Ultralong Carbon Nanotubes Research Articles

High-Performance Photodetectors Based on Suspended Ultralong Carbon Nanotubes.

Photodetectors are in huge demand in multiple fields, such as remote sensing, chemical detection, security, and medical imaging. Carbon nanotubes (CNTs) are promising candidates for high-performance photodetectors due to their extraordinary optical and electrical properties. However, the performance of previously reported CNT-based photodetectors is far from the intrinsic photoelectrical properties of CNTs because of the noncontinuous lengths, structural defects, and unsatisfactory structural design of the previously used short CNTs. The key to improving the performance of CNT-based photodetectors is to increase the length and structural quality of the CNTs. Herein, high-performance photodetectors were fabricated by using high-density suspended ultralong CNTs (SUCNTs). The suspended structures of ultralong CNTs not only reduced the electron-phonon interactions generated by substrates but also largely avoided bolometric effects through efficient heat dissipation. Moreover, the characteristics of high areal density and defect-free structures of SUCNTs could increase the effective absorption areas and improve their carrier mobility, resulting in enhanced photoconductive responses. Consequently, compared with the nonsuspended short CNTs, the SUCNT-based photodetectors achieved significantly improved photodetection performance, such as high responsivity (0.181 A W-1), detectivity (1.20 × 109 cm Hz1/2 W-1), ultrafast response (0.13 ms), and broad detection range (405-850 nm).

Floating Bimetallic Catalysts for Growing 30cm-Long Carbon Nanotube Arrays with High Yields and Uniformity.

Ultralong carbon nanotubes (CNTs) are considered as promising candidates for many cutting-edge applications. However, restricted by the extremely low yields of ultralong CNTs, their practical applications can hardly be realized. Therefore, new methodologies shall be developed to boost the growth efficiency of ultralong CNTs and alleviate their areal density decay at the macroscale level. Herein, a facile, universal, and controllable method for the in situ synthesis of floating bimetallic catalysts (FBCs) is proposed to grow ultralong CNT arrays with high yields and uniformity. Ferrocene and metal acetylacetonates serve as catalyst precursors, affording the successful synthesis of a series of FBCs with controllable compositions. Among these FBCs, the optimized FeCu catalyst increases the areal density of ultralong CNT arrays to a record-breaking value of ≈8100CNTsmm-1 and exhibits a lifetime 3.40 times longer than that of Fe, thus achieving both high yields and uniformity. A 30-centimeters-long and high-density ultralong CNT array is also successfully grown with the assistance of FeCu catalysts. As evidenced by this kinetic model and molecular dynamics simulations, the introduction of Cu into Fe can simultaneously improve the catalyst fluidity and decrease carbon solubility, and an optimal catalytic performance will be achieved by balancing this tradeoff.

High-Area-Capacity Cathode by Ultralong Carbon Nanotubes for Secondary Binder-Assisted Dry Coating Technology.

Thick electrodes with high mass loading and increased content of active materials are critical for achieving higher energy density in contemporary lithium-ion batteries (LIBs). Nonetheless, producing thick electrodes through the commonly used slurry coating technology remains a formidable challenge. In this study, we have addressed this challenge by developing a dry electrode technology by using ultralong multiwalled carbon nanotubes (MWCNT) as a conductive additive and secondary binder. The mixing process of electrode compositions and the fibrillation process of the polytetrafluoroethylene (PTFE) binder were optimized. The resulting LiCoO2 (LCO) electrode exhibited a remarkable mass loading of 48 mg cm-2 and an active material content of 95 wt %. Notably, the thick LCO electrode demonstrated a superior mechanical strength and electrochemical performance. After 100 cycles at a current density of 1/3 C, the electrode still exhibited a capacity retention of 91% of its initial capacity. This dry electrode technology provides a practicable and scalable approach to the powder-to-film LIB electrode manufacturing process.

High-Performance Airflow Sensors Based on Suspended Ultralong Carbon Nanotube Crossed Networks.

