Preparation Of Carbon Nanotubes Research Articles

Equilibrium and kinetic studies on the removal of NaCl from aqueous solutions by electrosorption on carbon nanotube electrodes

In this paper, we prepared carbon nanotube (CNT) electrodes with polytetrafluoroethylene (PTFE) as binders to adsorb NaCl from water. The electrodes were characterized using scanning electron micrograph (SEM), nitrogen adsorption and cyclic voltammetry. The adsorption/electrosorption rate and capacity of CNT electrodes with different bias potentials were measured, and the electrosorption isotherms and kinetics were also investigated. The results showed that electrosorption can effectively increase the adsorption capacity and rate of NaCl on CNT electrodes. The adsorption/electrosorption of NaCl on CNT electrodes followed Langmuir isotherms and the pseudo-first-order adsorption kinetics. The equilibrium adsorption capacity at 1.2 V was 9.35 mg/g, which was nearly eight times higher than that at 0 V. Compared with the adsorption rate at 0 V, the adsorption rate at 1.2 V was increased by 58.9%. The enhancement of capacity and rate may be due to the forming an electric double layer on the surface of CNT electrodes in the solution.

Carbon Nanotubes can Enhance Phase Dispersion in Polymer Blends

A two-step method was used to prepare carbon nanotube (CNT)/ethylene-vinylacetate copolymer (EVA)/polyethylene (PE) and CNT/polycarbonate (PC)/PE composites. First, CNT-EVA and CNT-PC master batches were obtained by solution-phase processing, and second, the CNT masterbatches were melt-mixed with PE. Phase morphological observation indicates that there is a marked decrease in the size of the dispersed particles in the composites. This finding is of practical significance to develop new polymer materials based on blending concept.

The thermal properties of controllable diameter carbon nanotubes synthesized by using AB 5 alloy of micrometer magnitude as catalyst

We have synthesized multi-wall carbon nanotubes by catalytic chemical vapour deposition (CCVD) method using an AB 5 hydrogen storage alloy with diameter ranging from 38 to 150 μm as a catalyst. The H 2 uptake capacity of the carbon nanotubes prepared using an AB 5 alloy as a catalyst is about 4 wt.% through to the pressure of 8 MPa at room temperature. Differential thermal analysis–thermogravimetric analysis (DTA–TGA) technique has been applied to investigate the effect of the diameters of the AB 5 alloy catalyst of micrometer magnitude and the technique conditions in the CCVD process on the thermal properties of carbon nanotubes. As the catalyst diameter increases from 38 to 150 μm, the average diameter of the prepared carbon nanotubes increases and the diameter distribution also enlarges. Electron microscope, Raman spectrum and thermal analysis all indicated that the catalyst sizes affect the diameter and the thermal properties of the carbon nanotubes. When the catalyst diameter increases, the initial weight loss temperature and the differential thermal peak temperature of the carbon nanotubes increases, which shows that the lager the diameter of the carbon nanotubes is, the higher the oxidation temperature, and the better the anti-oxidizablity. However, if the diameter of the catalyst is larger than 100 μm, the anti-oxidizablity does not rise anymore but tend to be invariableness. In the CCVD preparation process, the anti-oxidizability of the carbon nanotubes increases, when raising the ratio of the hydrogen gas in the reaction gas in our experimental range (4:1, 3:1, and 2:1, respectively).

Carbon nanotubes show no sign of acute toxicity but induce intracellular reactive oxygen species in dependence on contaminants

Today nanosciences are experiencing massive investment worldwide although research on toxicological aspects of these nano-sized particles has just begun and to date, no clear guidelines exist to quantify the effects. In the present study, we focus on carbon nanotubes (CNTs), which represent one of the most widely investigated carbon nanoparticles. The present data indicate that CNTs are able to cross the cell membrane of rat macrophages (NR8383) and, therefore, might have an influence on cell physiology and function. NR8383 and human A549 lung cells were incubated with commercial single-walled (NT-1) and multi-walled (NT-2, NT-3) CNTs, carbon black and quartz as reference particles as well as an acid-treated single-walled CNT preparation (SWCNT a.t.) with reduced metal catalyst content. We did not observe any acute toxicity on cell viability (WST-1, PI-staining) upon incubation with all CNT products. None of the CNTs induced the inflammatory mediators NO, TNF-α and IL-8. A rising tendency of TNF-α release from LPS-primed cells due to CNT treatment could be observed. We detected however, a dose- and time-dependent increase of intracellular reactive oxygen species and a decrease of the mitochondrial membrane potential with the commercial CNTs in both cell types after particle treatment whereas incubation with the purified CNTs (SWCNT a.t.) had no effect. This leads us to the conclusion that metal traces associated with the commercial nanotubes are responsible for the biological effects.

