation and Preconcentration of Heavy Metals

L ‐cysteine functionalized multi‐walled carbon nanotubes (MWCNTs‐cysteine) are synthesized and characterized by XPS, FT‐IR, XRD, and TEM. The capability of MWCNTs‐cysteine for selective separation and preconcentration of heavy metal ions are statically and dynamically evaluated with Cd²⁺ as a model heavy metal ion. Unlike MWCNTs, the sorption of Cd²⁺ onto MWCNTs‐cysteine is not influenced by ionic strength in a wide range. The MWCNTs‐cysteine is demonstrated to be good column packings for on‐line microcolumn separation and preconcentration of Cd²⁺. Effective preconcentration of Cd²⁺ on the MWCNTs‐cysteine packed microcolumn is achieved in a pH range of 5.5 to 8.0. The retained Cd²⁺ is efficiently eluted with 0.5 mol L^?1 HCl for on‐line flame atomic absorption spectrometric determination. The MWCNTs‐cysteine exhibit fairly fast kinetics for the adsorption of Cd²⁺, and offer up to 1600‐fold improvement of the tolerable concentrations of co‐existing metal ions over the MWCNTs for on‐line solid‐phase extraction of Cd²⁺. With a preconcentration time of 60 s at a sample loading flow rate of 5.0 mL min^?1, an enhancement factor of 33 and a sample throughput of 36 h^?1 along with a detection limit (3s) of 0.28 µg L^?1 are obtained. The precision (RSD) for 11 replicate measurements is 1.6% at the 10 µg L^?1 level. The developed method using the MWCNTs‐cysteine as sorbent is successfully applied to determination of trace cadmium in a variety of biological and environmental materials.     

碳纳米管制备及其生长机制研究

采用乙醇催化燃烧法，以钴盐作为催化剂先体、薄铜片作为基底制备碳纳米管。分别以氯化钴、硝酸钴和硫酸钴作为催化剂先体，研究了不同催化剂先体对碳纳米管生长的影响；利用扫描电镜，透射电镜对碳纳米材料的形貌和结构进行了表征，研究了不同钴盐的催化剂先体对碳纳米管形态与结构的影响，讨论了碳纳米管的生长机制。实验发现，其他制备条件相同，当催化剂先体为氯化钴时，碳纳米管与大量絮状杂质缠绕在一起；当催化剂先体为硝酸钴时，碳纳米管容易形成弯曲、不规则的波浪形结构；而当催化剂先体为硫酸钴时，实验所得的碳纳米材料几乎全为取向规则、直径均一的碳纳米纤维，只观察到少量碳纳米管。     

碳纳米管制备及其生长机制研究

采用乙醇催化燃烧法,以钴盐作为催化剂先体、薄铜片作为基底制备碳纳米管。分别以氯化钴、硝酸钴和硫酸钴作为催化剂先体,研究了不同催化剂先体对碳纳米管生长的影响;利用扫描电镜,透射电镜对碳纳米材料的形貌和结构进行了表征,研究了不同钴盐的催化剂先体对碳纳米管形态与结构的影响,讨论了碳纳米管的生长机制。实验发现,其他制备条件相同,当催化剂先体为氯化钴时,碳纳米管与大量絮状杂质缠绕在一起;当催化剂先体为硝酸钴时,碳纳米管容易形成弯曲、不规则的波浪形结构;而当催化剂先体为硫酸钴时,实验所得的碳纳米材料几乎全为取向规则、直径均一的碳纳米纤维,只观察到少量碳纳米管。     

Luminescence of Functionalized Carbon Nanotubes as a Tool to Monitor Bundle Formation and Dissociation in Water: The Effect of Plasmid‐DNA Complexation

Functionalized carbon nanotubes (f‐CNTs) are explored as novel nanomaterials for biomedical applications. UV‐vis luminescence of aqueous dispersions of CNT–NH₃⁺ and CNT–NH–Ac (NH–Ac: acetamido) is observed using standard laboratory spectrophotometric instrumentation, and the measured fluorescence intensity is correlated with the aggregation state of the f‐CNTs: a high intensity indicates improved f‐CNT individualization and dispersion, while a decrease in fluorescence intensity indicates a higher degree of nanotube aggregation and bundling as a result of varying the sodium dodecyl sulfate (SDS) concentrations and pH in the aqueous phase. Moreover, utilization of this relationship between fluorescence intensity and the state of f‐CNT aggregation is carried out to elucidate the interactions between f‐CNTs and gene‐encoding plasmid DNA (pDNA). pDNA is shown to interact with CNT–NH₃⁺ primarily through electrostatic interactions that lead concomitantly to a higher degree of f‐CNT bundling. The CNT–NH₃⁺/pDNA interactions are successfully competed by SDS/f‐CNT surface interactions, resulting in the displacement of pDNA. These studies provide exemplification of the use of fluorescence spectrophotometry to accurately describe the aggregation state of water‐soluble f‐CNTs. Characterization of the complexes between pDNA and f‐CNTs elucidates the opportunities and limitations of such supramolecular systems as potential vectors for gene transfer.     

Preparation of Short Carbon Nanotubes and Application as an Electrode Material in Li‐Ion Batteries

A new approach is developed for cutting conventional micrometer‐long entangled carbon nanotubes (CNTs) to short ca. 200 nm long segments with excellent dispersion. CNTs with different lengths are used as anode materials in Li‐ion batteries. The reversible capacity of the Li‐ion batteries is increased and the irreversible capacity is decreased upon shortening the length of the CNTs. The reason for this is that the insertion/extraction of Li ions is easier into/from short CNTs as compared to long CNTs because of the shortened length and the presence of lateral defects. Moreover, short CNTs have a lower electrical resistance and Warburg prefactor, resulting in better rate performance at high current densities. The present study suggests that short segments of CNTs obtained by cutting long CNTs may possess novel properties that may be useful for a wide variety of applications.     

