Chemical Vapor Deposition Of Acetylene Research Articles

Carbon nanotubes grown by plasma enhanced chemical vapor deposition of acetylene in the presence of water vapor

Carbon nanotubes can be synthesized using various techniques. This work aims to study the experimental process of growing carbon nanotubes via plasma-enhanced chemical vapor deposition (PECVD). Additionally, the study aims to calibrate the reactor and develop a LabVIEW code to introduce water into the process, enabling a water-assisted PECVD procedure. The obtained samples are evaluated through the analysis of SEM images and Raman spectra.

Large-scale synthesis of 3D ordered microporous carbon at low temperature using cobalt ions exchanged zeolite Y as a template

Zeolite-templated carbons (ZTCs) have a unique three-dimensional (3D) ordered microporous structure and an extra-large surface area, and have excellent properties in adsorption and energy storage. Unfortunately, the lack of efficient synthesis strategies and the difficulty of doing this on a large-scale have seriously limited their development. We have developed a large-scale simple production route using a relatively low synthesis temperature and direct acetylene chemical vapor deposition (CVD) using Co ion-exchanged zeolite Y (CoY) as the template. The Co2+ confined in the zeolite acts as Lewis acid sites to catalyze the pyrolysis of acetylene through the d-π coordination effect, making carbon deposition occur selectively inside the zeolite at 400 °C rather than on the external surface. By systematically investigating the CVD temperature and time, the optimum conditions of 8 h deposition at 400 °C produces an excellent 3D ordered-microporous structure and outstanding structure parameters (3 000 m2 g−1, 1.33 cm3 g−1). Its CO2 adsorption capacity and selectivity are 2.78 mmol g−1 (25 °C, 100 kPa) and 98, respectively. This simple CVD process allows the synthesis of high-quality ZTCs on a large scale at a low cost.

Unraveling the mechanisms of carbon nanotube growth by chemical vapor deposition

The mechanisms of carbon nanotube (CNT) growth by chemical vapor deposition of acetylene on Fe/SiO2:Al2O3 (zeolite Y) catalyst are unraveled through a combined computational and experimental study. CNTs are synthesized in a horizontal reactor under atmospheric pressure within the temperature range 650 °C–850 °C and characterized by SEM, TEM and Raman spectroscopy. A macroscopic computational fluid dynamics (CFD) model accounting for fluid flow, heat transfer and species transport is developed for the process, incorporating also kinetic expressions for acetylene surface decomposition, acetylene gas-phase reactions, carbon diffusion through the bulk of the catalyst, carbon surface accumulation on the catalyst surface and eventually, CNTs growth. The experimental behavior of the CNTs growth can be accurately described by the proposed macroscopic model. Most importantly, theoretical predictions suggest that there are two distinct temperature regimes for CNTs formation: at the low temperature regime, the process is dominated by the competition between carbon diffusion through the catalyst and carbon impurity layer formation on the catalyst surface, while at higher temperature, the gas-phase reactions of acetylene prevails, releasing byproducts that deposit on the catalyst surface in the form of carbon impurities. Finally, using the developed computational approach, the catalyst lifetime, which is directly affected by these mechanisms, is correlated with the CNTs growth process.

Effect of bimetallic Co:Mo/MgO catalyst on the growth efficiency of single-walled carbon nanotubes

Carbon nanotubes (CNTs) are known for a wide range of applications due to their various properties. Because these unique properties of the carbon nanotubes strongly depend on the structure, the primary aim is high efficiency and controlling the nanotube diameter during the production. In this study, single-walled carbon nanotubes (SWCNTs) were synthesized by chemical vapor deposition of acetylene (C2H2) on the Co–Mo/MgO catalyst. The effects of different catalyst preparation methods, Co/Mo, and support material ratios on the SWCNT growth efficiency were investigated by thermogravimetric analysis. Raman spectroscopy, scanning electron microscopy, and an x-ray diffractometer were also used for the structural and morphological characterization of the SWCNTs. As a result of the experimental studies, the optimum Co:Mo and metal/support ratio was determined as 1:3.5 and 15%, respectively. Considerable CNT growth efficiency (73%) has been achieved with the Co:Mo = 1:3.5/15% MgO catalyst prepared by the solgel method.