Structural Health Monitoring for Carbon Fiber/Carbon Nanotube (CNT)/Epoxy Composite Sensor

Structural health monitoring for carbon nanotube (CNT)/carbon fiber/epoxy composite was verified by the measurement of electrical resistivity. This study has focused on the preparation of carbon nanotube composite sensors and their application for structural health monitoring. The change of the electrical resistance was measured by a digital multimeter under tensile loads. Although a carbon fiber was broken, the electrical connection was still kept by distributed CNT particles in the model composites. As the number of carbon fiber breakages increased, electrical resistivity was stepwise increased. The CNT composites were well responded with fiber damages during the electro-micromechnical test. Carbon nanotube composites can be useful sensors for structural health monitoring to diagnose a structural safety and to prevent a collapse.

First-principles study of field emission properties of gas adsorption on the carbon nanotubes

Carbon-containing gases usually present when preparing carbon nanotubes, and can affect the field emission of carbon nanotubes. Water vapor is also an important kind of gas for field emission, concerned by both experimental and theoretical studies. Under strong electric field, the gas molecules may be decomposed to radicals. Using DMol3 code based on density-functional theory, we calculated the adsorption of the gas molecules CH 4, CO and H 2O and the CH 3 and OH radicals under emission conditions. We found that the H 2O and the methyl have advantages to field emission and the CH 4, CO and the hydroxyl have disadvantages. The results of H 2O and CO are consistent with experiments, and the enhancement of current by CH 4 in the experiment may be due to the methyl decomposed from the CH 4.

Synthesis of Various Types of Nano Carbons Using the Template Technique

Abstract Using uniform nanochannels of an aluminum anodic oxide film as a template, uniform and unique multiwalled carbon nanotubes can be synthesized with a selectivity of 100%. This technique allows one to precisely control the diameters and the length of nanotubes. Moreover, it is possible to chemically modify only the inner surface of carbon nanotubes and to prepare carbon nanotubes with a double coaxial structure of heteroatom-doped multiwalls. The test tube like carbon prepared by this technique was found to be dispersible in water without any post treatment. In addition to this one-dimensional approach, unique microporous carbon can be prepared by the template technique using zeolite Y. The resulting microporous carbons are characterized by their regular ordering, originating from the regularity of the parent zeolite. When the synthesis conditions were optimized, the specific surface area and the micropore volume of the zeolite-templated carbon reach more than 4000 m2 g−1 and 1.8 cm3 g−1, respectively. This review introduces such a template-mediated approach and highlights how useful and versatile the template technique is for the production of nano carbons.

Electrochemical characteristics of facile prepared carbon nanotubes–ionic liquid gel modified microelectrode and application in bioelectrochemistry

The carbon nanotubes (CNTs) based microelectrode (ME) by modifying CNTs-room temperature ionic liquid (IL) gel at carbon fiber microelectrode (CFME) is easily prepared, which exhibits the typical cyclic voltammogram of ME with sigmoid shape and possesses good stability, high conductivity and enlarged current response and tunable dimension. The direct electron transfer of glucose oxidase has been greatly promoted showing reversible electrochemical behavior even at high scan rate. In addition, the CNTs based ME also exhibits effectively electrocatalytic oxidized ability to biomolecules, e.g. dopamine (DA), ascorbic acid (AA) and dihydronicotinamide adenine dinucleotide. The obvious separation of oxidized peak potential for DA and AA makes it possible to selectively determine DA in presence of AA. These phenomena show that the CNTs based ME has promising potential to detect various species in vivo and in vitro.

