Catalytic Chemical Vapor Deposition Method Research Articles

Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion

High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29nm and 57nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the ID/IG (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels.

Design and Fabrication of Single-Walled Carbon Nanonet Flexible Strain Sensors

This study presents a novel flexible strain sensor for real-time strain sensing. The material for strain sensing is single-walled carbon nanonets, grown using the alcohol catalytic chemical vapor deposition method, that were encapsulated between two layers of Parylene-C, with a polyimide layer as the sensing surface. All of the micro-fabrication was compatible with the standard IC process. Experimental results indicated that the gauge factor of the proposed strain sensor was larger than 4.5, approximately 2.0 times greater than those of commercial gauges. The results also demonstrated that the gauge factor is small when the growth time of SWCNNs is lengthier, and the gauge factor is large when the line width of the serpentine pattern of SWCNNs is small.

The cellular response of Saccharomyces cerevisiae to multi-walled carbon nanotubes (MWCNTs)

Nanoparticles (NPs) especially those of carbon nanotubes (CNTs) have remarkable properties that are very desirable in various biological and biomedical applications. This has necessitated the rapid study of CNT toxicities, to augment their safe use, particularly, in yeast cells. The yeast cell; Saccharomyces cerevisiae is a widely used industrial and biological organism with very limited data regarding their cellular behaviour in NPs. The current study examines the cellular response of S. cerevisiae to MWCNTs. The CNTs were produced by the swirled floating catalytic chemical vapour deposition (SFCCVD) method and covalently functionalised using 1,3-dipolar cycloaddition. The CNT properties such as size, surface area, quality and surface vibrations were characterized using TEM, SEM, BET, TGA and Raman spectroscopy, respectively. The cellular uptake was confirmed with a FITC functionalised MWCNTs using 1H NMR, SEM and TEM. The CNT concentrations of 2–40 μg/ml were used to determine the cellular response through cell growth phases and cell viability characteristics. The TEM and SEM analyses showed the production of MWCNTs with an average diameter of 53 ± 12 nm and a length of 2.5 ± 0.5 μm. The cellular uptake of FITC-MWCNTs showed 100% internalisation in the yeast cells. The growth curve responses to the MWCNT doses showed no significant differences at P > 0.05 on the growth rate and viability of the S. cerevisiae cells.

Free-standing Ni-microfiber-supported carbon nanotube aerogel hybrid electrodes in 3D for high-performance supercapacitors

Macroscopic Ni-microfiber-supported carbon nanotube aerogels (CNAGs) have been developed and demonstrate great potential as supercapacitor electrodes. The macroscopic carbon nanotubes (CNTs) are controllably prepared by a catalytic chemical vapour deposition method through CNT growth on a sinter-locked microfibrous structure (SMF) consisting of 5 vol% 8 μm Ni fibers. Polyimide is coated onto the CNTs rooted on the SMF-Ni by an impregnation/polymerization method and is subsequently carbonized by pyrolysis to create self-supporting CNAGs/SMF-Ni composite electrodes, wherein the Ni-fiber network serves as current collector and the CNTs grown on the Ni fiber act as nano conducting wires to link the charge-storage carbon aerogel (CAG) particles. This novel approach permits desirable large-area fabrication and provides a unique combination of high CNAG-loading (up to 71.0 wt%; CAG/CNT: 1.44 wt/wt), binder-free feature, excellent electrical conductivity, large surface area, macro-/meso-/micro-sized hierarchical porous structure and high permeability. A typical hybrid consisting of 68.5 wt% CNAG (CAG/CNT: 1.17 wt/wt) delivers not only a good capacitance (e.g., 359 F per gram CAG) at high rates but also excellent long-cycle life (5% loss after 300 cyclic voltammogram cycles and then almost unchanged through 1000 cycles).

