Growth Of Multi-walled Carbon Nanotubes Research Articles

Revealing the Mechanism of Multiwalled Carbon Nanotube Growth on Supported Nickel Nanoparticles by in Situ Synchrotron X-ray Diffraction, Density Functional Theory, and Molecular Dynamics Simulations

The mechanism of multiwalled carbon nanotube synthesis from methane chemical vapor deposition on a 5% Ni/MnO catalyst is studied at 873 and 1073 K by in situ transmission XRD using synchrotron radi...

Direct growth of MWCNTs on stainless steel by V-type flame: mechanism of carbon nanotube growth induced by surface reconstruction

Producing carbon nanomaterials adjustably on a large scale with existing manufacturing methods is a promising direction. Here, multiwalled carbon nanotubes (MWCNTs) were grown on stainless steel substrate using a self-built V-type flame burner under atmospheric pressure. The surface structure of mirror and wiredrawing stainless steel substrates was observed by scanning electron microscopy. Carbon nanotubes only grow on calcined wiredrawing stainless steel substrate. X-ray diffraction was used to investigate the crystallinity of MWCNTs synthesized on substrates that were heated at 400 °C, 600 °C, and 800 °C, indicating that the calcining temperature of the substrate affects the properties of MWCNTs growth. Products grown on the substrate calcined at 600 °C are optimal. Scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were employed to examine the morphology and chemical compositions of substrates calcined at different temperatures before growing carbon nanotubes. It was found that the morphology of the substrate surface is a key factor in controlling the growth of MWCNTs. Uniform particles with glossy boundaries are available for MWCNTs synthesis. Energy-dispersive spectroscopy was performed on single metallic particles found inside the nanotubes, clarifying that iron nanoparticles provide active sites for carbon nanotube growth on stainless steel instead of oxidation iron and other elements. A better understanding of the growth of carbon nanotubes on stainless steel using a V-type flame burner can help to adjust the properties of carbon nanotubes deposited on the required constructions, and provide additional insight into realization of large-scale and low-cost constructions covered with carbon nanotubes.

Directly Grown Multiwall Carbon Nanotube and Hydrothermal MnO2 Composite for High-Performance Supercapacitor Electrodes.

MnO2–MWNT–Ni foam supercapacitor electrodes were developed based on directly grown multiwalled carbon nanotubes (MWNTs) and hydrothermal MnO2 nanostructures on Ni foam substrates. The electrodes demonstrated excellent electrochemical and battery properties. The charge transfer resistance dropped 88.8% compared with the electrode without MWNTs. A high specific capacitance of 1350.42 F·g−1 was reached at the current density of 6.5 A·g−1. The electrode exhibited a superior rate capability with 92.5% retention in 25,000 cycles. Direct MWNT growth benefits the supercapacitor application for low charge transfer resistance and strong MWNT–current collector binding.

Effect of Ni incorporation in cobalt oxide lattice on carbon formation during ethanol decomposition reaction

In this work, we report the results of catalytic decomposition of ethanol over a porous mixed metal oxide of Ni-Co (NiCoO2) and analyze the effect of Ni incorporation in Co3O4 lattice on the activity and hydrogen selectivity from ethanol decomposition reaction. In-situ FTIR analysis was conducted between 50 °C to 400 °C for both, Co3O4 and NiCoO2, catalysts to understand the reaction mechanism leading to gas phase product distribution. On cobalt surface the reaction pathway proceeds via the formation of surface ethoxy intermediate that subsequently transforms to aldehyde and acetate intermediates before decomposing to release CO2, H2 and CH4 gases at high temperature. A similar pathway is followed on NiCoO2 surface, leading to aldehyde intermediate, which is relatively unstable and decomposes to release CO along with CH4 and H2 at 400 °C. The NiCoO2 catalyst shows relatively low selectivity for CO2, possibly due to the unstable aldehyde species providing little acetate intermediate that decomposes to release gaseous CO2. The addition of Ni improves the activity for ethanol decomposition by achieving a complete ethanol conversion at 350 °C as compared to 420 °C for cobalt alone. The crystallinity, morphology and particle analysis of the spent catalyst after the reaction was studied using XRD, SEM, and TEM respectively. The XRD shows a phase change of porous NiCoO2 to NiCo alloy, whereas SEM indicates the presence of fibrous structure on the surface with 91.7% of carbon while keeping 1:1 ratio of Ni and Co after the reaction. The detailed analysis of carbon structure using HRTEM-STEM shows the simultaneous growth of carbon nanofibers (CNFs) and multiwalled carbon nanotubes (MWCNTs) that were favored by larger and smaller crystallites respectively. A detailed mechanism of carbon deposition is also proposed.