Efficient Transfer of a VA-SWNT Film by a Flip-Over Technique

A transfer of a VA-SWNT film onto a conductive surface has been achieved using a novel "flip-over" technique. The top surface of a VA-SWNT film was covered by entangled bundles in an as-grown sample. When a VA-SWNT film was flipped over, an optically flat surface consisting of the tips of very well aligned, clean bundles from the bottom of the film are exposed while the top of the film is well contacted to the substrate. Thus, we expect this technique to provide us with means to prepare carbon nanotube electrodes for device applications such as super capacitors, thermo-electric devices, fuel cells, and field emission filaments.

Growth of branch carbon nanotubes on carbon nanotubes as support

A novel method combining the dense fluidized bed and the floating catalytically chemical vapor deposition method (FCCVD) to prepare carbon nanotubes (CNTs) was proposed. Propylene was decomposed at 660 °C, using the CNTs as supports and the metal particles from the in situ pyrolysis of ferrocene as catalyst. The conversion of propylene in this process was closed to 100% under an optimum condition. By SEM and TEM observations, the growth of new generation of CNTs was proven. It was demonstrated that the short and thin CNT branches exist on the tips or sidewalls of CNTs. Based on the analysis of the formation of catalytic sites in the FCCVD in a fluidized bed, a physical model of the formation of branches was proposed.

A study concerning the pretreatment of CNTs and its influence on the performance of NIB/CNTs amorphous catalyst

As prepared carbon nanotubes were pretreated with nitric acid (CNTs-HNO3) or ammonia (CNTs-NH3). Fourier transform infrared spectroscopy (FTIR) measurements showed that the surface of the nanotubes was functionalized with carboxylic and hydroxyl functional groups after the acid treatment and that basic groups containing nitrogen, such as N-H and C-N, were introduced to the surface of the nanotubes after the ammonia treatment. X-Ray diffraction analysis implied that the nickel residue in the CNTs was effectively removed by acid treatment. However, the nickel residue was only partially eliminated by ammonia pretreatment. NiB amorphous catalysts supported on CNTs-HNO3 and CNTs-NH3 were prepared by the impregnation-chemical reduction method and characterized by transmission electron microscopy (TEM), as well as inductively coupled plasma (ICP) spectroscopy and studied in the selective hydrogenation of acetylene. TEM measurements showed that a high density NiB particles of about 9 nm were homogeneously dispersed on the CNTs-NH3. However, NiB particles (13-23 nm)with amean size of 16 nm were scattered on the CNTs-HNO3.As a result, the activity and selectivity of NiB/CNTs-NH3 were higher than those of NiB/CNTs-HNO3 in the selective hydrogenation of acetylene.

Carbon nanotubes prepared by meltspinningof core-shell polymer particles

The present authors developed a new method to prepare carbon nanotubes (CNT), whereby fine core-shell polymer particles are elongated by melt-spinning and then stabilized and carbonized. However, after its removal, no trace of the core polymer can be found in the resultant CNT. This behavior is investigated by TG-Mass spectroscopy. The shell polymer is thermally decomposed into small chemical fragments and disordered loose residue. The former are released through the latter, together with small fragments formed from the core polymer at nearly the same temperature range. After the removal of the core polymer, the shell residue is gradually rearranged into a dense carbon with increasing temperature. No trace of the core polymer remains in the resultant CNT.

Novel ionic liquid supported synthesis of platinum-based electrocatalysts on multiwalled carbon nanotubes

Novel ionic liquids (ILs) were used to prepare carbon nanotube (CNT) supported platinum catalysts for the first time. The CNTs were pretreated in acid to get functional groups to promote the adherence of Pt nanoparticles. Ionic liquids added to the reaction system are suggested to contribute to the formation of homogeneous small Pt nanoparticles and to suppress the agglomeration of CNTs. The Pt/CNT electrocatalyst has a fairly homogeneous dispersion of Pt particles with small particle sizes. The electrochemical performance of the Pt/CNT electrocatalysts for PEM fuel cells was studied by cyclic voltammetry measurements. The results show that the ionic liquid has a significant impact on the surface of the as-prepared CNTs and that there is a strong interaction between ionic liquids and CNTs.