Controllable H2 Generation by Formic Acid Decomposition on a Novel Pd/Templated Carbon Catalyst

A novel Pd/templated carbon catalyst (Pd/TC) was developed, characterized, and tested in the dehydrogenation of formic acid (FA) under mild conditions, with the possibility to control the H2 generation rate, in the absence or presence of HCOONa (SF), by adjusting the Pd:FA and/or FA:SF ratios. The characterization results of the templated carbon obtained by the chemical vapor deposition of acetylene on NaY zeolite revealed different structural and morphological properties compared to other C-based supports. Therefore, it was expected to induce a different catalytic behavior for the Pd/TC catalyst. Indeed, the TC-supported Pd catalyst exhibited superior activity in the decomposition of FA, even at room temperature, with turnover frequencies (TOFs) of up to 143.7 and 218.8 h−1 at 60 °C. The H2 generation rate increased with an increasing temperature, while the H2 yield increased with a decreasing FA concentration. Constant generation of gaseous flow (H2 + CO2) was achieved for 11 days, by the complete dehydrogenation of FA at room temperature using a 2 M FA solution and Pd:FA = 1:2100. The presence of SF in the reaction medium significantly enhanced the H2 generation rate (535 h−1 for FA:SF = 3:1 and 60 °C).

Dispersive solid phase extraction of precious metal ions from electronic wastes using magnetic multiwalled carbon nanotubes composite

Rapid technological developments of electrical and electronic equipment raise a persistence demand for precious elements. The presence of precious metals (PMs) makes e waste recycling economically attractive. In the present study, magnetic multiwalled carbon nanotubes (Fe3O4-o-MWCNTs) were synthesized and utilized as a hydrometallurgical method for extraction of precious elements (Ag, Au, Pd and Pt) from e waste. MWCNTs were synthesized with chemical vapor deposition of acetylene using Ni-Fe-Co/Al2O3 catalyst, decorated with Fe3O4 nanoparticle via co-precipitation and characterized by multiple characterization techniques. Morphology shows that MWCNTs have been efficiently produced (having ~10–20 µm length and ~30 nm internal diameter) and successfully decorated with Fe3O4 nanoparticles. At optimized conditions the adsorbent shows 98% recovery with 3 mol/L nitric acid as eluent for Pd, Ag and Au. However, Pt elution was carried out with 1 mol/L sodium perchlorate. Maximum adsorption capacity calculated from Langmuir isotherm was found as 112, 57, 106 and 104 mg/g for Pd, Pt, Ag and Au, respectively. Results show that Fe3O4-o-MWCNTs composite is a good adsorbent material for extraction of precious metals from e waste due to its high efficiency, sensitivity, reusability and stability in acidic media.

Synthesis of Helical and Straight Carbon Nanofibers on Water Soluble Sodium Chloride Supported Catalyst

Carbon nanofibers are synthesised via chemical vapour deposition of acetylene as carbon source through using water soluble catalysts. The new water soluble catalyst is prepared by supporting the copper on sodium chloride salt. Copper acetate and copper nitrate salts are used for preparing catalysts through impregnation method. The yield of carbon deposits using the catalyst prepared by copper acetate is almost twenty times higher than the one prepared by copper nitrate precursor. The X-ray diffraction pattern and field emission scanning electron microscopy (FESEM) images confirm the formation of CuO in the catalyst after calcination process. The growth time for carbon material is 15 min. The FESEM images show the growth of helical and straight carbon nanofibers on the catalysts with metal loading of 5 wt% at 600, 650 and 680 °C. The results showed that the morphology of the carbon deposited on the catalyst depends on both the amount of metal loaded on the catalyst and reaction temperature, while there is a significant interaction between them. However, fishbone carbon nanofibers with diameters less than 100 nm are deposited on the catalysts with metal loading of 1 wt% at 650 °C.

