Showing papers by "Yury Gogotsi published in 2009"

Wet chemistry route to hydrophobic blue fluorescent nanodiamond.

Abstract: Hydrophobic blue fluorescent nanodiamond was synthesized by covalent linking of octadecylamine to the surface of nanodiamond particles. The material is easily dispersible in hydrophobic solvents, forming a transparent colloidal solution, and can be used in those applications where stable dispersions of nanodiamond in fuels, polymers or oils are required. Bright blue fluorescence of the octadecylamine-modified nanodiamond opens up new avenues for its use as a non-toxic quantum dot analogue for biomedical imaging of cellular membranes and other hydrophobic components of biological systems. Similar surface modification can be used for other carbon nanoparticles.

Nanodiamond-Polymer Composite Fibers and Coatings

Abstract: While nanocrystalline diamond is quickly becoming one of the most widely studied nanomaterials, achieving a large fraction of diamond nanoparticles in a polymer coating has been an unresolved problem. In this work, polymer nano- and microfibers containing high loadings of 5 nm diamond particles (up to 80 wt % in polyacrylonitrile and 40% in polyamide 11) have been demonstrated using electrospun nanofibers as a delivery vehicle. The electrospun nanofibers with a high load of nanodiamond in the polymers were fused into thin transparent films, which had high mechanical properties; an improvement of 4 times for the Young's modulus and 2 times for the hardness was observed already at 20% nanodiamond in polyamide 11. These films can provide UV protection and scratch resistance to a variety of surfaces, especially in applications where a combination of mechanical, thermal, and dielectric properties is required.

Contribution of Functional Groups to the Raman Spectrum of Nanodiamond Powders

Abstract: In depth understanding of Raman spectra of carbon nanomaterials led to the extension of this technique from simple carbon allotrope detection (fingerprinting) to analysis of the dimensions and ordering of graphene, graphite and nanotubes. In characterization of nanodiamond powders, which have been attracting attention as one of the most promising carbon nanomaterials, Raman spectroscopy is still mainly used only for detecting the diamond phase because of poor understanding of other spectral features. In this paper, we critically examine different explanations of the broad asymmetric Raman band between 1500 and 1800 cm−1 present in all nanodiamond powders and provide an assignment of the contributing peaks, solving one of the major remaining mysteries in Raman spectroscopy of nanodiamond. By using nanodiamond powders with different and well-controlled surface chemistries, as well as in situ Raman measurements at elevated temperatures, we show that these peaks originate from O−H bending vibrations either fr...

Microelectrode Study of Pore Size, Ion Size, and Solvent Effects on the Charge/Discharge Behavior of Microporous Carbons for Electrical Double-Layer Capacitors

Abstract: The capacitive behavior of TiC-derived carbon powders in two different electrolytes, NEt4BF4 in acetonitrile AN and NEt4BF4 in propylene carbonate PC, was studied using the cavity microelectrode CME technique. Comparisons of the cyclic voltammograms recorded at 10–1000 mV/s enabled correlation between adsorbed ion sizes and pore sizes, which is important for understanding the electrochemical capacitive behavior of carbon electrodes for electrical double-layer capacitor applications. The CME technique also allows a fast selection of carbon electrodes with matching pore sizes different sizes are needed for the negative and positive electrodes for the respective electrolyte system. Comparison of electrochemical capacitive behavior of the same salt, NEt4BF4, in different solvents, PC and AN, has shown that different pore sizes are required for different solvents, because only partial desolvation of ions occurs during the double-layer charging. Squeezing partially solvated ions into subnanometer pores, which are close to the desolvated ion size, may lead to distortion of the shape of cyclic voltammograms.

Phonon confinement effects in the Raman spectrum of nanodiamond

Abstract: Nanodiamonds (ND) exhibit unique properties due to their small size and high surface-to-volume ratio compared to bulk diamonds. A reduction in crystal size also affects ND Raman spectra. The confinement of optical phonons in nanocrystals $(l10\text{ }\text{nm})$ results in asymmetrically broadened Raman lines, which are shifted toward lower wavenumbers. The phonon confinement model (PCM) relates the observed changes in the Raman spectra to the crystal size and can be used for size characterization at the nanoscale. While the PCM was successfully applied to a variety of materials including Si and BN, results remained unsatisfactory in the case of ND. In order to improve the agreement between the predictions of the model and experimental Raman spectra of ND, effects such as crystal size distribution, lattice defects, and the energy dispersion of the phonon modes were taken into consideration and incorporated into the PCM. This work has shown that phonon wave vectors from small vibrational domains lead to a broad shoulder peak at $\ensuremath{\sim}1250\text{ }{\text{cm}}^{\ensuremath{-}1}$, that is often observed in the Raman spectrum of ND.

