Hyperporous Sponge Interconnected by Hierarchical Carbon Nanotubes as a High‐Performance Potassium‐Ion Battery Anode

Recently, commercial graphite and other carbon‐based materials have shown promising properties as the anode for potassium‐ion batteries. A fundamental problem related to those carbon electrodes, significant volume expansion, and structural instability/collapsing caused by cyclic K‐ion intercalation, remains unsolved and severely limits further development and applications of K‐ion batteries. Here, a multiwalled hierarchical carbon nanotube (HCNT) is reported to address the issue, and a reversible specific capacity of 232 mAh g^?1, excellent rate capability, and cycling stability for 500 cycles are achieved. The key structure of the HCNTs consists of an inner CNT with dense‐stacked graphitic walls and a loose‐stacked outer CNT with more disordered walls, and individual HCNTs are further interconnected into a hyperporous bulk sponge with huge macropore volume, high conductivity, and tunable modulus. It is discovered that the inner dense‐CNT serves as a robust skeleton, and collectively, the outer loose‐CNT is beneficial for K‐ion accommodation; meanwhile the hyperporous sponge facilitates reaction kinetics and offers stable surface capacitive behavior. The hierarchical carbon nanotube structure has great potential in developing high‐performance and stable‐structure electrodes for next generation K and other metal‐ion batteries.     

Carbon nanotube grafted carbon fibres: A study of wetting and fibre fragmentation

Carbon nanotubes (CNTs) were grafted on IM7 carbon fibres using a chemical vapour deposition method. The overall grafting process resulted in a threefold increase of the BET surface area compared to the original primary carbon fibres (0.57 m²/g). At the same time, there was a degradation of fibre tensile strength by around 15% (depending on gauge length), due to the dissolution of iron catalyst into the carbon; the modulus was not significantly affected. The wetting behaviour between fibres and poly(methyl methacrylate) (PMMA) was directly quantified using contact angle measurements for drop-on-fibre systems and indicated good wettability. Single fibre fragmentation tests were conducted on hierarchical fibre/PMMA model composites, demonstrating a significant (26%) improvement of the apparent interfacial shear strength (IFSS) over the baseline composites. The result is associated with improved stress transfer between the carbon fibres and surrounding matrix, through the grafted CNT layer. The improved IFSS was found to correlate directly with a reduced contact angle between fibre and matrix.     

Self‐Expansion Construction of Ultralight Carbon Nanotube Aerogels with a 3D and Hierarchical Cellular Structure

A novel and simple strategy is developed to construct ultralight and 3D pure carbon nanotube (CNT) aerogels by the spontaneous expansion of superaligned CNT films soaked in a piranha (mixed H₂SO₄ and H₂O₂) solution, followed by cryodesiccation. The macroscopic CNT aerogels have an extremely low apparent density (0.12 mg cm^?3), ultrahigh porosity (99.95%), high specific surface area (298 m² g^?1), and a hierarchical cellular structure with giant and ultrathin CNT sheets as cell walls. The pure CNT aerogels show high adsorption abilities for various kinds of solvents, and have great potential in widespread applications such as energy storage, catalysis, and bioengineering.     

The Application of Carbon Nanotube/Graphene‐Based Nanomaterials in Wastewater Treatment

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene‐based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene‐based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT‐ and graphene‐based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure–property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT‐ and graphene‐based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.     

碳纳米管光致电流的机理探究

将碳纳米管长丝搭接在两个电极之间,在光照情况下,测量了不同照射位置和不同偏压下的电流变化,探索碳纳米管光致电流的机理。光致电流的产生机理分为两步:一是碳纳米管内部的肖特基结在光照情况下光生载流子的产生;二是在自身的扩散和外加电场的作用下光生载流子的运动。     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Monodisperse CNT Microspheres for High Permeability and Efficiency Flow‐Through Filtration Applications

Carbon nanotube (CNT)‐based filters have the potential to revolutionize water treatment because of their high capacity and fast kinetics in sorption of organic, inorganic, and biological pollutants. To date, CNT filters either rely on CNTs dispersed in liquids, which are difficult to recover and cause safety concerns, or on CNT buckypaper, which offers high efficiency, but suffers from an intrinsic trade‐off between filter permeability and capacity. Here, a new approach is presented that bypasses this trade‐off and achieves buckypaper‐like efficiency combined with filter‐column‐like permeability and capacity. For this, CNTs are first assembled into porous microspheres and then are packed into microfluidic column filters. These microcolumns exhibit large flow‐through filtration efficiencies, while maintaining membrane permeabilities an order of magnitude larger then CNT buckypaper and specific permeabilities double that of activated carbon for similar flowrates (232 000 L m^?2 h^?1 bar^?1, 1.23 × 10^?12 m²). Moreover, in a test to remove sodium dodecyl sulfate (SDS) from water, these microstructured CNT columns outperform activated carbon columns. This improved filtration efficiency and permeability is an important step toward a broader implementation of CNT‐based filtration devices.     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

