Catalytic Chemical Vapor Deposition Research Articles

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.

Heteroatom doped carbon nanosheets from waste tires as electrode materials for electrocatalytic oxygen reduction reaction: Effect of synthesis techniques on properties and activity

The effective method for synthesis of heteroatom doped carbon nanosheets (CNS) from waste tires was developed. The process employed NiO loaded CaCO3 catalyst for catalytic chemical vapor deposition (CCVD) of the CNS from the non-condensable pyrolysis gas. The promotion of CaCO3 with NiO had beneficial effect on carbon growth compared to pure CaCO3, increasing the carbon yield by 2.8 and 8.0 times for the CCVD at 700 and 750 °C, respectively. On the contrary, the morphology and structure of synthesized S,O-doped CNS as well as oxygen reduction reaction (ORR) electrocatalytic activity were not influenced by the NiO addition. Based on the carbon yields and ORR electrocatalytic activities, the preferred CCVD temperature was 700–750 °C, resulting in the CNS with the ORR peak reduction potentials of −0.217 V to −0.220 V (versus −0.167 V for Pt electrode). The improvement of CCVD process was proposed decreasing the ORR peak reduction potential to −0.191 V. A mixture of NH3 and H2O was added to pyrolysis gas, promoting the development of mesoporosity and incorporation of N into the material structure. The developed technique is a viable solution for the conversion of non-condensable gases from tire pyrolysis into S,N,O-doped CNS for ORR.

Synthesis of graphene nanosheets by emitted black carbon and its sustainable applications

Abstract An approach has been made to convert Black carbon (BC) into two-dimensional novel Graphene nanosheets (GNS) by simpler approach carried-out for the conversion of facile using Black carbon (BC) by purging Catalytic-Chemical vapor deposition (C-CVD) technique. Iron and Nickel (Fe-Ni) bi-metallic catalyst supports 92 % GNS yield, as opposed to other lower yields method and using less-cost effective catalysts. The synthesized GNS is employed for the photo-catalytic degradation of Rhodamine-B (RhB) in addition with Janus Green (JG) in a single step which resolves two organic dye contaminant issues with non-toxic molecular intermediates at the same time, under influence of solar light exposure. The Anti-bacterial properties activity of selected gram-negative and gram-positive and fungal activity was systematically achieved. GNS is highly stable and shows less toxicity against the Human embryonic kidney (HEK-293) cell lines and safer to the environment. Furthermore, regeneration efficiency of GNS, which was still at its higher value even after five consecutive cycles of recycling testing, GNS can perform the quite superior result than the earlier reported studies on structurally altered graphene and other graphitic based materials. The fusion of these investigations introduces a new course, promising way to achieve the new era in environmental remediation and utilization of these materials in future eco-friendly approaches.

A lightweight CNWs-SiO2/3Al2O3·2SiO2 porous ceramic with excellent microwave absorption and thermal insulation properties

To obtain excellent microwave absorption and thermal insulation properties, carbon nanowires reinforced SiO2/3Al2O3·2SiO2 composite ceramics (CNWs-SiO2/3Al2O3·2SiO2) were fabricated by catalytic chemical vapor deposition (CCVD) using C2H4 as the carbon source. The content of CNWs in SiO2/3Al2O3·2SiO2 porous ceramics can be adjusted by controlling the concentration of the catalyst precursor and the CCVD time. A higher concentration of catalyst precursor and longer CCVD time are beneficial for the growth of CNWs and for improving the electromagnetic wave (EMW) absorption properties of CNWs-SiO2/3Al2O3·2SiO2. However, CNWs are harmful to impendence matching due to the strong reflection and weak absorption when the content exceeds the threshold (30 wt%) in SiO2/3Al2O3·2SiO2 porous ceramics. CNWs are also harmful to the thermal insulation properties due to their high thermal conductivity. The results show that CNWs-SiO2/3Al2O3·2SiO2 can attain good EMW absorption and thermal insulation properties if the content of CNWs is 30 wt% when the concentration of the catalyst precursor is 3 wt% and the CCVD time is 15 min. The effective absorption bandwidth (EAB) can cover from 8.2 to 12.4 GHz (the whole X-band), and the minimum reflection coefficient (RCmin) is -31 dB at 9.1 GHz. The temperature gradient is 218 °C, which can satisfy the design requirement. Thus, the dielectric and thermal insulation properties are designable for CNWs reinforced SiO2/3Al2O3·2SiO2 porous ceramics to obtain excellent EMW absorption and thermal insulation properties.