Airflow sensors are in huge demand in many fields such as the aerospace industry, weather forecasting, environmental monitoring, chemical and biological engineering, health monitoring, wearable smart devices, etc. However, traditional airflow sensors can hardly meet the requirements of these applications in the aspects of sensitivity, response speed, detection threshold, detection range, and power consumption. Herein, this work reports high-performance airflow sensors based on suspended ultralong carbon nanotube (CNT) crossed networks (SCNT-CNs). The unique topologies of SCNT-CNs with abundant X junctions can fully exhibit the extraordinary intrinsic properties of ultralong CNTs and significantly improve the sensing performance and robustness of SCNT-CNs-based airflow sensors, which simultaneously achieved high sensitivity, fast response speed, low detection threshold, and wide detection range. Moreover, the capability for encapsulation also guaranteed the practicality of SCNT-CNs, enabling their applications in respiratory monitoring, flow rate display and transient response analysis. Simulations were used to unveil the sensing mechanisms of SCNT-CNs, showing that the piezoresistive responses were mainly attributed to the variation of junction resistances. This work shows that SCNT-CNs have many superiorities in the fabrication of advanced airflow sensors as well as other related applications.

Thermo-oxidative degradation of carbon nanotubes and related nanostructures: role of acidic environment and chloride ions

It is shown that acid activation of ultralong carbon nanotubes synthesis products increases their reactivity during subsequent thermochemical treatment in air at 480 °C. Such an integrated approach of CNTs processing provides high purity and maximum yield of the target product. For example, the non-CNT fraction decreases by 3.2 times, while the residual iron content decreases by 17–24 times in comparison with thermochemical treatment without acid. Raman spectroscopy and low-temperature nitrogen adsorption showed that acid activation does not lead to extra surface defects, which could initiate further oxidation of carbon matrix in air. It is suggested that the increased reactivity of CNT synthesis products after acid activation during thermo-oxidative degradation may be due to the formation of an “adduct” of carboxyl groups on the surface of nanotube carbon matrix with hydrogen chloride. It was shown by thermogravimetric studies coupled with mass-spectra investigation of gas evolved, that under the constant heating, at the temperatures of the beginning of intensive oxidation (500–600 °C), the decomposition of the “adduct” occurs, bypassing the stage of formation of more temperature-resistant phenolic groups, which can inhibit further oxidation. Water released during the decomposition of the “adduct” can also accelerate the process of thermal oxidation.

Controlled synthesis, properties, and applications of ultralong carbon nanotubes.

Carbon nanotubes (CNTs) are typical one-dimensional nanomaterials which have been widely studied for more than three decades since 1991 because of their excellent mechanical, electrical, thermal, and optical properties. Among various types of CNTs, the ultralong CNTs which have lengths over centimeters and defect-free structures exhibit superior advantages for fabricating superstrong CNT fibers, CNT-based chips, transparent conductive films, and high-performance cables. The length, orientation, alignment, defects, cleanliness, and other microscopic characteristics of CNTs have significant impacts on their fundamental physical properties. Therefore, the controlled synthesis and mass production of high-quality ultralong CNTs is the key to fully exploiting their extraordinary properties. Despite significant progress made in the study of ultralong CNTs during the past three decades, the precise structural control and mass production of ultralong CNTs remain a great challenge. In this review, we systematically summarize the growth mechanism and controlled synthesis strategies of ultralong CNTs. We also introduce the progress in the applications of ultralong CNTs. Additionally, we summarize the scientific and technological challenges facing the mass production of ultralong CNTs and provide an outlook and in-depth discussion on the future development direction.

Fluidization and Application of Carbon Nano Agglomerations.

Carbon nanomaterials are unique with excellent functionality and diverse structures. However, agglomerated structures are commonly formed because of small-size effects and surface effects. Their hierarchical assembly into micro particles enables carbon nanomaterials to break the boundaries of classical Geldart particle classification before stable fluidization under gas-solid interactions. Currently, there are few systematic reports regarding the structural evolution and fluidization mechanism of carbon nano agglomerations. Based on existing research on carbon nanomaterials, this article reviews the fluidized structure control and fluidization principles of prototypical carbon nanotubes (CNTs) as well as their nanocomposites. The controlled agglomerate fluidization technology leads to the successful mass production of agglomerated and aligned CNTs. In addition, the self-similar agglomeration of individual ultralong CNTs and nanocomposites with silicon as model systems further exemplify the important role of surface structure and particle-fluid interactions. These emerging nano agglomerations have endowed classical fluidization technology with more innovations in advanced applications like energy storage, biomedical, and electronics. This review aims to provide insights into the connections between fluidization and carbon nanomaterials by highlighting their hierarchical structural evolution and the principle of agglomerated fluidization, expecting to showcase the vitality and connotation of fluidization science and technology in the new era.