The paper is concerned with the surface chemistry of several different carbon fibres subjected to various surface treatments. The microstructure and nanostructures of these fibres were investigated in the Part I of this series of papers. For analysis of the surface chemistry of the fibres, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) were employed; the first method was used for identification and semi-quantitative determination of functional surface groups, while the second method was used for a quantitative determination of these groups. The possible interactions of the various carbon-fibre surfaces due to different surface treatments (and therefore to different functional groups) were analysed by wetting studies using the Wilhelmy technique and aqueous solutions of different pH values as test liquids. By variation of the pH value of the test liquids, the distinct acid-base complexes that formed with the functional groups were identified. The same test liquids were used for characterization of the surface chemistry of the high-temperature thermoplastics (polycarbonate and polyethersulphone) used as matrix materials in the fabrication of the composites in this study. Acid-base interactions at the carbon-fibre surfaces are mainly determined by carboxylic groups of different acidity. The concentration of these groups as determined by desorption of carbon dioxide up to 500 °C is shown to be directly proportional to the measured work of adhesion of each group.     

Carbon nanotube reinforced polymer composites—A state of the art

Because of their high mechanical strength, carbon nanotubes (CNTs) are being considered as nanoscale fibres to enhance the performance of polymer composite materials. Novel CNT-based composites have been fabricated using different methods, expecting that the resulting composites would possess enhanced or completely new set of physical properties due to the addition of CNTs. However, the physics of interactions between CNT and its surrounding matrix material in such nano-composites has yet to be elucidated and methods for determining the parameters controlling interfacial characteristics such as interfacial shear stress, is still challenging. An improvement of the physical properties of polymer nanocomposites, based on carbon nanotubes (CNTs), is addicted to a good dispersion and strong interactions between the matrix and the filler.     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.     

Effects of Experimental Method on Aggregation State and Thermal Conductivity of Carbon Nanotube-Based Fluids

The thermal conductivity of liquids with carbon nanotubes (CNTs) is higher than that of liquids with spherical nanoparticles which results from low-resistance heat flow paths formed by CNT–CNT contact. Since CNTs easily precipitate or cluster in base liquids, path formation depends on the dispersion state of CNTs. A model of the thermal-conductivity enhancement of liquids with CNTs is presented by incorporating the aggregate state where such paths are formed. This model concludes that the anomalously wide range of enhancement values that have been observed recently is attributed to aggregate concentration. CNT clustering and sedimentation in base liquids are the causes of the decreased thermal-conductivity enhancement of such liquids due to the increase of the volume fraction of CNTs in aggregates. Predictions based on our model also show that experimental methods of obtaining liquids with uniformly dispersed CNTs can change the CNT geometry and aggregate concentration related to the thermal-conductivity enhancement. Surfactant addition, CNT surface treatment with acid, and sonication have characteristic effects on the CNT state and thermal conduction. The model from this study can prove helpful in explaining the magnitude of such effects quantitatively.     

A method for the chemical anchoring of carbon nanotubes onto carbon fibre and its impact on the strength of carbon fibre composites

This article proposes an alternative way to use carbon nanotubes to improve the performance of carbon fibre-reinforced composites. A chemical process, based on esterification of surface groups, is used to anchor nanotubes onto carbon fibre surface. Anchored nanotubes form a network surrounding the carbon fibres. After CNT anchoring, the tow is impregnated with an epoxy resin and tensile tests are performed on this minicomposite sample. By enhancing matrix properties and fibre/matrix interface, the CNT network has a significant influence on the composite strength.     

Tensile strength of glass fibres with carbon nanotube–epoxy nanocomposite coating: Effects of CNT morphology and dispersion state

The effects of carbon nanotube (CNT)–epoxy nanocomposite coating applied to glass fibre surface on tensile strength of single glass fibres are evaluated at different gauge lengths. The crack healing efficiencies obtained using two different types of CNTs with different structures, morphologies and dispersion characteristics in various concentrations are specifically studied. The results indicate that the tensile strength of single fibres increased significantly with increasing CNT content up to a certain level, depending on the type of CNTs. The crack healing efficiency was much higher for the fibres coated with straight, less entangled CNTs than those with highly entangled CNTs, indicating the CNT dispersion state in the coating played an important role. A strong correlation is established between the CNT dispersion state, the tensile properties of nanocomposite and the tensile strengths of fibres with the nanocomposite coating.     

Carbon nanotube superconducting quantum interference device

A superconducting quantum interference device (SQUID) with single-walled carbon nanotube (CNT) Josephson junctions is presented. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. In addition, a backgate electrode can vary the transparency of the QD barriers, thus permitting change in the hybridization of the QD states with the superconducting contacts. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the 'on' or 'off' state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate-controlled pi-junctions; that is, the sign of the current-phase relation across the CNT junctions can be tuned with a gate voltage. The CNT-SQUIDs are sensitive local magnetometers, which are very promising for the study of magnetization reversal of an individual magnetic particle or molecule placed on one of the two CNT Josephson junctions.     

