High-quality Carbon Nanotubes Research Articles

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Natural biochar catalyst: Realizing the co-valorization of waste cooking oil into high-quality biofuel and carbon nanotube precursor via catalytic pyrolysis process

Valorizing renewable precursors into high-quality biofuel and functional carbon nanomaterials can considerably improve the economic viability. Here, we propose a process for integrated production of high-quality biofuel and carbon nanotubes from waste cooking oil via catalytic pyrolysis coupling with chemical vapor deposition (CVD) technology. The natural biochar catalyst demonstrates excellent deoxygenation performance and good stability in catalytic pyrolysis process. The alkali/alkaline earth metal species (AAEMs) content in biochar catalysts has a strong correlation with the selectivity of esters and hydrocarbons in bio-oil. The biofuel obtained under optimal conditions exhibited potential as a precursor for jet fuel. The CVD process convert pyrolysis gas into carbon nanotubes with yield of 2.13%. The technical–economic analysis demonstrated the feasibility of the integrated process, projecting profitability and substantial total profit over a ten-year period. Overall, this study improves the economic viability of the waste cooking oil pyrolysis process and supports its wider commercial application.

Upcycling of composite packaging waste to carbon nanotubes via chemical vapor deposition of pyrolysis gas

Based on the necessity of evaluating composite packaging wastes from both environmental and economic perspectives, it aimed to obtain carbon nanotube (CNT) from the pyrolysis gas product of this material by the catalytic chemical vapor deposition method (CCVD) via an upcycling approach. In the first stage, composite packaging wastes were pyrolyzed. Secondly, the composition of the gas via gas chromatography was determined. In the third stage, CNT production studies were carried out by the CCVD method in a tubular reactor at four different temperatures between 600 and 900 °C with nickel catalyst. The effects of temperature and carbon source feeding ratio on the properties of the obtained CNTs were investigated. CNTs produced in this study were compared with a commercial product. As a result, high-quality multi-walled carbon nanotube of 20–30 nm diameter and in micrometer scale length comparable to commercial products were produced from the gaseous product at 800 °C under Ni-catalysis.

Preparing High-Quality Monolithic Carbon Nanotubes Reinforced Silica Aerogel Composites Based on a Vacuum Freeze-Drying Method

Preparing High-Quality Monolithic Carbon Nanotubes Reinforced Silica Aerogel Composites Based on a Vacuum Freeze-Drying Method

Synthesis and modification of carbon nanotubes

Carbon nanotubes (CNTs) are mono-dimensional carbon nanomaterials with remarkable properties. Since their discovery by Iijima, they have been found to exhibit remarkable properties in mechanical, physical, and chemical fields. However, due to their harsh synthesis conditions and limited inherent properties, the large-scale application of CNTs is challenging. With the aim of providing a reference for further research and development of carbon nanotubes, this review summarizes the currently reported methods for synthesizing carbon nanotubes, focusing on the cost-effective arc-discharge method and chemical vapor deposition (CVD) which produce high-quality carbon nanotubes with stable performance. In addition, two different directions of CNT modifications are presented, namely, CNT filling technology and CNT solubility modification. Among them, the CNT filling technology can use CNTs as templates for nanodevice fabrication and test tubes for microscopic reactions. Meanwhile, solubility modification of CNTs is the key strategy to overcome its inherent limitations and expand their application fields.

High-quality multi-walled carbon nanotubes toughened glass-ceramic by a two-dimension carbon nanotube film interlayer

The brittleness of bioglass/ceramics limits their applications in bone repair. The toughness of the glass matrix can be enhanced by adding nanoscale reinforcements at random; however, the effect is quite limited. This study proposes a novel strategy to prepare controllable fabricating lamellar precursors with multiwalled carbon nanotubes (MWCNTs) film/glass/MWCNTs film sandwich structure by a high-temperature foaming method. Subsequently, the precursor was sintered by spark plasma to obtain a composite material with strong cross-linking between MWCNTs and the glass matrix. The mechanical properties of the composites were characterized, and mechanisms were analyzed by the finite element method. The results revealed that the glass composite with 1.0 wt% MWCNTs had a significantly enhanced fracture toughness (2.65 MPa m1/2) and flexural strength (145 MPa), which were 2.1 times and 1.8 times higher than those of pure glass, respectively. This increase in toughness is attributed to the strong resistance of the well-combined bent and entangled MWCNTs to the fiber pull-out process. The glass/MWCNTs composite showed a low electrical resistivity of 5.8 Ω cm, which would aid skeletal restoration. Thus, this strategy paves a facile way to prepare the highly toughed bio-glass with multifunctional properties.