Measurement of Flexural Rigidity of Multi-Walled Carbon Nanotubes by Dynamic Scanning Electron Microscopy

In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required.

Synthesis and characterization of platinum multi-walled carbon nanotubes nanocomposite film electrode

Carbon nanotubes (CNTs) were synthesized by a bimetallic (Fe–Co/CaCO3) catalytic chemical vapour deposition (CCVD) method. The synthesized CNTs were purified with acid to remove the catalyst impurities to enhance the deposition of platinum (Pt) onto the CNTs surface. Platinum multiwall (Pt-MWCNTs) nanocomposites were produced by a wet impregnation technique dispersed in Texanol and Acrylic resins to form a paste. The paste was screen printed on an FTO glass substrate. Surface morphology, microstructure, chemical composition, crystallographic phase, surface area and electrical performance of the Pt-MWCNTs nanocomposites were measured by HRSEM, HRTEM, EDS, XPS and XRD. The electrical conductivity of the electrode produced was found to be 4.927 S m−1. The results showed that the prepared nanocomposites will be a good electrode material in solar cell applications.

Synthesis, morphology, magnetic and electrochemical studies of nitrogen-doped multiwall carbon nanotubes fabricated using banded iron-formation as catalyst

Abstract Natural catalysts are important for the low-cost and large-scale production of carbon nanostructures. In this study, we used a natural material obtained from thin bands of sedimentary rocks known as Banded Iron Formation (BIF). BIF powders (pristine and ball-milled) were used as catalysts for the large-scale production of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) via an aerosol-assisted catalytic chemical vapor deposition (AACCVD) experiment. The morphology and composition profiles of the BIF powders and N-MWCNT samples were analyzed by scanning and transmission electron microscopies, X-ray diffraction, X-ray photoelectron (XPS) and Raman spectroscopies, and thermogravimetric analysis. XRD characterizations revealed that the BIF powders were mainly composed of quartz and hematite. This result was also confirmed by Raman spectroscopy. The production efficiency of 340% wt./wt. of the N-MWCNTs was obtained by 1 h ball-milled BIF powders. The specific surface area of the N-MWCNTs reached 37.87 m2/g. The type of nitrogen doping, oxygen functional groups, silicon, and carbon species (sp2 and sp3) hosted at the surface of the N-MWCNTs were quantified by XPS. The electrochemical response of electrodes composed of the N-MWCNTs were studied via cyclic voltammetry, electrochemical impedance, and coulombic efficiency determination to assess the possible applications of our synthesized materials as energy storage or sensor systems. The magnetic properties and effects of acid and thermal treatments on the morphology of the N-MWCNTs are also presented.

Efficient Growth of Carbon Nanotube Carpets Enabled by In Situ Generation of Water

Catalytic chemical vapor deposition (CVD) utilizing the gaseous product mixture of Fischer–Tropsch synthesis (FTS-GP) offers the potential for scale-up and controlled growth of carbon nanotube (CNT...

Effect of Co-Mo catalyst preparation and CH4/H2 flow on carbon nanotube synthesis

Supported Co-Mo catalysts with a given ratio of metals were prepared from polyoxomolybdate Mo12O28(μ2-OH)12{Со(H2O)3}4 using impregnation and combustion methods. Effects of the type of catalyst and the ratio and flow of methane and hydrogen gases on the structure of carbon nanotubes (CNTs) synthesized by catalytic chemical vapor deposition (CCVD) method were studied using transmission electron microscopy and Raman spectroscopy. The catalyst prepared by combustion method yielded mainly individualized CNTs, while the CNTs were highly entangled or bundled when impregnation method was used. In both cases, addition of hydrogen to methane led to reduction of the CNT yield. The samples synthesized using two different catalysts and the same CH4/H2 ratio and flow of gases were tested in electrochemical capacitors. A higher specific surface area of the CNTs grown over impregnation-prepared catalyst caused a better performance at scan rates from 2 to 1000 mV/s.

