Morphology Of Carbon Nanotubes Research Articles

Amine-terminated ionic liquid functionalized carbon nanotubes for enhanced interfacial electron transfer of Shewanella putrefaciens anode in microbial fuel cells

An amine-terminated ionic liquid (IL-NH2) is applied to functionalize carbon nanotubes (CNTs) for improving the interfacial electron transfer of Shewanella putrefaciens (S. putrefaciens) anode in Microbial fuel cells (MFCs). The introduction of thin layer of ILs does not change the morphology of CNTs a lot but increases surface positive charges as well as nitrogen functional groups of the CNTs based anode. The CNT-IL composite not only improves the adhesion of S. putrefaciens cells but also promotes both of the flavin-mediated and the direct electron transfer between the S. putrefaciens cells and the anode. It is interesting that the CNT-IL is more favorable for the mediated electron transfer than for the direct electron transfer. The CNT-IL/carbon cloth anode delivers 3-fold higher power density than that of CNT anode and shows great long-term stability in the batch-mode S. putrefaciens MFCs. This CNT-IL could be a promising anode material for high performance MFCs.

Study of multilayer carbon nanotubes subjected to the impact of a nanosecond high-energy ion beam

The impact of a nanosecond high-energy ion beam on the structure and morphology of multilayer carbon nanotubes and their ensembles is studied using transmission electron microscopy and scanning electron microscopy. It is shown that ion-beam irradiation leads to a decrease in the outer diameters of carbon nanotubes, which is related to the destruction of their outer layers. In addition, the secondary growth of carbon nanotubes with smaller diameters and the growth of bulblike formations, inside which structures with interplanar distances that are close to those of nanodiamond are fixed, are observed.

Electromagnetic interference shielding and electrical properties of nanocomposites based on poly (styrene-b-ethylene-ran-butylene-b-styrene) and carbon nanotubes

In this work, poly (styrene-b-ethylene-ran-butylene-b-styrene) and carbon nanotube (SEBS/CNT) nanocomposites were prepared by melt compounding for electromagnetic shielding applications. The structural characteristics and the morphology of carbon nanotubes (CNT) and nanocomposites were investigated using Raman spectroscopy and Field Emission Gun Scanning Electron Microscopy. The DC electrical conductivity of the nanocomposites was evaluated by two-probe and four-probe methods, and the electrical percolation threshold was calculated. Dielectrical properties, shielding mechanisms, and the electromagnetic interference shielding effectiveness (EMI-SE) of the nanocomposites were evaluated for the 8.2–12.4GHz X-band microwave frequency range. A comparison between theoretical and experimental EMI-SE results was also reported. The nanocomposites studied exhibited a very sharp insulator-conductor transition at a CNT concentration of around 1wt%, and the electrical conductivity increased by 17 orders of magnitude upon addition of more than 2wt% CNT. Upon addition of 15wt% of CNT, an EMI-SE of 30.07dB, which corresponds to a reduction of 99.9% of the incident radiation, was obtained. The results indicate that the nanocomposites studied are promising candidates for electromagnetic shielding applications.

Anisotropy in CNT composite fabricated by combining directional freezing and gamma irradiation of acrylic acid

A novel fabrication process for composite consisting of organized modified carbon nanotubes (CNT) in the polyacrylic acid (PAA) matrix has been developed. The CNT were organized along crystallite domains during a directional freezing process and subsequently fixed by the gamma irradiation induced polymerization and crosslinking in solid state. Different morphology and distribution of CNT in fabricated and conventionally prepared composites were investigated by scanning and transmission electron microscopies. The interactions in the polymer matrix were elucidated by a broad dielectric spectroscopy. Importantly, the composite exhibited anisotropic electrical and mechanical properties studied by electrical conductivity measurement and dynamic mechanical analysis, respectively. Differences of two orders of magnitude in the electrical conductivity and 5 times higher storage modulus at 10−2Hz in the direction along and perpendicular to freezing in composite with 0.1% CNT in feed were observed.

