Catalytic Chemical Vapor Deposition Synthesis Research Articles

Improvement of Hybrid Electrode Material Synthesis for Energy Accumulators Based on Carbon Nanotubes and Porous Structures.

Carbon materials are promising for use as electrodes for supercapacitors and lithium-ion batteries due to a number of properties, such as non-toxicity, high specific surface area, good electronic conductivity, chemical inertness, and a wide operating temperature range. Carbon-based electrodes, with their characteristic high specific power and good cyclic stability, can be used for a new generation of consumer electronics, biomedical devices and hybrid electric vehicles. However, most carbon materials, due to their low electrical conductivity and insufficient diffusion of electrolyte ions in complex micropores, have energy density limitations in these devices due to insufficient number of pores for electrolyte diffusion. This work focuses on the optimization of a hybrid material based on porous carbon and carbon nanotubes by mechanical mixing. The purpose of this work is to gain new knowledge about the effect of hybrid material composition on its specific capacitance. The material for the study is taken on the basis of porous carbon and carbon nanotubes. Electrodes made of this hybrid material were taken as an object of research. Porous carbon or nitrogen-containing porous carbon (combined with single-, double-, or multi-layer carbon nanotubes (single-layer carbon nanotubes, bilayer carbon nanotubes or multilayer carbon nanotubes) were used to create the hybrid material. The effect of catalytic chemical vapor deposition synthesis parameters, such as flow rate and methane-to-hydrogen ratio, as well as the type of catalytic system on the multilayer carbon nanotubes structure was investigated. Two types of catalysts based on Mo12O28 (μ2-OH)12{Co(H2O)3}4 were prepared for the synthesis of multilayer carbon nanotubes by precipitation and combustion. The resulting carbon materials were tested as electrodes for supercapacitors and lithium ion intercalation. Electrodes based on nitrogen-containing porous carbon/carbon nanotubes 95:5% were found to be the most efficient compared to nitrogen-doped porous carbon by 10%. Carbon nanotubes, bilayer carbon nanotubes and multilayer carbon nanotubes synthesized using the catalyst obtained by deposition were selected as additives for the hybrid material. The hybrid materials were obtained by mechanical mixing and dispersion in an aqueous solution followed by lyophilization to remove water. When optimizing the ratio of the hybrid material components, the most effective porous carbon:carbon nanotubes component ratio was determined.

The Importance of Water for Purification of Longer Carbon Nanotubes for Nanocomposite Applications

Ultralong carbon nanotubes (UCNTs) are in high demand for nanocomposites applications due to their magnificent physical and chemical properties. UCNTs are synthesized by the catalytic chemical vapor deposition (CCVD) method and, before use as fillers in nanocomposites, should be purified of residual catalyst and non-CNT particles without significant destruction or scissoring of the UCNT. This study investigates the role of water vapor for purification of UCNTs from iron catalyst particles and the importance of water assistance in this process is confirmed. It was shown that wet air treatment of products of UCNTs CCVD synthesis under mild conditions can be used to sufficiently decrease residual iron catalyst content without significant carbon losses in comparison to the results obtained with dry air, while the residual iron content was shown to significantly influence the subsequent oxidation of different forms of carbons, including UCNTs. The increasing of D/G ratio of Raman spectra after wet air treatment of products of UCNTs CCVD synthesis makes it possible to conclude that iron catalyst particles transform into iron oxides and hydroxides that caused inner structural strains and destruction of carbon shells, improving removal of the catalyst particles by subsequent acid treatment. UCNTs purification with water assistance can be used to develop economically and ecologically friendly methods for obtaining fillers for nanocomposites of different applications.

Controlling the Structure of Carbon Deposit by Nitrogen Doping Catalytic Chemical Vapor Deposition Synthesis.

