Yield Of Carbon Nanotubes Research Articles

Processing, microstructure and mechanical properties of a novel mg matrix composites reinforced with urchin-like CNTs@SiCp

A Mg6Zn composite reinforced by novel urchin-like hybrid reinforcement of carbon nanotubes and silicon carbide (CNTs@SiCp) was fabricated via semisolid stirring assisted with ultrasonic vibration method and exhibits remarkable strengthening effect. Carbon nanotubes (CNTs) were in-situ and dispersed uniformly in the matrix with the assistance of silicon carbide particle (SiCp) as “vehicle”. A series of synthesis parameters were optimized to produce high-quality CNTs. The graphitization degree and the yield of CNT were evaluated by Raman spectra and Thermogravimetric analysis (TGA), respectively. Compared with mono-SiCp reinforced Mg6Zn composite (SiCp/Mg-6Zn), the CNTs@SiCp reinforced Mg6Zn composite with urchin-like reinforcement (CNTs@SiCp/Mg-6Zn) enhanced the yield strength, ultimate tensile strength and elongation by 14%, 20% and 18.2% respectively. Digital image correlation (DIC) investigation indicates that the CNTs enhanced the interface bonding between SiCp and the Mg matrix. A SiC-(CNT-Mg)-Mg interface layer was formed between the SiCp and Mg matrix, which could relieve the interface stress concentration and impede microcrack propagation in the matrix under applied load. This work highlights the strengthening and toughening effects of the urchin-like CNTs@SiCp reinforcement and provides a new approach to fabricate hybrid composites.

Catalytic Performance of Calcium Titanate for Catalytic Decomposition of Waste Polypropylene to Carbon Nanotubes in a Single-Stage CVD Reactor

Calcium titanate mixed metal oxides with different contents were used as supports for NiMo catalyst prepared by the sol–gel method. The activities of these catalysts were tested in the catalytic decomposition of waste polypropylene (PP) for the synthesis of carbon nanotubes (CNTs) using a single-stage chemical vapor deposition technique. The physico-chemical properties of the catalysts and deposited carbon over the catalysts were checked by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), N2 physisorption, transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis (TGA). The TEM and XRD results presented a high dispersion of the active metal species on the surface of the support materials. The result showed that increasing the support content led to an increased crystallite size of the catalysts and a resultant reduction in CNTs yield from 44% to 35%. NiMo-supported CaTiO3 catalyst displayed good catalytic activity and stability toward CNTs growth. Furthermore, the effect of calcination temperature on the morphology, yield, and quality of CNTs was also studied, and it was observed that thermal treatment up to 700 °C could produce well graphitized, high-quality, and high-yield CNTs from the waste PP.

Waste plastics recycling for producing high-value carbon nanotubes: Investigation of the influence of Manganese content in Fe-based catalysts

Thermo-chemical conversion is a promising technology for the recycle of waste plastics, as it can produce high-value products such as carbon nanotubes (CNTs) and hydrogen. However, the low yield of CNTs is one of the challenges. In this work, the addition of Mn (0 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%) to Fe-based catalyst to improve the production of CNTs has been investigated. Results show that the increase of Mn content from 0 wt.% to 10 wt.% significantly promotes CNTs yield formed on the catalyst from 23.4 wt.% to 32.9 wt.%. The results show that Fe-particles in the fresh catalysts are between 10−25 nm. And the addition of Mn in the Fe-based catalyst enhanced the metal-support interactions and the dispersion of metal particles, thus leading to the improved catalytic performance in relation to filamentous carbon growth. In addition, the graphitization of CNTs is promoted with the increase of Mn content. Overall, in terms of the quantity and quality of the produced CNTs, 5 wt.% of Mn in Fe-based catalyst shows the best catalytic performance, due to the further increase of Mn content from 5 wt.% to 10 wt.% led to a dramatic decrease of purity by 10 wt.%.