In Situ Intracellular Spectroscopy with Surface Enhanced Raman Spectroscopy (SERS)-Enabled Nanopipettes

Abstract: We report on a new analytical approach to intracellular chemical sensing that utilizes a surface-enhanced Raman spectroscopy (SERS)-enabled nanopipette. The probe is comprised of a glass capillary with a 100−500 nm tip coated with gold nanoparticles. The fixed geometry of the gold nanoparticles allows us to overcome the limitations of the traditional approach for intracellular SERS using metal colloids. We demonstrate that the SERS-enabled nanopipettes can be used for in situ analysis of living cell function in real time. In addition, SERS functionality of these probes allows tracking of their localization in a cell. The developed probes can also be applied for highly sensitive chemical analysis of nanoliter volumes of chemicals in a variety of environmental and analytical applications.

Electrical Double-Layer Capacitance of Zeolite-Templated Carbon in Organic Electrolyte

Abstract: Downlo Electrical Double-Layer Capacitance of Zeolite-Templated Carbon in Organic Electrolyte C. Portet,* Z. Yang, Y. Korenblit, Y. Gogotsi,** R. Mokaya, and G. Yushin A. J. Drexel Nanotechnology Institute and Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

An in situ Raman spectroscopy study of stress transfer between carbon nanotubes and polymer.

Abstract: The transfer mechanism of applied stress in single-wall carbon nanotube (SWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites was investigated using in situ Raman spectroscopy on composite fibers. These SWCNT/PMMA nanocomposite fibers have no specific SWCNT-polymer interactions and the high degree of nanotube alignment minimizes the contributions from nanotube-nanotube interactions. Although tensile testing found significantly improved overall mechanical properties of the fibers, effective stress transfer to SWCNTs is limited to a small strain regime (epsilon<0.2%). At higher strains, the stress on the SWCNTs decreases due to the slippage at the nanotube-polymer interface. Slippage was also evident in scanning electron micrographs of fracture surfaces produced by tensile testing of the composite fibers. Above epsilon = 0.2%, the strain-induced slippage was accompanied by irreversible responses in stress and Raman peak shifts. This paper shows that efficient stress transfer to nanotubes as monitored by Raman spectroscopy is crucial to improving the mechanical properties of polymer nanocomposites and to detecting internal damage in nanocomposites.

Capacitance of KOH activated carbide-derived carbons.

Abstract: Chemical activation of CDC leads to capacitance values in an organic electrolyte as high as 180 F/g, 30% larger than those of as-produced samples, due to the surface area and microporosity development occurring as a consequence of the activation.

Purification of carbon nanotubes by dynamic oxidation in air

Abstract: We describe a new approach to the purification of single-walled carbon nanotubes (SWCNTs), based on the selective oxidation of carbonaceous impurities by heating at a constantly increasing temperature (i.e. dynamic oxidation) in air. Using UV-VIS-NIR spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM) we demonstrate the superior purity of dynamically oxidized SWCNTs. In addition to being faster than other methods, dynamic oxidation allows for an efficient removal of carbonaceous impurities without significant loss of nanotubes. It is hypothesized that the advantages of dynamic oxidation arise from the exposure of the raw material to a wider range of temperatures than in conventional isothermal oxidation.

Pseudocapacitive Behavior of Carbon Nanoparticles Modified by Phosphomolybdic Acid

Abstract: Chemically modified carbon nanomaterials, such as nanodiamond (ND) soot, onionlike carbon (OLC), and carbon nanotubes (CNTs), were investigated as electrodes for electrochemical capacitors in high rate applications, that is, applications that drain power very fast. A layer of Keggin-type polyphosphomolybdate (PMo 12 ) was coated on carbons through "layer-by-layer" deposition by alternating electrostatic adsorption of cationic [i.e., poly(diallyldimethylammonium)chloride] and anionic (i.e., PMo 12 ) species to add pseudocapacitance to improve current response and increase capacitance. This modification was successful on OLCs and CNTs but not on ND soot. This difference is due to variations in surface chemistry, structure, and sp 2 /sp 3 content of those materials. In particular, the modified OLC exhibited a 20% increase in capacitance with up to 600 mF/cm 2 capacitance at 5 V/s, illustrating its high rate capability.