Fluid-solid coupling for microscale transport of nanoparticles in ultralong carbon nanotubes

Achieving microscale motion of nanoparticles is crucial for the development of various nanodevices. Here we propose a novel fluid-solid coupling device that leverages a thermally-induced water flow to enable long-range nanoparticle transport within carbon nanotubes (CNTs). Our device comprises an ultralong CNT composed of repeated units filled with water. Each unit experiences an asymmetrical thermal gradient induced by intentionally incorporating asymmetrical configurations of atomic vacancies on the CNT surface. Through molecular dynamics (MD) simulations, we demonstrate that these repeated units with periodic thermal fields effectively induce a steady water flow, enabling continuous transportation of a nanoparticle (e.g., a C60 fullerene) within the ultralong CNT over microscale distances. Moreover, we reveal that the device can be also designed with various alternative options (e.g., Stone–Wales defects or carbon/boron-nitride heterojunctions). Our proposed device holds promising potential for microscale nanoparticle transport applications.

Study of interwall interaction during the pull separation of ultra-long double-walled carbon nanotubes under lateral loading

The successful fabrication of ultra-long carbon nanotubes (CNTs) makes CNTs ideal candidates for bearing systems due to the long sliding distance with low interwall interaction. However, it is difficult to measure the pull-out forces of ultra-long CNTs along their axes in real-time because of the difficulty of performing long-distance pull-out experiments. In this study, we proposed a lateral loading method to measure the interwall interaction force of ultra-long CNTs. By using a theoretical model and multi-scale finite element simulations, we could predict the interwall interaction force from the pull-out force in lateral loading. This pull-out force depends on the length of CNTs, and a critical length divides the pull-out force into two categories: maximum pull-out force due to local buckling and steady pull-out force due to sliding. In order to correctly measure the interwall interaction force by lateral loading, for the DWCNTs with the outer tube diameter of 0.955 nm, we have to make sure the lengths are greater than this critical value (54.2 nm) as experimental subjects.

Comparing Ultralong Carbon Nanotube Growth from Methane over Mono- and Bi-Metallic Iron Chloride Catalysts.

This research endeavours to study the growth of ultralong carbon nanotubes (UL-CNTs) from methane using diverse catalysts, namely FeCl3, bi-metallic Fe-Cu, Fe-Ni, and Fe-Co chlorides. Aqueous catalyst solutions were evenly dispersed on silica substrates and grown at 950 °C in the presence of hydrogen via a horizontal chemical vapour deposition (CVD) furnace. The samples underwent characterisation by Raman spectroscopy, scanning electron microscopy (SEM), and optical microscopy to identify the quality of CNTs and enumerate individual UL-CNTs. Our findings revealed that FeCl3, as a mono-metallic catalyst, generated the longest UL-CNTs, which measured 1.32 cm, followed by Fe-Cu (0.85 cm), Fe-Co (0.7 cm), and Fe-Ni (0.6 cm), respectively. The G/D ratio (graphene to defects) from the Raman spectroscopy was the highest with the FeCl3 catalyst (3.09), followed by Fe-Cu (2.79), Fe-Co catalyst (2.13), and Fe-Ni (2.52). It indicates that the mono-iron-based catalyst also produces the highest purity CNTs. Moreover, this study scrutinises the vapour-liquid-solid (VLS) model for CNT growth and the impact of carbide formation as a precursor to CNT growth. Our research findings indicate that forming iron carbide (Fe3C) is a crucial transition phase for amorphous carbon transformation to CNTs. Notably, the iron catalyst generated the longest and densest CNTs relative to other iron-based bi-metallic catalysts, which is consistent with the temperature of carbide formation in the mono-metallic system. From correlations made using the phase diagram with carbon, we conclude that CNT growth is favoured because of increased carbon solubility within the mono-metallic catalyst compared to the bi-metallic catalysts.

