Chemical Vapor Deposition Of Methane Research Articles

Structural control of nanoporous frameworks consisting of minimally stacked graphene walls

This mini-review provides an in-depth analysis of the formation and post-processing of nanoporous graphene materials via methane chemical vapor deposition (CH4-CVD) using nanostructured metal oxide templates, including Al2O3, MgO, and SiO2. Initially, the formation of graphene sheets is discussed in terms of the role of CH4-CVD, the influence of templates, and the underlying mechanism for tailoring the structures of the graphene-based materials. Following this, the discussion extends to the post-graphene formation process. We focus on key steps, including template removal and graphene repair via zipping reactions at high temperatures. Additionally, we evaluate the conditions to prevent undesired structural transformations. The correlation between the structural features and transformations occurring during post-processing is also examined. The materials fabricated through these methods exhibit impressive properties of high porosity, minimal edge sites, superior oxidation resistance, and elasticity, positioning them as promising materials in various applications.

Silicon Radical-Induced CH4 Dissociation for Uniform Graphene Coating on Silica Surface.

Due to the manufacturability of highly well-defined structures and wide-range versatility in its microstructure, SiO2 is an attractive template for synthesizing graphene frameworks with the desired pore structure. However, its intrinsic inertness constrains the graphene formation via methane chemical vapor deposition. This work overcomes this challenge by successfully achieving uniform graphene coating on a trimethylsilyl-modified SiO2 (denote TMS-MPS). Remarkably, the onset temperature for graphene growth dropped to 720°C for the TMS-MPS, as compared to the 885°C of the pristine SiO2. This is found to be mainly from the Si radicals formed from the decomposition of the surface TMS groups. Both experimental and computational results suggest a strong catalytic effect of the Si radicals on the CH4 dissociation. The surface engineering of SiO2 templates facilitates the synthesis of high-quality graphene sheets. As a result, the graphene-coated SiO2 composite exhibits a high electrical conductivity of 0.25Scm-1. Moreover, the removal of the TMP-MPS template has released a graphene framework that replicates the parental TMS-MPS template on both micro- and nano- scales. This study provides tremendous insights into graphene growth chemistries as well as establishes a promising methodology for synthesizing graphene-based materials with pre-designed microstructures and porosity.

Synthesis of MWCNTs by chemical vapor deposition of methane using FeMo/MgO catalyst: role of hydrogen and kinetic study

This study aims to investigate the role of hydrogen on CNTs synthesis and kinetics of CNTs formation. The CNTs were synthesized by catalytic chemical vapor deposition of methane over FeMo/MgO catalyst. The experimental results revealed that hydrogen plays an important role in the structural changes of catalyst during the pre-reduction process. The catalyst structure fully transformed into metallic FeMo phases, resulting in an increased yield of 5 folds higher than those of the non-reduced catalyst. However, the slightly larger diameter and lower crystallinity ratio of CNTs was obtained. The hydrogen co-feeding during the synthesis can slightly increase the CNTs yield. After achieving the optimum amount of hydrogen addition, further increase in hydrogen would inhibit the methane decomposition, resulting in lower product yield. The hydrogenation of carbon to methane was proceeded in hydrogen co-feed process. However, the hydrogenation was non-selective to allotropes of carbon. Therefore, the addition of hydrogen would not benefit neither maintaining the catalyst stability nor improving the crystallinity of the CNT products. The kinetic model of CNTs formation, derived from the two types of active site of dissociative adsorption of methane, corresponded well to the experimental results. The rate of CNTs formation greatly increases with the partial pressure of methane but decreases when saturation is exceeded. The activation energy was found to be 13.22 kJ mol−1, showing the rate controlling step to be in the process of mass transfer.

