Production Of Carbon Nanotubes Research Articles

Application of Carbon Nanotubes from Waste Plastics As Filler to Epoxy Resin Composite.

Carbon nanotubes (CNTs) are promising nanofillers to enhance the mechanical performance of polymers. Through catalytic conversion, waste plastics can be converted into CNTs, which could be an alternative to commercial CNTs (cCNTs). Exploring a practical application of waste-plastic-derived CNTs will largely promote the technology development related to waste plastic management and CNT production. In this work, CNTs produced from plastics, named pCNTs, were applied as fillers to epoxy resin (EP), while commercial CNTs (cCNTs) were used as a reference. The carboxyl groups were effectively inserted on the CNT skeleton by a facile purification and modification. After ultrasonic dispersion, the modified pCNTs (M-pCNTs) were uniformly dispersed and loaded in the EP matrix. Better mechanical properties than EP were attained with a Young’s modulus of 3776.9 MPa, a tensile strength of 37.3 MPa, a fracture strain of 6.32%, and a fracture strength of 111.7 MPa with 2 wt % M-pCNT loading. Thus, pCNTs enhanced the toughness of the EP composites and simultaneously retained the stiffness. It was suggested that CNT pull-out and bridging were predominant toughening mechanisms for pCNT/EP composites. Notably, the coated film developed between residual metal in M-pCNTs and EP built a strong interfacial interaction and reinforced the EP composites.

Formation of Thermally Stable, High-Areal-Density, and Small-Diameter Catalyst Nanoparticles via Intermittent Sputtering Deposition for the High-Density Growth of Carbon Nanotubes.

We report the formation of thermally stable catalyst nanoparticles via intermittent sputtering deposition to prevent the agglomeration of the nanoparticles during thermal chemical vapor deposition (CVD) and for the high-density growth of carbon nanotubes (CNTs). The preparation of high-areal-density and small-diameter catalyst nanoparticles on substrates for the high-density growth of CNTs is still a challenging issue because surface diffusion and Ostwald ripening of the nanoparticles induce agglomeration, which results in the low-density growth of large-diameter CNTs during high-temperature thermal CVD. Enhancing the adhesion of nanoparticles or suppressing their diffusion on the substrate to retain a small particle diameter is desirable for the preparation of thermally stable, high-areal-density, and small-diameter catalyst nanoparticles. The intermittent sputtering method was employed to deposit Ni and Fe metal nanoparticles on a substrate for the synthesis of high-areal-density CNTs for Fe nanoparticle catalyst films. The metal particles deposited via intermittent sputtering with an interval time of over 30 s maintained their areal densities and diameters during the thermal CVD process in a vacuum for CNT synthesis. An interval of over 30 s was expected to oxidize the metal particles, which resulted in thermal stability during the CVD process. The intermittent sputtering method is thus a candidate process for the preparation of thermally stable catalyst films for the growth of a high density of long CNTs, which can be combined with the present CNT production process.

Controlled Transition Metal Nucleated Growth of Carbon Nanotubes by Molten Electrolysis of CO2

The electrolysis of CO2 in molten carbonate has been introduced as an alternative mechanism to synthesize carbon nanomaterials inexpensively at high yield. Until recently, CO2 was thought to be unreactive, making its removal a challenge. CO2 is the main cause of anthropogenic global warming and its utilization and transformation into a stable, valuable material provides an incentivized pathway to mitigate climate change. This study focuses on controlled electrochemical conditions in molten lithium carbonate to split CO2 absorbed from the atmosphere into carbon nanotubes (CNTs), and into various macroscopic assemblies of CNTs, which may be useful for nano-filtration. Different CNT morphologies were prepared electrochemically by variation of the anode and cathode composition and architecture, variation of the electrolyte composition pre-electrolysis processing, and variation of the current application and current density. Individual CNT morphologies’ structures and the CNT molten carbonate growth mechanisms are explored using SEM (scanning electron microscopy), TEM (transmission electron micrsocopy), HAADF (high angle annular dark field), EDX (energy dispersive xray), X-ray diffraction), and Raman methods. The principle commercial technology for CNT production had been chemical vapor deposition, which is an order of magnitude more expensive, generally requires metallo-organics, rather than CO2 as reactants, and can be highly energy and CO2 emission intensive (carries a high carbon positive, rather than negative, footprint).