Raman and XPS depth profiling technique to investigate the corrosion behavior of FeSiAl alloy in salt spray environment

Abstract As a promising material for electromagnetic microwave absorption, FeSiAl (FSA) alloy always suffers from inadequate corrosion resistance in the marine environment. Herein, the Raman and X-ray photoelectron spectroscopy (XPS) depth profiling techniques are adopted to investigate the basic corrosion behavior of FSA in salt spray environment. The Raman analysis contributes to the understanding of the composition change at various corrosive periods while the XPS depth profiling reveals the corrosion process of Fe0→Fe2+→Fe3+ in a sequence. The observed corrosion rates (CRs) of FSA immersed in 5 wt% NaCl solution for 1, 24 and 48 h are 2.99 × 10−12, 4.90 × 10−12 and 5.85 × 10−12 m/s, respectively. The increasing value of CRs as a function of time demonstrates the accelerated corrosion tendency. Moreover, to suppress the corrosive behavior of FSA alloy, carbon is decorated on its surface by catalytic chemical vapor deposition method using acetylene as the carbon source. The carbon coating restrains the corrosion process by impermeability and hydrophobicity of carbon materials in corrosive mediums. This study will help in the designing of microwave absorbers which can resist corrosion in harsh reaction conditions as well as available at commercial level to save the economy.

Preparation of CNT–Co@TiB2 by catalytic CVD: Effects of synthesis temperature and growth time

Owing to its excellent properties, titanium boride (TiB2) has drawn considerable attention. This study focuses on in-situ synthesis of carbon nanotubes (CNTs) on the surfaces of TiB2 particles by using Co as a catalyst in catalytic chemical vapor deposition to improve the toughness of TiB2 through the toughening effect of CNTs. Analyses of crystal structure, phase and microstructure confirm the successful grafting of CNTs on TiB2 matrix. Carbon yield is also calculated to estimate the effects of carbon deposition. Raman spectroscopy indicates that the CNTs grafted on TiB2 at 850 °C for 150 min exhibit low ID/IG, suggesting satisfactory quantity and quality of CNTs. An appropriate increase in synthesis temperature can promote the rapid growth of CNTs at the beginning, extending the growth time of CNTs. Meanwhile, sufficient growth time would allow the process of carbon precursor conversion to CNTs, enhancing the purity and graphitization of CNTs.

Active Phase of Cobalt Oxide (Co3O4) as a Promising Catalyst for Graphene Growth by Alcohol Catalytic Chemical Vapor Deposition

The presence of active catalyst during graphene growth by alcohol catalytic chemical vapour deposition is a compulsory. This study is aimed to validate the effect of annealing temperature for the formation of active cobalt oxide (Co3O4) film on the graphene growth by alcohol catalytic chemical vapour deposition technique. Active Co3O4 film was prepared on silicon wafers by sol-gel process, using cobalt acetate tetrahydrate as the precursor compound and absolute ethanol as the solvent. The active Co3O4 phase was achieved by annealing process at 450, 500, 550 and 600 °C. The graphene is grown from active Co3O4 film under 900 °C of chemical vapor deposition (CVD) processing temperature for 5 minutes. The obtained Co3O4 was characterized by x-ray diffraction and Raman spectroscopy. The as-grown graphene from active Co3O4 film annealed at 450 ⁰C was characterized by Raman spectroscopy and field emission scanning electron microscope (FESEM). The results demonstrate that spinel type cubic structure of Co3O4 could be produced at the varied annealing temperatures but the optimum XRD result was at 500 ⁰C annealing temperature. The presence of active Co3O4 phase was supported with the exhibited peaks of four Raman-active phonon modes in the Raman spectra. The quality of as-grown graphene determined from the ratio of 2D-band over G-band intensities is 1.010; an indication of few layers of graphene. Active Co3O4 film is able to produce good quality of graphene comparable with Ni and Cu catalysts. And graphene can be used in many devices, including electronic device, energy storage device, power device, and others.