Weakening the strong Fe-La interaction in A-site-deficient perovskite via Ni substitution to promote the thermocatalytic synthesis of carbon nanotubes from plastics

The variation of metal-support interaction (MSI) plays a key role in the synthesis of carbon nanotubes (CNTs) based on chemical vapor deposition process. This work concentrates on weakening the interaction of Fe-La in an A-site-deficient perovskite (La0.8FeO3-δ) via Ni partial substitution. After reductive treatment, the catalysts were employed for thermocatalytic synthesis of CNTs from plastics. Following the structural, morphological and chemical changes, the catalytic activities of the reductive La0.8NixFe1-xO3-δ (H-LNxF1-x, x = 0, 0.15, 0.5, 0.85) were correlated with the degree of MSI. Compared with H-LF sample, the H-LN0.15F0.85 sample exhibited the highest catalytic activity, which was attributable to the highest surface coverage of metals as well as the synergistic effect of Fe and Ni species. The yield of CNTs produced from low density polyethylene was 1.44 g/gcatalyst over the H-LN0.15F0.85 sample, which was much higher than that over H-LF sample (0.38 g/gcatalyst).

Catalytic Preparation of Carbon Nanotubes from Waste Polyethylene Using FeNi Bimetallic Nanocatalyst.

In this work, carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis from waste polyethylene in Ar using an in-situ catalyst derived from ferric nitrate and nickel nitrate precursors. The influence factors (such as temperature, catalyst content and Fe/Ni molar ratio) on the formation of CNTs were investigated. The results showed that with the temperature increasing from 773 to 1073 K, the carbon yield gradually increased whereas the aspect (length-diameter) ratio of CNTs initially increased and then decreased. The optimal growth temperature of CNTs was 973 K. With increasing the Fe/Ni molar ratio in an FeNi bimetallic catalyst, the yield of CNTs gradually increased, whereas their aspect ratio first increased and then decreased. The optimal usage of the catalyst precursor (Fe/Ni molar ratio was 5:5) was 0.50 wt% with respect to the mass of polyethylene. In this case, the yield of CNTs reached as high as 20 wt%, and their diameter and length were respectively 20–30 nm, and a few tens of micrometers. The simple low-cost method developed in this work could be used to address the environmental concerns about plastic waste, and synthesize high value-added CNTs for a range of future applications.

Maximization of carbon nanotube yield by solid carbon-assisted dewetting of iron catalyst films

Further understanding of how nanoparticle catalyst composition influences the yield of carbon nanotubes (CNTs) is key to their scalable, cost-effective manufacture. In particular, the role of trace carbon deposits on promoting CNT nucleation from the catalyst has been studied recently by our team. Here, we show that deposition of solid carbon onto an iron catalyst film prior to dewetting effectively amplifies the CNT yield. We investigated the effect of the amount of C and Fe on particle formation and reduction, and growth kinetics using a combination of in situ techniques – Raman spectroscopy, X-ray photoelectron spectroscopy and environmental transmission electron microscopy. We found that CNT growth rate and yield are maximized for specific relative thicknesses of C and Fe (∼0.2 and 0.8 nm, respectively). The presence of carbon causes accelerated dewetting of the catalyst, and more rapidly forms a population of metallic Fe particles that grow CNTs at a higher yield. These factors also cumulatively result in a lower incubation time and improved yield. Therefore, loading of catalyst particles with solid carbon is a straightforward and practical route towards boosting CNT yield and improving the efficiency of CNT growth by chemical vapor deposition.

Methane decomposition with a minimal catalyst: An optimization study with response surface methodology over Ni/SiO2 nanocatalyst

Nowadays, methane cracking in the presence of an efficient catalyst is one of the most investigating areas aiming hydrogen and nanocarbon synthesis. This research contribution systematically investigated the influence of methane partial pressure (PCH4), decomposition temperature, and weight of Ni/SiO2 nanocatalyst (n-Ni/SiO2) on carbon nanotube (CNT) yield. The optimum reaction condition for optimal methane cracking resulted in maximum CNT yield is derived using Design Expert Software. A series of experiments conducted to develop a quadratic polynomial model for CNT yield using response surface methodology. Surprisingly, the optimum catalyst quantity was the lowest (0.30 g) in the experimented parameter range, which exhibited the highest CNT production at 610 °C temperature and 0.8 atm PCH4. The minimal catalyst quantity for the optimum CNT production, which needs only 0.26% of the total volume of the pilot plant reactor, is a breakthrough finding in methane cracking research. It could help to overcome the reactor blockage limitation issues of the process in large scale applications. Thanks to the uniquely supported n-Ni/SiO2 catalyst prepared via co-precipitation cum modified Stöber method. The fresh and used catalysts investigated using different types of characterization techniques such as XRD, BET, Raman spectra, HRTEM, and FESEM-EDX. Characterization results evidenced the presence of differently structured CNTs formed at optimum reaction conditions.