Synthesis and Characterization of Flower-like Carbon-encapsulated Fe-C Nanoparticles for Application as Adsorbing Material.

Carbon-encapsulated Fe-C (Fe-C@C) nanoparticles with a divergently flower-like morphology were successfully synthesized for application as an adsorbing material by using freeze-drying and chemical vapor deposition (CVD) methods. The Fe metallic source was first loaded onto a sodium chloride (NaCl) supporter via freeze-drying to obtain the Fe/NaCl composite powder. Then, Fe-C@C nanoparticles were synthesized in the temperature range of 300–450 °C via CVD of acetylene in the Fe/NaCl composite powder using Fe nanoparticles as catalysts and NaCl as supporters. Because the NaCl supporter is water-soluble, the synthesized Fe-C@C nanoparticles were easy to purify, and a high purity was obtained by simple washing and centrifugation. The optimal Fe-C@C nanoparticles, synthesized at 400 °C, possessed a unique divergently flower-like structure and a high specific surface area of 169.4 m2/g that can provide more adsorption sites for contaminants. Adsorption experiments showed that the flower-like Fe-C@C adsorbent exhibited high adsorption capacity (90.14 mg/g) and fast removal of methylene blue (MB). Moreover, the magnetic properties of the nanoparticles, with saturation magnetization of 36.544 emu/g, facilitated their magnetic separation from wastewater. Therefore, the novel flower-like Fe-C@C nanoparticles with integrated adsorptive and magnetic properties have the potential to be an effective adsorbent in dye wastewater treatment.

Core@shell@shell structured carbon-based magnetic ternary nanohybrids: Synthesis and their enhanced microwave absorption properties

High encapsulation efficiency of core@shell@shell structured carbon-based magnetic ternary nanohybrids have been synthesized in high yield by chemical vapor deposition of acetylene directly over octahedral-shaped Fe2O3 nanoparticles. By controlling the pyrolysis temperature, Fe3O4@Fe3C@carbon nanotubes (CNTs) and Fe@Fe3C@CNTs ternary nanohybrids could be selectively produced. The optimal RL values for the as-prepared ternary nanohybrids could reach up to ca. −46.7, −52.7 and −29.5 dB, respectively. The excellent microwave absorption properties of the obtaiend ternary nanohybrids were proved to ascribe to the quarter-wavelength matching model. Moreover, the as-prepared Fe@Fe3C@CNTs ternary nanohybrids displayed remarkably enhanced EM wave absorption capabilities compared to Fe3O4@Fe3C@CNTs due to their excellent dielectric loss abilities, good complementarities between the dielectric loss and the magnetic loss, and high attenuation constant. Generally, this strategy can be extended to explore other categories of core@shell or core@shell@shell structured carbon-based nanohybrids, which is very beneficial to accelerate the advancements of high performance MAMs.

Preparation of silica-graphene nanohybrid as a stabilizer of emulsions

In the present study, a novel silica-graphene nanohybrid was synthesized through a facile and single step chemical vapor deposition of acetylene on silica aerogel in the presence of hydrogen as a reducing agent at atmospheric pressure and 600°C. The physiochemical properties of the nanohybrid were thoroughly characterized by XRD, TGA, Raman, BET, DLS, FT-IR, SEM, and TEM. The amount of graphene in the silica-graphene nanohybrid was found to be 16wt% while a remarkable specific surface area about 843.64m2/g has been accomplished. The as-prepared nanohybrid was employed for stabilization of decalin/water emulsion. In addition, the effective factors on the droplets size and condition of stabilization for emulsion preparation were investigated through Taguchi L16 statistical design. Ultimately, the Wilhemy plate method shows that by dispersion of nanohybrid in water/decalin emulsion the interfacial tension (IFT) can be considerably declined from 55 to 30.12mN/m.

