Catalyst For Growth Of Carbon Nanotubes Research Articles

Iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with well-dispersed active sites favoring carbon nanotubes growth for high-performance microwave absorption

Traditional catalysts for carbon nanotubes growth require specific substrates to prevent catalyst aggregation, then designing environmentally friendly and efficient catalysts remains enormous challenges. Herein, we developed an iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with catalytic active sites for the low-cost growing of carbon nanotubes (CNT) in chemical vapor deposition (CVD) system. This (Fe1-xMgx)O·Fe2O3 was prepared by solid-phase sintering of iron oxide and magnesium oxide uniformly mixed in mass ratio of 3%∼20 wt% MgO at 1400 °C. The introduction of magnesium oxide possesses some advantages of reducing the decomposition temperature of iron oxide and hindering the aggregation of as-formed Fe catalyst during CVD process. Furthermore, the in-situ growing CNT wrapped up the magnetic (Fe1-xMgx)O·Fe2O3 catalyst to form the 3D CNT/(Fe1-xMgx)O·Fe2O3 with the high-performance of microwave absorption. The maximum absorption of the three-dimensional carbon nanocomposites at 11.8 GHz with a thickness of 2.0 mm is −37.3 dB. The coupling of dielectric loss of CNTs and magnetic loss of (Fe1-xMgx)O·Fe2O3 results in the enhancement of microwave absorption. Therefore, this study provides a low-cost and green route to design the efficient catalyst for carbon nanotubes as well as high-performance absorbing materials.

Integration of Carbon Nanotubes in an HFCVD Diamond Synthesis Process in a Methane-Rich H2/CH4 Gas Mixture.

In this work, we present experimental data on carbon nanotubes integration during diamond synthesis. Carbon nanotubes layers were preliminarily deposited on silicon and diamond substrates, after which the substrates were loaded into the HFCVD reactor for further growth of the diamond phase. The CVD process was held in an argon-free H2/CH4 working gas mixture without the use of a catalyst for carbon nanotubes growth. It is shown that in a wide range of studied working gas composition (CH4 concentration up to 28.6 vol.%) nanotubes etched from the substrate surface before the diamond growth process began.

Study on Bimetallic Catalysts for Carbon Nanotube Growth on the Surface of Continuous Carbon Fibres

We investigated the influence of bimetallic catalysts with various compositions on the growth of carbon nanotubes (CNTs) on the surface of continuous carbon fibers (CFs). The samples were analyzed and characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectrometry. The catalyst plays an essential role in the catalytic chemical vapor deposition of CNT. The performance of these catalysts was estimated referenced to both catalyst and CNT morphologies, while the influences of each catalytic components were summarized according to the results. This work prepared and studied six different bimetallic catalysts composed by Cu, Fe, and Ni, and pure Fe catalyst was employed as a control group. Fe and Ni have been widely studied, while the reports of catalysts containing Cu are rare. We found that pure Fe catalyst leads to banded and clustered CNT distribution, and the addition of Cu can provide uniform and slender CNTs. The efficiency of catalyst can be significantly increased by adding Ni, producing CNTs as well as superfluous amorphous carbon. We determined that bimetallic catalyst can utilize multiple catalytic abilities of various metals by adjusting its composition, which can contribute to obtaining high-quality CNTs on CF surface.

Simple and efficient preparation of uniformly dispersed Carbon nanotubes reinforced Copper matrix composite powders by in situ chemical vapor deposition without additional catalyst

Carbon nanotubes (CNTs) reinforced Copper (Cu) matrix composite powders have been successfully prepared by in situ chemical vapor deposition (CVD) using Cu-0.6 wt% Al alloy powders without additional catalyst. The catalyst for CNTs growth is nano-copper particle (∼28 nm), and the interaction between Cu and Al2O3 would promote the formation of nano-copper particles (∼28 nm). The high quality multi-walled CNTs obtained dispersed uniformly on and well bonded to the composite powders. And the formation mechanism was discussed, the results show that part of the growth of CNTs follows tip-growth mode and the others without catalyst particles at the top follow the base-growth mode. This providing a simple and effective method for in situ preparation of CNTs/Cu composite powder with uniform dispersion of CNTs.

