Growth Of Multi-walled Carbon Nanotubes Research Articles

High-yield synthesis of carbon nanotubes in-situ on iron ore tailing

This study reports the high-yield, “in-situ” growth of multi-walled carbon nanotubes on iron ore tailing. The final product is a pioneering approach on the use of nanostructured tailing to produce mortar with improved mechanical properties in a simple, effective methodology. Four different high-yield catalysts were developed to identify the most efficient parameters for the synthesis of carbon nanotubes (CNT) via Chemical Vapor Deposition on iron ore tailing (IOT). The process yields 1800% in carbon mass, an unprecedented result. Nanostructured IOT was used to produce mortar with different CNT quantities, including concentrations highly above the limits found in the literature, and resulted in increases of in flexural strength (up to 30%). Water loss after thermal treatment, consistency index and water absorption as a function of the CNT concentration in the mortar mass were also investigated. The proposed method delineates a viable way of incorporating CNT-reinforced macromaterials into cementitious matrices without functionalization, additives, or surfactants, which represents an advance for the nanocomposites industry. It also contributes to social and environmental development by aggregating value to iron ore tailing that would be otherwise stored in huge, and sometimes dangerous, disposal dams.

Synthesis and characterization of catalytic CVD growth pristine and functionalized MWCNT

The catalyzed CVD method is considered significant for the production of low cost and high yield carbon nanostructures. In this study, multiwall carbon nanotubes (MWCNTs) were synthesized using a facile and efficient way with the modified CVD method, using Co nanoparticles as the metallic catalysis for MWCNT growth, in a distinct temperature range of 650–750 °C. The structural and magnetic properties of pristine and functionalized MWCNT (p-MWCNT and f-MWCNT) are investigated in the temperature range of 10–300 K. The phase structure of all MWCNT samples was analyzed using various characterization techniques, namely, x-ray diffraction, Raman, and x-ray photoelectron spectroscopy. Scanning electron microscopy and particle size analysis suggested that the diameter of MWCNTs increases with a rise in the growth temperature, but the nanotube density decreases at 750 °C. Temperature-dependent magnetization studies of the p-MWCNT and f-MWCNT samples were investigated using a quantum design physical property measurement system-vibrating sample magnetometer mode. The magnetic properties and the effect of the growth temperature and acid functionalization on the morphology of MWCNT were also investigated. The results revealed that the diamagnetism effect of the graphitic nanotubes is dominating for p-MWCNT, and it reduces for f-MWCNT. A possible explanation for this feature is discussed in detail in the later part of this article. It may be considered that this study, which emerged with different growth temperatures of MWCNTs using a facile method for gaining control over magnetic properties, can be fundamental for further consideration of magnetic MWCNTs for various potential applications.

Simple technique of multiwalled carbon nanotubes growth on aluminum foil for supercapacitors

A promising method for the direct growth of multiwalled carbon nanotubes (MWCNTs) on aluminum foil for supercapacitor electrodes has been developed. Mild oxidation of aluminum foil in a nickel nitrate solution was used to give catalytic properties to aluminum. After the treatment, the detected concentration of nickel in the surface layer of the aluminum foil was 20 wt%. Low-temperature deposition of MWCNTs was carried out by catalytic pyrolysis of ethanol vapor using liquid ethanol as the only precursor. The resulting MWCNTs layers had excellent adhesion to aluminum foil. A symmetrical two-electrode cell as well as a classical three-electrode cell, were used for electrochemical testing of the obtained materials. The cell with MWCNTs/Al foil electrodes exhibits the behavior of an electric double layer capacitor (EDLC). The specific capacity of the MWCNTs reaches 60F/g. This result is comparable to the characteristics of similar materials obtained by other methods. Excellent resistance to multiple charge–discharge cycles is also shown.