Nitrogen doped multi-walled carbon nanotubes and other carbon nanoparticles were synthesized by catalytic chemical vapor deposition of tripropylamine and acetylene on CaCO₃-supported cobalt catalyst (5 wt%), prepared by impregnation, and various precursors. Each synthesis was performed by using either the pure nitrogenous organic compound or its mixture with acetone. Transmission electron microscopy studies revealed a significant difference both in the yield and the diversity of the carbon deposits. Every synthesis resulted in bamboo-like nanotubes, and nearly all of them also in onion-like structures. Electron energy loss spectroscopy studies of the samples indicated the presence of nitrogen and calcium (caused by the catalyst support). High-resolution transmission electron microscopy and X-ray diffraction measurements were also performed to characterize the samples.

A semi-grand canonical kinetic Monte Carlo study of single-walled carbon nanotube growth

Single-walled carbon nanotubes exist in a variety of different geometries, so-called chiralities, which define their electronic properties. Chiral selectivity has been reported in catalytic chemical vapor deposition synthesis experiments, but the underlying mechanisms remain poorly understood. In this contribution, we establish a simple model for the prediction of the growth rates of carbon nanotubes of different chiralities as a function of energies characterizing the carbon nanotube–catalyst interface and of parameters of the synthesis. The model is sampled efficiently using kinetic Monte Carlo simulations in the semi-grand canonical ensemble, uncovering the interplay of the external experimental conditions and the configuration and energetics of the interface with the catalyst. In particular, the distribution of chiral angle dependent growth rates follows non-monotonic trends as a function of interface energies. We analyze this behavior and use it to identify conditions that lead to high selectivity for a variety of chiral angles.

Fe-assisted catalytic chemical vapor deposition of graphene-like carbon nanosheets over SrO

The application of graphene-like carbon nanosheets (GCN) for energy storage has attracted tremendous interest in industry. Thus, synthesis pathways producing GCN with high yield, good electrical conductivity and large accessible surface area are interesting option to obtain the desirable electrode materials. Here, a method to increase yield and functional properties of GCN is proposed using Fe-assisted catalytic chemical vapor deposition (CCVD) over SrO catalyst. In this process design, the ethanol vapor is passed through iron particle bed before reaching SrO catalyst for a CCVD synthesis at 950 °C. It is found that Fe modified conversion pathways of ethanol producing a material with 65% higher yield, better crystallinity and lower defect density compared to GCN synthesized over SrO only. Furthermore, the higher yield and low density of defects can also be retained in GCN after KOH activation (800 °C) resulting in a 3D hierarchically porous material with 34% higher specific capacitance, 12% higher capacitance retention and lower charge transfer resistance than materials obtained through a conventional CCVD process with SrO only. The obtained data suggest that the proposed Fe-assisted CCVD synthesis is a promising strategy towards the synthesis of advance functional materials, e.g. with applications in supercapacitors.

Adsorption of Reactive Blue 116 Dye and Reactive Yellow 81 Dye from Aqueous Solutions by Multi-Walled Carbon Nanotubes.

The multi-walled carbon nanotubes obtained by catalytic chemical vapour deposition synthesis are used as a solid matrix for the adsorption of the Reactive Blue 116 dye and the Reactive Yellow 81 dye from aqueous solutions at different pH values. The batch tests carried out allowed us to investigate the different effects of pH (2, 4, 7, 9 and 12) and of the contact time (2.5 ÷ 240 min) used. The liquid phase was analysed using ultraviolet-visible spectrophotometry in order to characterise the adsorption kinetics, the transport mechanisms and the adsorption isotherms. The adsorption of the optimal dye was observed at pH 2 and 12. The pseudo-first order kinetic model provided the best approximation of experimental data compared to the pseudo-second order kinetic model. The predominant transport mechanism investigated with the Weber and Morris method was molecular diffusion for both Reactive Yellow 81 and Reactive Blue 116, and the equilibrium data were better adapted to the Langmuir isothermal model. The maximum adsorption capacity for Reactive Yellow 81 and Reactive Blue 116 occurred with values of 33.859 mg g−1 and 32.968 mg g−1, respectively.