Single-step synthesis of graphene nanosheets-carbon nanotubes hybrid structure by chemical vapor deposition of methane using Fe-Mo-MgO catalysts

A set of Fe-Mo-Mg catalysts with varying Mo/Mg weight ratios (40/10, 30/20, 20/30, and 10/40) were prepared and evaluated for the synthesis of graphene nanosheets/carbon nanotubes (GNS/CNT) hybrid materials via methane chemical vapor deposition. The results showed that changing the Mo/Mg ratio had a significant impact on the yield and the nature of the deposited carbon. The XRD and TPR results revealed that the iron molybdate and magnesioferrite species were the main components of Fe-Mo-Mg catalysts. TEM images showed that GNS-CNT hybrid materials were successfully grown on the surface of all Fe-Mo-Mg systems, except for the catalyst with the Mo/Mg ratio of 10:40, which produced CNT only. Raman spectroscopy results revealed that all carbon products were of high quality, with ID/IG ratios ranging from 0.14 − 0.41. It was also noticed that increasing the MgO content in the catalyst composition increases the amount of CNT compared to GNS. The total carbon yield increased from 170% to 284% for Fe-40Mo-10Mg and Fe-10Mo-40Mg, respectively. The gradual incorporation of Mg into the Fe-Mo catalyst significantly increased catalytic growth activity due to the presence of numerous mixed oxide species with diverse structures, such as MgFeOx, MgMoOx, and FeMoOx.

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

Cobalt supported on carbon nanotubes for methane chemical vapor deposition for the production of new carbon nanotubes

Well-structured CNT were produced over Co/CNT catalysts. The final products do not require a purification procedure for support catalyst removal.

Single wall carbon nanotubes growth over cobalt-iron mesoporous MCM-41 bimetallic catalyst under methane chemical vapor deposition, an experimental and DFT evaluation

Cobalt and iron MCM-41 catalysts were synthesized through an in-situ incorporation process starting from commercial iron and cobalt nitrates. The incorporation was confirmed by diffuse reflectance UV spectroscopy (DRS-UV) inspecting the cobalt and iron silicate-like photon absorption features and comparing with pure MCM-41-Co and MCM-41-Fe catalysts. Additionally it was found that the incorporation of cobalt and iron does not compromise the mesoporous structure of MCM-41 as confirmed by N2 adsorption isotherms. All catalysts showed high surface areas (∼1100 m2g−1). Catalysts performance was conducted in a simple methane chemical vapor deposition (CVD) set up at 800 °C to produce single wall carbon nanotubes (SWCNT) under a constant flow of methane for 30 min. CVD products were characterized by thermogravimetric analysis (TGA) and Raman spectroscopy, finding that the iron content in the catalysts favors the selectivity and yield of graphitic-like structures, and confirming the presence of SWCNT by the appearance of a characteristic radial breathing mode (RBM) signals. These results were supported by Density Functional Theory (DFT) simulations of the methane dissociation (CH4 +TM → H3C –TMH) over Con (n = 1–5) and ComFe (m = 1–4), finding a different activation energy trend where ComFe (m = 1–4) clusters have the lower activation energy. The DFT study also revealed a charge difference (δC − δTM) higher in the case of dissociation over ComFe (m = 1–4) which may lead to an electrostatic stabilization of the transition metal, diminishing the activation energy of those clusters and leading to a faster carbon uptake.

Synthesis of carbon nanotubes with controllable diameter by chemical vapor deposition of methane using Fe@Al2O3 core–shell nanocomposites

A novel and simple synthetic approach toward core–shell Fe@Al2O3 nanocomposites were developed in this study. The as-synthesized catalyst was applied to convert the methane into carbon nanotubes. Moreover, due to the properties of the core–shell structure, the amount of surfactant can be adjusted to control the pore size of the shell and further control the diameter of the carbon nanotubes. In this study, the conversion of CH4 was up to 97% and the carbon production was 135 mgC/gcat.*h, which is much higher than traditional supported catalysts under similar reaction conditions. In addition, the carbon product quality (IG/ID) was up to 1.96. The enhanced CH4 catalytic activity for the core–shell Fe@Al2O3 catalyst originated from the combined acidic sites on the surface of the Al2O3 shell and the high carbon diffusion rate of the Fe core, which led to the high efficiency of CH4 conversion and longer lifetime of the catalyst.