Acute toxicity and 28-day repeated dose studies of multi-walled carbon nanotubes

In the light of the increased production and use of multi-walled carbon nanotube (MWCNT) in consumer products, there is a need for screening the potential toxicity of this nanomaterial. In the present study, the researchers have investigated the acute dermal and acute eye irritation in rabbits and acute oral irritation and 28-day repeated administration of MWCNT in rats. A single dose of 5000 mg/kg was used to test Albino Rabbits for acute dermal and eye irritation test. Similar dose was given to Sprague Dawley Rats for the acute oral and 28-day repeated dose test. Clinical signs/manifestations were closely observed for the first four (4) hours post sample administration and was continued for 1,2,3,7 and 14-day observation period. In acute toxicity study, no treatment-related death or toxic signs were observed with MWCNT. In the 28-day repeated dose study, no significant differences in hematology and clinical biochemistry were detected between control and MWCNT. However, histopathology results revealed mild periarteriolar lymphoid cell depletion in the spleen and mild tubular cell degeneration on the cortex and medulla of both kidneys of the rats while no remarkable lesions were seen on the other organs of both female and male rats.

Feasibilities of Producing High-Value Carbon Nanotubes from Waste Plastics by Spray Pyrolysis

Feasibilities of Producing High-Value Carbon Nanotubes from Waste Plastics by Spray Pyrolysis

The Concept of Managing the Process System for the Production of Carbon Nanotubes

The Concept of Managing the Process System for the Production of Carbon Nanotubes

Experimental study of thiophene and ferrocene in synthesis of single-walled carbon nanotubes in rich premixed hydrogen/air flames

The effects of varying concentrations of ferrocene and thiophene on the synthesis of carbon nanotubes (CNT) in a floating catalyst, flame-based reaction system were investigated. Pre-vapourised ethanol and a surrounding premixed H2/air flame were used as carbon feedstock and heat source. Samples of the synthesised material were collected and analysed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction to determine their compostitions and properties. Sulphur to iron mass ratios mS/Fe were varied from 0 up to 10.1, by changing the relative amounts of thiophene and ferrocene. The latter was found to marginally improve the yield of CNTs, but rather led to an enhanced yield of iron oxide nanoparticles. In comparison, the addition of sulphur resulted in an improved production of CNTs in terms of number density and lengths. An optimum window of mass ratios mS/Fe for CNT production was identified as 0.1–2. A numerical model for the diffusion of species coupled with an equilibrium chemical model for the resulting species has been constructed to understand the mechanisms of the synthesis process, which demonstrates the range of elemental proportion conditions and residence times favourable to high yield of CNTs.

The Influences of Oxygen Concentration and External Heating on Carbon Nanotube Growth in Diffusion Flame

Tight control of the carbon nanotube (CNT) synthesis process in flames remains a challenge due to the highly non-uniform gradient of flame thermochemical properties. The present study aims to establish a baseline model for flame-enhanced chemical vapor deposition (FECVD) synthesis of CNT and to analyze the CNT growth region at varying flame and furnace conditions. The numerical model comprises a computational fluid dynamics (CFD) simulation that is coupled with the CNT growth rate model to simulate the flow field within the furnace and the CNT growth respectively. Validation of the flame shape, flame length, and temperature profile are carried with a reasonable comparison to experimental measurements. A parametric study on the effects of furnace heating capacity and oxidizer concentration is conducted. The results of the CNT growth rate model reveal that there is a positive correlation between the heater power and CNT length. Supplying a higher concentration oxidizer at a fixed furnace power is predicted to result in further improvement in CNT length and high yield region. Flame structure analysis showed that with the heater turned on at 750 W (corresponding to heat flux of 21,713W/m2), the growth region expands twofold when oxygen concentration is increased from 19% to 24%. However, the growth region shrinks when the oxygen concentration is further increased to 27% which indicates depletion of carbon source for CNT growth due to excess oxygen. The finding of this research could guide and optimize the experiment of the flame-assisted CNT production in the future.