Mesoporous Single-Atom-Doped Graphene–Carbon Nanotube Hybrid: Synthesis and Tunable Electrocatalytic Activity for Oxygen Evolution and Reduction Reactions

Mesoporous heteroatom-doped carbon-based nanomaterials are very promising as catalysts for electrochemical energy conversion and storage. We have developed a one-step catalytic chemical vapor deposition method to grow a highly graphitized graphene nanoflake (GF)–carbon nanotube (CNT) hybrid material doped simultaneously with single atoms of N, Co, and Mo (N–Co–Mo–GF/CNT). This high-surface-area material has a mesoporous structure, which facilitates oxygen mass transfer within the catalyst film, and exhibits a high electrocatalytic activity and stability in oxygen reduction and evolution reactions (ORR and OER) in alkaline media. We have shown that in this metal (M)–N–C catalyst, M (Co, Mo)–C centers are the main sites responsible for OER, while, for ORR, both M and N–C centers synergistically serve as the active sites. We systematically investigated tuning of the ORR and OER activity of the porous catalyst depending on the choice of the underlying substrate. The ORR kinetic current and OER activity for N–Co–Mo–GF/CNT were significantly enhanced when the catalyst was deposited onto a Ni substrate, resulting in an advanced electrocatalytic performance compared to the best bifunctional ORR/OER catalysts reported so far. Using a developed scanning electrochemical microscopy analysis method, we demonstrated that the higher OER reactivity on Ni was attributable to the formation of underlying catalyst/Ni interfacial sites, which are accessible due to the porous, electrolyte-permeable structure of the catalyst.

Bifunctional carbon-encapsulated FeSiAl hybrid flakes for enhanced microwave absorption properties and analysis of corrosion resistance

Designing of materials which can resist aging and corrosion in harsh reaction conditions is required to mitigate the omnipresent issue of electromagnetic interference pollution. Particularly, FeSiAl alloy is a relevant composite material, however, it always suffers aging and corrosion when exposed to crude saline environment. Herein, Carbon-encapsulated FeSiAl (FeSiAl@C) hybrid flakes are developed by catalytic chemical vapor deposition (CCVD) technique through the reaction of FeSiAl precursor with acetylene (C2H2) gas at 300 °C for 5 min. The carbon coating efficiently improves the impedance matching characteristics of FeSiAl powder leading to enhance microwave absorption. Not only that, the carbon capsule also plays an effective shielding function to prevent the alloy from corroding. Specifically, the FeSiAl@C-300 °C delivers increased complex permeability and permittivity in the frequency range of 7–14 GHz, as well as improved impedance matching. In addition, the corrosion resistance is measured using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 5 wt% NaCl solution. The results indicate that the synthesized hybrid exhibits excellent corrosion resistance capability. So, the composite synthesis is a worthy approach to design hybrid materials for effective microwave absorption and corrosion resistance properties for practical applications.

Temperature dependence of iron oxide-graphene oxide properties for synthesis of carbon nanotube/graphene hybrid material

Iron oxide embedded on graphene oxide (Fe2O3/GO) was prepared by chemical exfoliation followed by wet impregnation. Reduced Fe2O3/GO could be employed as catalyst for synthesizing carbon nanotubes CNTs via catalytic chemical vapor deposition CCVD of n-hexane within a temperature range of 700-1000 °C. It was found that during the synthesis process, pretreatment affected the transformation of iron nanoparticles in the Fe2O3/GO, leading to significant difference in formation of carbon nanoparticles. When the Fe2O3/GO was employed within a temperature range of 700−900 °C, Fe2O3 was reduced to α-Fe, yielding CNT growth on the graphene surface. However, the α-Fe could be transformed to γ-Fe when the Fe2O3/GO was subject to the temperature of 1000 °C, resulting in formation of carbon spheres instead of CNTs. After experimentally verified, conceptual scenarios of CNT/graphene hybrid material formation with respect to the pretreatment and synthesis temperature were proposed and discussed.

Active Cobalt Catalyst for Carbon Powder Growth: Sol-gel Process and Alcohol Catalytic CVD Technique

Introduction: The unique properties of carbon nanotubes trigger a lot of ideas to study the ability of the material in many fields. Experimental: The research started with the preparation of cobalt catalyst by using the sol-gel method, which used cobalt acetate tetrahydrate and 2-amino ethanol solvent, followed by the actual growth of carbon nanotube by using the prepared catalyst in alcohol catalytic CVD. Results: The crystal structure, microstructure, and size of particles of the resulting cobalt-based powders were characterized by using X-ray Diffraction, Optical Microscopy, and Particle Size Analyzer, followed by, carbon nanotube growth at 700, 750, 800, and 850°C, where other parameters were fixed in order to determine the effect of CVD processing and temperature on the quality of resulting carbonbased materials. The graphitic structure of the carbon-based materials was analyzed by using Raman Spectroscopy. Conclusion: It was found that the optimum CVD processing temperature was 850°C with IG/ID ratio of 1.052.