Effects of Catalyst Pretreatment on Carbon Nanotube Synthesis from Methane Using Thin Stainless-Steel Foil as Catalyst by Chemical Vapor Deposition Method.

Synthesis of carbon nanotubes (CNTs) was carried out using methane as a carbon source via the chemical vapor deposition (CVD) method. A thin stainless-steel foil was used as catalyst for CNT growth. Our results revealed that pretreatment step of the stainless-steel foil as a catalyst plays an important role in CNT formation. In our experiments, a catalyst pretreatment temperature of 850 °C or 950 °C was found to facilitate the creation of Fe- and Cr-rich particles are active sites on the foil surface, leading to CNT formation. It is noted that the size of metallic particles after pretreatment is closely related to the diameter of the synthesized CNTs. It is interesting that a shorter catalyst pretreatment brings the growth of semiconducting typed CNTs while a longer pretreatment creates metallic CNTs. This finding might lead to a process for improving the quality of CNTs grown on steel foil as catalyst.

Precise Identification of the Active Phase of Cobalt Catalyst for Carbon Nanotube Growth by In Situ Transmission Electron Microscopy.

Revealing the active phase and structure of catalyst nanoparticles (NPs) is crucial for understanding the growth mechanism and realizing the controlled synthesis of carbon nanotubes (CNTs). However, due to the high temperature and complex environment during CNT growth, precise identification of the active catalytic phase remains a great challenge. We investigated the phase evolution of cobalt (Co) catalyst NPs during the incubation, nucleation, and growth stages of CNTs under near-atmospheric pressure using an in situ close-cell environmental transmission electron microscope (ETEM). Strict statistical analysis of the electron diffractograms was performed to accurately identify the phases of the catalyst NPs. It was found that the NPs belong to an orthorhombic Co3C phase that remained unchanged during CNT growth, with errors in lattice spacing <5% and in angle <2°, despite changes in their morphology and orientation. Theoretical calculations further confirm that Co3C is the thermodynamically preferred phase during CNT growth, with the supply of carbon atoms through the surface and NP-CNT interfacial diffusion.

Transforming Waste Poly(Ethylene Terephthalate) into Nitrogen Doped Carbon Nanotubes and Its Utility in Oxygen Reduction Reaction and Bisphenol-A Removal from Contaminated Water.

Till date, waste plastics are either down-cycled to cheap products like fibers or burnt in incinerators to generate heat. In this manuscript, we report a simple and effective technique for microwave induced transformation of waste polyethylene terephthalate (wPET) to carbon nano-tubes (CNT). Iron nano-particles dispersed on graphene substrate acted as catalyst for CNT growth whereas urea served the dual role of de-polymerisation of wPET and also as nitrogen doping agent. Application of our newly synthesized 3-D meso-porous graphene-nitrogen doped carbon nanotube- iron electrode (Fe@NCNT-rGO) as electro-catalyst for oxygen reduction reaction (ORR) shows a positive half-wave potential (E1/2) of 0.75 V vs. RHE (reversible hydrogen electrode), nearly ideal four-electron pathway and excellent methanol tolerance when compared to commercial 20% Pt/C. The utility of Fe@NCNT-rGO for removal of bisphenol A from contaminated waters is also reported.

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.