Manual spray coating: A cheap and effective method to build catalyst layers for carbon nanotube forest growth

The main goal of the current work is to investigate the usefulness of manual spray coating method for building Fe-Co layers on titanium substrate, then to grow vertically aligned carbon nanotubes via catalytic chemical vapor deposition (CCVD) technique. The effects of various parameters during both layer formation and CCVD synthesis were investigated to check the tunability of the catalyst layer. The quality of as-prepared samples was examined by scanning and transmission electron microscopies, Raman spectroscopy and X-ray diffraction analysis. The following factors significantly influenced the catalyst layer together with the formation of carbon nanotube forest: (1) application of various synthesis parameters during layer construction, (2) pretreatment of the Ti plate, (3) concentration and composition of catalyst ink. By investigating the effects of various synthesis conditions it was concluded, that the system is not overly sensitive to the CCVD parameters such as reaction time and the volume of water vapor in gas feed.

Isotope Analytical Characterization of Carbon-Based Nanocomposites

ABSTRACTCarbon-based nanomaterials of different dimensions (1–3D, tubes, bundles, films, papers and sponges, graphene sheets) have been created and their characteristic properties have been discussed intensively in the literature. Due to their unique advantageous, tunable properties these materials became promising candidates in new generations of applications in many research laboratories and, recently, in industries as well. Protein-based bio-nanocomposites are referred to as materials of the future, which may serve as conceptual revolution in the development of integrated optical devices, e.g. optical switches, microimaging systems, sensors, telecommunication technologies or energy harvesting and biosensor applications. In our experiments, we designed various carbon-based nanomaterials either doped or not doped with nitrogen or sulfur during catalytic chemical vapor deposition synthesis. Radio- and isotope analytical studies have shown that the used starting materials, precursors and carriers have a strong influence on the geometry and physico-/chemical characteristics of the carbon nanotubes produced. After determining the 14C isotope constitution 53 m/m% balance was found in the reaction center protein/carbon nanotubes complex in a sensitive way that was prepared in our laboratory. The result is essential in determining the yield of conversion of light energy to chemical potential in this bio-hybrid system.

Adsorption and interactions of the bovine serum albumin-double walled carbon nanotube system

Adsorption and interactions of Bovine Serum Albumin (BSA) with Double Walled Carbon Nanotubes (DWNT) prepared by catalytic chemical vapor deposition (CCVD) synthesis were studied. Adsorption kinetics and equilibrium were investigated by means of in situ UV-spectroscopy. The extent of adsorption at different temperatures was determined at the end of a 420-min adsorption period. The adsorption equilibrium experiments were performed using various amounts of nanotubes at pH4 and 40°C, and the adsorption parameters were evaluated comparing the experimental data with models such as the Freundlich and Langmuir isotherms. The maximum protein adsorption capacity (Q0) of DWNT was determined as 1221mg·g−1. The effect of temperature on the adsorption rate experiments was investigated for constant amount of adsorbent at pH4. Adsorption kinetics followed the pseudo-first-order rate. Zeta potential measurements were performed with respect to solution pH for understanding the protein-surface interactions. The interactions between positively charged BSA molecules with negatively charged DWNT at pH4 were found to be electrostatic attractions. Thermodynamic parameters, ΔH0 and ΔS0 were found as 9.40kJ·mol−1 and 321.5J·mol−1K−1, respectively. ΔH0 value indicated that BSA adsorption on DWNT was a physisorption process.