Oxidising and carburising catalyst conditioning for the controlled growth and transfer of large crystal monolayer hexagonal boron nitride

Hexagonal boron nitride (h-BN) is well-established as a requisite support, encapsulant and barrier for 2D material technologies, but also recently as an active material for applications ranging from hyperbolic metasurfaces to room temperature single-photon sources. Cost-effective, scalable and high quality growth techniques for h-BN layers are critically required. We utilise widely-available iron foils for the catalytic chemical vapour deposition (CVD) of h-BN and report on the significant role of bulk dissolved species in h-BN CVD, and specifically, the balance between dissolved oxygen and carbon. A simple pre-growth conditioning step of the iron foils enables us to tailor an error-tolerant scalable CVD process to give exceptionally large h-BN monolayer domains. We also develop a facile method for the improved transfer of as-grown h-BN away from the iron surface by means of the controlled humidity oxidation and subsequent rapid etching of a thin interfacial iron oxide; thus, avoiding the impurities from the bulk of the foil. We demonstrate wafer-scale (2″) production and utilise this h-BN as a protective layer for graphene towards integrated (opto-)electronic device fabrication.

Carbon nanotube-zeolite composite catalyst - characterization and application

“Support on support” (SoS) core-shell nanostructure was prepared by using zeolite beads as supports for nitrogen-doped bamboo-like carbon nanotubes (N-BCNTs). The N-BCNTs were synthetized with catalytic chemical vapor deposition (CCVD) onto the surface of the beads to use later as primary catalyst support. On the SoS composite Pd, Rh, and Pt nanoparticles were successfully deposited (2 w/w%) with high dispersity. The prepared three catalytic systems (Pd-, Rh- and Pt-SoS) were characterized and tested in butene hydrogenation. The reactions were followed by FTIR spectroscopy. The butene conversion reached the maximum after about 6 minutes. Each catalyst was easy to handle and applicable in the studied reaction.

Vertically aligned growth of small-diameter single-walled carbon nanotubes by alcohol catalytic chemical vapor deposition with Ir catalyst

We showed that vertically aligned single-walled carbon nanotubes (VA-SWCNTs) can be grown by alcohol chemical vapor deposition (CVD) with an Ir catalyst in a cold-wall CVD system. VA-SWCNTs were grown on SiO2/Si substrates without any buffer layers under an ethanol pressure of 1 × 10−1 Pa at 800 °C. The SWCNT length increased with increasing growth time. The VA-SWCNT thickness reached almost 5 μm for a growth time of 180 min. Raman and photoluminescence spectroscopies showed that the diameters of the grown SWCNTs were mainly between 0.8 and 1.1 nm; this is much smaller than those of VA-SWCNTs grown with Fe and Co catalysts in previous studies. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectroscopy showed that the Ir catalyst retained the metallic state during SWCNT growth. We suggest that highly efficient suppression of aggregation, an appropriate carbon–Ir bond strength and dissociation of ethanol molecules led to the growth of vertically aligned small-diameter SWCNTs with an Ir catalyst.

Doping free transfer of graphene using aqueous ammonia flow.

Doping-free transfer of graphene produced by catalytic chemical vapor deposition (CVD) on copper foil, is still a technical challenge since unintentional doping of the transferred graphene layer yields an uncontrolled shift of Dirac point in graphene-based field-effect transistors (FETs). Typically, CVD graphene is released from the growth template by etching of the template, i.e. copper. During the etching process, ions adhere to the graphene layer resulting in unintentional doping. We demonstrate that washing a CVD graphene layer in an aqueous ammonia flow bath after etching copper, removes the majority of the unintentional dopants. FETs fabricated from graphene after washing in DI-water display a large scattering in Dirac bias with lowered mobility. In contrast, FETs from graphene that is washed in ammonia furnish better performance with high geometrically normalized mobility exceeding 2.4 × 104 cm2 V−1 s−1, balanced transport and a Dirac voltage near zero. We attribute the improved FET behavior to effective removal of the ions with a typical density of 4 × 1012 cm−2 from the graphene layer.