Multiwall carbon nanotubes tailored porous carbon fiber paper-based gas diffusion layer performance in polymer electrolyte membrane fuel cell

In the present investigation, porous carbon fiber paper as a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cell was modified by nano-structuring. It was modified by incorporating multiwall carbon nanotubes (MWCNTs) in chopped carbon fiber preform by two approaches; first by incorporating in the matrix phase and second by the in-situ growth of MWCNTs on the carbon fiber preform by chemical vapor deposition technique, followed by impregnation of phenolic resin and processed to carbonization at 1000 and 1800 °C.The effect of MWCNTs incorporation was ascertained by characterizing carbon fiber paper by various techniques. It is found that incorporation of MWCNTs reveals an increase in electrical conductivity from 66 S/cm to 175 S/cm and flexural modulus from 5 GPa to 20 GPa. The extent of increase in electrical conductivity was greater in MWCNTs mixed with phenolic resin as compared to MWCNTs grown over the carbon fiber preform. There is a significant improvement in power density from 361 to 594 mW/cm2 of MWCNTs grown based GDL. The BET contact angle increases the hydrophobicity of GDL, reduced the blockage of gas diffusion path. Also, higher value of electrical conductivity, surface area and optimal pore sizes results in the enhancement of I-V performance.

Diffusion effect for the catalytic growth of carbon nanotubes on metal alloys substrate

Multiwall carbon nanotube (MWCNT) films were synthesized on a metal-alloy probe using thermal chemical vapor deposition (CVD) at low temperature (550 °C). The morphology of the Ni catalyst deposited on Co and Ta barrier layers on the metal-alloy substrate was investigated. In addition, we studied the tuning of the thickness of the Ni catalyst (without Co and Ta barrier layers), pretreatment time in a NH3, and the C2H2/NH3 ratio for growing MWCNTs. We showed that buffer layers were unstable during Ni catalyst nucleation on the metal-alloy probe during CNT growth because it diffused into the surface of probe and recrystallized during pretreatment. The results suggest that only using a thicker Ni catalytic layer (50 nm) could it allow for the growth of MWCNTs on the metal-alloy probe. The length of the MWCNTs was ~10 μm. In this paper, we propose a mechanism for thermal CVD of MWCNTs on a metal-alloy probe without barrier layers under a C2H2/NH3 atmosphere.

Influence of the nanostructure of silica supports on the growth and morphology of MWCNTs synthesized by CCVD method

Abstract Due to the influence of its superficial physical parameters on the interaction with catalyst, mesoporous silica is commonly referred as suitable support to grow carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CCVD) method. Faced with the various possibilities of applying nanostructured SiO2/CNTs composites, this work aims to evaluate and clarify the influence of the silica mesoporosity and morphology on the quality and amount of CNTs produced by CCVD process. Five different nanostructured silicas (n-SiO2) were produced by sol-gel method. Basically, four silica samples were synthesized with the addition of an acidic catalyst and one with a basic catalyst. Thermogravimetric analysis, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy were used to characterize the silica supports and the as-grown CNTs produced in this work. The obtained results show differences in the morphology of the synthesized CNTs according to the physical properties of each n-SiO2. The mesoporous silica structure, due to different pore size distribution and volume, affected the interaction between the support and the catalyst, and, consequently, the quality and amount of the synthesized multi-walled carbon nanotubes (MWCNTs). Silica supports with either high mesopore volume, or high mesopore size, provide the highest quantities of as-grown CNTs materials. However, in terms of quality of as-grown CNTs, the supports with lower mesopores volume were more adequate to the MWCNTs synthesis. Nevertheless, the presence of pores with compatible size may have allowed an improved anchorage of catalyst particles inside these pores favoring the growth of CNTs with good quality.