Influence of synthesis parameters on CCVD growth of vertically aligned carbon nanotubes over aluminum substrate

In the past two decades, important results have been achieved in the field of carbon nanotube (CNT) research, which revealed that carbon nanotubes have extremely good electrical and mechanical properties The range of applications widens more, if CNTs form a forest-like, vertically aligned structure (VACNT) Although, VACNT-conductive substrate structure could be very advantageous for various applications, to produce proper system without barrier films i.e. with good electrical contact is still a challenge. The aim of the current work is to develop a cheap and easy method for growing carbon nanotubes forests on conductive substrate with the CCVD (Catalytic Chemical Vapor Deposition) technique at 640 °C. The applied catalyst contained Fe and Co and was deposited via dip coating onto an aluminum substrate. In order to control the height of CNT forest several parameters were varied during the both catalyst layer fabrication (e.g. ink concentration, ink composition, dipping speed) and the CCVD synthesis (e.g. gas feeds, reaction time). As-prepared CNT forests were investigated with various methods such as scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. With such an easy process it was possible to tune both the height and the quality of carbon nanotube forests.

Extended alcohol catalytic chemical vapor deposition for efficient growth of single-walled carbon nanotubes thinner than (6,5)

We performed a comprehensive exploration on alcohol catalytic chemical vapor deposition (ACCVD) synthesis of single-walled carbon nanotubes (SWCNTs), and with more than 70 temperature-pressure sets, we presented an extended ACCVD parametric map that covers a wide range of temperature from 340 to 950 °C and a wide pressure range over 6 orders of magnitude. Efficient synthesis of high quality SWCNTs becomes possible at temperatures down to 400 °C and pressure as low as 10−2 Pa, which benefits from the strong correlation between temperature and pressure newly discovered in this exploration. The underlying mechanism is clarified through a kinetic model, and two growth boundaries on the extended experimental map are explained by a transfer-free transmission electron microscopy (TEM) observation. Most importantly, after extending growth window of ACCVD, successful synthesis at extreme low temperature and pressure gives a significantly enhanced yield for super-small diameter SWCNTs (0.8 nm > dt > 0.62 nm) thinner than (6, 5) that are rarely observed from direct synthesis.

Carbon nanotube synthesis via the catalytic chemical vapor deposition of methane in the presence of iron, molybdenum, and iron–molybdenum alloy thin layer catalysts

In this study, we documented the catalytic chemical vapor deposition synthesis of carbon nanotubes (CNTs) using ferrocene and molybdenum hexacarbonyl as catalyst nanoparticle precursors and methane as a nontoxic and economical carbon source for the first time. Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, wavelength dispersive X-ray spectrometry and transmission electron microscopy of the thin layer catalyst as a simple and cost effective catalyst preparation after methane decomposition reaction, along with Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the growth of CNTs, from bimetallic nanoparticles, which are converted into iron–molybdenum alloy nanoparticles at 700 °C for pretreatment by hydrogen after chemical vapor deposition of thin layers. An investigation of the weight percentages of the chemical elements present in the CNTs synthesized from iron–molybdenum catalyst using quartz sheet substrate at 750 °C, confirmed a significant carbon yield of 75.4% which represents high catalyst activity. Additionally, multi-walled carbon nanotubes (∼16–55 nm in diameter and 1.2 µm in length) were observed in the iron–molybdenum alloy sample after methane decomposition reaction at 750 °C for 35 min. To show the role of iron and molybdenum coated on silicon substrate as two thin layer catalysts, samples were considered for CNTs growth (diameter ∼47–69 nm) at 800 °C and 830 °C, respectively. Moreover, the effect of hydrogen pretreatment was evaluated in terms of active metal coating properly. The best graphitic structure due to Raman spectroscopy outcomes (ID/IG ratio) was obtained for iron coated on a quartz sheet, which was estimated at 0.8505. Thermogravimetric analysis proved the thermal stability of the synthesized CNTs using iron thin-layer catalyst up to 350 °C.

Effect of Nitrogen and Hydrogen Gases on the Synthesis of Carbon Nanomaterials from Coal Waste Fly Ash as a Catalyst.