One-step synthesis of highly porous carbon graphite/carbon nanotubes composite by in-situ growth of carbon nanotubes for the removal of humic acid and copper (II) from wastewater

Porous carbon graphite/carbon nanotubes composite was prepared in a one-step process. Carbon nanotubes (CNTs) were grown in-situ simultaneously with the formation of the porous carbon material. Two plastic pastes, with and without ferrocene as catalyst for CNTs growth were prepared by mixing at room temperature a thermosetting phenolic resin, a graphite powder and cellulose derivatives. Both pastes were shaped and carbonized at 800 °C under N2. The porosity of materials was correlated to the weight losses induced by the cellulose derivatives decomposition and phenolic resin carbonization.Both X-ray powder diffraction and Raman analysis showed that iron nanoparticles and FexC complexes were formed following the decomposition of ferrocene and apparently catalyzed the growth of CNTs. Moreover, SEM and TEM images demonstrated that CNTs were grown in different shapes and sizes. High porosities of 45.4% and 52.3% were achieved for carbon graphite and carbon graphite/CNT composite, respectively. The presence of the CNTs drastically changed the surface properties and the electrical conductivity of the material.When tested as adsorbents of humic acid and copper (II) ions from aqueous solutions, it turned out that CNTs presence enhanced the adsorption. Furthermore, oxidation of the carbon graphite/CNT composite enhanced significantly the adsorption but had no effect on the pure carbon graphite material.

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.

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.

Refractory-Metal Diffusion Inhibitors Slow Erosion of Catalytic Metal Particles in the growth of Carbon Nanotubes

ABSTRACTCatalytic growth of substantial amounts of Carbon Nanotubes (CNTs) to lengths greater than 1 – 2 cm is currently limited by several factors, including especially the deactivation of the catalyst particles due to erosion of catalyst atoms from the catalyst particles at elevated CNT growth temperatures. Inclusion of refractory metals in the CNT growth catalyst has recently been proposed as a method to prevent this catalytic particle erosion and deactivation, allowing the CNT to grow for greater times and reach substantially greater lengths. Here are presented results of recent investigations into this method. The system investigated employs Molybdenum as the erosion inhibitor and Iron as the CNT growth catalyst. Results show that inclusion of Mo leads to substantially longer catalyst particle lifetimes.

Review of Metal Supported on Mesoporous MCM41 as Catalyst for CNTs Growth

Carbon nanotubes (CNTs) is one of the most unique nanomaterials in the field of nanotechnology because of their high strength, stiffness and electrical conductivity. Growth CNTs through chemical vapour deposition (CVD) method offers controlled synthesis of ordered and aligned CNTs. Catalytic growth also can be designed CNTs in variety forms either straight filament, helically wound tubes and bent. Recently, transition metal incorporated Mobil Composition Matter (known as MCM41 ) molecular sieves as growth catalyst has been used for the production of CNTs. The invention of mesoporous molecular sieves by Mobil researchers in 1992 has given a new direction to the field of porous materials. MCM41 exhibit a good hexagonal arrangement, uniform channel structure, tuneable pore size (15-100 Å) and large surface area (≈1200 m2g−1). Transition metal catalysts can be incorporated into the pore walls of the mesoporous molecular sieves and stabilizing the dispersed catalytic sites. The mesoporosity and the well-defined pore structure in combination with high surface area make MCM41 materials as promising candidates for the synthesis of CNTs. In this article, we review and discuss the role of catalyst and their catalyst support using MCM mesoporous material.

Scalable synthesis of γ-Fe2O3/CNT composite as high-performance anode material for lithium-ion batteries