Structural comparison of multi-walled carbon nanotubes produced from polypropylene and polystyrene waste plastics

Polypropylene and polystyrene were processed in a pyrolysis/catalytic reactor with a Ni-Fe/Al2O3 catalyst to produce carbon nanotubes (CNTs). A high yield of catalyst carbon deposits were produced; 33.5 g 100 g−1 polypropylene and 29.5 g 100 g−1 polystyrene and consisted of multi-walled carbon nanotubes (MWCNTs). X-ray diffraction (XRD) of the Ni-Fe/Al2O3 catalyst suggested the active metal was a Ni-Fe alloy which was confirmed using X-ray absorption near edge structure (XANES); extended X-ray absorption fine structure (EXAFS) analysis showed that the alloy was primarily FeNi2. Electron microscopy showed that the MWCNTs were entangled, several μm in length and ~50 nm in diameter comprising ~30 graphene layers. Optical Raman spectroscopy confirmed the carbons to be of high purity and crystallinity with polypropylene showing a higher degree of graphitisation and fewer defects compared to those produced from polystyrene. X-ray Raman scattering spectroscopy of the MWCNTS confirmed their graphitic carbon composition, but demonstrated poor alignment. Commercially produced MWCNTs showed a high degree of graphitisation, with less metal impurities and were of long length (several μm), straighter, smaller diameter (~10 nm) and with fewer number of graphene layers (~12) in the CNT wall compared with the plastic derived MWCNTs.

Production and characterization of carbon nanotubes by methane decomposition over Ni–Fe/Al2O3 catalyst and its application as nanofillers in polypropylene matrix

This paper studies the influence of metal precursors in the CVD´s catalyst synthesis of carbon nanotubes (CNTs) used as fillers in a polypropylene (PP) matrix (∼0.3 wt%). Two catalytic schemes, Fe/Al2O3 (50:50) and Ni–Fe/Al2O3 (40:10:50), were prepared to determine the influence of the reduction temperature over the characteristics and mechanical properties of CNT as PP fillers. The conversion temperature was varied to see the dependance of the CNT structure to this variable (700 °C–750 °C–800 °C). CNTs products were characterized by SEM and Raman spectroscopy. The SEM micrographs showed a sharper fiber type CNTs for the bimetallic catalyst and the Raman confirmed that better crystallites are obtain over the Fe catalyst. The Fe–PP composite presented enhanced mechanical properties when compare with Fe–Ni–PP, with tensile strength, hardness, and impact properties are higher in 16%, 9%, and 9% respectively. Other carbonaceous materials, as CNF, with less crystallinity presented poorer mechanical properties. Finally, can be stated that for the use of CNF as fillers in PP composites a Fe/Al2O3 catalyst, and a reaction temperature 700 °C–750 °C will produce a CNF with 60 nm mean diameter, is better than the use of Fe-Ni based catalysts.

The Effect of Cobalt Catalyst Loading at Very High Pressure Plasma-Catalysis in Fischer-Tropsch Synthesis