Real Understanding of the Nitrogen-Doping Effect on the Electrochemical Performance of Carbon Materials by Using Carbon-Coated Mesoporous Silica as a Model Material.

The main aim of the present work is to precisely understand the sole effect of nitrogen doping on the electrochemical performance of porous carbon materials. To achieve this objective, the whole surface of mesoporous silica (SBA-15) was coated with a thin layer of carbon (about 0.4 nm) with and without N-doping by using acetonitrile and acetylene chemical vapor deposition, respectively. The resulting N-doped and nondoped carbon-coated silica samples have mesopore structures identical to those in the original SBA-15, and they are practically the same in terms of not only the pore size and pore structure but also the particle size distribution and particle morphology, with the exception of N-doping, which makes them unique model materials to extract the sole effect of nitrogen on the performances of electrochemical capacitors and electrocatalytic oxygen reduction. Moreover, the outstanding features of the carbon-coated silica samples allow even a quantitative understanding of the pseudocapacitance induced by nitrogen functionalities on the carbon surface in an acidic aqueous electrolyte.

Facile, soot free approach toward synthesis of carbon nanoropes via chemical vapor deposition of acetylene in the presence of MnFe2O4 coated on stainless steel

High density, soot free, novel and a facile approach toward synthesis of carbon nanoropes (CNRs) were successfully carried out in a chemical vapor deposition (CVD) process. Manganese ferrite (MnFe2O4) coated on stainless steel foil (SS 316 grade) was used as a catalyst to initiate the growth of CNR. The coated catalyst was introduced into the CVD and the chamber temperature was set at 700°C later followed with the release of acetylene (50sccm) and nitrogen (500sccm) gas, respectively. Total reaction continued until 30min. No purification or oxidation process of the soot was involved. Analysis reveals the presence of intermingled CNRs with semi crystalline nature of the sample. The elemental analysis confirms the presence of manganese and iron whereas Raman spectrum shows the characteristic narrow G and D bands. The sample displays a super-paramagnetic behavior and is thermally stable up to 500–550°C presenting a strong exothermic reaction.

Synthesis of carbon nanotubes by arc-discharge and chemical vapor deposition method with analysis of its morphology, dispersion and functionalization characteristics

AbstractIn this paper, multi-walled carbon nanotubes are synthesized by arc-discharge and chemical vapor decomposition methods. Multi-walled carbon nanotubes are synthesized on thin film of nickel sputtered on silicon substrate by thermal chemical vapor deposition of acetylene at a temperature of 750°C. The flow of current in arc-discharge method varies in the range 50–200 A. Further arc-synthesized carbon nanotubes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the results are compared with nanotubes grown by chemical vapor deposition method. XRD result shows a characteristic peak (0 0 2) at 26.54° corresponding to the presence of carbon nanotubes. SEM and TEM results give morphology of as-synthesized multi-walled nanotubes. TEM results indicate synthesis of well-graphitized carbon nanotubes by arc-discharge method. Dispersion of arc-synthesized nanotubes in SDS solution under the effect of different sonication times is studie...

Heteroatom Doped Carbon Nanofibers Synthesized by Chemical Vapor Deposition as Platinum Electrocatalyst Supports for Polymer Electrolyte Membrane Fuel Cells

Aimed at improved durability and catalytic activity for oxygen reduction reaction, carbon nanofibers(CNFs) with nitrogen, phosphorus and boron dopants have been synthesized by chemical vapor deposition of acetylene on electrolessly-plated copper foams. The as-prepared CNFs were extensively characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy and Raman analysis. Without any functionalization, the as-prepared CNF was employed as support for 40wt.% Pt electrocatalyst (Pt/CNF). In an accelerated stability test (AST), Pt/CNF displayed higher stability relative to the state-of-the-art electrocatalyst from Johnson Matthey (Pt/C-JM) with the same Pt loading. TEM images after AST for Pt/CNF were obtained and found that the doped carbon nanofiber support is more resistant to corrosion. At the meantime, the catalytic activity to oxygen reduction for Pt/CNF surpassed Pt/C-JM by more positive on-set potential. CNFs with N, P and B dopants synthesized in this work should have promised applications for polymer electrolyte membrane fuel cells.