Complex Phenomenal Growth of Multi-walled Carbon Nanotubes in Conventional Arc Discharge Process

Complex Phenomenal Growth of Multi-walled Carbon Nanotubes in Conventional Arc Discharge Process

Enhanced light absorption and through-thickness heat conduction of vertically aligned transferable carbon nanotube/silicone rubber composite films

Easily manageable flexible films of multi-walled carbon nanotubes (MWCNT) were prepared and characterized. For the preparation of the MWCNTs pulsed laser-induced dewetting (PLiD) of stainless steel surfaces is employed to generate freely designable arrays of catalytic nanoparticles (NP), which facilitate the MWCNT growth in a chemical vapor deposition (CVD) process. The density of the NP fields, and thus the areal density of the CNTs grown, can be controlled through the used laser parameters. As prepared CNT-arrays were soaked with silicone and cross-linked to form a flexible detachable film that may be reattached onto any other surface. The silicone matrix increases reflection only minimally by about 2%. The vertically aligned CNT (VACNT) arrays were undisturbed during capillary filling of silicone. The anisotropic heat transfer properties of the VACNTs are preserved. Such films are excellent light-absorbers and e.g. may enhance the effectiveness of solar panels or transfer heat from microprocessors to a cooling system.

Facile synthesis of multidimensional nanoscaled-carbon via simplified arc underwater: An integrated process for 0-D, 1-D and 2-D

An adaptable and simplified arc underwater set-up is designed for synthesis of nanostructured carbon materials (NSCM) such as carbon onions (CO), multi-walled carbon nanotubes (MWCNTs) and nanoscale graphitic carbon (NGC). Essentially, the set-up consists of a DC power supply, two graphite electrodes and a container for de-ionized water storage. Transmission electron microscopic analysis confirmed that the cathode deposit, floating particles and settled materials consist of MWCNTs, CO and NGC, respectively. The kind of NSCM formation is critically governed by temperature gradient and cooling rate created due to bubble collapse in nucleate boiling during the arcing process. Based on the anode consumption, the total yield of the carbon materials is about ∼25.5 wt% which consists 5 wt% of FP, 8.5 wt% of CD and remaining 12 wt% of SP. FP, CD, and SP presented crystallite size of 23.69 nm, 11.84 nm, and 28.91 nm, respectively. The high rate and moderate rate of cooling will determine the growth of MWCNTs and CO, respectively. NGC exhibited specific capacity of 325 mAhg−1 with lithium half-cell after 50 cycles at a current density of 100 mAg−1.

SiO2-promoted growth of single-walled carbon nanotubes on an alumina supported catalyst

Developing supported catalyst and elucidating the catalyst activation mechanism are of significant importance for large scale synthesis of single-walled carbon nanotubes (SWNTs). In the work, we designed an alumina-supported iron (Fe–Al2O3) catalyst for catalytic growth of carbon nanotubes by CO chemical vapor deposition (CVD). In the temperature range of 800–1000 °C, the prepared powder catalyst only affords the growth of carbon fibers or multi-walled carbon nanotubes. In contrast, when placing the powder catalyst on flat SiO2 substrates, such as SiO2/Si and quartz, SWNTs were observed to grow at the catalyst-substrate interface, highlighting the contributions of the SiO2 substrate in SWNT synthesis. Systematic characterizations on both the catalysts and carbon nanotubes revealed that the SiO2 substrate promotes the reduction of iron oxide in the adjacent Fe–Al2O3 catalyst, facilitating the generation of small Fe particles at the catalyst-substrate interface, which act as the active phase for the subsequent growth of SWNTs. This work opens a new avenue for growing SWNTs from supported catalyst and sheds light on enhancing SWNT growth efficiency by tuning catalyst reduction behaviors.

Low-cost synthesis of multi-walled carbon nanotubes using red soil as catalyst

Low-cost catalysts are of great significance for the batch synthesis of carbon nanotubes. In this study, the low-cost red soil was directly used as a natural catalyst to catalyze the growth of multi-walled carbon nanotubes (MWCNTs). The results of SEM, TEM, Raman, TG and carbon yields of the products consistently showed that 400 °C calcined red soil lead to high quality MWCNTs growth, the Raman IG/ID of the product is 1.66, which indicates that the product has exceeded the graphitization of many industrially synthesized MWCNTs. The high catalyzation efficiency may be attributed to the fact of composition characteristics that red soil lacks alkali metals and alkaline earth metals but is rich in iron and aluminum oxide, making the composition of red soil similar to the catalyst composition used in the synthesis of carbon nanotubes by common chemical vapor deposition method. Meanwhile the impurity content is less than other natural catalytic materials. The porous structure formed after proper calcination has also played a positive role to the catalytic growth of MWCNTs, which improved catalyst utilization by facilitating the gas phase diffusion. We explored a technique for synthesis of high-quality MWCNTs at low cost using soil as a catalyst.