Dual growth of graphene nanoplatelets and carbon nanotubes hybrid structure via chemical vapor deposition of methane over Fe–MgO catalysts

In this study, Fe–MgO catalyst substrates with various Fe and MgO combinations were evaluated for the growth of different types of carbon nanostructure materials (CNMs), particularly graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) via chemical vapor deposition using methane as a carbon source. The hydrogen yield was also determined as a valuable by-product in this process. Therefore, a set of Fe–MgO catalysts with different iron loadings (30, 80, 85, 90 and 100 wt %) were prepared by the combustion method to realize this target. The physicochemical properties of freshly calcined Fe–MgO catalysts were investigated by XRD, TPR and BET, while the as-grown CNMs were studied by HR-TEM, XRD and Raman spectroscopy. The results verified that the morphology of as-grown CNMs as well as the H2 yield was directly correlated to the iron content in the catalyst composition. The XRD and TPR results showed that various FeMgOx species with deferent levels of interactions were produced with the gradual incorporation of MgO content. TEM images indicated that GNPs were individually grown on the surface of high loaded iron-containing catalysts (90–100 wt %) due to the presence of highly aggregated iron particles. While multi-walled carbon nanotubes (MWCNTs) with uniform diameters were grown on the low iron-loaded catalyst (30%Fe/MgO) due to the formation of highly dispersed FeMgOx particles. On the other hand, GNPs/MWCNTs hybrid materials were grown on the surface of 80%Fe and 85%Fe/MgO catalysts. This behavior can be interpreted by the co-existence of highly aggregated and highly dispersed Fe2O3 particles in the catalyst matrix. The results demonstrated that the catalyst composition has a notable effect on the nature of CNMs products and H2 yield.

Synthesis of carbon molecular sieve for carbon dioxide adsorption: Chemical vapor deposition combined with Taguchi design of experiment method

In this study, the chemical vapor deposition of methane on the activated carbon has been identified as an effective approach to prepare the CMS for the adsorption of CO2. The effects of deposition parameters on the properties of the CMSs were both experimentally and statistically investigated. The deposition temperature as the most influential factor on the CO2 adsorption capacity was determined based on the response table. CMS6 exhibited large volume of narrow-micropore centered at 0.56 nm in size, showed a maximum CO2 adsorption of 1.7275 mmol g−1 at 273 K and 1 bar. The isosteric heat of adsorption and CO2/N2 selectivity were 40.37 kJ mol−1 and 22.84 at 273 K and 1 bar, respectively. As a result, this particular study can be used for the main challenges associated with the design of CMS adsorbents to provide a perspective and opportunities to accelerate novel molecular sieve carbon production in the future.

Application of carbon nanotubes prepared from CH4/CO2 over Ni/MgO catalysts in CO2 capture using a BEA–AMP bi-solvent blend

Abstract Carbon nanotubes (CNTs) were synthesized by the chemical vapour deposition of methane and carbon dioxide over a Ni/MgO catalyst. The synthesized CNTs were then mixed with K/MgO catalyst at different ratios and used as the catalyst for CO2 absorption in butylethanolamine-2-amino-2-methyl-l-propanol bi-solvent blend. The catalysts were characterized using X-ray diffraction, scanning electron microscopy, butylethanolamine, thermal gravimetric analysis and temperature-programmed desorption of carbon dioxide in order to determine the characteristics responsible for good CO2-absorption performance. The results showed that, with the addition of a catalyst into the amine solution, the amine reached equilibrium CO2 loading faster than without a catalyst. Also, the increase in the CNT content of the KMgO/CNTs catalyst made the CO2 absorption reach equilibrium much more quickly compared with just KMgO alone and without a catalyst. The KMgO/CNTs at a ratio of 1:4 yielded the fastest time to reach CO2-loading equilibrium at 240 min, which was mainly due to the increase in strong basic sites as well as the highest total basic sites with an increase in CNT content. In addition, because of the extremely large specific surface area and pore volume generated due to the CNT, the number of exposed active centres per unit mass increased tremendously, leading to a corresponding tremendous increase in CO2 absorption.