The influence of different catalyst cobalt loadings on the C1–C3 hydrocarbon product yields and energy consumption in plasma-catalytic Fischer-Tropsch synthesis (FTS) was investigated from the standpoint of various reactor operating conditions: pressure (0.5 to 10 MPa), current (250 to 450 mA) and inter-electrode gap (0.5 to 2 mm). This was accomplished by introducing a mullite substrate, coated with 2 wt%-Co/5 wt%-Al2O3, 6 wt%-Co/5 wt%-Al2O3 or 0 wt%-Co/5 wt%-Al2O3 (blank catalyst), into a recently developed high pressure arc discharge reactor. The blank catalyst was ineffective in synthesizing hydrocarbons. Between the blank catalyst, 2 wt%, and the 6 wt% Co catalyst, the 6 wt% improved C1–C3 hydrocarbon production at all conditions, with higher yields and relatively lower energy consumption at (i) 10 MPa at 10 s, and 2 MPa at 60 s, for the pressure variation study; (ii) 250 mA for the current variation study; and (iii) 2 mm for the inter-electrode gap variation study. The inter-electrode gap of 2 mm, using the 6 wt% Co catalyst, led to the overall highest methane, ethane, ethylene, propane and propylene yields of 22 424, 517, 101, 79 and 19 ppm, respectively, compared to 40 ppm of methane and <1 ppm of C1–C3 hydrocarbons for the blank catalyst, while consuming 660 times less energy for the production of a mole of methane. Furthermore, the 6 wt% Co catalyst produced carbon nanotubes (CNTs), detected via transmission electron microscopy (TEM). In addition, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD) showed that the cobalt catalyst was modified by plasma treatment.

Carbon nanotubes for production and storage of hydrogen: challenges and development

Carbon nanotubes for production and storage of hydrogen: challenges and development

Catalytic pyrolysis of sugarcane bagasse by zeolite catalyst for the production of multi-walled carbon nanotubes

Recently, the disposal of waste by beneficial and environmentally friendly methods has attracted great attention. In this work, we have studied the production of high-value carbon nanotubes (CNTs) which have remarkable applications by catalytic pyrolysis of sugarcane bagasse (SCB) as an agricultural waste using a two-stage process. Various reaction factors including the effects of zeolite types (HZSM-5, HMOR, and HY), pyrolysis temperatures (450−700°C), and SCB/ZSM-5 ratios (3−12) on SCB pyrolysis were investigated to generate CNTs from pyrolysis products. A Co-Mo/MgO catalyst was used for growing CNTs via the decomposition of pyrolysis products. The morphological structure and quality of CNTs were characterized using TEM and Raman spectroscopy, while the fresh Co-Mo/MgO catalyst was characterized by XRD and TPR analyses. The results showed that zeolite type, pyrolysis temperature, and SCB/ZSM-5 ratio had significant effects on the CNTs yield. The optimum carbon yield (24.9%) was achieved using the HZSM-5 catalyst at the pyrolysis temperature of 500°C and with the SCB/ZSM-5 ratio of 6. TEM observations confirmed the growth of bamboo-like carbon nanotubes (BCNTs) and carbon nano-onions (CNOs) in different proportions according to the reaction parameters. Also, CNTs with the largest diameter distribution range (7−76 nm) were produced using the SCB/ZSM-5 ratio of 6. Raman spectra demonstrated the production of high-quality CNTs under all studied conditions.

Mass Production and Growth Mechanism of Carbon Nanotubes in Optimized Mechanothermal Method

There are a lot of major parameters in the mechanothermal approach which play a key role in the quality and quantity of the carbon nanotubes (CNTs). In this study, these factors were optimized to maximize the efficiency of the process, and also the growth mechanism of CNTs was investigated. For these purposes, the milling of graphite was performed in a high alloy steel vial for 330 h at the vial speed of 300 rpm in a planetary ball mill. The morphology and crystal structures of the graphite powder during the mechanical activation were studied by x-ray diffraction (XRD), Zeta-Sizer, and scanning electron microscope/energy-dispersive x-ray spectroscopy (SEM/EDX). After the heat treatment of amorphous carbon at 1400 ˚C, the CNTs were synthesized and their quality and quantity were analyzed by transmission electron microscopy (TEM), atomic force microscopy (AFM), XRD, Raman spectroscopy, and differential thermal analysis/thermogravimetric analysis (DTA/TGA). A special type of tip-growth mechanism based on the motion of the catalyst particles was proposed regarding the TEM images. According to this mechanism, the diameter, length, and shape of the CNT are completely dependent on a random motion of the catalyst particle at the tip of the nanotube. As a consequence, the growth mechanism in the mechanothermal process does not follow a certain pattern and this is the main reason for the spring-like and curved shape of the nanotubes. Furthermore, results of the differential thermal analysis revealed that the yield of fabricated multi-walled carbon nanotubes (MWCNTs) is more than 97% of the precursor.