Smart and sensitive nanomaterial-based electrochemical sensor for the determination of a poly (ADP-ribose) polymerase (PARP) inhibitor anticancer agent

In this research, we propose a novel approach for constructing a sensitive and selective electrochemical sensor utilizing high-quality multi-walled carbon nanotubes functionalized with amino groups (MWCNT-NH2) for the detection of Talazoparib (TLZ), a poly (ADP-ribose) polymerase (PARP) enzyme inhibitor, in real samples. The MWCNT-NH2-based sensor exhibited remarkable performance characteristics, including excellent repeatability, reproducibility, and high selectivity against various interferences. Under optimized conditions, the sensor demonstrated a wide linear concentration range of 1.0–5.0 μM, with a low limit of detection (LOD) of 0.201 μM. Substantiated by rigorous analysis of pharmaceutical and biological matrices, our methodology emerges as a paragon of reliability, boasting recovery rates within the satisfactory bracket of 96.38–105.25%. The successful application of the MWCNT-NH2-based sensor in practical sample analysis highlights its potential for implementation in clinical and pharmaceutical settings. This research not only advances the application of MWCNT-NH2 in electrochemical sensing but also opens new avenues for the development and monitoring of innovative anticancer treatments. The insights gained from our study have far-reaching implications, pointing toward a future where precision and innovation converge to improve patient care and treatment outcomes.

Supercapacitor Performance of NiO, NiO-MWCNT, and NiO-Fe-MWCNT Composites.

The NiO-CNT and NiO-Fe-CNT composites that have been prepared from waste high density polyethylene plastic and their carbon nanotube (CNT) quality-dependent supercapacitance tuning have been reported here. Multiwalled CNT (MWCNT) formation has been confirmed from TEM and Raman spectra with an ID/IG ratio of 0.77, which stands for high graphitization. The specific surface area (SSA) of MWCNTs in the NiO-Fe-CNT composite was 87.8 m2/g, while in the NiO-CNT composite, it was 25 m2/g. NiO-Fe-CNT displayed higher specific capacitance and energy density (1360 Fg-1 and 1180 W h kg-1) than NiO-CNT (1250 Fg-1 and 1000 W h kg-1), which may be due to the presence of higher-quality MWCNTs in the NiO-Fe-CNT composite. NiO-Fe-CNT displayed higher contributions of electric double-layer capacitor (59%) behavior compared to NiO-CNT (38%) and represented a hybrid supercapacitor. NiO-Fe-CNT also displayed a capacitive retention of 96% after 1000 charge-discharge cycles. Furthermore, studies in acidic electrolytes revealed higher performance of NiO-Fe-CNT than NiO-CNT, displaying specific capacitances of NiO-Fe-CNT to be 1147 Fg-1 in 2 M H2SO4 and 943 Fg-1 in 2 M HCl. It has been qualitatively explored that the quality of CNTs, SSA, and quantum confinement effects in the composites may be the factors responsible for the performance difference in NiO-Fe-CNT and NiO-CNT. The present work is geared toward the low-cost fabrication of high-quality CNT composites for supercapacitors and energy storage applications. The present work also contributes quantitatively to the understanding of CNT quality as an important parameter for the performance of CNT-composite-based supercapacitors.

(Invited) Laser-Induced Graphene on Polymers: From Process Science to Applications

Nanocarbons like graphene and carbon nanotubes (CNTs) are promising for various applications including advanced electronic devices, novel energy systems, and next-generation healthcare diagnostics. This is owing to the excellent physical, chemical and electrochemical properties arising from the ordered atomic structure, the hierarchical nanoscale morphology, and tunable chemistry of nanocarbons. In particular, low-dimensional carbon electrodes for biosensors and neural interfaces have consistently been shown to have superior performance when compared to state-of-the-art metal electrodes. Nevertheless, major manufacturing challenges still hinder our ability to scalably produce graphene-based electrodes with tailored morphology and surface chemistry, especially on flexible substrates. While chemical vapor deposition (CVD) processes enable the synthesis of high quality graphene and CNTs, the extreme environments of high temperatures and hydrocarbon-rich gaseous atmosphere in such reactors limit the choice of substrates to silicon, quartz, metals or other rigid temperature-resistant materials. On the other hand, many emerging flexible devices require the fabrication of such nanocarbon electrodes on the surface of polymer substrates. Unlike different transfer technique of CVD-grown nanocarbons, this talk will focus on a unique bottom-up approach for directly growing different types of graphenic nanocarbons on polymer films by laser irradiation. The speaker will show how this direct-write process, often referred to as laser-induced graphene (LIG), can be controlled to produce spatially-varying morphologies and chemical compositions of LIG electrodes, by leveraging gradients of laser fluence. Moreover, a method will be introduced to control the heteroatom doping of these LIG electrodes based on controlling the molecular structure of the polymer being lased. Finally, a demonstration of these functional LIG electrodes as electrochemical biosensors will be presented for the detection of the neurotransmitter dopamine with nanomolar sensitivity.