Mass Transport Through Carbon Nanotube–Polystyrene Bundles

Carbon nanotubes have been widely used as test channels to study nanofluidic transport, which has been found to have distinctive properties compared to transport of fluids in macroscopic channels. A long-standing challenge in the study of mass transport through carbon nanotubes (CNTs) is the determination of flow enhancement. Various experimental investigations have been conducted to measure the flow rate through CNTs, mainly based on either vertically aligned CNT membranes or individual CNTs. Here, we proposed an alternative approach that can be used to quantify the mass transport through CNTs. This is a simple method relying on the use of carbon nanotube–polystyrene bundles, which are made of CNTs pulled out from a vertically aligned CNT array and glued together by polystyrene. We experimentally showed by using fluorescent tagging that the composite bundles allowed measureable and selective mass transport through CNTs. This type of composite bundle may be useful in various CNT research areas as they are simple to fabricate, less likely to form macroscopic cracks, and offer a high density of CNT pores while maintaining the aligned morphology of CNTs.

Effects of amino group on the properties of carbon nanotubes

ABSTRACTThe surfaces of multi-walled carbon nanotubes were grafted with amino functional groups by reacting acyl-chloride-functionalized carbon nanotubes (CNTs) with hexamethylene diamine, which improves the surfactivity of CNTs. The dispersity, surface morphology, and thermogravimetry of acid-treated and amino-functionalized CNTs were investigated. Amino-functionalized CNTs were added into epoxy resin to analyze the effects of amino functional groups on the properties of resin composites. It was found that the properties of CNTs, such as morphology and scale, were not affected by amino functional groups, but the dispersity in water was highly improved. Amino-functionalized CNTs are better dispersed in resin matrix, and the mechanical properties of composites are improved significantly, whereas the conductivity of composites is not enhanced as expected.

Effect of substrate material on the growth and field emission characteristics of large-area carbon nanotube forests

Carbon nanotubes (CNTs) are a promising replacement for tungsten filaments as electron emitters in conventional x-ray sources, owing to their higher aspect ratio, superior mechanical stability, chemical inertness, and high electrical and thermal conductivities. Conditions for realizing the best emission behavior from CNTs have been formulated over the last few years. In this paper, we report the relatively less-investigated factor, namely, the influence of the nature of substrate material on the growth as well as field emission characteristics of large-area multiwalled CNTs for their practical application in medical x-ray sources. We compare the morphology of CNTs on a variety of substrates such as stainless steel, copper, molybdenum, graphite, few-layer graphene, and carbon nanowalls grown by thermal chemical vapor deposition following a simple drop-coating of catalyst. We find that CNTs grown on stainless steel and graphite show the best combination of emission characteristics under pulsed operation mode. These studies are helpful in selecting the optimum substrate material for field emission applications. Ex situ studies on field emission degradation of CNTs are presented towards the end.

Effect of different acid oxidation on morphology, dispersion and optical band-gap of multi-walled carbon nanotubes

ABSTRACTIn this paper the effect of different acid oxidation on morphology, dispersion and optical band gap of multi-walled carbon nanotubes (CNTs) is reported. Oxidation of CVD synthesized MWCNTs were carried out in 8M HNO3, 8M H2SO4, 8M HNO3/H2O2 and 8M H2SO4/HNO3. Oxidized nanotubes sample were characterized by XRD, SEM, FT-IR, TGA, UV-Vis spectroscopy and Raman analysis. Oxidized-nanotubes show a lower shift in XRD peak and an increase in d-spacing, which implies deterioration of MWNTs. New peaks in FT-IR spectra of oxidized-nanotube samples at around 1742 cm−1 confirms the presence of carbonyl groups. Optical bandgap, molar absorptivity coefficient is estimated for pristine and oxidized nanotubes sample using UV-Vis spectroscopy data and Tauc plot. It is observed that optical bandgap decreases on oxidation and lowest bandgap 2.92 eV is observed for H2SO4 treated MWNTs. The information on the optical bandgap of the MWNTs is of great importance for the development of optoelectronic devices.