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...

Development of the Effective Reaction Model for Diamond Deposition Simulation within the Continuous Media Approach

Three models for diamond growth process by the chemical vapor deposition of methane are proposed. They differ in the degree of detail of the surface reaction description. The most complete model contains the reactions of deposition, etching and insertion. Gas-dynamic simulations have been performed for all those models. The species delivery to the substrate and the contribution from different species to the growth process is analysed. It is shown that different surface reaction models lead to different profiles of the species concentrations in the immediate vicinity of the substrate, thus, the experimental data on the growth rate may give information on the growth mechanism.

Doping of boron or nitrogen to multilayered graphene grown on copper by thermal chemical vapor deposition of methane and vapor of phenylboronic acid or melamine

AbstractEither boron or nitrogen doped multilayered graphene was prepared by thermal chemical vapor deposition (CVD). Obtained heteroatom doped graphene was examined by Raman scattering, x-ray photo electron spectroscopy (XPS) and temperature dependence of sheet resistance. From the Raman scattering, obvious increase of ID/IG ratio could not be detected by boron doping, while it increased by ∼0.2 or more for nitrogen doped sample. From XPS, doping rates of boron and nitrogen were estimated to be in the range of 5∼12 at% and 1∼2 at%, respectively. XPS also showed that the boron and nitrogen atoms would locate at the doping sites of both graphitic and neighborhood of atomic defect. Magnitude of sheet resistance was decreased by either doping of boron or nitrogen.

Effect of impregnation solutions on the synthesis of Ni-Cu/Al2O3 catalyst to obtain carbon nanofibers

The present work reports on the influence of nickel molar loading and impregnation solutions, nitrate salts and copper and nickel ammonium complexes, on the synthesis of Ni-Cu catalyst supported on alumina for obtaining carbon nanofibers by catalytic chemical vapor deposition of methane. These catalysts were characterized by N2 adsorption-desorption, x-ray Diffraction, Thermo-Gravimetric Analysis and Scanning Electron Microscopy for the carbon nanostructures analysis. The catalytic activity was studied through the carbon deposition under different conditions of temperature (600 °C and 650 °C) and pressure (in ultra-low pressure conditions and 0.5 bar). As a main result, catalyst using nitrate salts impregnation leads to the major carbon nanofibers yielding at the temperature of 600 °C. On the other hand, catalysts synthesized by ammonium complexes impregnation present also improved characteristics compared to conventional catalysts that allows considering this methodology as an interesting alternative in carbon nanofibers producing.

Single Wall Carbon Nanotubes Synthesis through Methane Chemical Vapor Deposition over MCM-41–Co Catalysts: Variables Optimization

MCM-41–Co catalysts were tested in the synthesis of single wall carbon nanotubes (SWCNTs) through methane chemical vapor deposition (CVD), varying total cobalt content, synthesis temperature, methane flow rate, and deposition time. All variables showed a relationship with total carbon deposition, graphitic quality according to Raman results. Cobalt content showed a maximum activity at 4%, but the structural quality is best at 3%. Flow rate does not affect the quality up to 300 cm3 min−1, but deposition time leads to the formation of highly disordered carbon species passing methane for periods longer than 30 min, concluding that optimal variables are a methane deposition temperature of 800 °C, a 300 cm3 min−1 methane flow rate, and a 30 min of methane injection time, leading to a 5.4% carbon mass content and 5.1 G/D area ratios.