Various reducing and inert gases have been used in the catalytic chemical vapour deposition (CCVD) synthesis of carbon nanomaterials (CNMs). In this paper we report on the effects that hydrogen and nitrogen gases have on the production of CNMs from acetylene on fly ash catalysts. Parameters such as temperature and gas environments were investigated. Transmission electron microscopy (TEM) revealed that CNMs of various morphologies such as carbon nanofibers (CNFs) and carbon nanospheres (CNSs) were formed. When hydrogen was used the carbonaceous products were formed in higher yields as compared to when nitrogen was used. This could be due to the multifunctional roles that hydrogen plays as compared to nitrogen. Laser Raman and Mössbauer spectroscopy measurements revealed that three types of products were formed, namely: amorphous carbon, graphitic carbon and iron carbide. Significantly cementite (Fe3C) was identified as the main intermediate carbide species in the catalytic growth of well-ordered CNMs.

Size Dependent Phase Diagrams of Nickel-Carbon Nanoparticles.

The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3nm (807 Ni atoms). A tight binding model for interatomic interactions drives the grand canonical MonteCarlo simulations used to locate solid, core shell and liquid stability domains, as a function of size, temperature, and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should lead to a better understanding of the nanotube growth mechanisms.

Assessing carbon nanotube arrangement in polystyrene matrix by magnetic susceptibility measurements

Multi-wall carbon nanotubes filled with iron nanoparticles were combined with polystyrene to evaluate interface interactions and nanotube orientation in composite using magnetic susceptibility measurements. Iron-containing species were introduced into MWCNT cavities as the result of catalytic chemical vapor deposition synthesis using ferrocene as a catalyst source. Polystyrene loaded with certain quantity of MWCNTs was uniaxially stretched to provide the nanotube alignment. Magnetic susceptibility measurements performed in three perpendicular directions of magnetic field confirmed the alignment in the stretching direction. The composites showed a large diamagnetic response in a magnetic field perpendicular to the nanotube axis and low response in a parallel field. In a quantitative sense, anisotropy exceeds by more than an order of magnitude the effect expected from intrinsic susceptibility of nanotubes. Apparently, the graphitic nature of the nanotube lattice results in strong non-covalent interactions with uniaxially stretched polymer matrix, and aromatic rings as side groups of polystyrene align parallel to the nanotube surface, contributing to strong diamagnetism. As magnetic susceptibility is a penetrative but non-destructive type of measurement, it can successfully characterize both the alignment of one-dimensional or two-dimensional carbon allotropies and the arrangement of the macromolecules around them, contributing to the optimal design and performance of nanocomposites.

Hierarchical composites with high-volume fractions of carbon nanotubes: Influence of plasma surface treatment and thermoplastic nanophase-modified epoxy

A scaled-up catalytic chemical vapor deposition synthesis approach has been used to grow carbon nanotubes (CNTs) onto quartz and alumina fibers to prepare novel hierarchically structured composites with high volume fractions of CNTs. The as-synthesized CNT-coated fibers were functionalized using atmospheric oxygen plasma, prior to infusing an epoxy polymer matrix, in order to improve wettability and bonding. The polymer matrix was further modified by adding a triblock copolymer to provide nanoscale toughening. Direct adhesion tests show that CNT and plasma treatments increase the shear strength of quartz or alumina/epoxy films by 30%. CNT–quartz/epoxy composites show an 80% increase in the in-plane shear strength while the CNT–alumina/epoxy composites show more than a threefold increase in shear strength. The failure mechanisms of the films and the fiber composites are dominated by fracture through the catalytic iron nanoparticles and the improvements are limited by the CNT to fiber adhesion. The composites also have very high in-plane electrical conductivity, over 3S/cm. The carbon nanotubes form a piezoresistive sensing network surrounding the fibers. Under flexural loading the change in electrical resistance can detect damage initiation and impending fracture, particularly for the alumina composites.