Effect of Reaction Temperature on Carbon Yield and Morphology of CNTs on Copper Loaded Nickel Nanoparticles

This investigation was attempted to introduce carbon nanotubes (CNTs) onto surface of copper powders in order to improve heat transfer performance of copper matrix for engineering application of electrical packaging materials. The Ni/MgO catalyst was formed on the copper powders surface by means of codeposition method. CVD technique was executed to fabricate uniform CNTs on copper powders and effect of reaction temperature on the morphology of CNTs was surveyed. The results showed that CNTs products on the copper powder surface were distributed uniformly even if reaction temperature was different. The diameter dimension of CNTs was within the scope of 30~60 nm. Growth behaviors of CNTs by CVD method were considered to be “tip-growth” mechanism. Raman spectra of CNTs proved that intensity ratio of D-band to G-band (ID/IG) increased as deposition reaction temperature increased, which implied that order degree of graphitic structure in synthesized CNTs improved.

The synthesis of carbon nanomaterials using chlorinated hydrocarbons over a Fe-Co/CaCO3 catalyst

The effect of chlorine on the morphology of carbon nanotubes (CNTs) prepared from a Fe-Co/CaCO 3 catalyst was investigated using chlorobenzene (CB), dichlorobenzene (DCB), trichlorobenzene (TCB), dichloroethane (DCE), trichloroethane (TCE) and tetrachloroethane (TTCE) as chlorine sources using a catalytic chemical vapour deposition (CCVD) method. Toluene was used as a chlorine-free carbon source for comparison. Multi-walled carbon nanotubes (MWCNTs) were successfully synthesized. The physicochemical properties of the CNTs were studied using transmission electron microscopy (TEM), Raman spectroscopy, thermal gravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The inner and outer diameters of the MWCNTs increased with an increase in the number of chlorine atoms contained in the reactant. Chlorine incorporation into the MWCNTs was observed by EDS analysis for all reactants. Formation of ‘bamboo-like’ structures for the MWCNTs generated from TCE and TTCE was also observed, facilitated by the presence of the high percentage of chlorine in these reactants. Numerous MWCNTs revealed the presence of small carbon nanostructures that grew on top of the dominant CNTs, suggesting an unexpected secondary carbon growth mechanism. KEYWORDS Multi-walled carbon nanotubes, CVD, synthesis, chlorine, benzenes, ethanes.

Carbon dioxide adsorption on nano/micro-scale porous adsorbents

The objective of this paper is to investigate the physicochemical properties of the composites, carbon nanotubes (CNTs)/activated carbon fibres (ACFs), and determine the adsorption capacity of CO2 on CNTs/ACFs. The chemical vapour deposition method was used for growth of CNTs without or with nitrogen doping. The spaghetti-like and a little randomly oriented CNTs with a high density and homogeneity were observed to grow onto the ACFs, while the morphology of nitrogen-doped CNTs on ACFs looked short, coarse and entangled. The result of high resolution of XPS N1s peak showed that the pyridine-type N and quaternary N were the predominant functional groups on all samples. Specifically, nitrogen-doped CNTs were characterised by the pyridine-like structures of six-member rings and hydrophobicity due to deficiency of oxygen atoms. The adsorption capacities of CO2 on all samples decreased gradually as the temperature increased, implying the exothermic reaction on adsorption. The adsorption capacities of CO2 based on surface areas at 25°C and 1 bar were between 1.60-2.69 µmole/m2, and the ACFs grafted with nitrogen-doped CNTs exhibited the best performance for CO2 adsorption.

Influence of Chemical Treatment on the Morphology and Functionalization of Carbon Nanotubes.

Multi-walled carbon nanotubes (MWCNTs) were functionalized by different oxidative treatments to insert polar groups on their surface. The treatments included sulfuric/nitric acid mixture, 6 M nitric acid solution, concentrated hydrochloric acid, sulfuric/potassium permanganate solution, and alkaline solution. The procedures succeeded in eliminating catalyst residues remaining from the MWCNT synthesis. Physical treatment by sonication was used to modify the intertubular distances and to reduce the average particle size. The materials obtained were characterized by X-ray diffraction and their morphology was studied by TEM. Particle size was analyzed by dynamic light scattering. FTIR spectroscopy was used to confirm the presence of functional groups and thermo-gravimetry (TGA) was employed to estimate the oxidation degree attained. The results confirmed polar group insertion on the surface of treated carbon nanotubes. Oxidation with 6 M nitric acid followed by sonication in xylene was found to be the most effective treatment.