Catalytic Chemical Vapor Deposition Synthesis of Carbon Aerogels of High-Surface Area and Porosity

In this work carbon aerogels were synthesized by catalytic chemical vapor deposition method (CCVD). Ferrocene were employed as a source both of catalytic material (Fe) and of carbon. Gaseous hydrogen and argon were used as reductant and carrier gas, respectively. The products of reaction were collected over alumina. The morphology and textural properties of the soot produced in the reaction chamber were investigated using Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, X-ray photoelectron spectroscopy, and N2physisorption (BET and BHJ methods). After the evaluation of the porous structure of the synthesized products, 780 ± 20 m2/g ofSBETand 0.55 ± 0.02 cm3/g ofVBJHwere found. The presence of iron carbide and the partial oxidation of carbon nanostructures were revealed by XPS.

Dramatic change of water-cluster accessibility of highly pure double-walled carbon nanotubes with high temperature annealing

Highly pure double-walled carbon nanotubes (DWCNTs) synthesized by a catalytic chemical vapour deposition method have a well-ordered bundle structure giving explicit diffraction peaks by synchrotron X-ray diffraction measurement. The changes of nanopore structural properties and water adsorptivity of DWCNTs with high-temperature heat treatment were investigated using molecular probe adsorption methods. It was founded that their nanoporosities and apparent hydrophilicities decreased with thermal annealing. However, a specific surface area of 275 m(2) g(-1) and the residual microporosity of more than 60% even after heat treatment at 2673 K suggest their unique applications.

Carbon nanotubes/ceria composite layers deposited on surface acoustic wave devices for gas detection at room temperature

Surface acoustic wave (SAW) sensor on ATquartz piezoelectric substrate has been designed and fabricated. Test devices were based on asynchronous single-port resonators operating near the 434-MHz-centered industrial, scientific, and medical band. Multi-Walled Carbon Nanotubes/Ceria (MWNTs/CeO2) nanocomposites were used as sensitive layers. The MWNTs were synthesized by catalytic chemical vapor deposition method and coated with nanosized ceria oxide. The composites were deposited on SAW quartz resonator using air-brush technique. MWNTs/CeO2 nanocomposites were characterized using X-ray diffraction, transmission electron and atomic force microscopy. The sensor responses were tested under acetone (C3H5OH) and ethanol (C2H5OH) gases. The output signal was done by S11 parameter of the SAW device and was monitored using a network analyzer. Frequency changes were observed under acetone and ethanol vapors. These changes depended on the surface conductivity of the nanocomposites deposited on the sensor. The single-port SAW gas sensor coated with the MWNTs/CeO2 presented the highest sensitivity in the case of acetone vapor interacting with these layers, with a frequency shift of 200kHz at room temperature.

Experimental study on the heat transfer enhancement of MWNT-water nanofluid in a shell and tube heat exchanger

Heat transfer enhancement of multi-walled carbon natube(MWNT)/water nanofluid in a horizontal shell and tube heat exchanger has been studied experimentally. Carbon nanotubes were synthesized by the use of catalytic chemical vapor deposition (CCVD) method over Co–Mo/MgO nanocatalyst. Obtained MWNTs were purified using a three stage method. COOH functional groups were inserted for making the nanotubes hydrophilic and increasing the stability of the nanofluid. The results indicate that heat transfer enhances in the presence of multi-walled nanotubes in comparison with the base fluid.

Fantastic Improvement in Quality and Quantity of Carbon Nanotubes Synthesized on Al<SUB>2</SUB>O<SUB>3</SUB>–SiO<SUB>2</SUB> Supports by N<SUB>2</SUB> Pretreatment