Large-scale synthesis of high-quality zeolite-templated carbons without depositing external carbon layers

Zeolite-templated carbons (ZTCs) possess extra-large surface areas (⩾2000m2g−1) and micropore volumes (⩾1.0cm3g−1), which allow superior electrochemical performances and gas adsorption properties compared with conventional activated carbons. Unfortunately, ZTCs have been mostly synthesized at a small laboratory-scale due to the limited reproducibility of carbon structures at a large-scale synthesis. The biggest challenge in the carbon replication of zeolites is the deposition of dense carbon layers at the external surface of zeolite crystallites before the complete zeolite micropore filling with carbon. The formation of external carbon layers hinders a faithful carbon replication of zeolite structure, and also significantly limits the adsorption properties of the resultant template-free ZTCs. Here, we demonstrate that acetylene chemical vapor deposition (CVD) at a relatively mild temperature (823K), followed by thermal treatment at 1073K, can selectively deposit carbons in the micropores of zeolites, regardless of the synthesis batch size. By combining the mild CVD condition and the use of a rotary tubular furnace, which allows the continuous agitation of zeolites during the synthesis, 50g NaX and BEA zeolite could be faithfully replicated to ZTCs with a high BET surface area (>2700m2g−1) and micropore volume (>1.10cm3g−1) without depositing nonporous external carbon layers that significantly hinder the bulky molecular diffusion.

Evaluation of Catalytic Activity of Acid Activated Multiwalled Carbon Nanotubes in an Esterification Reaction

Multiwalled carbon nanotubes (MWCNTs) synthesized earlier by catalytic chemical vapor deposition of acetylene, were used to develop heterogeneous supported acid catalysts by sonicating with 50% aqueous solutions of H2SO4, H3BO3 and H3PO4. The effect of acid treatment of MWCNTs, on their textural properties such as crystallinity, surface area, nature of the surface functional groups and elemental composition was investigated by appropriate instrumental methods of analysis such as BET surface area, Powder XRD, FT-IR, SEM-EDS, TEM and XPS. Acidity of the materials was estimated by n-butyl amine back titration method and the catalytic activity was evaluated in an acid catalyzed esterification reaction between benzyl alcohol and acetic acid. Further, the effect of duration and temperature of the reaction on the conversion of benzyl alcohol to benzyl acetate was studied. The product analysis was made by GC, LC-MS and 1HNMR techniques. The characterization techniques indicated that, the textural properties of the acid activated MWCNTs were distinctly different from those of the pristine MWCNTs inferring a possible incorporation of oxoacids into the mesoporous structure of MWCNTs. All the materials showed catalytic activity in the esterification of benzyl alcohol with acetic acid resulting benzyl acetate with 100% selectivity and 10-88% yield depending on the experimental conditions. Sulphuric acid activated MWCNTs exhibited highest surface acidity and catalytic activity. These catalysts were also found to be recyclable up to 5 times without any significant loss in its catalytic activity. Keywords: Acid activation, benzyl acetate, carbon nanotubes, catalytic activity, esterification, surface acidity.

Hierarchically designed three-dimensional macro/mesoporous carbon frameworks for advanced electrochemical capacitance storage.