Assessment of the Reaction Time on the Morphology and Quality of Carbon Nanotubes – Silica Microparticles

Carbon nanotube has been grafted in-situ on the surface of spherical silica gel via floating-catalyst chemical vapour deposition method. The reaction temperature was set to be 760°C and 5wt. % of ferrocene catalyst (dissolved in toluene) injected into the furnace at a rate of 0.04ml/min. The reaction time was varied from 1 hour to 8hours, with one hour interval. It was found that the reaction time of 3hours yields the best quality hybrid particles. Prolonging the reaction time more than 3hours resulted in the formation of CNT that consists of thicker tubes, based on the observation via Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM). Secondary overgrowth was observed via TEM for tubes synthesized at 7hours and 8hours. These results were in agreement with Raman Spectroscopy analysis where the IG/ID ratio were very small, indicating high defects and impurities in the samples synthesized at reaction time higher than 3hours.

A method for the direct growth of carbon nanotubes on macroscopic carbon substrates

A simple and general approach is reported for the direct growth of carbon nanotubes (CNTs) on macroscopic carbon substrates. Two typical geometries of biomass materials, cellulose fibers or rice husks, are chosen to act as the precursor of carbon substrates, and commercial polypropylene (PP) pellets are used as the carbon source of CNTs with the presence of Ni–Mo–Mg catalysts. This simple and general strategy was realized by a direct pyrolyzation of the PP blends containing biomass materials and Ni–Mo–Mg catalysts in a chemical vapor deposition device at 800 °C under nitrogen’s protection. The carbon products were characterized by various techniques such as X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis. Results show that the CNTs are successfully grown on the macroscopic carbon substrate derived from cellulose fibers or rice husks, whereas the addition of biomass materials as carbon precursors has to some extent an influence on the morphology of CNTs in the carbon products.

Influence of Duration of Mechanical Activation of Plant Material Pyrolysis Products on Thermal Stability of Moldable Multilayer Carbon Nanotubes

The influence of duration of mechanical activation of amorphous carbon produced by plant material pyrolysis on the morphology of moldable multilayer carbon nanotubes is studied. The maximum nanotube yield is observed when amorphous carbon is mechanically activated for 36 hours. The nanotube yield depends a great deal on the type of plant materials submitted to pyrolysis. It is demonstrated that prolonged mechanical activation of carbon composite in a vario-planetary mill leads to formation of aggregates consisting of multilayer nanotubes and amorphous carbon and to loss of thermal stability of nanotubes. This fact is responsible for the decrease in carbon nanotube content in products of vacuum annealing carried out for nanotube purification.

Enhancement of cobalt catalyst stability in Fischer–Tropsch synthesis using graphene nanosheets as catalyst support

The effect of morphology and structure of graphene nanosheets (GNS) and carbon nanotubes (CNT) as support on the stability of cobalt catalyst for Fischer–Tropsch synthesis (FTS) was investigated using a fixed bed micro-reactor.15.0wt.% of cobalt was loaded on the supports by impregnation method. The deactivation of the two catalysts was studied at 220°C, 1.8MPa and 45 STP mL/min feed flow rate. Characterization of the supports, calcined fresh and used catalysts were studied by Raman spectroscopy, BET, XRD, TEM, TPR and H2 chemisorption techniques. XRD confirmed formation of cobalt oxides on the used catalysts. According to the TEM and H2 chemisorption tests, 480h continuous FT synthesis increased the average cobalt particle size from about 6 to 6.8nm for Co/GNS catalyst and from about 7.5 to 9.5nm for Co/CNT catalyst. The initial CO conversion of the Co/GNS catalyst was 12% higher than that of the Co/CNT. For the Co/GNS, 480h continuous FT synthesis decreased the CO conversion by 3.9%, whereas, under the same reaction conditions the CO conversion for Co/CNT decreased by 20.7%. Regeneration of the Co/GNS and Co/CNT recovered 99.3 and 92.8% of the initial activities of the catalysts, respectively. Significant stability of Co/GNS catalyst in FT synthesis, introduces graphene as an excellent support for the cobalt catalysts.