The raw materials, condition and the method of preparing the catalysts play an important role in the growth of high quality Carbon Nanotubes by Catalytic Chemical Vapor Deposition method. In this work, the efficiency of Carbon Nanotubes growth was increased by a simple controlled preheating of the catalyst in N2 atmosphere. Supports were prepared by mixing alumina powder with tetraethyl orthosilicate (TEOS) by a chemical method at low temperature. Afterwards, the supports were impregnated with iron. The dried and ground catalyst was heated in N2 atmosphere at 500 degrees C for 1 hour followed by cooling down to room temperature. Methane was passed over the prepared catalyst bed at 900 degrees C. Supports, supported catalysts and Carbon Nanotubes samples have been characterized by Transmission Electron Microscopy, Scanning Electron Microscopy, Gas Adsorption/Desorption Analysis, X-Ray Diffraction and Raman Spectroscopy. Scanning Electron Microscopy images of the nanotubes showed a drastic increase in the growth rate, length and straightness of the Nanotubes in comparison to the growth without preheating and even preheating in air atmosphere. Raman Spectroscopy of the samples and Transmission Electron Microscopy pictures showed bundles, mostly equi-diameter Single Wall Nanotubes. In fact, the growth rate, length, and purity of the Nanotubes, also the homogeneity of the tubes improved. The conclusion can be made with the help of proposed theory of nucleation and growth of Nanotubes based on comparative results of the characterizations with and without preheat-treatment. It seems that the preheat-treatment in N2 affected the catalyst structure and its interaction with support as well as distribution of the catalyst particles on the support. These changes in return affect the quality and quantity of final production.

Role of Carbon Source in the Synthesis of Carbon Nanotubes via Catalytic Chemical Vapour Deposition

Development of technology in synthesizing a novel nanoscale material has been the main concern in the current material science. This study investigates the effect of two different carbon sources on the formation of carbon nanotubes (CNTs) via catalytic chemical vapour deposition (CCVD) method. Two types of carbon source i.e. acetylene gas and ethanol liquid were used for the synthesis of CNTs. The catalysts used in the synthesis of CNTs were formulated from nickel (Ni), copper (Cu) and praseodymium (Pr) using the wet impregnation method. The as-synthesized CNTs obtained were characterized using field emission-scanning electron microscope (FE-SEM), Thermal gravimetric analysis (TGA) and transmission electron microscope (TEM). The analysis result confirmed that the prepared catalysts were active for the production of CNTs. TEM analysis revealed that different morphologies of CNTs were formed when different carbon source was used. FE-SEM micrographs confirmed that acetylene proficient in producing multi walled carbon nanotubes (MWCNTs) and ethanol in producing heterojunctions CNTs with diameter range of 60 to 120 nm and 10 to 40 nm, respectively. Meanwhile, TGA analysis revealed thermal stability of each type of CNTs at different temperature of decomposition. Generally, this research has successful produced different types of CNTs when different carbon source is used.

Preparation of vertically aligned carbon nanotube arrays grown onto carbon fiber fabric and evaluating its wettability on effect of composite

Vertically aligned carbon nanotube (CNT) arrays have been grown onto the carbon fiber fabric using a catalytic chemical vapor deposition (CCVD) method. The as-synthesized CNT arrays are about 20μm in height, and the nanotube has a mean inner and outer diameter of 2.6nm, 5.5nm, respectively. The CNT-grafted carbon fabric shows a hydrophobic property with a contact angle over 145°, and the single CNT-grafted carbon fiber shows a sharp increase of dynamic contact angle in de-ionized water from original 71.70° to about 103°, but a little increase does in diiodomethane or E-51 epoxy resin. However, the total surface energy of carbon nanotube-grafted carbon fiber is almost as same as that of as-received carbon fiber. After CNTs growth, single fiber tensile tests indicated a slight tensile strength degradation within 10% for all different lengths of fibers, while the fiber modulus has not been significantly damaged. Compared with the as-received carbon fibers, a nearly 110% increase of interfacial shear strength (IFSS) from 65 to 135MPa has been identified by single fiber pull-out tests for the micro-droplet composite, which is reinforced by as-received carbon fiber or CNT-grafted carbon fiber.

Influence Analysis for the Controllable Growth of Carbon Nanotubes with CCVD Method

To control the length and morphology of carbon nanotubes(CNTs) is difficult in its producing process. Influencing factors of length and morphology of carbon nanotubes have been analyzed in the catalytic chemical vapor deposition (CCVD) process. According to the growth characteristic of carbon nanotubes, the diffusion model was developed. Over time, the diffusion potential decreases due to a reduction in the carbon atom concentration gradient. With the model, the shape of catalytic particle is analyzed. From theoretical derivation, it is demonstrated that with the temperature ranging from 1173K to1373K, the growth rate raises up sharply with the increasing of temperature. Growth rate of CNTs increases with increasing layers at the same temperature.