In situ synthesis of CNTs in HfB2 powders by chemical vapor deposition of methane to fabricate reinforced HfB2 composites

Carbon nanotubes (CNTs) were synthesized over a Ni/Y2O3/HfB2 catalyst by chemical vapor deposition of methane at temperatures ranging from 800 °C to 1200 °C. Results of X-ray diffraction, scanning electron microcopy, transmission electron microcopy, and Raman spectroscopy indicated that 1100 °C was the most suitable synthesis temperature for the CNT growth using the Ni/Y2O3/HfB2 catalyst. Spark plasma sintering was then conducted on the well-synthesized composite powder at 1600 °C for 10 min under a uniaxial load of 30 MPa in vacuum to obtain fully dense bulk composite. The flexural strength and fracture toughness of the in situ synthesized CNT(Ni/Y2O3)–HfB2 composite were increased to 942 ± 34 MPa and 9.2 ± 0.5 MPa m1/2, respectively. These values were considerably higher than those of traditional HfB2-based composites. Crack deflection, crack bridging, CNTs debonding, and pull-out were identified as the main reinforcing mechanisms for the improvement of mechanical properties.

Fabrication and properties of CNT/Ni/Y/ZrB2 nanocomposites reinforced in situ

AbstractCarbon nanotubes (CNTs) were synthesized in situ by chemical vapor deposition of methane over nano‐ZrB2 matrix using Ni/Y catalysts. Well‐grown CNTs with tangled and long bodies and mainly composed of well‐crystallized graphite were obtained when the Ni content reaches 10 wt%. The CNT/ZrB2 nanocomposites obtained by spark plasma sintering at 1400°C exhibited full density and optimal mechanical properties. The flexural strength and fracture toughness of the nanocomposites were 1184 ± 52 MPa and 10.8 ± 0.3 MPa·m1/2, respectively. Results indicated that the dispersion of CNTs in situ can improve composite performance, rendering the mechanical properties of the CNT/ZrB2 nanocomposites synthesized in situ considerably superior to those of monolithic ZrB2 nanoceramics and CNT/ZrB2 nanocomposites synthesized using the traditional method. The toughening mechanisms included crack deflection, crack bridging, CNT debonding, pull‐out, and fracture.

Low-level doping of nitrogen to multilayered graphene by chemical vapor deposition of methane including melamine vapor

Growth of graphene doped with the low level of nitrogen is carried out on the copper foil by conventional chemical vapor deposition. Melamine is used as nitrogen source. Melamine vapor is generated by heating and carried by an argon flow (carrier flow) to a main flow of Ar including methane. Ratio of the number of molecules, melamine/methane, is controlled by changing the mixing rate of the carrier flow and the main flow. Measurements of Raman scattering, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy and sheet resistance clarify the feature of prepared sample. At low melamine/methane ratio in the order of 10−3, quaternary N doped graphene is grown. Then the growth of pyridinic N doped graphene is going to start as increasing the melamine/methane ratio in the order of 10−2. Magnitude of the sheet resistance per one graphene layer decreases by ~ 75% when the nitrogen is in the quaternary site, while it increases twice or more when the pyridine-like configuration increases.

Influence of Mo or Cu doping in Fe/MgO catalyst for synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of methane

ABSTRACTA series of mono-, bi- or tri-metallic Fe–Mo-Cu/MgO catalysts with the same metal loading of 6 wt% were prepared by impregnation method and used as catalysts for synthesis single-walled carbon nanotubes (SWCNTs) via methane decomposition. XRD, H2-TPR, and nitrogen physisorption techniques were used to characterize the freshly calcined catalysts, while HRTEM, Raman spectroscopy and TGA were employed to investigate the morphology and microstructure of the SWCNTs product. The obtained results indicated that the introduction of Mo or Cu in the Fe/MgO catalyst enhanced the catalytic growth activity. TEM images showed that both bundles and isolated SWCNTs were obtained over Mo containing catalysts, whereas only SWCNTs bundles were grown over the Fe-Cu/MgO catalyst. The obtained SWCNTs having a diameter of around 0.9–2.4 nm. Raman analysis illustrated that all promoted catalysts produced high quality of SWCNTs compared to the unpromoted Fe/MgO catalyst.