In-situ synthesis of high-quality carbon nanotubes on Cu powder by constructing an Al2O3 barrier layer

The synthesis of high-quality carbon nanotubes (CNTs)-Cu composite powder by chemical vapor deposition remains a persistent challenge due to catalyst deactivation resulting from its diffusion into Cu powder at elevated temperatures. To overcome this obstacle, a novel approach involving pre-coating Cu powder with an Al2O3 barrier layer was proposed to facilitate the in-situ growth of CNTs. Experimental results demonstrated that synthesized CNTs exhibited a desirable combination of uniform distribution, high aspect ratio and tunable structures achieved by utilizing different carbon source precursors. Notably, single/double-walled CNTs (S/DMCNTs) with exceptional structural integrity was achieved on Cu powder, which has not been reported previously. The Raman ID/IG ratio of present S/DMCNTs-Cu composite powder reached approximately 0.18, which was significantly superior compared to the relevant reported data.

Incandescent annealing purification of carbon nanotube films with high efficiency and non-destructiveness

Impurities in carbon nanotube (CNT) films can introduce unpredictable deleterious effects in carbon-based electronic devices and composites. To purify CNT films, a key obstacle is the removal of impurities without damaging the structure of CNTs. Herein, we present an efficient, rapid, energy-saving, and eco-friendly incandescent annealing purification (IAP) to prepare ultrahigh-purity and high-quality CNT films. The results showed that Fe-containing impurities in CNT films were reduced from 9.48 wt% to less than 0.05 wt%, the ratio between Raman D and G peak intensities decreased from 0.52 to 0.44, and the XPS C/O ratio enhanced from 19.16 to 70.71. The purification efficiency is up to 99.47%, much higher than the conventional electro-oxidation (E-Oxi) purification (71.20%). The IAP-treated CNT and its composite film exhibited excellent advantages in mechanical performance, ablation resistance, and stable electro-heating. Furthermore, the rapid IAP within just a few seconds also leads to the orders of magnitude reduction in energy cost, making it super practical.

Evaluation of highly active and stable SiO2 supported Fe-based catalysts for the catalytic methane decomposition into COx free hydrogen and CNTs

Catalytic methane decomposition is believed to be an economic and environmental friendly route for the production of COx free hydrogen and high quality carbon nanotubes. However, the development of active and stable catalysts remains a significantly challenging research topic. This study focuses on the development of highly active and stable silica-supported Fe-based catalysts for the thermal decomposition of methane into hydrogen and high quality carbon nanotubes. A series of Fe/SiO2 catalysts with varying Fe loading in the range between 25 wt% and 100 wt% were synthesized by the solution combustion synthesis (SCS) method. The synthesized catalysts were characterized by various bulk sensitive and surface sensitive analytical tools, such as SEM, XRD, HRTEM, BET and Raman spectroscopy. All supported catalysts exhibited comparatively high activity than the unsupported 100 wt% Fe (denoted as 100F) catalyst which was the least active. Moreover, the catalytic activity in terms of methane conversion, methane decomposition rate, growth activities as well as carbon yields increased with an increase in the Fe loading. At an operating temperature of 650 °C and a GHSV of 8000 h−1, the 75FS catalyst, with a composition of 75 wt%Fe/SiO2, demonstrated the highest methane decomposition rate of 0.75gCH4/g-cat.h among the investigated catalysts. Additionally, after achieving initial stability at about 120 min, this catalyst remained active throughout testing on stream for 900 min. TEM and SEM analysis of the spent catalyst showed that the supported 75FS catalyst produced multi-walled carbon nanotubes with uniform diameters of 28 nm and with Id/Ig ratio of 0.454 whereas the unsupported 100F catalyst mainly produced graphene sheets.

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.