Research on the utilization of ultra-long carbon nanotubes in lithium-ion batteries based on an environment-friendly society.

To build an environment-friendly society, clean transportation systems, and renewable energy sources play essential roles. It is critical to improve the lifetime mileage of electric vehicles' batteries for reducing the cycle life cost and carbon footprint in green transportation. In this paper, a long-life lithium-ion battery is achieved by using ultra-long carbon nanotubes (UCNTs) as a conductive agent with relatively low content (up to 0.2% wt.%) in the electrode. Ultra-long CNT could realize longer conductive path crossing active material bulks in the electrode. Meanwhile, the low content of UCNTs can help to minimize conductive agent content in electrodes and obtain higher energy density. The film resistance and electrochemical impedance spectroscopy (EIS) confirmed that the use of UCNTs could markedly enhance electronic conductivity in the battery. The battery's life and life mileage can be prolonged by almost half due to the superior electronic conductivity of UCNTs. The life cycle cost and carbon footprint are also significantly reduced, which could markedly increase economic and environmental performance.

The Importance of Water for Purification of Longer Carbon Nanotubes for Nanocomposite Applications

Ultralong carbon nanotubes (UCNTs) are in high demand for nanocomposites applications due to their magnificent physical and chemical properties. UCNTs are synthesized by the catalytic chemical vapor deposition (CCVD) method and, before use as fillers in nanocomposites, should be purified of residual catalyst and non-CNT particles without significant destruction or scissoring of the UCNT. This study investigates the role of water vapor for purification of UCNTs from iron catalyst particles and the importance of water assistance in this process is confirmed. It was shown that wet air treatment of products of UCNTs CCVD synthesis under mild conditions can be used to sufficiently decrease residual iron catalyst content without significant carbon losses in comparison to the results obtained with dry air, while the residual iron content was shown to significantly influence the subsequent oxidation of different forms of carbons, including UCNTs. The increasing of D/G ratio of Raman spectra after wet air treatment of products of UCNTs CCVD synthesis makes it possible to conclude that iron catalyst particles transform into iron oxides and hydroxides that caused inner structural strains and destruction of carbon shells, improving removal of the catalyst particles by subsequent acid treatment. UCNTs purification with water assistance can be used to develop economically and ecologically friendly methods for obtaining fillers for nanocomposites of different applications.

Synthesis of Ultralong Carbon Nanotubes with Ultrahigh Yields.

Ultralong carbon nanotubes (CNTs) are in huge demand in many cutting-edge fields due to their macroscale lengths, perfect structures, and extraordinary properties, while their practical application is limited by the difficulties in their mass production. Herein, we report the synthesis of ultralong CNTs with a dramatically increased yield by a simple but efficient substrate interception and direction strategy (SIDS), which couples the advantages of floating-catalyst chemical vapor deposition with the flying-kite-like growth mechanism of ultralong CNTs. The SIDS-assisted approach prominently improves the catalyst utilization and significantly increases the yield. The areal density of the ultralong CNT arrays with length of over 1 cm reached a record-breaking value of ∼6700 CNTs mm-1, which is 2-3 orders of magnitude higher than the previously reported values obtained by traditional methods. The SIDS provides a solution for synthesizing high-quality ultralong CNTs with high yields, laying the foundation for their mass production.