Maghemite (γ-Fe2O3) is considered more stable than α-Fe2O3 as an anode material for lithium-ion batteries because it has adequate vacancy sites and lower surface energy. However, the facile synthesis of γ-Fe2O3 is still a technological challenge. In this work, a composite based of γ-Fe2O3 and carbon nanotubes (CNTs) is successfully synthesized by a facile one-step direct current arc-discharge approach. Under an atmosphere of low-pressure air, Fe particles act as catalysts for carbon nanotube growth and are subsequently oxidized in situ to γ-Fe2O3 with a mean diameter of about 10 nm deposited on the carbon nanotubes. The as-synthesized γ-Fe2O3/CNT composite shows a stable cycling capacity of 1186.8 mAh g−1 after 400 cycles at 200 mA g−1. In addition, the γ-Fe2O3/CNT composite delivers excellent rate performance of 611.8 mAh g−1 at 4000 mA g−1 and a high reversible capacity of 518.5 mAh g−1 remains after 300 cycles at 4000 mA g−1. The highly stable γ-Fe2O3 particles and highly conductive carbon nanotubes are the key factors that provide the extraordinary performance of the composite. Most importantly, γ-Fe2O3/CNT composite and the arc-discharge fabrication method hold great potential for further industrial applications in energy storage.

In-situ catalytic growth carbon nanotubes from metal organic frameworks for high performance lithium-sulfur batteries

The highly uniformed hybrid carbon material has been prepared by in-situ growth carbon nanotubes (CNTs) from metal organic frameworks, with the cobalt species as the catalyst for CNTs growth and dicyandiamide (DICY) as a sacrificial agent for the formation of graphitic carbon. The CNTs with extraordinary conductivity supply more electron transport to the cathode and make much more sense in enhancing the rate performance of the sulfur cathode. In the matrix, cobalt nanoparticles and heteroatom nitrogen can help in immobilizing sulfur species, leading to the improvement of polysulfide shutting. Moreover, the increased specific surface area and mesoporous channel enhance the sulfur loading and facilitate electrolyte diffusion. On integrating these fascinating benefits into one electrode material, as a result, the hybrid composite (CNT@CoNC/S) cathode presents a high initial capacity of 1316.1 mAh/g at the current rate of 0.1C. Even at high current rate of 5C, a decent capacity of 620.7 mAh/g can still be achieved. The capacity of hybrids materials can be maintained at 970 mAh/g after 500 cycles at 0.2C, and a capacity retention of 79.8%, revealing it great potential for energy storage application.

Catalytic effect of montmorillonite nanoparticles on thermal decomposition of coal tar pitch to carbon

The work studies the structure of two types of coal tar pitches (CTPs) modified with montmorillonite (MMT) in the form of nanopowder after annealing to 1000 and 2000 °C. The CTPs differed in polycyclic aromatic hydrocarbons (PAH) content and coking value (CV). The study of scanning electron microscope (SEM), transmission electron microscope (TEM) and x-ray diffraction (XRD) showed that the heat treatment of PAH-containing pitches modified with the ceramic filler to 1000 °C is a way to obtain a new clay-carbon nanocomposite, composed of turbostratic carbon, graphitic carbon, carbon nanotubes (CNT) and MMT. MMT act as a catalyst for carbon nanotubes growth via the gas phase at 1000 °C. Carbon nanotubes growth in pitch-derived carbon material occurred as a result of the presence of hydrocarbon compounds containing PAH evolved during thermal conversion to the carbon phase. Catalytic growth of carbon nanotubes from aromatic hydrocarbons-containing gaseous phase allows to reduce PAH emission during pitch-derived carbon thermal processing.The montmorillonite – modified carbon samples contained a graphitic phase built of preferred orientation crystallites. This phase consisted of well-ordered crystallites with the c-axis spacing, d002 = 0.335 nm. The process occurred due to catalytic graphitization at 1000 °C in the presence of montmorillonite.

Fe–Mo and Co–Mo Catalysts with Varying Composition for Multi‐Walled Carbon Nanotube Growth

The formation of active component of Fe–Mo and Co–Mo catalysts for carbon nanotube growth with variable Mo content is studied with in situ XRD, XPS, and STEM&amp;EDX. The activation of bimetallic Fe–Mo catalysts under the growth conditions leads to the formation of Fe–Mo alloy particles in contrast to Co‐containing catalysts in which active alloy incorporates only a small portion of Mo (&lt;2–3 at.%). The stable carbide formation for these systems is not detected. The effect of Mo content in Fe–Mo and Co–Mo catalysts on the properties of MWCNTs is additionally investigated using the Raman spectroscopy in combination with measurements of the temperature dependence of conductivity. It is shown that MWCNT defectiveness depends on the active component composition for both Fe–Mo and Co–Mo catalysts. The current carrier concentration for the MWCNTs grown on Fe–Mo catalysts slightly increases with the Mo content. The opposite effect is observed for the tubes grown on Co–Mo catalysts, showing a decrease in the current carrier concentration with the increase of Mo concentration.