Effect of buffer layer nature on multiwall carbon nanotube growth rate by PECVD

In this work, vertically aligned multiwall carbon nanotubes (MWCNTs) were produced, at 600 °C, by plasma enhanced chemical vapour deposition (PECVD), in an electron cyclotron resonance (ECR) plasma chamber using a C2H2/NH3 gas mixture. The MWCNTs were directly grown onto a carbon buffer thin film (a-C) or a titanium nitride film (TiN) deposited on a silicon surface. For this purpose, nickel (Ni) nanoparticles were deposited on the both buffer layers, by an electrochemical procedure, and used as a catalyst for the MWCNT growth. The effect of the buffer layer on MWCNT growth rate during different growth times was investigated in this work. It was found that MWCNT produced over the a-C buffer grow faster compared with those grown over the TiN buffer. Moreover, when the growth time increases, the MWCNTs deposited on the a-C buffer can maintain a relatively high density compared with those grown on the TiN layer. Using in-situ X-ray photoelectron spectroscopy, the effect of both buffers on the MWCNT growth rate is discussed with reference to changes in the state of Ni catalysts annealed at 600 °C. The results demonstrate the benefit of using the a-C layer for MWCNT grown by PECVD for specific applications including electrochemical biosensors and electrochemical capacitors.

Carbon nanotube – Carbon fiber reinforced polymer composites with extended fatigue life

In this study, uniform and patterned multiwall carbon nanotubes (MWCNTs) forests were grown over carbon fiber fabrics utilizing a relatively non-destructive synthesis technique; graphitic structures by design (GSD). Carbon fiber reinforced epoxy polymer composites (CFRPs) were fabricated based on the carbon fibers with surface grown MWCNTs and examined under monotonic tensile tests. The fabricated composites were also examined under a tension-tension fatigue loading at three stress levels of 85, 90 and 95% of their monotonic strength using a cyclic stress ratio of 0.10 to investigate the effects of the various topologies of the surface grown MWCNTs on the fatigue damage progression and life of the CFRPs. Results revealed that the fatigue life of the CFRPs with patterned growth of MWCNTs exhibited a significant fatigue life improvement of 150%. The fractography analysis elucidated the role of MWCNTs in protecting the fiber yarn against the matrix cracks leading to significant fatigue life improvement.

Controlled Syntheses of Multi-walled Carbon Nanotubes from Bimetallic Fe–Co Catalyst Supported on Kaolin by Chemical Vapour Deposition Method

Multi-walled carbon nanotubes (MWCNTs) were synthesized via acetylene gas deposition over bimetallic Fe–Co/kaolin catalyst by chemical vapour deposition method. The effects of synthesis parameters such as calcination temperatures, reaction time, argon and acetylene flow rates on the CNTs yield were examined using $$2^{4}$$ full factorial experimental design. The as-prepared nanomaterials were characterized by HRSEM/EDS, HRTEM, TGA, DLS, XRD, XPS and BET. The HRSEM/TGA revealed well dispersion of the metallic particles on the kaolin support with high thermal stability. XRD analysis of the catalyst confirmed the formation of mixed oxides of different intensities which can favour the growth of MWCNTs. The optimum conditions to obtain high catalyst yield of 88.9% were: mixing ratio of 1.6, stirring speed 1000 rpm, calcination temperature $$500\,{^{\circ }}\hbox {C}$$ and calcination time 14 h. The HRSEM, HRTEM and XRD analyses showed that optimal controlled conditions to obtain homogeneous growth of high-quality graphitic MWCNTs of different inner and outer diameters were: reaction temperature of $$700\,{^{\circ }}\hbox {C}$$ , growing time 55 min, argon flow rate 220 mL/min and acetylene flow rate 180 mL/min. The BET analysis showed that the surface area of unpurified MWCNTs was $$275.5~\hbox {m}^{2}/\hbox {g}$$ while pure MWCNTs increased to $$330.6~\hbox {m}^{2}/\hbox {g}$$ after acid treatment. The statistical analysis showed that deposition temperature and acetylene flow rate positively exerted significant influence on the CNTs yield than other synthesis parameters, an evidence of thermodynamic-controlled mechanism. This study demonstrated that kaolin can act as an excellent substrate for MWCNTs growth compared to other commercial supports such as $$\hbox {CaCO}_{3}$$ , MgO, $$\hbox {Al}_{2}\hbox {O}_{3}$$ , $$\hbox {SiO}_{2}$$ .