Effect of Co-Mo catalyst preparation and CH4/H2 flow on carbon nanotube synthesis

Supported Co-Mo catalysts with a given ratio of metals were prepared from polyoxomolybdate Mo12O28(μ2-OH)12{Со(H2O)3}4 using impregnation and combustion methods. Effects of the type of catalyst and the ratio and flow of methane and hydrogen gases on the structure of carbon nanotubes (CNTs) synthesized by catalytic chemical vapor deposition (CCVD) method were studied using transmission electron microscopy and Raman spectroscopy. The catalyst prepared by combustion method yielded mainly individualized CNTs, while the CNTs were highly entangled or bundled when impregnation method was used. In both cases, addition of hydrogen to methane led to reduction of the CNT yield. The samples synthesized using two different catalysts and the same CH4/H2 ratio and flow of gases were tested in electrochemical capacitors. A higher specific surface area of the CNTs grown over impregnation-prepared catalyst caused a better performance at scan rates from 2 to 1000 mV/s.

Chemical Vapor Deposition Synthesis of Carbon Nanotube Using Pyrolysis Gas Products of Apricot Kernel Shell

The results of a study of carbon nanotubes (CNTs) growth using apricot stone (AS) as a carbon source are presented. The described method here is two-zone thermal chemical vapor deposition (CVD) that uses cobalt acetate directly as deposition medium at different geometries under argon flow of 100 mL min–1. Argon gas was fed into the oven until pyrolysis of apricot kernel started. Since pyrolysis started, argon was passed through toluene immersed in hot water in the gas washing flask and sent to the furnace for CNT formation. This method allows the bulk metal acetate surface over a quartz road and in a quartz boat to act as catalyst for CNT growth. Our recent results obtained from the toluene assisted growth. The effect of growth temperature and purification of CNTs was studied. As-grown and purified CNTs were characterized by scanning electron microscopy (SEM), X-ray diffraction, differential thermal analysis and surface analysis. High yield of CNTs were obtained over quartz road at 900 °C and at the same temperature with 48 hours deposition time in quartz boat. The obtained CNTs were purified by refluxing using nitric acid.

In situ grown metallic nickel from X–Ni (X=La, Mg, Sr) oxides for converting plastics into carbon nanotubes: Influence of metal–support interaction

The process of pyrolysis and in-line catalysis was employed for converting plastics into value-added carbon nanotubes (CNTs). The metallic nickel catalysts Ni/X (X = La, Mg, Sr) were prepared through in situ growth from parent X–Ni oxides under reductive conditions and used for the catalytic synthesis of CNTs. The results showed that the activities of nickel catalysts decreased in the order of Ni/La > Ni/Sr > Ni/Mg, which strongly depended on the degree of metal–support interaction. The strong metal–support interaction in Ni/Mg catalyst was not favorable for the exsolution of large amount of metallic Ni, resulting in the lowest yield of CNTs. On the other hand, the weak metal–support interaction in Ni/Sr was unfavorable for the high coverage of Ni nanoparticles, leading to the simultaneous growth of carbon nano-onions and CNTs. The Ni/La catalyst with moderate metal–support interaction exhibited the highest yield of CNTs due to optimized amount, size and surface coverage of Ni nanoparticles. The microstructure, graphitization degree, quality and purity of obtained carbon products were characterized using X-ray diffraction, electron microscopy, Raman spectroscopy and thermogravimetric analysis. This study demonstrated an effective and delicate approach to tune the supported metal nanoparticles, leading to enhanced catalytic activity.