Simultaneous production of hydrogen and carbon nanotubes from biogas: On the effect of Ce addition to CoMo/MgO catalyst

In this study, hydrogen and carbon nanotubes (CNTs) are simultaneously produced via a synergistic combined process of CO2 methanation (METH) and chemical vapor deposition (CVD) processes using biogas as a feedstock. METH process could upgrade CO2 containing biogas into CH4-rich gas which then decomposed into H2 and forming CNTs over CoMo/MgO catalyst by CVD process. The effects of Ce addition to CoMo/MgO were investigated. Comprehensive characterization confirms that all as-synthesized samples composed of well-aligned multi-walled carbon nanotubes (MWCNTs) with a narrow size distribution. The Ce addition improved CoMo dispersion on MgO, resulting in smaller and uniform CNTs. The small addition of Ce into CoMo/MgO catalyst could enhance the production CNTs yield. The higher Ce addition would, however, result in the CNTs yield decreased, attributed to a high basicity of CeO2 surface and a large coverage of CeO2 on the catalyst surface. The IG/ID increased with increased Ce addition, while the surface area monotonically decreased, attributed to a decrease in defects of nanotubes. In addition, this wisely combined process could result in a remarkable 100%CO2 elimination, while high CH4 conversion of 90% was obtained. The H2 production yield could gain more than 30 vol% with respect to H2 in the feed stream. The H2 yield and purity in the effluent gas stream were approximately 90%.

Conversion of pyrolytic non-condensable gases from polypropylene co-polymer into bamboo-type carbon nanotubes and high-quality oil using biochar as catalyst

The conversion of low-value plastic waste into high-value products such as carbon nanomaterial is of recent interest. In the current study, the non-condensable pyrolysis gases, produced from Polypropylene Copolymer (PPC) feedstock, was converted into bamboo-type carbon nanotubes (BCNTs) through catalytic chemical vapour deposition using biochar. Experiments were conducted in a three-zone furnace fixed bed reactor, where PPC was pyrolysed in the second zone and carbon nanotubes (CNTs) growth was eventuated in the third zone. The effects of different growth temperatures (500, 700, 900 °C) and biochar particle sizes (nanoparticle as well as 0–100 and 100–300 μm) were investigated to optimise the production of hydrogen and the yield of carbon nanotubes on the biochar surface. Biochar samples used in the synthesis of CNTs were obtained from the pyrolysis of saw dust at 700 °C in a muffle furnace. Analyses performed by using Scanning electron microscopy, Transmission electron microscopy, X-ray diffraction, and Raman spectroscopy techniques suggested that the best crystalline structure of CNTs were obtained at 900 °C with nano-sized biochar as a catalyst. The strong gas-solid contact and void fraction of nano-sized particles enhances the diffusion–precipitation mechanism, leading to the growth of CNTs. The nano-sized biochar increased hydrogen production at 900 °C and reduced the polycyclic aromatic hydrocarbons content in oil to only 1%, which is advantageous for further utilisation. Therefore, the production of high-value CNTs from waste plastic using low-cost biochar catalyst can be a sustainable approach in the management of waste plastic while participating in the circular economy.

Development of pressureless sintered and hot‐pressed CNT/alumina composites including mechanical characterization

AbstractA process for the production of carbon nanotube (CNT)/alumina composites on the basis of an aqueous suspension and without any extensive pretreatment was developed. Pressureless sintering and hot‐pressing of the nanocomposites were extensively researched and optimized. The influence of varying CNT contents, different alumina powders, sintering temperature and pressure on mechanical properties were investigated. Optimal hot‐pressing conditions are specified at 1550°C, 15 min dwell time, and 80 MPa applied pressure. Dense nanocomposites up to 3 wt.% and 0.5 wt.% CNT content were achieved by hot‐pressing and pressureless sintering, respectively. Furthermore, a 20% increase in hardness for CNT contents below 1.0 wt.% was detected, which is independent from the applied force and the alumina matrix. A highly anisotropic fracture toughness at increased CNT contents was detected by an indentation‐based method. The developed process provides a possibility to produce CNT/alumina composites with improved mechanical properties under reasonable effort, which could also be used for industrial production.

