Synthesis, Characterization and Pseudocapacitive Behaviour of MnOx/CNT Heterostructures

Manganese oxide based nanoparticles were synthesized by sol-gel process. Methanol, ethanol, and propanol were used as alternative solvent during sol-gel process with manganese acetate as precursor for the preparation of pristine manganese oxide. Hybrid MnOx modified by additions of carbon nanotubes was further prepared. Smallest particle size was observed for manganese oxide prepared from propanol, with diameters range from 16 nm to 50nm. XRD results showed that the as prepared manganese oxide based samples at calcination temperature of 300°C and above were composed of Mn2O3 as dominant phase, with Mn3O4 as minor phase. Specific capacitance measured from two electrode systems of manganese oxide prepared from methanol, ethanol, and propanol at scan rate of 10 mV/s were 88.3, 66.0, 104.8 F/g and the result for the hybrid sample was 140.5 F/g. The highest capacitance of the MnOx revealed a specific capacitance of 231.4 F/g when a 1:1 mixture of propanaol and methanol was employed as the solvent for the sol preparation. Results from electrochemical impedance spectroscopy (EIS) also showed superior electrochemical properties of the hybrid sample over pristine manganese oxide samples.

Ferrocene derived carbon nanotubes and their application as electrochemical double layer capacitor electrodes

We report on the synthesis of carbon nanotubes (CNTs) by direct thermal decomposition of ferrocene (Fe(C5H5)2). Our studies indicate that presence of a small amount of sulfur along with the ferrocene in the decomposition process strongly affects the quality of the CNTs produced and is crucial for obtaining thin diameter nanotubes. Raman spectroscopic investigations suggest that the atomic ratio of sulfur to the total iron plus sulfur content of approximately 0.09 yields CNTs with highly crystalline structure having diameters ranging from 0.85 nm to 1.75 nm. Electrochemical double layer capacitor electrodes fabricated from these CNTs show impressive energy storage properties, capable of delivering a maximum power density of approximately 27 KW/kg and energy density of approximately 2.12 Wh/Kg.

Time and temperature dependence of multi-walled carbon nanotube growth on Inconel 600

The growth kinetics of vertically aligned multi-walled carbon nanotubes (MWNTs) on conductive substrates is investigated by synthesizing MWNTs at different growth temperatures and measuring ex situ the length of the nanotubes as a function of growth duration. A typical 'root growth' mechanism (saturation of MWNT lengths with increasing growth duration) was observed. The value of the activation energy (E(a)≈136 ± 5 kJ mol(-1)) of the MWNT growth reaction is suggestive of carbon diffusion through the bulk of the iron catalyst particle versus diffusion on its surface. These findings will help in optimizing MWNT growth on conductive substrates for various applications.

First-principles study of defect-induced magnetism in carbon

We have studied the role of defects on the magnetic properties of carbon materials using first-principles density functional methods. We show that, while the total magnetization decreases both for diamond and graphite with increase in vacancy density, the magnetization decreases more rapidly for graphitic structures. The presence of nitrogen nearby a vacancy is shown to produce larger macroscopic magnetic signals as compared to a standalone carbon vacancy. The results indicate the possibility of tuning magnetization in carbon by controlled defect generation and doping.

Direct growth of aligned carbon nanotubes on bulk metals

There are several advantages of growing carbon nanotubes (CNTs) directly on bulk metals, for example in the formation of robust CNT-metal contacts during growth. Usually, aligned CNTs are grown either by using thin catalyst layers predeposited on substrates or through vapour-phase catalyst delivery. The latter method, although flexible, is unsuitable for growing CNTs directly on metallic substrates. Here we report on the growth of aligned multiwalled CNTs on a metallic alloy, Inconel 600 (Inconel), using vapour-phase catalyst delivery. The CNTs are well anchored to the substrate and show excellent electrical contact with it. These CNT-metal structures were then used to fabricate double-layer capacitors and field-emitter devices, which demonstrated improved performance over previously designed CNT structures. Inconel coatings can also be used to grow CNTs on other metallic substrates. This finding overcomes the substrate limitation for nanotube growth which should assist the development of future CNT-related technologies.

