Showing papers by "Yury Gogotsi published in 2005"

Carbon Nanotubes Loaded with Magnetic Particles

Abstract: We describe a simple and versatile technique to produce magnetic tubes by filling carbon nanotubes (CNTs) with paramagnetic iron oxide particles (∼10 nm diameter). Commercial ferrofluids were used to fill CNTs with an average outer diameter of 300 nm made via chemical vapor deposition into alumina membranes. Transmission electron microscopy study shows a high density of particles inside the CNT. Experiments using external magnetic fields demonstrate that almost 100% of the nanotubes become magnetic and can be easily manipulated in magnetic field. These one-dimensional magnetic nanostructures can find numerous applications in nanotechnology, memory devices, optical transducers for wearable electronics, and in medicine.

Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage.

Abstract: The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.

Synthesis of Carbide-Derived Carbon by Chlorination of Ti2AlC

Abstract: Nanoporous carbide-derived carbon (CDC) was synthesized starting with Ti2AlC powders via chlorination in the 400−1200 °C temperature range. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) confirmed a structural dependence on chlorination temperature. At low chlorination temperatures, the CDC structure appeared primarily amorphous. Graphitic ribbons, as well as sharply bent graphitic structures, were observed at 800 °C. As the chlorination temperature was further increased to 1000 °C, the width of the graphitic ribbon increased. No significant increase in graphitization occurred between 1000 and 1200 °C. Sorption measurements determined the presence of micropores (0.40−2.0 nm) after chlorination at 400 °C; chlorination at 800 °C or higher resulted in both micro- and mesopores (0.35 to >7 nm).

Double-Layer Capacitance of Carbide Derived Carbons in Sulfuric Acid

Abstract: Nanoporous carbons obtained by selective leaching of Ti and Al from Ti2AlC, as well as B from B4C, were investigated as electrode materials in electric double-layer capacitors. Cyclic voltammetry tests were conducted in 1 M H2SO4 from 0-250 mV on carbons synthesized at 600, 800, 1000, and 1200°C. Results show that the structure and pore sizes can be tailored and that the optimal synthesis temperature is 1000°C. Specific capacitances for Ti2AlC CDCs and B4C CDCs were 175 and 147 F/g, respectively, compared to multiwall carbon nanotubes and two types of activated carbon, measured herein to be 15, 52, and 125 F/g, respectively. © 2005 The Electrochemical Society. @DOI: 10.1149/1.1921134# All rights reserved.

Guiding water into carbon nanopipes with the aid of bipolar electrochemistry

Abstract: The targeted bipolar electrodeposition of polypyrrole was carried out onto the tips of hydrophilic carbon nanopipes. By aligning an external electric field relative to the nanopipes, the deposition of polypyrrole onto selected ends could be achieved without physically contacting the nanopipes. After deposition, carbon nanopipes with both partially open and fully blocked tips were found. Experiments conducted in an environmental scanning electron microscope showed that water enters the nanopipes through the tip with polypyrrole due to the higher hydrophilicity of the polymer compared to the tube walls. As a result, it was possible to guide the entry of water from a specific end of the tube and fill the tube from the selected side. Condensation experiments conducted on nanopipes with polypyrrole on both tips shows the difference in hydrophilicity of the nanopipes compared to the polypyrrole. The ability to selectively control the site of condensation and uptake of fluid by carbon nanotubes or nanopipes is very important for the development of nanotube-based nanofluidic devices.

Theoretical and experimental investigation of aqueous liquids contained in carbon nanotubes

Abstract: The dynamic response—as caused by different means of thermal stimulation or pressurization—of aqueous liquid attoliter volumes contained inside carbon nanotubes is investigated theoretically and experimentally. The experiments indicate an energetically driven mechanism responsible for the dynamic multiphase fluid behavior visualized in real time with high spatial resolution using electron microscopy. The theoretical model is formulated using a continuum approach, which combines temperature-dependent mass diffusion with intermolecular interactions in the fluid bulk, as well as in the vicinity of the carbon walls. Intermolecular forces are modeled by Lennard-Jones potentials. Several one-dimensional and axisymmetric cases are considered. These include situations which physically represent liquid volume pinchoff, jetting, or fluid relocation due to thermal stimulation by a steady or modulated electron beam, as well as liquid precipitation (condensation) from vapor due to overcooling or pressurization. Comparisons between theoretical predictions and experimental data demonstrate the ability of the model to describe the characteristic trends observed in the experiments.

Effect of carbon nanofibre structure on the binding of antibodies

Abstract: Potential biomedical applications for carbon nanofibres include, but are not limited to, biosensors and drug delivery vehicles. For such applications, it is essential to know how carbon nanotubes interact with antibodies and proteins. We report on the successful adsorption of monoclonal CD3 antibodies on two types of carbon nanofibre produced by the same method and having the same average size and shape, but differing in surface structure and chemistry due to dissimilar post-treatments. Binding of proteins to nanofibres is enhanced by poly (L-lysine) (PLL) and improves with increasing disorder and hydrophilicity of the nanofibres' surface. Oxidized and disordered surfaces of pyrolytically stripped nanofibres show improved wetting and attachment of PLL and proteins compared to hydrophobic and well-ordered surfaces of heat-treated nanofibres. These results show that the surface of carbon nanofibres can be tailored for their use in biomedical applications.