Carbon nanotubes synthesis using Fe-Co-Mo/MgO tri-metallic catalyst: study the effect of reaction temperature, reaction time and catalyst weight

MgO supported tri-metallic catalyst containing combination of transition metals Fe, Co, and Mo was used to synthesise carbon nanotubes (CNT) from liquefied petroleum gas by chemical vapour deposition (CVD) method. The effect of reaction temperature, reaction time and catalyst weight to the yield and the CNT properties was investigated. It found that the CNT yield increased with increasing the reaction temperature. Besides, increasing the reaction temperature lead to the increase of the diameter and wall thickness of the CNT. Moreover, it was found that the crystallinity of the synthesised CNT increase when the reaction temperature is raised. The meso pores dominate the pore structure of the CNT product and contribute around 90% of the total pores volume. Meanwhile, micro pores with pore size range around 0.3–0.4 nm dominate the micro pores and contribute approximately 50–60% of the total micro pores volume. It also found that the CNT yield is decreased along with the increasing catalyst weight.

Effect of temperature on multiple competitive processes for co-production of carbon nanotubes and hydrogen during catalytic reforming of toluene

The effects of reaction temperature (range from 500 °C to 800 °C) on multiple competitive processes were studied for the co-production of hydrogen and carbon nanotubes (CNTs) during catalytic reforming of toluene over Ni/α-Al2O3. With the temperature raising from 500 to 800 °C, H2 yield increased by 7 times while H2 proportion slightly decreased 5 vol% due to the competitive effect between steam reforming and reverse water–gas shift (WGS) reaction. Coke amounts (including amorphous carbon and CNTs) firstly increased and then decreased, which was determined by the competitive rate of formation and consumption reaction. Detailed characterization indicated the yield and quality of CNTs improved with the temperature increasing from 500 to 650 °C and reached the maximum at 650 °C, resulting from the enhancing transformation from amorphous to CNTs and consumption of amorphous carbon by steam. However, the growth of CNTs was suppressed by further increasing temperature, and almost no CNTs were generated at 800 °C. The higher temperature aggravated the sintering of Ni and enlarged their particle size, which was not conduced to CNTs growth.

Direct synthesis of carbon nanotubes on fly ash particles to produce carbon nanotubes/fly ash composites

Fly ash was used as catalytic support for carbon nanotubes (CNTs) growth by chemical vapor deposition (CVD) due to having ideal compositions (SiO2,Al2O3, and Fe2O3). In this paper, CNTs were synthesized on Ni catalyst/fly ash substrate using CVD method. The influence of parameters (e.g., reaction temperature and gas flow rate) on the carbon yield and structure of the resulting CNTs was on the carbon yield and structure of the resulting CNTs was investigated by thermo-gravimetric analyses, Scanning electron microscopy, and Raman spectroscopy analysis. The results indicated that the growth temperature controlling had a significant effect on the diameter of CNTs. And the proper acetylene and hydrogen flow rate would decrease in defect density and increase in yield of as-grown CNTs on fly ash. Finally, the amorphous carbon on the surface of as-grown CNTs were removed by heating in air. Experimental results showed that the hydrophobic of the annealed CNTs was weak due to introducing functional groups to the surface of CNTs.

Features of obtaining the catalyst for the synthesis of carbon nanotubes

In this paper, the features of obtaining a Co-Mo/Al2O3 catalyst to synthesize carbon nanotubes (CNTs) by thermal decomposition were studied. It was revealed that the duration of the pre-catalyst thermal decomposition stage in the process of developing a metal oxide system has a significant impact on its activity in the synthesis of carbon nanostructured materials by chemical vapor deposition (CVD). It was proved that an effective catalyst for CNTs synthesis can be obtained by through thermal decomposition of the pre – catalyst, without calcination of the metal oxide system. The use of the Co-Mo/Al2O3 catalyst, synthesized in such a way, in the CVD process makes it possible to reduce the cost of synthesized CNTs. Using scanning electron microscopy, it was shown that the size of the grains, and specific surface area of the formed Co-Mo/Al2O3 catalyst depend on the thermal treatment conditions of the pre-catalyst. Under the conditions for the implementation of the pre-catalyst thermal decomposition stage (temperature, volume, duration, etc.), it is possible to contro not only the characteristics of the resulting catalyst (specific surface area, efficiency), but also the characteristics of the CNTs (diameter, degree of defectiveness). In the course of experiments, the optimal modes of implementation of the method for obtaining the Co-Mo/Al2O3 catalyst allowed forming a system with a specific surface area of ~ 108 m2/g. The use of the resulting catalyst in the synthesis of nanostructured materials provides a high specific yield of multi-walled CNTs with a diameter of 8-20 nm and a degree of defectiveness of 0.97.