不同分散剂中碳纳米管的定向操控技术

利用介电电泳可以实现悬浮液中碳纳米管的定向操控．碳纳米管可以用表面活性剂和有机溶剂进行分散．对比了表面活性剂（十二烷基苯磺酸钠,黏滞系数为1.312mPa·s）和有机溶剂（二甲基甲酰胺,黏滞系数为0．802mPa·s）,发现表面活性剂悬浮液中碳纳米管的溶解和分散效果好于有机溶剂中的溶解和分散效果,能实现单根分散．根据介电电泳原理,悬浮液中的碳纳米管在外加电场诱导下产生极化从而被驱动;分析了表面活性剂悬浮液和有机溶剂中碳纳米管的定向效果,发现有机溶剂中碳纳米管的定向效果好于表面活性剂悬浮液中的效果,表面活性剂悬浮液的黏滞系数大是阻碍外加电场有效定向操控碳纳米管的原因．     

Designing Nanogadgetry for Nanoelectronic Devices with Nitrogen‐Doped Capped Carbon Nanotubes

A systematic analysis of electron transport characteristics for 1D heterojunctions with two nitrogen‐doped (N‐doped) capped carbon nanotubes (CNTs) facing one another at different conformations is presented considering the chirality of CNTs (armchair(5,5) and zigzag(9,0)) and spatial arrangement of N‐dopants. The results show that the modification of the molecular orbitals by the N‐dopants generates a conducting channel in the designed CNT junctions, inducing a negative differential resistance (NDR) behavior, which is a characteristic feature of the Esaki‐like diode, that is, tunneling diode. The NDR behavior significantly depends on the N‐doping site and the facing conformations of the N‐doped capped CNT junctions. Furthermore, a clear interpretation is presented for the NDR behavior by a rigid shift model of the HOMO‐ and LUMO‐filtered energy levels in the left and right electrodes under the applied biases. These results give an insight into the design and implementation of various electronic logic functions based on CNTs for applications in the field of nanoelectronics.     

电化学表面处理提高碳纤维复合材料界面性能的机理研究

电化学处理是一种很有效的提高碳纤维及其复合材料界面强度的方法 ,但是 ,其机理现在仍未很清楚。本文综述了 3种不同的观点 ,即 :活性官能团的引入从而提高了碳纤维与树脂基体之间的相互作用力 ;表面薄弱外层的去除 ;以及纤维表面的被刻蚀 ,从而提高了纤维与树脂间的机械作用力。     

Adsorption of selected volatile organic vapors on multiwall carbon nanotubes

Carbon nanotubes are expected to play an important role in sensing, pollution treatment and separation techniques. This study examines the adsorption behaviors of volatile organic compounds (VOCs), n-hexane, benzene, trichloroethylene and acetone on two multiwall carbon nanotubes (MWCNTs), CNT1 and CNT2. Among these VOCs, acetone exhibits the highest adsorption capacity. The highest adsorption enthalpies and desorption energies of acetone were also observed. The strong chemical interactions between acetone and both MWCNTs may be the result from chemisorption on the topological defects. The adsorption heats of trichloroethylene, benzene, and n-hexane are indicative of physisorption on the surfaces of both MWCNTs. CNT2 presents a higher adsorption capacity than CNT1 due to the existence of an exterior amorphous carbon layer on CNT2. The amorphous carbon enhances the adsorption capacity of organic chemicals on carbon nanotubes. The morphological and structure order of carbon nanotubes are the primary affects on the adsorption process of organic chemicals.     

Carbon/Carbon – an inverse composite structure

Carbon/carbon composites are a type of material, which combines the refractory properties of carbon with the high strength and stiffness of carbon fibres. Although one could not expect a reinforcement by the combination of a carbon matrix with carbon fibres the fibre properties can be used. Additionally the material shows a pseudoplastic fracture behaviour in spite of its ceramic nature. Explanations for this inverse behaviour in comparison to other composite structures will be presented including mechanical viewpoints, interactions at the interface between fibre and matrix, their influence to the fracture characteristics and micromechanical behaviour as well as the interactions between modulus and microstructure. Furtheron examples for some industrial applications are described.     

Self‐Assembled Hybrid Materials Based on Organic Nanocrystals and Carbon Nanotubes

Organic crystalline materials are used as dyes/pigments, pharmaceuticals, and active components of photonic and electronic devices. There is great interest in integrating organic crystals with inorganic and carbon nanomaterials to create nanocomposites with enhanced properties. Such efforts are hampered by the difficulties in interfacing organic crystals with dissimilar materials. Here, an approach that employs organic nanocrystallization is presented to fabricate solution‐processed organic nanocrystal/carbon nanotube (ONC/CNT) hybrid materials based on readily available organic dyes (perylene diimides (PDIs)) and carbon nanotubes. The hybrids are prepared by self‐assembly in aqueous media to afford free‐standing films with tunable CNT content. These exhibit excellent conductivities (as high as 5.78 ± 0.56 S m^?1), and high thermal stability that are superior to common polymer/CNT hybrids. The color of the hybrids can be tuned by adding various PDI derivatives. ONC/CNT hybrids represent a novel class of nanocomposites, applicable as optoelectronic and conductive colorant materials.