CVD method for carbon nanotubes preparation based on orthogonal experiment using C3H6

Carbon nanotubes (CNTs) have potential applications in many fields, chemical vapor deposition (CVD) is an effective method for CNTs preparation. By CVD, the catalytic pyrolysis temperature, pyrolysis time and the size of the raw gas flow have a great influence on yield rate of CNTs and their form. In this paper, the orthogonal experiment analysis method is used for studying the influence factors of yield rate of CNTs. Research results show that, in the suitable temperature range of preparing CNTs, there is relatively more CNTs with excellent morphology, otherwise, if the temperature is too low, the growth of CNTs will not be sufficient; if the temperature is too high, then CNTs will be generated with excessive defects; with longer growth time of suitable pyrolysis of CNTs, higher yield of CNTs will be obtained; CNTs morphology with reaction time is not proportional; too low or too high raw gas flow rate is not conducive to the growth of CNTs. We have found the optimum conditions for the CNTs preparation: pyrolysis temperature 680 °C, pyrolysis time 35 min, propylene flow rate of 180 mL/min. The results have a reference value for the preparation of CNTS and their composites.

Carbon Nanotubes (CNTs) for Prolonging the Life of Micropunch

Carbon nanotubes (CNTs) coated on the WC/Co micropunch with diameter in 150 μm for prolonging the life of micropunch was investigated. Carbon nanotubes were synthesized by homemade method. With scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the morphology and structure of CNTs had been expressed. After the punching test with Ti as substrate, the effect of CNTs for prolonging the life of micropunch on the wear loss and the surface morphology of micropunch had been studied by confocal laser, SEM, digital balance etc. Results show the wear of CNTs coated micropunch decreases obviously. Even in the severe wear period the wear loss is less than that of non-CNTs coated micropunch. Compared with the micropunch without CNTs coating, the promising results are due to the formation of a transfer film at the contact region by rubbing of the CNT forest, CNTs produced adheres to the micropunch surface avoiding direct contact during the punching period and providing lubricant properties to the interface by virtue of their graphitic nature. Also, the relevant mechanism was illustrated primarily.

Hyperelasticity of three-dimensional carbon nanotube sponge controlled by the stiffness of covalent junctions

To expand the applications of carbon nanotubes (CNTs) at macroscale, a heteroatom doping technique has been employed to fabricate isotropic 3-D CNT architectures by inducing elbow-like covalent junctions into multiwalled CNTs. As the junctions modify the topology of each CNT by favoring the stable bends in CNTs, junction stiffness and the consequence of junction-related morphology changes in sponge's hyperelasticity remain largely elusive. In this study, two types of 3-D multiwalled CNT sponges were fabricated by inducing boron-doped or nitrogen-doped covalent junctions into CNTs. Hyperelastic properties of the sponges were experimentally quantified as the functions of CNT morphology. A novel microstructure informed continuum constitutive law was developed specifically for such isotropic CNT sponges with junctions. Analyzing the experimental data with the new theory demonstrated that, for the first time, the effective modulus of boron-doped junctions (∼100 GPa) is higher than that of nitrogen-doped junctions (∼20 GPa), and the junction stiffness is a key factor in regulating the hyperelastic compressive modulus of the material. Theoretical analysis further revealed that increased number of junctions and shorter segments on each individual CNT chain would result in stronger hyperelastic 3-D CNT networks. This study has established a fundamental knowledge base to provide guidance for the future design and fabrication of 3-D CNT macrostructures.

Water treatment by H2O2 and/or UV affects carbon nanotube (CNT) properties and fate in water and tannic acid solution.

The objective of the study was to estimate how water treatment (stimulation of real conditions) by H2O2 and/or UV affects carbon nanotube (CNT) properties and fate (stability/aggregation) in water and tannic acid solution. The processes studied had only a slight effect on SBET, porosity, and surface composition of CNTs. There was a change in the morphology of CNTs. After H2O2 and/or UV treatment, CNTs underwent shortening, opening up of their ends, and exfoliation. Treatment with H2O2 increased the content of oxygen in CNTs. A decrease was observed in the surface charge and in the mobility of CNTs, which caused an increase in their stability. UV irradiation of CNTs led to an increased incidence of defects that were manifested by both an increase of zeta potential and an increased mobility of CNT, whereas the presence of H2O2 during UV irradiation had only a slight effect on the parameters of the porous structure of nanotubes.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-015-5208-x) contains supplementary material, which is available to authorized users.