Mesoporous carbon (m-C) has potential applications as porous electrodes for electrochemical energy storage, but its applications have been severely limited by the inherent fragility and low electrical conductivity. A rational strategy is presented to construct m-C into hierarchical porous structures with high flexibility by using a carbon nanotube (CNT) sponge as a three-dimensional template, and grafting Pt nanoparticles at the m-C surface. This method involves several controllable steps including solution deposition of a mesoporous silica (m-SiO2 ) layer onto CNTs, chemical vapor deposition of acetylene, and etching of m-SiO2 , resulting in a CNT@m-C core-shell or a CNT@m-C@Pt core-shell hybrid structure after Pt adsorption. The underlying CNT network provides a robust yet flexible support and a high electrical conductivity, whereas the m-C provides large surface area, and the Pt nanoparticles improves interfacial electron and ion diffusion. Consequently, specific capacitances of 203 and 311 F g(-1) have been achieved in these CNT@m-C and CNT@m-C@Pt sponges as supercapacitor electrodes, respectively, which can retain 96 % of original capacitance under large degree compression.

Investigation of the Effect of Reaction Time, Weight Ratio, and Type of Catalyst on the Yield of Multi-Wall Carbon Nanotubes via Chemical Vapor Deposition of Acetylene

The synthesis of multi-wall carbon nanotubes (MWCNTs) was studied using catalytic chemical vapor deposition of acetylene at 500°C for 30 and 60 min. Catalysts were prepared by impregnating Fe, Co, Ni, V, and bimetallic mixture of Fe-Co on MgO with a weight ratio of 1:100, 5:100, and 10:100. The effects of the reaction time, the type, and the weight ratio of the catalysts on the carbon yield of MWCNTs were investigated. Experimental results showed that the 10:100 weight ratio of Fe-Co:MgO had the highest carbon yield (81.97%) and the MWCNT to amorphous carbon ratio (100.6), whereas 10:100 V:MgO had the lowest carbon yield (8.44%). Statistical analyses indicated that increasing weight ratio enhanced the carbon efficiencies of Fe, Co, Fe-Co, and Ni catalyst; moreover, increasing the reaction time had a positive effect on the carbon efficiencies of Fe and V catalysts.

Preparation and microwave-absorbing property of BaFe12O19 nanoparticles and BaFe12O19/Fe3C/CNTs composites

A novel kind of BaFe12O19/Fe3C/CNTs composite was developed by the acetylene chemical vapor deposition process. The composites perform great improvement in the microwave absorbing properties compared with pure BaFe12O19 ferrite in 2–18 GHz range.

Correlation Between Periodicity and Catalytic Growth Activity of Bimetallic Co-group VI/MgO Catalysts for Production of Carbon Nanotubes by Acetylene Using Chemical Vapor Deposition

This work aims to discover a relationship between the periodicity and catalytic growth activity of carbon nanotubes by acetylene chemical vapor deposition. Hence, the effect of addition of group VI metals (25% of Cr, Mo, or W) of the periodic table to 25 wt% Co supported on MgO has been investigated. The fresh catalysts and carbon nanomaterials were characterized by XRD, TPR, TEM, Raman spectroscopy, BET surface measurements, and TG analysis. The results revealed that the addition of group VI metals induces a strong interaction with the structural MgO crystals associated with an enhancement in surface properties. XRD data shows that the appearance of group VI metal oxides in the diffraction patterns primarily dependent on the corresponding atomic weights. TGA data shows that the Co–W/MgO catalyst exhibited higher carbon nanotubes (CNTs) yield compared to the Co–Cr or Co–Mo containing catalysts. The yield of CNTs increases gradually with increasing the atomic weight of group VI metals (W > Mo > Cr). This finding can be attributed to the higher surface coverage of Co-W/MgO and consequently the larger amount of metal sites which are responsible for the higher yield of MWCNTs compared to the other bimetallic catalysts. The higher metallic surface permits decomposing a larger amount of C2H2 molecules more efficiently. XRD, TEM, and Raman spectroscopic data revealed that highly graphitized MWCNTs were produced over all catalysts under study.