Proposal of Analytical Model of Tensile Property of Untwisted Carbon Nanotube Yarn and Estimation of Tensile Property of Carbon Nanotube

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform for composite fabrication with high mechanical performance. In this study, untwisted carbon nanotube yarns with varied densities were prepared by using spinnable carbon nanotube forests, and the tensile properties were examined. Furthermore, an analytical model of tensile properties for untwisted carbon nanotube yarns was proposed based on the shear-lag model. The proposed model can predict the tensile behavior of an untwisted yarn from the tensile modulus and strength of a carbon nanotube, the volume packing fraction of carbon nanotubes for the untwisted yarn, and shear stress exerted on the slipped region of a carbon nanotube. Then, the proposed model was applied to estimate the elastic modulus and tensile strength of a carbon nanotube from the tensile properties of untwisted carbon nanotube yarns. In our case, the estimated tensile elastic modulus of a carbon nanotube was about 200 GPa, and the estimated tensile strength of a carbon nanotube was about 1.9 GPa.

Nanostructure engineering by surficial induced approach: Porous metal oxide-carbon nanotube composite for lithium-ion battery

Developing efficient materials is urgent to reach the challenging demand of next-generation energy devices from portable electronic devices to electric grids and electric vehicles. Nanostructure interface engineering is an emerging strategy to prepare advanced materials according to demand. Herein, we reported the surface induced metal organic frameworks (MOFs) on the layered double hydroxide (LDH) following the controlled pyrolysis, which results in the formation of various structural morphologies. Among others, in situ produced carbon nanotubes (CNTs) anchored Co-Ox are proposed as advantageous materials with coped properties suitable for next generation electrochemical devices such as Li-ion batteries. The MOF-inherited higher surface area and porosity with CNTs channels improved the easily transport of ions during charging/discharging process. Further, the well exposed Co-Ox are structurally flexible and own accessible sites for Li+ extraction/insertion that can alleviate drastic volumetric fluctuations during charge/discharge cycling. For the realization of concept, we assembled LIB, which showed a high initial specific discharge capacity of 948 mA h g−1 at 1 A g−1 of current density, a high reversible capacity of 723 mA hg−1 after a long cycling up to 500 cycles at 1 A g−1 of current density and excellent rate capability with ~ 97% capacity retention. Hence, the high electrochemical activity is ascribed to the porous carbon/carbon nanotubes stabilized by metal oxides nanoparticles, which is reflection of our synthetic strategy.

Gaussian Process Surrogate Modeling Under Control Uncertainties for Yield Prediction of Carbon Nanotube Production Processes

Abstract A large-scale production of carbon nanotubes has been of great interest due to their practical needs, which is limited by the difficulty of producing them with controlled structures and properties. We seek for a surrogate modeling to predict the process yield for a given process configuration under control uncertainties. The predictive power can be used to optimize the process configuration in a closed-loop production system. A challenge in the surrogate modeling is that some process conditions are controlled by other manipulating factors, and the control precision is not high. Therefore, the process conditions vary significantly even under the same setting of the manipulating factors. Due to this variation, the surrogate modeling that directly relates the manipulating factors to the process outcome does not provide a great predictive power on the outcome. At the same time, the model relating the process conditions to the outcome is not appropriate for the prediction purpose because the process conditions cannot be accurately set as planned due to the control uncertainties for a future process run. Motivated by the example, we propose a two-tiered Gaussian process (GP) model, where the bottom tier relates the manipulating factors to the process conditions with control variation, and the top tier relates the process conditions to the outcome. It explicitly models the propagation of the control uncertainty to the outcome through the two modeling tiers. The benefits of the approach over the standard GP approach are illustrated with multiple simulated scenarios and carbon nanotube production processes.