Microwave-carbon fiber cloth co-ignited catalytic degradation of waste plastic into high-yield hydrogen and carbon nanotubes

Environmental pollution and waste of resources caused by the massive accumulation and landfill of plastic waste has been prompting the research considering its reclamation. In this work, a microwave-carbon fiber cloth (CFC) co-ignited cracking strategy is proposed for highly-efficient conversion of polyethylene to hydrogen and high-quality carbon nanotubes conducted in a simple multimode microwave reactor. When FeAlOx@C is used as the catalyst, a hydrogen yield of 64.5 mmol g−1plastic is achieved while biochar powder as the ignitor only give yield to 30.6 mmol H2 g−1plastic, demonstrating the superiority of the CFC strategy where the carbon ignitor has little contact with the reactants. Further, FeAlOx@C treated by air plasma with rich oxygen vacancies is used as the catalyst. The yield is enhanced significantly, especially at low microwave power, resulting in a hydrogen yield of 67.3 mmol g−1plastic at a microwave power of 900 W, which was the highest as far as we know in the literature under direct catalytic cracking processes. Notably, the integrity of the CFC piece is maintained well, and is highly recyclable. Numerical simulation suggests that the position of CFC plays a key role in initiating the enhanced catalytic cracking process enabled by direct microwave heating.

Printability enhancement and mechanical property improvement via in situ synthesis of carbon nanotubes on aluminium powder

A strategy of powder surface functional modification involving in situ synthesis of carbon nanotubes (CNTs) on Al powder is described to address the poor forming ability and inferior mechanical properties of Al parts produced by laser powder bed fusion. The obtained CNTs-Al composite powder exhibited a combination of high sphericity and flowability of powder, as well as good dispersion uniformity, bonding force and structural integrity of CNTs. The presence of CNTs significantly reduced the laser reflectivity and enhanced the printability of Al powder. The in situ synthesized CNTs contributed to reinforcement after printing and enhanced the tensile properties of printed sample. The printing behavior of powder, the distribution of reinforcement, and the tensile properties of printed sample were optimized by tuning the content of CNTs. The CNT-content in the composite powder was optimized at 0.96 wt% to achieve the synergy of high forming quality, densification and good tensile properties. • High-quality carbon nanotubes (CNTs) were in situ synthesized on Al powder. • Coating CNTs effectively increased the laser absorptivity of Al powder. • The incompatible issue of Al powder with laser additive manufacturing was addressed. • High forming quality and good properties of were obtained in the printed composite.

Controlled optical near-field growth of individual free-standing well-oriented carbon nanotubes, application for scattering SNOM/AFM probes

Abstract Exploiting localized heat-generation density and the resulting enhanced temperature-rise for controlled growth of carbon nanotubes (CNTs) is reported, and its potentials for batch-production of high-quality CNT probes are demonstrated. Optical near field chemical vapor deposition (ONF-CVD) benchtop fabrication schemes are developed for the localized integration of individual well-aligned carbon nanotubes without bending/buckling exactly at desired nanoscale sites. It is demonstrated that generating self-aligned catalyst nanoparticles superimposed on top of silicon nanotips, along with near-field induced absorption confinement, provide the ability to localize the generated heat at the nanotips apexes, and control the CNT growth locations. The nanoscale maskless controllability of the growth site is shown by properly tailoring ONF-CVD conditions to overcome overall heat exposure of the substrate for selective activation of catalyst nanoparticles located at apexes, from those dispersing all over the tips. The calculated local power densities and temperature profiles of the simulated tips, clearly demonstrate the confined heat and optimal gradient of generated temperature rise as the main factors affecting the growth. In addition to determining necessary processing conditions to control the localization and orientation of the growth, parameters affecting the length and diameter of the localized individually grown nanotubes are also presented. Optical near-field-based growth schemes can be extended for localized maskless fabrication of other nanoscale devices, beyond the diffraction limit, using photothermal effects.

Effective Self-Support Growth of Spring-Like Carbon Nanotube Arrays with Ultra-Large Specific Surface Area

Carbon nanotube (CNT) long array with higher aspect ratio is an ideal electrode material for high performance supercapacitors due to its excellent conductivity and high specific surface area (SSA). How to quickly and concisely prepare high-quality CNT long-arrays is the key to achieving large-scale application. Herein, high-quality spring-like CNT (tube diameter 5–8[Formula: see text]nm) long arrays (100–400[Formula: see text][Formula: see text]m) with high purity (96.2% after purification) and ultrahigh graphitization ([Formula: see text]) were fabricated in a high yield (eight times) by a self-supporting catalyst chemical vapor deposition (CVD) method, and its formation process was first investigated under specific conditions of iron content in catalyst, growth temperature and carbon source species. The SSAs can reach 728[Formula: see text]m2/g, which is more than twice that of MWCNTs on the market. The high graphitization and ultra-large SSAs of this spring-like CNT arrays as electrodes exhibit potential electrochemical performance.