The Inherent Thermal Effect of Substrates on the Growth of Ultralong Carbon Nanotubes

AbstractUltralong carbon nanotubes (CNTs) are believed to be ideal candidates for various high‐end applications because of their macroscale lengths, perfect structures, and excellent mechanical and electrical properties. The key to the wide application of ultralong CNTs is their controlled synthesis and mass production. Ultralong CNTs usually follow a flying kite‐like growth mechanism, during which process there exists a thermal buoyancy that keeps ultralong CNTs floating in the gas flow. However, it remains vague for a long time about the origin of this thermal buoyancy. Herein, a simple and quantitative heat balance model is proposed to describe the inherent thermal effect of substrates, which explains the origin of the temperature difference between the substrate and the gas flow. The inherent thermal effect is found to be positively correlated with the emissivity of the substrates. Then, the local temperature gradient induced by the inherent thermal effect is found to result in both natural convection and thermophoresis. Thermophoretic force is proven to be the dominant driving force for lifting the ultralong CNTs up from the substrates. By utilizing the inherent thermal effect and designing the local temperature distribution, the areal density and orientation of ultralong CNT arrays are modulated.

Molecular Evolutionary Growth of Ultralong Semiconducting Double-Walled Carbon Nanotubes.

The self-assembling preparation accompanied with template auto-catalysis loop and the ability to gather energy, induces the appearance of chirality and entropy reduction in biotic systems. However, an abiotic system with biotic characteristics is of great significance but still missing. Here, it is demonstrated that the molecular evolution is characteristic of ultralong carbon nanotube preparation, revealing the advantage of chiral assembly through template auto-catalysis growth, stepwise-enriched chirality distribution with decreasing entropy, and environmental effects on the evolutionary growth. Specifically, the defective and metallic nanotubes perform inferiority to semiconducting counterparts, among of which the ones with double walls and specific chirality (n, m) are more predominant due to molecular coevolution. An explicit evolutionary trend for tailoring certain layer chirality is presented toward perfect near-(2n, n)-containing semiconducting double-walled nanotubes. These findings extend our conceptual understanding for the template auto-catalysis assembly of abiotic carbon nanotubes, and provide an inspiration for preparing chiral materials with kinetic stability by evolutionary growth.

Physical properties enhancement of carbon fiber obtained from isotropic pitch doped by ultra-long carbon nanotubes

• DWCNT-doped isotropic petroleum pitch used successfully for carbon fiber formation • DWCNT doping leads to jump in both thermal and electrical conductivity of fibers • Inner cavities appear in the fibers at DWCNT content close to 1.0 wt. % • Hollow filaments formed at high DWCNT content paving way to hollow fiber technology Carbon fibers (CF) were formed from carbon nanotube-doped isotropic petroleum pitch. Ultra-long (the length of a single filament is more than 10,000 nm) double-walled carbon nanotubes (DWCNT) were used for doping in concentrations from 0.1 to 1.0 wt. %. The produced CF were investigated both in pristine and graphitized form. Physical properties (electrical resistivity, thermal conductivity coefficient), as well as X-ray diffraction (XRD) analysis and Raman spectroscopy of obtained DWCNT-doped CF were investigated. The influence of DWCNT concentration on the properties is nonlinear due to the influence on the CF molding mode and heterogeneity of the DWCNT distribution in the filament body. An increase in the DWCNT concentration, on the one hand, causes an enhancement in the thermal conductivity coefficient, and a decrease in the electrical resistivity of the fibers, on the other hand, it leads to local inhomogeneities formation in the material structure («gas bubbles»), as well as distortions of the CF outer surface. An increase in the DWCNT concentration also leads to an increase in CF average diameter and hollow filaments formation. This feature is paving the way to the development of novel technological methods to control CF properties and morphology, especially to feasible hollow CF composites manufacture.