Irradiation-induced magnetism in carbon nanostructures

Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.

Flow-induced planar assembly of parallel carbon nanotubes and crossed nanotube junctions

We report the in-situ assembly of carbon nanotubes by chemical vapor deposition of hydrocarbon precursor (a solution of ferrocene dissolved in isopropyl alcohol). We utilized the vapor stream inside the reaction chamber to comb carbon nanotubes along the same direction and obtained two-dimensional (planar) assembly of nanotubes with tunable distributions. When the carbon source was flowing at a relatively higher rate of approximately 0.2 ml/min, most of nanotubes were driven along the vapor flow direction during their growth process and formed a thin freestanding mat featured with a parallel arrangement, whereas a lower flowing rate (approximately 0.05 ml/min) only resulted in random spider-web structures consisting of crossed nanotube junctions with a variety of configurations (e.g., "+", "Y", "T" shapes and twists). The measured direction-dependent electrical resistance of these two assemblies was in agreement with respective structures, which was anisotropic for parallel nanotubes and nearly isotropic for random networks. Such large-area planar carbon nanotube arrays with controlled orientation and various junction configurations will facilitate the design and fabrication of electronic and mechanical devices.

Carbon nanotube filters

Over the past decade of nanotube research, a variety of organized nanotube architectures have been fabricated using chemical vapour deposition. The idea of using nanotube structures in separation technology has been proposed, but building macroscopic structures that have controlled geometric shapes, density and dimensions for specific applications still remains a challenge. Here we report the fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres. These cylindrical membranes are used as filters to demonstrate their utility in two important settings: the elimination of multiple components of heavy hydrocarbons from petroleum-a crucial step in post-distillation of crude oil-with a single-step filtering process, and the filtration of bacterial contaminants such as Escherichia coli or the nanometre-sized poliovirus ( approximately 25 nm) from water. These macro filters can be cleaned for repeated filtration through ultrasonication and autoclaving. The exceptional thermal and mechanical stability of nanotubes, and the high surface area, ease and cost-effective fabrication of the nanotube membranes may allow them to compete with ceramic- and polymer-based separation membranes used commercially.

Mobility of carbon nanotubes in high electric fields

The influence of electric fields on carbon nanotubes is experimentally demonstrated. Alignment of nanotubes along field lines, directed motion of nanotubes between electrodes separated by several thousand micrometers, and impressive solid-state actuation behavior of nanotube-embedded structures are demonstrated, taking into account the polarization and charging of the nanotubes. These effects are reported for long strands of nanotubes, nanotubes dispersed on substrates, and nanotube-embedded polymer strips. The relative magnitude of the field responsible for polarization and directed motion was found to be dependent on the morphology of the nanotubes used. These observations may foreshadow novel electromechanical applications for nanotube elements.

Higher coverage gas adsorption on the surface of carbon nanotubes: evidence for a possible new phase in the second layer

We present adsorption isotherm results for Ne, CH4, and Xe on bundles of close-ended single-wall carbon nanotubes, for coverages above the completion of the first layer. We find a small, sharp, substep present in the second-layer data for Ne and CH4, and a weaker feature, that produces an isothermal compressibility peak, for Xe. The size and location of the feature allows its tentative identification as a new, second-layer, one-dimensional phase, in which the atoms sit atop high binding energy sites in the second layer.

Possible existence of a higher coverage quasi-one-dimensional phase of argon adsorbed on bundles of single-walled carbon nanotubes

We present results of Ar adsorption isotherms at very low coverages in the first layer and, beyond monolayer completion, on bundles of close-ended single-walled carbon nanotubes. The low coverage results were used to determine the isosteric heat of adsorption and the binding energy of Ar in the groove sites in the first layer. The higher coverage results show evidence of the possible formation of a second-layer groove phase, beyond monolayer completion. Our results for higher coverages are compared with recent computer simulations for this system.