New way of the nickel catalyst preparation for carbon nanotubes synthesis by pyrolysis of ethanol vapor

The process of carbon nanotubes (CNTs) synthesis by the method of catalytic pyrolysis of ethanol vapor was studied. It was shown that the synthesis can be carried out in a simple flow reactor by feeding liquid ethanol into the reactor without using carrier gas and hydrogen. Nickel nitrate hexahydrate (Ni(NO3)2•6H2O) was used as a catalyst precursor. A new method of preliminary preparation of the catalyst by decomposition of the precursor in alcohol vapor has been proposed. The activity of catalysts obtained by thermal decomposition of the precursor in air (type I) and in alcohol vapor (type II) was compared. The influence of the synthesis temperature, the process duration, and the reagent consumption rate on the output of CNTs and the degree of alcohol conversion was studied. The obtained carbon nanomaterials were examined by scanning electron microscopy and Raman spectroscopy. It is shown that the type II catalyst in all parameters exceeds the type I catalyst. The yield of CNTs to the mass of the catalyst exceeds 10000%, the degree of ethanol conversion approaches 100%, which roughly corresponds to the synthesis of 100 g of product from 1 liter of alcohol. Proposed improvements make the described method one of the most simple and appropriate for the production of large quantities of inexpensive CNTs that are promising for use as sorbents, catalyst carriers, supercapacitor materials, etc.

Identification of appropriate catalyst system for the growth of multi-walled carbon nanotubes via catalytic chemical vapor deposition process in a single step batch technique

Large quantities of well-aligned and purified Carbon nanotubes (CNTs) are to be produced for commercial applications. For this purpose, the design of an efficient catalyst system is very essential, which should have high catalytic activity, stability, and high diffusion of carbon. In this investigation, an attempt has been made to find a possible catalyst system that supports high yield with a defect-less structure of CNTs. Catalytic chemical vapor deposition (CCVD) single step batch process was used to synthesize CNTs in a single experiment (run) using six different mono-metallic and bi-metallic catalysts (NiO, CoO, CuO, NiO/CuO, NiO/CoO, CoO/CoO) systems. The catalyst materials were synthesized by the impregnation method. The mono-metallic and bi-metallic catalyst particles were characterized by SEM, XRD, and TGA. The carbon products obtained from different catalysts compositions were analyzed using FESEM, HRTEM, and Raman spectroscopy. The yield percentage of multi-walled CNTs was calculated. The aerial density of the CNTs grown on different catalyst compositions was found using image J technique. The diameter distribution of both catalyst compositions and grown CNTs were evaluated using their respective SEM and FESEM images. From this investigation, it was found that NiO/CuO produced higher yield of CNTs with well-aligned structure. CuO/CoO catalyst system produced amorphous carbon. The bi-metallic catalyst compositions grow higher yield and well-aligned CNTs as compared to mono-metallic catalyst systems.

Optimizing electromagnetic wave absorption performance: Design from microscopic bamboo carbon nanotubes to macroscopic patterns

Achieving ideal electromagnetic wave absorbing materials and effective artificial super structures design are increasingly attractive for their irreplaceable role in aerospace stealth structure, Over the Air (OTA) test and civil wireless communication systems. In this work, the bamboo carbon nanotubes (CNTs) were prepared by a simple thermal treatment method. The microstructure and yields of bamboo CNTs were tunable by changing the feeding amounts of polypropylene fabrics precursors. The optimal reflection losses (RL) value of as-prepared bamboo CNTs was up to −54.5 dB at 14.45 GHz with 1.85 mm, meanwhile the effective bandwidth (fe) covered from 12.31 to 17.76 GHz. With subsequent macroscopic honeycomb architecture design based on the as-fabricated bamboo CNTs, the artificial structures with variable radius, thickness and height exhibited more than 90% absorption in 8.5–18 GHz. The results suggested that combination of developing microscopic microwave absorbers and macroscopic structure design would fundamentally optimize the electromagnetic wave absorption with low matching thickness and extensive effective bandwidth.