Strength and fracture behaviors of ultralong carbon nanotubes with defects

The presence of structural defects can result in large discrepancies between theoretical and experimental values of the strength of CNTs. To reveal the relationship between the strength and defects of CNTs, experiments accompanied with an experiment-based molecular dynamics simulation were conducted in this paper, where defects were introduced using oxygen plasma irradiation and the strength of the defective CNTs was measured by uniaxial tensile experiments. It was found that the strength of CNTs was controlled by the feature length of defects and the introduction of the single adatom, C–C bond breaking, and vacancy defect could decrease the strength by 8.2%, 23.2%, and 18.5%, respectively. Especially, when these defects synergized, the strength of CNTs ranged from 0 to 76.8% of the theoretical strength, which was confirmed by the experiments. Moreover, by defining cracks based on the atomic stress distributions around defects, the fracture of CNTs obeyed the Griffith's brittle fracture criterion and the atomic stress distributions along the crack plane obeyed the classical fracture mechanics theory except for some deviation near the crack tip. This work gives a perspective on reasons for the theory-experiment discrepancies on the strength of CNTs over the years, obtains the quantitative relationship between the size of defects and the strength of CNTs and provides a research paradigm for verifying the validity of fracture mechanics theories at nanoscale. • The adatom, C–C bond breaking, and vacancy defects are introduced to CNT by oxygen plasma irradiation. • The feature length of defects controls the strength of CNTs when these defects synergize. • The fracture of CNTs obeys the Griffith's brittle fracture criterion by regarding defects as cracks. • Atomic stress distributions obeys the classical fracture mechanics theory except for some deviation near the crack tip. • The characteristic length in GES is to separate two atoms from the maximum interaction to the interaction can be ignored.

Morphology investigation on direct growth ultra-long CNTs by chemical vapour deposition method for high performance HER applications

Carbon nanotube (CNT) is prepared by chemical vapor deposition method and their electrochemical behaviors for instance oxygen evolution (OER) and hydrogen evolution (HER) reaction have been successfully studied. In recent times, Pt-free electrocatalysts have been greatly attractive in electrochemical hydrogen evolution reactions for the replacement of fossil fuels and development of sustainable energy carriers. Chemical vapor deposition method was used as an efficient way to synthesize CNTs directly. The as prepared free-standing and multifunctional CNT electrodes are used for overall water splitting applications. In this work, we have designed CNT as electrode material as well as current collector using Ni-foil and Ni-foam substrate and their fundamental characterizations confirm the structural, morphological behaviors of CNTs. Moreover, the well-ordered growth of CNT was obtained in Ni-foam CNTs 1 and 2, whereas in the Ni foil CNTs 1 and 2 less growth of CNT and amorphous carbon sponge was exceeded, which was further confirmed by the SEM images. The achieved electrochemical HER results displayed that the Ni-foam-CNT-2 exhibited lower overpotential, smallest Tafel slope and lower resistance value of 110 mV, 240 mV/dec and 0.24 Ω respectively. Moreover, Ni-foam-CNT-2 revealed excellent stability with 86.6 % retention over 20 h. Hence, it is one of the cost-effective and reliable materials for electrochemical hydrogen evolution reaction.

Propagation of Microwaves in Composites Containing Ultralong Carbon Nanotubes

Propagation of Microwaves in Composites Containing Ultralong Carbon Nanotubes

Facile crafting of ultralong N-doped carbon nanotube encapsulated with FeCo nanoparticles as bifunctional electrocatalyst for rechargeable zinc-air batteries

The rational design and facile preparation of highly efficient bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) still remain challenge. Herein, we report the facile preparation of a bifunctional electrocatalyst consisting of FeCo alloy nanoparticles embedded in ultralong N-doped carbon nanotube (denoted FeCo/LNCNT) by capitalizing on the coordination interaction between triphenylimidazole-containing crosslinked polymer and metal salts followed by the two-step pyrolysis under the presence of melamine. The FeCo alloy nanoparticles play the crucial role in the formation of ultralong carbon nanotube with increasing pyrolysis time under the assistance of melamine. The resulting FeCo/LNCNT manifests remarkable ORR and OER activity together with outstanding durability. The small potential gap (0.756 V) of FeCo/LNCNT demonstrates a promising application as ORR/OER bifunctional elctrocatalyst. The assembled zinc-air battery using FeCo/LNCNT as the air anode exhibits higher open-circuit voltage (1.52 V), specific capacity (779 mAh g −1 Zn ) and power density (144 mW cm −2 ) than the Pt/Ir counterpart. Notably, the zinc-air battery assembled with FeCo/LNCNT can remain stable for more than 600 cycles without significant voltage drop and efficiency loss, representing an excellent cycling stability. • Ultralong N-doped carbon nanotube decorated with FeCo alloy is prepared. • The resulting FeCo/LNCNT manifests remarkable ORR and OER activity. • The assembled zinc-air battery exhibits high specific capacity and power density.