The synergistic mechanism between coke depositions and gas for H2 production from co-pyrolysis of biomass and plastic wastes via char supported catalyst

Co-pyrolysis of biomass and polyethylene(PE) wastes with different blending ratios were performed in a bench-scale fixed bed over Ni/char catalyst. The synergistic mechanism between coke depositions and gas products during co-pyrolysis was studied for better regulation of H2 production. The results showed that feedstock blending ratio played a decisive role in competitive growth of amorphous coke and multi-walled carbon nanotubes (CNTs) on the catalyst surface. For low PE ratio (≤50 wt%) a negative synergy on H2 yield was generated. It was ascribed to more oxygenates that were more inclined than hydrocarbons to be absorbed by porous char to form amorphous coke, which encapsulated Ni active sites and internal pore channel of catalyst, thus resulting in deactivation of catalyst. For higher PE content, Ni/char catalyst produced more than triple the amounts of H2 yield (42.28 mmol/gfeedstock) as compared to low PE ratio (11.3 mmol/gfeedstock). A maximum positive synergy on syngas quality was yielded at 75% PE. Despite the high yield (37.8 wt%) of deposited coke, more hydrocarbon gas from plastic pyrolysis condensed on catalyst and promoted CNTs growth via dehydrogenation and polymerization, simultaneously generating H2. The unique hollow tubular structure and tip-growth mode of CNTs exposed more Ni active sites and endowed catalyst with lower deactivation extent. The scission of more chain hydrocarbons was subsequently enhanced to interact with oxygenated compounds. Therefore, appropriate PE ratios (>50%) can exert a positive synergy on gaseous conversion by regulating coke nature during co-pyrolysis of biomass and plastics. Furthermore, coke structure rather than content seems to exert more significant effect.

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.

Atmospheric-pressure growth of multi-walled carbon nanotubes over Ni–Fe nanosheets supported on α-Al2O3 foam

A novel Ni–Fe nanosheets catalyst supported on α-Al2O3 foam ceramic was synthesized by a hydrothermal method and used to obtain multi-walled carbon nanotubes (MWNTs) via the propane partial oxidation. Catalytic performance tests were carried out at 600 °C and atmospheric pressure using a fixed-bed reactor. The synthesized catalysts and carbon materials were analyzed using various characterization methods. According to the field emission scanning electron microscope (FESEM) results, the catalyst morphology was a 3D grid structure consisting of nanosheets 800 nm length and 80 nm width. Additionally, the quantity and quality of the carbon nanotubes were greatly influenced by different oxygen-to-propane molar ratios, defined as the equivalence ratio ϕ (ϕ = 1.5, 1.78, 2). Transmission electron microscope (TEM) images showed that carbon nanotubes over all catalysts were MWNTs. In addition, the thermogravimetric analysis and Raman data showed that a high yield of MWNTs was obtained at ϕ = 1.78, but the accumulated MWNTs at ϕ = 1.5 exhibited a higher degree of graphitization (ID/IG = 0.89) compared with the other two equivalence ratios.

Cobalt doping of α-Fe/Al2O3 catalysts for the production of hydrogen and high-quality carbon nanotubes by thermal decomposition of methane

Fe–Co/Al2O3 catalysts were developed and tested in the catalytic decomposition of methane (CDM) for the synthesis of multi-wall carbon nanotubes (MWCNT) and the CO2-free hydrogen production. While Fe (54.5–66.7 mol.%) is the main active phase for the carbon formation on the catalyst, Co acts as dopant aiming to improve its overall catalytic behaviour. Catalysts with Co contents of up to 18.2 M% showed the presence of α-Fe and Fe–Co crystallites with different size and lattice parameter. Fe1-xCox alloy with bcc crystal system was identified only for Co contents of 14.0% and above, and presented a lattice constant lower than α-Fe, which would modify the carbon diffusion of the metal particle during the MWCNT growth. Co inhibited the Fe3C formation during CDM resulting in higher carbon formations and longer activity times. This phase, shown in undoped catalysts, favored the presence of bamboo-type carbon nanotubes.