Elongation factor-1 alpha is a selective regulator of growth factor withdrawal and ER stress-induced apoptosis

To identify genes that contribute to apoptotic resistance, IL-3 dependent hematopoietic cells were transfected with a cDNA expression library and subjected to growth factor withdrawal. Transfected cells were enriched for survivors over two successive rounds of IL-3 withdrawal and reconstitution, resulting in the identification of a full-length elongation factor 1 alpha (EF-1alpha) cDNA. Ectopic EF-1alpha expression conferred protection from growth factor withdrawal and agents that induce endoplasmic reticulum stress, but not from nuclear damage or death receptor signaling. Overexpression of EF-1alpha did not lead to growth factor independent cell proliferation or global alterations in protein levels or rates of synthesis. These findings suggest that overexpression of EF-1alpha results in selective resistance to apoptosis induced by growth factor withdrawal and ER stress.

Existence of novel quasi-one-dimensional phases of atoms adsorbed on the exterior surface of close-ended single wall nanotube bundles

We present results of adsorption measurements for Xe and Ar which confirm experimentally the formation of one-dimensional phases for these gases when adsorbed on the outer surfaces of close-ended single-wall carbon nanotube (SWNT) bundles. The existence of such phases had been predicted in recent computer simulations, but had remained, until the present work, unconfirmed. Experimental results for Xe and Ar on close-ended bundles of SWNT's are compared to, and found in substantial quantitative agreement with, those obtained in the computer simulation studies. The characteristics of the phases formed appear to be strongly influenced by steric effects.

Growth factor signaling in cell survival: implications for cancer treatment

Cells of multicellular organisms require extracellular signals to survive. Numerous studies have implicated a variety of intracellular signaling pathways, including PI-3 kinase/Akt, Ras/mitogen-activated protein kinase, and Jak/signal transducers and activators of transcription, as effectors of these extracellular trophic factors. Binding of growth factors to their respective receptors results in the activation of individual and combined pathways resulting in pleiotropic effects on cellular biochemistry. Over the past decade, investigation of these pathways has provided insight into the mechanism of cell survival and apoptosis itself. The results of these studies are providing new clues for therapeutic intervention in human disease. In this review, we focus on advances in our current understanding of the receptor signaling pathways that regulate apoptosis. Implications for the pharmacological manipulation of apoptosis in the treatment of cancer are also discussed.

Akt and Bcl-xL promote growth factor-independent survival through distinct effects on mitochondrial physiology

A comparison of Akt- and Bcl-x(L)-dependent cell survival was undertaken using interleukin-3-dependent FL5.12 cells. Expression of constitutively active Akt allows cells to survive for prolonged periods following growth factor withdrawal. This survival correlates with the expression level of activated Akt and is comparable in magnitude to the protection provided by the anti-apoptotic gene Bcl-x(L). Although both genes prevent cell death, Akt-protected cells can be distinguished from Bcl-x(L)-protected cells on the basis of increased glucose transporter expression, glycolytic activity, mitochondrial potential, and cell size. In addition, Akt-expressing cells require high levels of extracellular nutrients to support cell survival. In contrast, Bcl-x(L)-expressing cells deprived of interleukin-3 survive in a more vegetative state, in which the cells are smaller, have lower mitochondrial potential, reduced glycolytic activity, and are less dependent on extracellular nutrients. Thus, Akt and Bcl-x(L) suppress mitochondrion-initiated apoptosis by distinct mechanisms. Akt-mediated survival is dependent on promoting glycolysis and maintaining a physiologic mitochondrial potential. In contrast, Bcl-x(L) maintains mitochondrial integrity in the face of a reduced mitochondrial membrane potential, which develops as a result of the low glycolytic rate in growth factor-deprived cells.

Gases Do not adsorb on the interstitial channels of closed-ended single-walled carbon nanotube bundles

We have experimentally determined the binding energies of Xe, CH4, and Ne on samples of closed-ended single-wall nanotube (SWNT) bundles. We find values for these quantities which are larger by approximately 75% on the SWNT samples than the values found for the same adsorbates on planar graphite. We have also determined the monolayer capacity of a SWNT sample using Xe and Ne adsorption. A comparison of all of our results leads us to conclude that none of the gases studied adsorb on the interstitial channels in the SWNT bundles.