Effects of protection gas flow rate on the electrochemical capacitance of activated carbon nanotubes

The effects of protection gas (nitrogen gas) flow rate on the electrochemical capacitance of activated carbon nanotubes (CNT) have been investigated. Nitrogen gas flow rate in the process of activated CNT preparation can great affect the activated CNT electrochemical capacitance, which carries out by virtue of its effects on activated CNT BET specific surface area. When the electrochemical capacitance of activated CNT reaches its maximum, there is an optimal value to nitrogen gas flow rate.

A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites

A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites

Silica Nanobeads-decorated Multi-walled Carbon Nanotubes by Vapor-phase Method

Abstract We report a new concise route to prepare carbon nanotube–silica nanobeads composites. The assembly of silica beads and nanotube by vapor-phase method make these structures an excellent platform for the development of biosensors, or for optical, magnetic and catalytic applications.

鋳型法によるナノカーボンの合成とその応用

Using uniform nano-channels of aluminum anodic oxide film as a template, uniform and unique multiwalled carbon nanotubes can be synthesized with a selectivity of 100%. This technique allows one to precisely control the diameters and the length of nanotubes. Moreover, this method makes them possible to chemically-modify only the inner surface of carbon nanotubes and to prepare carbon nanotubes with double coaxial structure of heteroatom-doped multiwalls. Metal or metal oxide filled nanotubes can also be synthesized by this method and highly-crystallized inorganic nano-rods or nano-ribbons cab be fabricated using the cavity of the carbon-coated nano-channels as a reaction field. In addition to one dimensional nano-carbons like carbon nanotubes, unique nano-porous carbon can be prepared by the template technique. Micro and mesoporous carbons with surprisingly regular ordering can be synthesized using zeolite and mesoporous silica templates, respectively. In this review, we introduce such template-mediated approach and highlight how useful and versatile the template technique is for the production of nano-carbons.

Production of hydrogen and carbon nanotubes from methane decomposition in a two-stage fluidized bed reactor

Methane decomposition over a Ni/Cu/Al 2O 3 catalyst is studied in a two-stage fluidized bed reactor. Low temperature is adopted in the lower stage and high temperature in the upper stage. This allows the fluidized catalysts to decompose methane with high activity in the high temperature condition; then the carbon produced will diffuse effectively to form carbon nanotubes (CNTs) in both low and high temperature regions. Thus the catalytic cycle of carbon production and carbon diffusion in micro scale can be tailored by a macroscopic method, which permits the catalyst to have high activity and high thermal stability even at 1123 K for hydrogen production for long times. Such controlled temperature condition also provides an increased thermal driving force for the nucleation of CNTs and hence favors the graphitization of CNTs, characterized by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and XRD. Multistage operation with different temperatures in a fluidized bed reactor is an effective way to meet the both requirements of hydrogen production and preparation of CNTs with relatively perfect microstructures.

Vertically aligned carbon nanotubes grown by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition, which enables growth of carbon nanotubes directly onto substrates, is potentially suitable for preparing carbon nanotubes as electron sources in field emission displays. In this article, we report the growth of aligned carbon nanotubes by microwave plasma enhanced chemical vapor deposition and investigate the effect of various parameters on the growth. Comparison among three catalysts (Fe, Co, and Ni) revealed that Fe gives the longest carbon nanotubes, while Co gives the carbon nanotubes with the smallest diameter. The growth of the carbon nanotubes strongly depends on the treatment time in the plasma. Field emission characteristics from the carbon nanotubes grown by the microwave plasma enhanced chemical vapor deposition are also shown.

Mechanochemical formation of novel catalyst for preparing carbon nanotubes: nanocrystalline yttrium aluminum iron perovskite

The first mechanochemical synthesis of nanosized YAl 1− x Fe x O 3 ( x=0 to 1) perovskite powders is reported. Continuous ball-milling of the yttria, aluminum hydroxide and iron oxide powders over 24 h led to the formation of nanocrystals with a size of nearly 20 nm. It has been found that the material exhibits a catalytic property for preparing carbon nanotubes.