Frustule as the supporting catalyst for the large-scale growth of Multiwalled carbon nanotubes and its application in Lithium ion battery

Frustule as the supporting catalyst for the large-scale growth of Multiwalled carbon nanotubes and its application in Lithium ion battery

Research on MWCNT growth process through on-line intermittent monitoring in a fluidized bed reactor

Carbon nanotubes (CNTs) have been extensively investigated in the past two to three decades owing to their superior properties. Most people focus on studying the role of catalyst, reaction temperature, partial pressure, and carbon source in the growth of CNTs. However, research on the effect of different reaction times on the growth process of multiwall CNTs (MWCNTs) remains insufficient. Here, through on-line intermittent monitoring technology, we studied the growth process of MWCNTs on Fe–Co–Mo/Al2O3 catalyst at high temperature using propylene decomposition to solid carbon and gaseous hydrogen in a self-made fluidized bed reactor proposed in the previous study that utilized the effect of cone angle instead of the role of distributor. A parametric systematic study on the effect of intermittent time (5–60 ​min) on the MWCNT morphology, quality, quantity, and particle properties was performed by using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. It was found that the carbon source conversion rate decreased at a lower linear rate of 0.15, the MWCNT yield increased at a higher linear rate of 1.45, the lowest ash content reached 2.04% at 60 ​min, and the mean diameter remained at 12.5 nm. A formula with empirical coefficient and time dependence was proposed to predict the carbon source conversion rate.

Direct growth of multiwall carbon nanotube on metal catalyst by chemical vapor deposition: In situ nucleation

Carbon nanotubes (CNTs) are among the most promising materials for applications in future nanotechnology. The combination of excellent physical and mechanical properties beside chemical resistance seems very interesting for different industrial applications. However, the commercialization of nanotube-based nanocomposites has been hampered by their high cost and minuscule production. In the present study, we have tried to understand the fundamental aspects of multiwall carbon nanotubes (MWCNTs) direct growth on metal catalyst particles via thermal chemical vapor deposition (T.CVD) in the presence of zirconium hydride (ZrH2) and aluminum nanoparticles. The effects of different parameters such as gas flow rates, metal catalyst systems, and temperature on the quality and quantity of the obtained MWCNTs were investigated and some interesting results were obtained. It was found that at moderate temperatures, MWCNTs growth rate on iron-based (Fe) catalyst was much more than that on nickel (Ni) and cobalt (Co) particles. Transmission electron microscopy (TEM) results and TGA analysis revealed that metal nanoparticles as the nucleation sites come from the fragmentation of catalyst surfaces and the application of relatively small amounts of ZrH2 significantly enhances this mechanism. Besides, crystalline structure of MWCNTs was performed by Raman spectroscopy, X-ray diffraction (XRD) and selected area electron diffraction (SAED) technique. This method shows great promise for achieving the goal of mass-production due to its high quality and yield; simplicity, and ease of scale-up.

An investigation of microstructural, magnetic and microwave absorption properties of multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4

The enhancement of microwave absorbing properties in nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) via multiwall carbon nanotubes (MWCNT) growth is studied in this research work. Ni0.5Zn0.5Fe2O4 was initially synthesized by mechanical alloying followed by sintering at 1200 °C and the microstructural, electromagnetic and microwave characteristics have been scrutinized thoroughly. The sintered powder was then used as a catalyst to grow MWCNT derived from chemical vapor deposition (CVD) method. The sample was mixed with epoxy resin and a hardener for preparation of composites. The composite of multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 shown a maximum reflection loss (RL) of −19.34 dB at the frequency and bandwidth of 8.46 GHz and 1.24 GHz for an absorber thickness of 3 mm for losses less than −10 dB. This acquired result indicates that multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 could be used as a microwave absorber application in X-band.