SYNTHESIS OF CARBON NANOTUBES VIA CATALYTIC CHEMICAL VAPOR DEPOSITION METHOD AND THEIR MODIFICATION WITH PREYSSLER ANION, [NaP5W30O110]14-

Multiwalled carbon nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition method using Fe/Co catalyst over CaCO3 support and acetylene gas as a carbon precursor in the temperature range of 650–800°C, and were modified with Preyssler anion nanostructures via impregnation method. The existence of nanoheteropolyacid [NaP5W30O110]14- inside the MWCNTs was confirmed by infrared spectroscopy and transmission electron microscopy.

Electrocatalytic oxygen-reduction reaction on a carbon nanofiber/carbon paper composite

A carbon nanofiber/carbon paper (CNF/CP) composite was synthesized directly on CP by a catalytic chemical vapor-deposition method, and the physicochemical properties of and oxygen-reduction reaction (ORR) on this composite were investigated. Scanning electron microscopy shows that the CNFs are uniformly distributed on the CP, and high-resolution transmission electron microscopy results show that the CNFs have a narrow size distribution. The CNF/CP composite has a large surface area, and its mesoporous character is confirmed by N 2 physisorption. Raman spectrum studies show that the CNF/CP composite has a high ratio of edge atoms to basal atoms compared with that of CP. From cyclic voltammetry studies, the CNF/CP composite was found to be more active than CP in terms of ORR, which may be due to the contribution from the CNFs. The CNF/CP composite shows a higher exchange current density and more positive equilibrium potential than CP, as verified by Tafel analysis. Moreover, linear-sweep voltammetry confirms that ORR on the CNF/CP composite is conducted through a two-electron reaction pathway.

Diameter-dependent thermal-oxidative stability of single-walled carbon nanotubes synthesized by a floating catalytic chemical vapor deposition method

In this paper, purified single-walled carbon naotubes (SWCNTs) with three different diameters were synthesized using a floating catalytic chemical vapor deposition method with ethanol as carbon feedstock, ferrocene as catalyst, and thiophene as growth promoter. The thermal-oxidative stability of different-diameter SWCNTs was studied by using thermal analysis (TG, DTA), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. The results indicate that small diameter SWCNTs (∼1 nm) are less stable and burn at lower temperature (610 °C), however, the larger diameter SWCNTs (∼5 nm) survive after burning at higher temperature (685 °C), the oxidation rate varies inversely with the tube diameter of SWCNTs, which may be concluded that the higher oxidation-resistant temperature of larger diameter SWCNTs can be attributed to the lower curvature-induced strain by rolling the planar graphene sheet for the larger diameter, so small tubes will become thermodynamically unstable.

Inner-diameter enlargement of multi-walled carbon nanotubes by adding HBO 3 in catalyst

Multi-walled carbon nanotubes (MWCNTs) with large inner diameter were synthesized by the catalytic chemical vapor deposition method using HBO 3 as the accessorial catalyst in reaction precursors. A ratio D in/D out is defined as an index to evaluate the hollow degree of MWCNTs, where D in and D out are the inner and outer diameter of one CNT, respectively. When no HBO 3 was added in the reaction mixtures, the MWCNTs are straight with thick wall. The average D in/D out value is only 0.08 ± 0.02. The X-ray diffraction (XRD) result shows the relatively low crystallinity. When HBO 3 was added in the reaction precursors, the MWCNTs have large inner cavity and the average D in/D out value reaches 0.57 ± 0.10. The crystallinity was also improved remarkably. These results indicate that HBO 3 in the catalyst system has great influence on the growth of MWCNTs.