Biological path for functional nanostructure fabrication and nanodevices

The fabrication of nanostructures by biomolecules is proposed. The process utilises biotemplated biomineralisation of inorganic materials and self-assembly, termed the ‘bio–nano process’ (BNP). Artificial proteins are designed to construct functional nanometric structures in combination with top–down miniaturisation technologies. Genetically modified cage-shaped proteins, ferritin and deoxyribonucleic acid-binding protein from starved cells, are the most studied biotemplates for the BNP. The inner cavity is used as a spatially restricted chamber for the synthesis of homogeneous metal, metal-complex and semiconductor nanoparticles (NPs). Proteins with NP cores are delivered onto specific substrate locations or carbon nanotube surfaces by electrostatic interaction or specific binding peptides. These NPs realise a variety of functions such as charge storage nodes for floating gate memory, catalysts for carbon nanotube growth, quantum wells in heterogeneous junctions and nanoetching masks. Cage-shaped protein-based bioconjugates play an important role and expand the application fields. The BNP is capable of producing functional nanostructures that are otherwise impossible through other methods.

Carbon rich fly ash and their nanostructures

Carbon rich fly ash was recently reported to have compositions that are ideal for use as a precursor and catalyst for carbon nanotube growth. This fly ash powder is mostly composed of pure carbon, predominantly present as sp2. In this work, the effect of sonication time on the morphology and structural properties of carbon rich fly ash particles is reported. The obtained results show that ultrasound treatment is an effective tool for producing ultrafine particles/fragments with higher porosity, which might be suitable for the adsorption of gasses. Moreover, carbon nanoparticles (CNPs) of this fly ash were produced in parallel using the ball milling technique, and were evaluated as reinforcements for epoxy based composites. These CNPs have almost spherical shapes with particle sizes of around 30 nm. They were found to have strong C=O carbonyl group bonds, which might be generated during the ball milling process. The tensile testing results of a fly ash CNP reinforced epoxy composite showed significant improvements in the mechanical properties, mainly in the stiffness of the polymer. The stiffness value was increased by around 23% of that of neat epoxy. These CNPs with chemically active groups might also be useful for other applications.

Impact of Silicon Nanocrystal Oxidation on the Nonmetallic Growth of Carbon Nanotubes.

Carbon nanotube (CNT) growth has been demonstrated recently using a number of nonmetallic semiconducting and metal oxide nanoparticles, opening up pathways for direct CNT synthesis from a number of more desirable templates without the need for metallic catalysts. However, CNT growth mechanisms using these nonconventional catalysts has been shown to largely differ and reamins a challenging synthesis route. In this contribution we show CNT growth from partially oxidized silicon nanocrystals (Si NCs) that exhibit quantum confinement effects using a microwave plasma enhanced chemical vapor deposition (PECVD) method. On the basis of solvent and a postsynthesis frgamentation process, we show that oxidation of our Si NCs can be easily controlled. We determine experimentally and explain with theoretical simulations that the Si NCs morphology together with a necessary shell oxide of ∼1 nm is vital to allow for the nonmetallic growth of CNTs. On the basis of chemical analysis post-CNT-growth, we give insight into possible mechanisms for CNT nucleation and growth from our partially oxidized Si NCs. This contribution is of significant importance to the improvement of nonmetallic catalysts for CNT growth and the development of Si NC/CNT interfaces.