Catalytic growth of MWCNT using CVD and its application as opto-electronic humidity sensor

The present paper describes the effect of co-catalyst on the growth of multiwall carbon nanotube (MWCNT) by chemical vapor deposition (CVD) technique. The fascinating properties of CNT make them a suitable material for optoelectronic devices such as sensors, LED, solar cell, and field emission displays. MWCNTs were fabricated using CVD, by decomposing ethanol over finely dispersed Co metal as a catalyst at 750 °C. The effects of growth condition on the quality and morphology of MWCNTs were investigated by SEM, FTIR and XRD. SEM photographs show that the nanotubes are densely packed having a diameter of 10–15 nm. The bandgap was calculated by UV–visible spectroscopy and it was found varying from 3.08 to 3.5 eV by changing the substrates. The average size of tubes (length) was found to be 250 nm. FTIR exhibited that the synthesized MWCNTs were semiconducting in nature with the oxygen vacancies causing the variations in refractive index with the exposure of moisture.

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.

Growth region characterization of carbon nanotubes synthesis in heterogeneous flame environment with wire-based macro-image analysis

Identification of carbon nanotube (CNT) growth region is paramount in a heterogeneous environment of flame to ensure an improved yield and growth rate. Previously, the growth region analysis in flame synthesis has been done based on repetitive scanning electron microscope (SEM) characterization that tends to be costly and time-consuming for a large heterogeneous environment. A systematic evaluation of the experimental method for growth region characterization is very limited. Therefore, the present study provides a detailed sensitivity and accuracy evaluation of a simple wire-based macro-image analysis (WMA) method for the measurement of steady-state and temporal change of growth region size for multiwalled carbon nanotubes (MWCNT) in a methane diffusion flame with varied air flow rate at atmospheric condition. The WMA method was developed to simplify the MWCNT deposit region identification using the image produced by digital single-lens reflex (DSLR) camera and post-processed using baseline data that was gathered through a one-time SEM analysis. Pure nickel wire was positioned in the flame with a stainless-steel wire grid placed on top of the substrate wire to redistribute the flow field. The MWCNT deposit region that is confined in the fuel-rich region at the inner side of the flame sheet shifts toward the flame centerline with the increase of the air flow rate from 1 to 10 slpm due to the shift of the flame sheet in the same direction. The inception and growth of MWCNT are consistently observed together with the formation of amorphous carbon layer, which has been verified based on detailed SEM analysis. The formation of amorphous carbon layer happens due to the higher rate of carbon supply compared to that of the carbon diffusion rate in nickel catalyst for CNT growth. These phenomena serve as the fundamental basis of the present WMA method. At 10 mm above the burner, the WMA method at steady state successfully detected the change in size and spatial distribution of deposit region by a factor of 2.28 and 2.68 respectively at varying air flow rate with ± 0.5 mm accuracy. The present method demonstrated high sensitivity to capture the temporal change of the deposit region length within the exposure time for the growth rate measurement of the deposit region. More than twofold increase in effective growth rate was successfully captured at a high air flow rate due to the change in equivalence ratio from rich to stoichiometry that promotes the increase in heat release rate. The present flame setup was able to produce a widest CNT deposit region with an optimum growth rate at 6 slpm air flow rate. High-resolution transmission electron microscopy (HRTEM) analysis verified that the synthesized CNT is hollow with multiwalled internal structure and Raman spectroscopy analysis indicated that crystallinity level of the produced MWCNT is relatively constant with the change in air flow rate.

Effect of Reaction Time and Catalyst Feed Rate towards Carbon Nanotubes Yields and Purity by using Rotary Reactor

Continuous production of multi-walled carbon nanotubes (MWCNTs) by chemical vapor deposition (CVD) method was investigated in a rotary reactor. The aim of the study was to investigate the effect of catalyst feeding rate and reaction time on the MWCNTs production yield and purity. Bimetallic Co-Mo supported on MgO was used for the growth of MWCNTs and methane gas was used as the carbon precursor. The results indicated that the highest yield of MWCNTs production was attained at the reaction time of 180 min and catalyst feeding rate of 100 mg/min; this sample also had the highest purity (99.16%). SEM and TEM analyses of the synthesized product confirmed that most of the MWCNTs were sinuous and entangled with a uniform diameter. Raman spectroscopy indicated that the as-produced MWCNTs were mostly graphitic with few disordered carbon and impurities. The results highlighted that synthesized MWCNTs were highly pure which eliminates the need for MWCNTs purification process.