Tailoring of surface melting of oxide based catalyst particles by doping to influence the growth of multi-walled carbon nano-structures

In catalytic chemical vapor deposition method, the growth of multi-walled carbon nano-tubes (MWCNT), nano-rods/fibers or nano-tapes takes place over cobalt oxide based catalyst particles at a growth temperature higher than the temperature for surface melting of the catalyst particles. Doping of cobalt oxide by copper oxide has been used to decrease the surface melting temperature of the oxide based catalyst particles in the size range of about 200–500 nm, which is important in determining the type of carbon nano structures growing over the catalyst. It has been observed that MWCNT forms at a small difference between the growth temperature and the surface melting temperature while nano-rods or nano-tapes form at relatively larger difference between these temperatures. The present study indicates the possibility of controlling surface melting temperature by the level of doping in order to get the desired nano-structure at a given growth temperature.

Hydrophobic Properties of Polytetrafluoroethylene Thin Films Fabricated at Various Catalyzer Temperatures Through Catalytic Chemical Vapor Deposition Using a Tungsten Catalyzer

Using the catalytic chemical vapor deposition (Cat-CVD) method, polytetrafluoroethylene (PTFE) thin films were fabricated on Si(100) substrates at various catalyzer temperatures, using a tungsten catalyzer, and Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS) were used to confirm the fabrication of the films. An atomic-force microscope (AFM) and a scanning electron microscope (SEM) were employed to study the correlation between the wettability and surface morphology of the samples. It was found that the wettability of the PTFE thin films fabricated via Cat-CVD is strongly correlated with the sizes of the film surfaces' nanoprotrusions, and that superhydrophobic PTFE thin-film surfaces can be easily achieved by controlling the sizes of the nanoprotrusions through the catalyzer temperature. The comparison of the wettability values and surface morphologies of the films confirmed that nanoscale surface roughness enhances the hydrophobic properties of PTFE thin films. Further, the detailed analysis of the films' surface morphologies from their AFM images with the use of the Wenzel and Cassie models confirmed that the nanoscale surface roughness enhanced the hydrophobic property of the PTFE films. Further, the variations of the wettability of the PTFE thin films prepared via Cat-CVD are well explained by the Cassie model. It seems that the increase in the trapping air and the reduction of the liquid-solid contact area are responsible for the superhydrophobicity of the PTFE thin films prepared via Cat-CVD.

Investigation of Fe/MgO Catalyst Support Precursors for the Chemical Vapour Deposition Growth of Carbon Nanotubes

Carbon nanotubes have been grown by the catalytic chemical vapour deposition (CCVD) method using an Fe catalyst supported on MgO. The influence of using either pure MgO or Mg(NO3)2 x 6H2O as the source of the MgO catalyst support as well as the effects of varying the Fe metal loading on the support has been investigated. The catalyst was prepared at room temperature by the wet impregnation method from a mixture of Fe2(SO4)3 x xH2O and either MgO or Mg(NO3)2 x 6H2O in aqueous solution; the weight percent of Fe/MgO was varied between 5, 10, and 15. Preparation of CNTs was carried out in a horizontal furnace at 900 degrees C under methane gas with flow rate of 6 litres/min. The supported catalysts and carbon nanotubes (CNTs) were investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction pattern (XRD) and Fourier Transform (FT)-Raman spectroscopy. Results revealed that the number of nanotubes was maximised by using MgO as a support precursor instead of Mg(NO3)2 x 6H2O and also by increasing the amount of Fe.

Single-walled carbon nanotube growth using cobalt nanoparticles prepared by vacuum deposition on a surface-active liquid

We demonstrate that the Co nanoparticles prepared by vacuum deposition on a surface-active liquid can be used as catalysts of single-walled carbon nanotube (SWCNT) growth using alcohol catalytic chemical vapor deposition method. These Co nanoparticles are embedded in the y-type zeolite powder. The Co nanoparticles used in this study is the highly efficient catalysts for CNT growth, which is comparable to the commonly-used Co–Fe binary metal catalysts embedded in the y-type zeolite. The preparation method of the metal nanoparticles used in this study is very simple. Thus, such metal nanoparticles might be promising as catalysts of CNT growth.