Nanotube-based sensors and probes

Abstract: Described herein are novel devices for the study of transport characteristics of complex or simple fluids, interactions among molecules in suspension, interactions between molecules in suspension and wall-bound molecules, and biochemical sensing devices made of reservoirs for fluid containment linked by a nanotubes. Also disclosed are methods of delivering medicaments and monitoring fluidic interactions of molecules or analytes.

Dielectrophoretic assembly of carbon nanofiber nanoelectromechanical devices

Abstract: We report a technique for the assembly of bottom-up nanomechanical devices. This technique employs the dielectrophoretic manipulation of nanostructures within a multiple layer lithography process. Mechanical resonators were specifically produced by assembling and clamping tubular carbon fibers onto prefabricated pads. Our preliminary results showed that an assembled cantilevered fiber with length L=5 /spl mu/m and width of W=180 nm possessed a resonant frequency of f=1.17 MHz. A shorter L=3-/spl mu/m-long singly clamped resonator of similar width showed a resonance of f=3.12 MHz. This frequency range is in agreement with the low gigapascal bending moduli previously reported for carbon structures showing extensive volume defects. This technology would allow the integration of bottom-up nanostructures with other more established fabrication processes, thus allowing the deployment of engineered nanodevices in integrated systems.

Systems-level questions in Drosophila oogenesis.

Abstract: This paper describes computational and experimental work on pattern formation in Drosophila egg development (oogenesis), an established experimental model for studying cell fate diversification in developing tissues. Epidermal growth factor receptor (EGFR) is a key regulator of pattern formation and morphogenesis in Drosophila oogenesis. EGFR signalling in oogenesis can be genetically manipulated and monitored at many levels, leading to large sets of heterogeneous data that enable the formulation of increasingly quantitative models of pattern formation in these systems.

Methods for bulk synthesis of carbon nanotubes

Abstract: Methods for synthesizing single-wall carbon nanotubes by extracting metals from a carbide by halogen treatment at a temperature ranging between 700 to 1700° C. at ambient or low pressure are provided.

Oxidation behaviour of an aluminium nitride-hafnium diboride ceramic composite

Abstract: An aluminium nitride–hafnium diboride electroconductive particulate composite was produced via hot isostatic pressing without sintering aids. Oxidation kinetics studies were performed up to 1350 °C under a flow of pure oxygen using a microbalance. The reaction products were analysed using SEM and XRD techniques. This composite had a high oxidation resistance up to 1200 °C. The kinetic curves had an asymptotic or paralinear shape. The formation of a protective oxide scale containing hafnia (HfO2) and aluminium borate (Al18B4O33) phases embedded in a glassy phase was observed. The evaporation of B2O3 was limited by the formation of refractory aluminium borate. Above 1200 °C, morphological observations showed the formation of a Maltese cross structure associated with the cracking of the oxide scale along the edges resulting in sigmoidal oxidation kinetics and in a high oxidation rate of the ceramic composite.

Carbothermal Synthesis of Al‐O‐N Coatings Increasing Strength of SiC Fibers

Abstract: Non-bridging Al-O-N coatings have been synthesized on the surface of Tyranno ZMI SiC fibers by a low-cost carbothermal nitridation method. First, a nanoporous carbide-derived carbon (CDC) layer is produced on the surface of SiC fiber by the extraction of Si with chlorine; the CDC layer on the fiber is then infiltrated by AlCl3 solution, and finally nitrided in ammonia at atmospheric pressure to produce the coating. The intermediate carbon layer acts as a template for the coating, facilitates the formation of aluminum oxynitride, and helps to build a strong bonding between the fiber and coating. Optimization of the process parameters led to a more than 65% improvement in the tensile strength (up to ∼5.1 GPa) and a three-time increase in the Weibull modulus for the fiber with 200 nm coating compared to the as-received fibers. The coated fiber exceeds the strength of all other small-diameter SiC fibers reported in the literature. Al-O-N coating may also provide oxidation protection for the fibers in high-temperature applications.

Electron Microscope Visualization of Multiphase Fluids Contained in Closed Carbon Nanotubes

Abstract: Aqueous multiphase fluids trapped in closed multiwall carbon nanotubes are visualized with high resolution using transmission electron microscopy (TEM). The hydrothermally synthesized nanotubes have inner diameter of 70 nm and wall thickness 20 nm, on average. The nanotubes are hydrophilic due to oxygen groups attached on their wall surfaces. Segregated liquid inclusions contained in the nanotubes under high pressure can be mobilized by heating. A resistive heating stage is utilized to heat a thin membrane inside a nanotube, causing the membrane to evaporate slowly and eventually pinch off. Focused electron beam heating is employed as a second means of thermal stimulation, which results in localized heating. With the latter method, gas/liquid interface motion is observed inside the thin channel of a carbon nanotube. Experiments like the ones presented herein may help understand the dynamics of fluids contained in nanoscale channels.

Methods for bulk synthesis of single-wall carbon nanotubes

Abstract: Methods for synthesizing single-wall carbon nanotubes by extracting metals from a carbide by halogen treatment at a temperature ranging between 700 to 1700oC at ambient or low pressure are provided. Also provided are single-wall carbon nanotubes produced in accordance with these methods.