Direct growth of MWCNTs on modified stainless steel surface for flexible lithium ion batteries

Abstract Multi-walled carbon nanotubes (MWCNTs) were grown directly on a modified surface of stainless steel foil (304 SS) using thermal chemical vapor deposition (CVD). Before the MWCNT growth, the polishing procedure followed by the oxidation treatment on 304 SS was considered as a modified process. To understand the effects of this modification on the growth of MWCNTs, the as-received 304 SS and the polished 304 SS without oxidation treatment were further investigated for comparisons. Scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction were used to study the morphology of MWCNTs and their substrates. It was found that the good quality and the dense growth of MWCNTs were grown on the modified 304 SS. Furthermore, the electrochemical measurements were performed within 1M LiCl electrolyte to assess the possibility to use the MWCNTs coupled to 304 SS as electrode material. The optimum oxidation period for the representative capacitive behavior of MWCNTs grown on polished 304 SS is 45 seconds. This finding may lead to a pre-process for improving the MWCNTs grown on metal alloy substrates used for flexible electrode in lithium ion batteries (LIBs) and other flexible electrode works.

Growth of Multiwall Carbon Nanotubes at 300°C Using CO2 as a Weak Oxidant to (CH4+H2) Microwave Plasma

Abstract Multiwall carbon nano-tubes (MWCNTs) were successfully grown at a low temperature ∼300°C using a CH4–CO2–H2 gas mixture in microwave (MW) PECVD and characterized by Raman spectroscopy and different electron microscopy e.g., AFM, SEM and TEM. Physical properties of the CNTs were found to be highly dependent on the gas ratio between CO2 and CH4. CO2 as a weak oxidizer played important roles in promoting the tip growth process, selectively removing the amorphous carbon from the catalyst surface and maintaining the growth of CNTs at low temperatures.

Empirical relationship between band gap and synthesis parameters of chemical vapor deposition-synthesized multiwalled carbon nanotubes

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on CaCO3 was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature (700oC), time (55 min), argon flow rate (230.37 mL min–1) and acetylene flow rate (150 mL min–1) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

Arrays of vertically aligned multi-walled carbon nanotubes grown on silicon and copper substrates by thermal decomposition of ferrocene-toluene aerosol

Arrays of multi-walled carbon nanotubes (MWCNTs) were grown vertically on the surfaces of SiO2/Si substrates using aerosol-assisted catalytic chemical vapour deposition (CCVD) method. Aerosol was produced by injecting a solution of ferrocene (catalyst source) in toluene (carbon source) into a hot zone of a horizontal CVD reactor. Dependences of the height and density of the MWCNT array on the synthesis temperature and ferrocene concentration were determined. The found optimal parameters were used for the MWCNT growth on copper substrates. For this purpose, a copper foil was covered by alumina layer and we showed that the thickness of this layer should be not less than 17 nm to provide the MWCNT growth over the entire foil surface. The vertically aligned MWCNT array tightly bonded with copper substrate can be used as a heat-exchange surface in various micro and nano heat-transfer devices.

Fullerene-to-MWCNT Structural Evolution Synthesized by Arc Discharge Plasma

The growth of multi-walled carbon nanotubes (MWCNTs) has been extensively studied using electron microscopy. The ex situ structural behavior was examined to investigate the growth of the MWCNTs under different environments and pressures using electron microscopy. The arc discharge plasma technique was applied to synthesize the MWCNTs by evaporating carbon through the arc plasma between two cylindrical graphite rods, with a background pressure of 10−2 to 102 mbar, inside a vacuum chamber under different ambient environments. The results showed that long MWCNT structures were successfully grown. We suggest that the mechanism involves: (i) fullerene formation; (ii) the elongation of fullerenes; and (iii) the growth of MWCNTs. Agglomeration with other structures then forms MWCNT bundles. We note that the pressure and environment in the vacuum chamber can affect the structure of the MWCNTs.

MWCNTs produced by electrolysis of molten carbonate: Characteristics of the cathodic products grown on galvanized steel and nickel chrome electrodes

Electrolytic synthesis in molten salts has excellent possibilities for the production of various carbonaceous materials, nevertheless, a study of the synthesis conditions is necessary for that the carbon products obtained is in the carbon nanotube (CNT) structure. In this work, the possibility of production of MWCNTs (multi walled carbon nanotubes) by the electrolytic synthesis of molten salts has been shown. The product structure and morphology can be controlled by choosing the right electrolysis conditions (type of electrode, applied current and electrolysis time). The properties of the produced carbon-containing products were analyzed by XRD, TEM, HRTEM and Raman spectroscopy. A correlation of product properties with synthesis conditions and parameters has been made. When using steel and nickel chrome as cathode, the products have lower levels of defects and are partially filled with metal phase when 1 A and 4 h of electrolytic synthesis were used. The metal phase acts as a catalyst for the nanotubes generation in the electrolytic synthesis from molten salts. Even so, after electrolysis for 4 h, these products are 90% MWCNT. The MWCNT growth on the galvanized steel or nickel-chrome cathodes is similar to an average external diameter of 100–125 nm and internal diameter is 25–40 nm. However, when grown in nickel-chrome cathode, the nanotubes have better quality and smaller walls. No additional treatments are necessary.