Deformation of Carbon Nanotubes by Exposure to Water Vapor

Abstract: The condensation of water inside multiwalled carbon nanotubes has been monitored and controlled using environmental scanning electron microscopy. Undersaturated vapor condenses inside nanotubes and forms nanometer-thick water films. Simultaneously, nanotubes deform and decrease their apparent diameter. When the vapor pressure in the chamber approaches the saturation pressure, we observe the formation of menisci and spontaneous buckling of the nanotubes. We derive a criterion of the buckling instability caused by capillary condensation. Remarkably, the buckling criterion appears to be independent of the meniscus shape. Using our experiments and models, we estimated the circumferential Young's modulus of large-diameter carbon nanotubes with disordered wall structure produced by the chemical vapor deposition method (CVD) to be E(thetatheta) approximately 13-18 MPa. It appears to be at least 2 orders of magnitude lower than the longitudinal modulus of nanotubes produced by arc discharge or catalytic CVD methods. The reported experiments and proposed theory suggest possible applications of "soft" nanotubes as sensors to probe minute concentrations of absorbable gases and vapors.

Manufacturing Nanosized Fenofibrate by Salt Assisted Milling

Abstract: Purpose The aim of this study is to develop a new process for manufacturing a nano-sized form of the popular cholesterol-reducing drug fenofibrate which can be implemented on industrial scale with minimal changes of currently used production schemes.

Metal or metal oxide deposited fibrous materials

Abstract: A method for electrospraying nanosized metal or metal oxide particles onto a substrate. A metal oxide deposited fibrous material comprising a substrate, fibers and metal oxide particles may be made using the method. The material may be a flexible and porous fibrous matrix on which metal oxide particles may be uniformly deposited on a surface thereof. In an exemplary embodiment, the invention is directed to an electrospun nanofibrous material on which electrosprayed photocatalytic metal oxide particles are uniformly deposited without agglomeration.

Effects of Deposition Conditions on the Structure and Chemical Properties of Carbon Nanopipettes

Abstract: Carbon nanopipettes (CNPs) are integrated devices combining a nanometer-size carbon tip with a glass pipette. The carbon tip is produced by catalytic CVD. In this paper, it is demonstrated that the structure of the CNPs can be controlled by varying the synthesis parameters. Increased carbon graphitization is observed as the synthesis temperature increases from 890 °C to 950 °C. A similar effect is achieved by lowering the carbon precursor (methane) concentration from 60% to 20%. Changes in the amount of catalyst do not have a significant effect on the carbon graphitization. At the same time, CNPs with relatively large amounts of hydrogen bonds on the surface are obtained by using a high methane concentration. This finding is used to facilitate the functionalization of the CNPs with gold nanoparticles.

Method for Making Carbon Nanotubes with Embedded Nanoparticles

Abstract: The invention concerns methods for producing carbon nanotubes with embedded nanoparticles comprising providing a template comprising an anodized aluminum oxide membrane with a pore diameter of 20-200 nm; contacting the template with a solution containing nanoparticles; exposing the template and solution containing nanoparticles to sonication; removing the template from the solution; forming a carbon structure via chemical deposition of carbon on said template; and removing the template by exposing the template to a basic solution.

Titania dispersion and method for making

Abstract: A novel method for preparing a titania dispersion by blending two different titania dispersions synthesized by a solvothermal process and a hydrolysis process. The titania dispersion has a plurality of titania particles substantially uniformly dispersed therein and can be blended to provide a high concentration of titania with an anatase crystalline structure to provide the desired level of photocatalytic activity. The present invention also permits the preparation of transparent titania dispersions. The solution may be used for various decontamination and clean energy generation applications.

Nano discharges in liquids

Abstract: The present invention is direct to a nano-probe corona tool and uses thereof. A nano-probe corona tool is disclosed having a tip with a diameter in the nano-scale, typically around 100 nm. The nano-probe corona tool is constructed of electrically conductive material. On the other end of the tool, a pulsed voltage source outputs a pulsed voltage to generated a pulsed electrical potential at the tip. The pulsed electrical potential at the tip causes a plasma discharge corona to occur. Uses of the corona discharge include, but are not limited to, optical emission spectroscopy, in the enhancement of deposition of coatings and nanoscale welding, e.g., nanotube or nanowires to a contact pad and welding two nanowires together, and in nanoscale surgery. For example, a nano-probe comprising CNTs may be inserted into cell membranes. The resulting corona discharge may be used to destroy tumors within the cell.

Supercapacitor compositions, devices and related methods

Abstract: Disclosed are supercapacitor materials comprising compositions having pores that are optimally sized to maximize capacitance Also disclosed are related methods for fabricating such supercapacitors