Synthesis, Sorting, and Applications of Single-Chirality Single-Walled Carbon Nanotubes.

The synthesis of high-quality chirality-pure single-walled carbon nanotubes (SWCNTs) is vital for their applications. It is of high importance to modernize the synthesis processes to decrease the synthesis temperature and improve the quality and yield of SWCNTs. This review is dedicated to the chirality-selective synthesis, sorting of SWCNTs, and applications of chirality-pure SWCNTs. The review begins with a description of growth mechanisms of carbon nanotubes. Then, we discuss the synthesis methods of semiconducting and metallic conductivity-type and single-chirality SWCNTs, such as the epitaxial growth method of SWCNT (“cloning”) using nanocarbon seeds, the growth method using nanocarbon segments obtained by organic synthesis, and the catalyst-mediated chemical vapor deposition synthesis. Then, we discuss the separation methods of SWCNTs by conductivity type, such as electrophoresis (dielectrophoresis), density gradient ultracentrifugation (DGC), low-speed DGC, ultrahigh DGC, chromatography, two-phase separation, selective solubilization, and selective reaction methods and techniques for single-chirality separation of SWCNTs, including density gradient centrifugation, two-phase separation, and chromatography methods. Finally, the applications of separated SWCNTs, such as field-effect transistors (FETs), sensors, light emitters and photodetectors, transparent electrodes, photovoltaics (solar cells), batteries, bioimaging, and other applications, are presented.

Plasma-modified flaky FeSiAl alloy for efficient growth of carbon nanotube arrays with high carbon conversion rate

The large-scale fabrication of high-quality carbon nanotube (CNT) arrays with highly uniform orientation is challenging due to the relatively low carbon conversion rate. Herein, a plasma-modified flaky FeSiAl (FSA) catalyst was developed for the high- efficiency conversion from acetylene to CNT arrays by catalytic chemical vapor deposition (CCVD). The surface nanoparticles of plasma-modified FSA were refined and oxidized, resulting in an increase in the catalytic active oxides as well as a high carbon conversion rate up to ~97.2%. The growth mechanism analysis confirmed the base-symmetric growth mode of CNT arrays and the maximum theoretical CNT array yield was predicted to be ~8.20 g when using 0.5 g plasma-modified FSA catalysts. The apparent activation energy of CNT arrays was calculated to be ~53.17 kJ/mol, indicating the coexistence of surface diffusion on the catalysts and step-edge diffusion at the graphene-catalyst interface. This work provides a highly efficient methodology for the low-cost and large-scale production of CNT arrays with potential application in the field of high-performance energy storage.

Corn Cob Char as Catalyst Support for Developing Carbon Nanotubes from Waste Polypropylene Plastics: Comparison of Activation Techniques.

The future and continuity of nanomaterials are heavily dependent on their availability and affordability. This could be achieved when cheap materials are actively employed as starting materials for nanomaterials synthesis. In this study, waste corn cob char was used as support during the preparation of the NiMo catalyst, and the effect of different char-activating techniques on the microstructure, yield and quality of carbon nanotubes (CNTs) obtained from waste polypropylene (PP) plastics using the chemical vapor deposition (CVD) technique was investigated. Properties of the catalysts and obtained nanomaterials were evaluated by XRD, SEM, N2 physisorption experiment, FTIR, Raman spectroscopy and TEM. Results showed improved surface properties of the NiMo catalyst supported on chemically (NiMo/ACX) and physically activated char (NiMo/ACT) compared to the NiMo catalyst supported on non-activated char (NiMo/AC0). High-quality CNTs were deposited over NiMo/ACT compared to NiMo/ACX and NiMo/AC0. It was also observed that different activation methods resulted in the formation of CNTs of different microstructures and yield. Optimum yield (470.0 mg CNTs/g catalyst) was obtained with NiMo/AC0, while NiMo/ACT gave the least product yield (70.0 mg CNTs/g catalyst) of the as-produced nanomaterials. Based on the results of the analysis, it was concluded that utilizing a cheap pyrogenic product of waste corn cob as a catalyst support in a bimetallic NiMo catalyst could offer a promising approach to mass producing CNTs and as a low-cost alternative in CNTs production from waste plastics.