Application of γ-alumina as catalyst support for the synthesis of CNTs in a CVD reactor

The continuous search for effective and efficient engineered materials towards solving human challenges is in continuous needs. This study reports the preparation of alumina from kaolin as catalyst support using methanol as precipitant for the synthesis of multiwalled carbon nanotubes (MWCNTs) in a horizontal chemical vapour deposition (CVD) reactor. The process involved thermal treatment of kaolin in a static air furnace, leaching of the treated kaolin in tetraoxosulphate(VI) acid , precipitation in methanol medium, washing in distilled water and calcination at . The alumina in the kaolin was successfully leached and a cubic structure alumina of high thermal stability was synthesized. The alumina was then characterised and utilised as support for the bimetallic catalyst (Fe-Ni) using wet impregnation method. The produced catalyst was used to produce CNTs in a CVD reactor. The thermal properties, surface morphologies, surface functional groups, crystallinity, elemental analyses, and surface areas of the starting kaolin, alumina, prepared bimetallic catalyst (Fe-Ni/alumina) and the synthesized MWCNTs were determined using TGA/DTA, HRSEM, FTIR, XRD, EDX, and BET respectively. The XRD analysis of the bimetallic catalyst was employed to determine its average crystalline particle size to be 26.23 nm using Scherer equation. Tip growth mechanism of MWCNTs was observed during the MWCNTs nucleation process with 41.2 nm external diameters, length and 340 aspect ratio using dynamic light scattering (DLS) technique. The purified MWCNTs showed high antibacterial activities at long exposure time. The results of the various analysis conducted show that the synthesized alumina has potential properties as catalyst support for MWCNTs growth via CVD technique.

Growth of Wall-controlled MWCNTs by Magnetic Field Assisted Arc Discharge Plasma

Carbon nanotubes have long attracted great scientific interest because of their simplicity, ease of synthesis and unique properties. The novel properties of nanostructured carbon nanotubes including its high surface area, stiffness, tensile strength, thermal and electrical properties which become suitable for the application in the fields of energy storage, hydrogen storage, electrochemical supercapacitor, field-emitting devices, transistors, nanoprobes and sensors, composite material, templates, etc. In this study, carbon nanotubes were synthesized through arc discharge plasma with two different configurations, transverse and axial field, applied across arc plasma synthesis process to enable a much rapid rate growing of tubular carbon multi-walled carbon nanotubes (MWCNTs). TEM, FESEM, RAMAN, FTIR and XRD were used to investigate the morphology and structural evolution of the MWCNT samples produced with different synthesis environment. Introduction of magnetic field during the MWCNTs synthesized through arc discharge plasma technique has also been found to enhance the carbon nanotube growth, increase the high aspect ratio and its chemical stability, and shows potential for regulating the number of walls formed.

Direct Growth of Multi-Walled Carbon Nanotubes on Ni Foil by Chemical Vapor Deposition Method for Supercapacitor Applications

Direct Growth of Multi-Walled Carbon Nanotubes on Ni Foil by Chemical Vapor Deposition Method for Supercapacitor Applications

Work function and electrical properties of individual multiwalled carbon nanotube: influenced by nature of catalyst and substrate

To employ the multiwalled carbon nanotubes (MWCNTs) in electronic devices, their growth on conductive substrates is a prerequisite. Since electronic properties of MWCNT might be influenced by catalyst and substrate, therefore, to understand their influence on the work function and electrical resistance, individual MWCNT needs to be studied. In this report, we have demonstrated the growth of MWCNTs on conducting substrates such as copper, stainless steel, and insulating SiO2 using thermal CVD technique. First, as-grown MWCNTs on different substrates have been characterized with scanning electron microscopy and Raman spectroscopy. Furthermore, electrical measurements on as-grown individual MWCNT has been performed using electrostatic force microscopy and conductive atomic force microscopy. Performed measurements reveal that work function and electrical resistance of MWCNT vary from 4.32 to 5.32 eV and 4–498 kΩ, respectively, depending on the nature of catalyst as well as substrates. We envision that performed study might boost the on-going research activity in the area of MWCNT-based nanoelectronic devices.