Segmental nitrogen doping and carboxyl functionalization of multi-walled carbon nanotubes

Partial nitrogen doping was performed during the catalytic chemical vapor deposition (CCVD) synthesis of multi-walled carbon nanotubes. A special reactor was created to facilitate the execution of syntheses with different reaction conditions. The synthesized samples were analyzed by transmission electron microscopy (TEM) in order to provide information about the tubular and nontubular morphology of particles and their deformation gained after the reaction conditions were changed. The incorporation of nitrogen into the carbon structure was studied by X-ray photoelectron spectroscopy (XPS), whereas X-ray diffraction (XRD) and Raman spectroscopy evaluations showed the degree of graphitization. The samples then were carboxyl functionalized in varied concentrations of nitric acid solutions and photosynthetic reaction center protein (RC-26) purified from purple bacteria was linked to the carboxyl groups in order to make the degree of functionalization visible. The protein-linked samples were characterized by atomic force microscopy (AFM). Our experiments indicated that the syntheses carried out in the new reactor were successful and resulted in carbon nanotubes partially doped with nitrogen. TEM studies revealed that the expected deformations are localized only in a defined segment of carbon nanotubes therefore nitrogen doping is most possibly presented there. The nitrogen content in the samples represented in atomic ratios was between 0.9% and 2.9%. The deformations facilitate the functionalization at that certain area, thus the location of carboxyl groups can be determined.

Growth mechanism and controllable synthesis of graphene on Cu–Ni alloy surface in the initial growth stages

Catalytic chemical vapor deposition (CVD) on transition metals is a promising and versatile technique for graphene (and graphene film) growth. Recently, substrate alloying has been used to improve graphene synthesis by CVD. However, the underlying mechanism is still elusive. In this work, taking the Cu–Ni alloy surface as an example, we study the mechanism of carbon nucleation on the alloy surface in the initial stages using first-principles calculations. The energetics and kinetics of C-dimer formation are considered. Our calculations reveal that substrate alloying may strongly affect the carbon dimerization in CVD synthesis. Both the adsorption strength of C species and the dimerization barriers vary with the alloy composition. In addition, carbon migration, an important step in graphene growth, can also be controlled by alloying. Our findings may provide an understanding of the mechanisms by which alloying controls graphene (and graphene film) growth in CVD.

In situ CCVD synthesis of carbon nanotubes within zeolite crystal coated porous ceramic foam

In this study, consolidated zeolite crystal coated porous ceramic foams containing a large quantity of carbon nanotubes (CNTs) within micro-metre sized pores were prepared. An alumina-silica porous ceramic body, having an average pore size of less than 100 m, was produced by the direct foaming technique. Well-shaped zeolite crystals having an average size of 180 nm were synthesized and homogeneously coated on the porous ceramic body by an in situ process. An Fe-supported zeolite/ceramic matrix, which is used for CNT synthesis, was prepared using ion-exchange by immersing the zeolite-coated porous ceramic body into FeCl2 aqueous solution. The CNTs were synthesized by a catalytic chemical vapour deposition (CCVD) process for four different reaction times. Both acicular-shaped and randomly bundled networks of multi-walled carbon nanotubes (MWCNTs) were synthesized using these different reaction times. Moreover, the yield of CNTs produced showed a tendency to increase with increasing reaction time.

Ni–Mo and Co–Mo alloy nanoparticles for catalytic chemical vapor deposition synthesis of carbon nanotubes

Here, we show for the first time a catalytic chemical vapor deposition (CCVD) synthesis of carbon nanotubes (CNTs) using polyoxomolybdate clusters Mo12O28(μ2-OH)12{Ni(H2O)3}4 and Mo12O28(μ2-OH)12{Co(H2O)3}4 as a source of catalyst nanoparticles. X-ray diffraction analyses indicated that the products of thermal decomposition of the clusters contain NiMoO4 and CoMoO4 phases, which are converted into Ni–Mo and Co–Mo alloys at 900°C in hydrogen environment. High-resolution transmission electron microscopy in combination with energy-dispersive X-ray spectroscopy confirmed the CNT growth from bimetallic nanoparticles. Synergism between two metals in an alloy resulted in large-scale production of non-bundled few-walled CNTs with narrow diameter distribution and high quality.