In Situ Growth of Mesoporous SnO2 on Multiwalled Carbon Nanotubes: A Novel Composite with Porous‐Tube Structure as Anode for Lithium Batteries

A novel mesoporous‐nanotube hybrid composite, namely mesoporous tin dioxide (SnO₂) overlaying on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesoporous SnO₂ on the surface of MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure‐directing agents. Nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analysis techniques were used to characterize the samples. It was observed that a thin layer tetragonal SnO₂ with a disordered porous was embedded on the surface of MWCNTs, which resulted in the formation of a novel mesoporous‐nanotube hybrid composite. On the base of TEM analysis of products from controlled experiment, a possible mechanism was proposed to explain the formation of the mesoporous‐nanotube structure. The electrochemical properties of the samples as anode materials for lithium batteries were studied by cyclic voltammograms and Galvanostatic method. Results showed that the mesoporous‐tube hybrid composites displayed higher capacity and better cycle performance in comparison with the mesoporous tin dioxide. It was concluded that such a large improvement of electrochemical performance within the hybrid composites may in general be related to mesoporous‐tube structure that possess properties such as one‐dimensional hollow structure, high‐strength with flexibility, excellent electric conductivity and large surface area.     

Degradable Conjugated Polymers: Synthesis and Applications in Enrichment of Semiconducting Single‐Walled Carbon Nanotubes

Polymers which enrich semiconducting single‐walled carbon nanotubes (SWNTs) and are also removable after enrichment are highly desirable for achieving high‐performance field‐effect transistors (FETs). We have designed and synthesized a new class of alternating copolymers containing main‐chain fluorene and hydrofluoric acid (HF) degradable disilane for sorting and preferentially suspending semiconducting nanotube species. The results of optical absorbance, photoluminescence emission, and resonant Raman scattering show that poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐co‐1,1,2,2‐tetramethyl‐disilane] preferentially suspends semiconducting nanotubes with larger chiral angle (25°–28°) and larger diameter (1.03 nm–1.17 nm) (specifically (8,7), (9,7) and (9,8) species) present in HiPCO nanotube samples. Computer simulation shows that P1 preferentially interacts with (8,7) (semiconducting) over (7,7) (metallic) species, confirming that P1 selects larger diameter, larger chiral angle semiconducting tubes. P1 wrapped on the surface of SWNTs is easily washed off through degradation of the disilane bond of the alternating polymer main chain in HF, yielding “clean” purified SWNTs. We have applied the semiconducting species enriched SWNTs to prepare solution‐processed FET devices with random nanotube network active channels. The devices exhibit stable p‐type semiconductor behavior in air with very promising characteristics. The on/off current ratio reaches up to 15 000, with on‐current level of around 10 μA and estimated hole mobility of 5.2 cm² V^?1 s^?1.     

碳纳米管冷阴极材料制备及其场发射性能研究

在场发射显示器技术领域,碳纳米管被认为是目前最有前途的场发射冷阴极材料之一。碳纳米管具有低的场发射阈值电场,高的发射电流密度使它们比传统的热阴极材料以及其他的场发射冷阴极材料更适于实际的技术应用。介绍了碳纳米管的制备方法和场发射原理,并对碳纳米管的场发射性能研究进行了综合的评述。     

碳纳米管在微机电系统(MEMS)中的应用研究

碳纳米管研究的不断发展为其与微机电系统(MEMS)的结合提供了可能,这种结合“Top—down”与“Bottom—up”的方法是微米／纳米技术的一个发展趋势。介绍了碳纳米管的特性及其在MEMS上的潜在应用,综述了碳纳米管的制备方法以及与MEMS技术的兼容性,列举了目前一些碳纳米管与MEMS结合研究的典型,并对其发展趋势进行了分析。     

催化剂组分对制取单壁碳纳米管的影响

采用温控电弧炉,以FeS,Ni,Mg的混和粉末作为催化剂,起弧电压为32V,放电时间为10min;研究了催化剂组成与成分对制取单壁碳纳米管的影响,确定了优化参数。在环境温度为600℃时,起弧电流为100A,催化剂FeS/Ni/Mg的组成和成分含量分别为2∶1∶2(%),5%,氦气气氛,气氛真空度为5.7×104Pa,单壁碳纳米管的产量和纯度都分别达到了12g/h和70%上,其管径为1.24～1.36nm。     

钯膜上CVD法制备碳纳米管薄膜的研究

采用化学气相沉积法,以乙炔为碳源,在各种钯膜上制备了碳纳米管薄膜。通过电子显微镜观察了碳管薄膜和钯膜的表面形貌。结果表明,在真空气氛下磁控溅射的钯膜上无法生长碳纳米管。对溅射的钯膜进行大气气氛下的退火处理,则可生长出稀疏的碳纳米管团聚颗粒。采用在氧气气氛下磁控溅射的钯膜作为催化剂,则可显著提高碳管的生长密度和纯度,从而获得致密均匀的碳纳米管薄膜。     

Carbon Nanotubes: High Electromechanical Response of Ionic Polymer Actuators with Controlled‐Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes (Adv. Funct. Mater. 19/2010)

Recent advances in fabricating controlled‐morphology vertically aligned carbon nanotubes (VA‐CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter‐VA‐CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA‐CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA‐CNTs to further enhanced performance.