Synthesis of Carbon Nanotubes by Plasma-Enhanced Chemical Vapor Deposition Using Fe1−xMnxO Nanoparticles as Catalysts: How Does the Catalytic Activity of Graphitization Affect the Yields and Morphology?

The choice of a catalyst for carbon nanotube (CNT) growth is critical to controlling the morphology and chirality of the final product. Plasma-enhanced chemical vapor deposition (PECVD) can alleviate the requirements of the catalyst, i.e., they must be active for both the decomposition of the source gas and graphitization in the conventional thermal CVD. However, it is still not well understood how the catalytic activity of the graphitization affects the yield and quality of CNTs. In this paper, we systematically investigated the influence of the catalytic activity of graphitization by tuning the composition of Fe1−xMnxO (x = 0–1) nanoparticles as catalysts. As the Mn component increased, the number of CNTs decreased because Mn has no catalytic function of the graphitization. The quality of CNTs also affected by the inclusion of the Mn component. Our study may provide useful information to develop a new catalyst for CNT growth in PECVD.

Isolating the Roles of Hydrogen Exposure and Trace Carbon Contamination on the Formation of Active Catalyst Populations for Carbon Nanotube Growth.

Limited understanding of the factors influencing the yield of carbon nanotubes (CNTs) relative to the number of catalyst particles remains an important barrier to their large-scale production with high quality, and to tailoring CNT properties for applications. This lack of understanding is evident in the frequent use of Edisonian approaches to give high-yield CNT growth, and in the sometimes-confusing influence of trace residues on the reactor walls. In order to create conditions wherein CNT yield is reproducible and to enable large-scale and reliable CNT synthesis, it is imperative to understand-fundamentally-how these common practices impact catalytic activity and thus CNT number density. Herein, we use ambient pressure-X-ray photoelectron spectroscopy (AP-XPS) to reveal the influence of carbon and hydrogen on the coupling between catalyst reduction and CNT nucleation, from an iron catalyst film. We observe a positive correlation between the degree of catalyst reduction and the density of vertically aligned CNTs (forests), verifying that effective catalyst reduction is critical to CNT nucleation and to the resulting CNT growth yield. We demonstrate that the extent of catalyst reduction is the reason for low CNT number density and for lack of self-organization, lift-off, and growth of CNT forests. We also show that hydrocarbon byproducts from consecutive growths can facilitate catalyst reduction and increase CNT number density significantly. These findings suggest that common practices used in the field-such as reactor preconditioning-aid in the reduction of the catalyst population, thus improving CNT number density and enabling the growth of dense forests. Our results also motivate future work using AP-XPS and complementary metrology tools to optimize CNT growth conditions according to the catalyst chemical state.

Carbon-assisted catalyst pretreatment enables straightforward synthesis of high-density carbon nanotube forests

Despite extensive academic and commercial development, a comprehensive understanding of the principles necessary for high-yield production of carbon nanotubes (CNTs) is lacking, whether in oriented films, bulk powders, or other forms. In chemical vapor deposition growth of CNT films on substrates, trace contaminants of carbon, such as deposits on the reactor tube walls, are known to cause inconsistency in key production metrics, including CNT density and alignment. In this study, we show that trace exposure of the catalyst to carbon during initial heating of the catalyst film is a critical determinant of CNT yield, and this carbon exposure accelerates catalyst nanoparticle formation via film dewetting and increases the probability of CNT nucleation and the resultant density of the CNT population. By controlled exposure of the catalyst to a trace amount of carbon, we show up to a 4-fold increase in bulk mass density for a given forest height, an 8-fold increase in local CNT number density, and a 2-fold increase in the growth lifetime, relative to a reference condition. We discuss potential mechanisms to explain the role of carbon exposure on the probability of CNT nucleation from nanoparticle catalysts, supported by microscopy and gas analysis.