共查询到20条相似文献,搜索用时 15 毫秒
1.
Ali Shahverdi Keun Su Kim Yasaman Alinejad Gervais Soucy 《Journal of nanoparticle research》2012,14(2):660-10
A simple, cost-effective and energy-efficient approach was developed for in situ purity enhancement and surface modification
of single-walled carbon nanotubes (SWCNTs) produced using an induction thermal plasma process. In this process, SWCNT-containing materials are thermally treated with oxygen flow inside a filtration chamber, while they are assembled into the
sheets during the synthesis process. Owing to selective thermal oxidation, the amount of amorphous carbon was significantly
reduced in the final product resulting in higher purity SWCNT-containing materials. Parametric study indicated that the amorphous
carbon content was noticeably diminished in the product at an oxygen volume concentration of 10% in the synthesis system.
Raman analysis indicated a decrease in the population of the SWCNTs with diameters smaller than 1.3 nm after in situ exposure
to 10 vol.% of oxygen. In addition to the successful reduction of amorphous carbon content, the oxygen-functionalized SWCNTs
were also observed in the final product using this process. 相似文献
2.
A CoSb3/nano-carbon-web composite was synthesized by an in situ method using polypropylene as both the reductive agent and carbon source. Hydrogen and carbon from the pyrolysis of polypropylene provide a strong reductive atmosphere and ensure the reduction of Co2+ (and Sb3+) to form CoSb3, and the residual carbon would in situ wrap around the freshly crystallized CoSb3. Electrochemical measurements show that CoSb3/nano-carbon-web as Li-ion battery anode reaches an initial charge capacity of 770 mA hg?1 and remains above 430 mA hg?1 after 20 cycles. The in situ synthesis route has the potential as a general method for the preparation of other metal (or alloy)/nano-carbon-web composites. 相似文献
3.
The electron concentration and temperature are measured when elements having various ionization potentials are introduced
into the carbon-helium plasma that forms in a high-frequency atmospheric-pressure arc discharge. The effect of the introduced
elements on the relative fullerene content in a carbon condensate is also studied. The plasma parameters are determined by
in situ emission spectral analysis during the synthesis of fullerene derivatives with scandium, sodium, and silicon. The variation
of the atomic and molecular line intensities of the plasma radiation with the distance from the carbon-arc axis is investigated
upon the introduction of various doping substances. The optimal temperature conditions for the synthesis of fullerene derivatives
with Sc, Na, and Si are found. 相似文献
4.
《Journal of Physics and Chemistry of Solids》2001,62(9-10):1561-1565
Electron beam induced formation of carbon nanorods was realized in situ under high resolution scanning electron microscopy (HRSEM). When a CVD deposited carbon nanotube sample was irradiated with an electron beam in an HRSEM, progressive etching of the sample, expanding of the nanotubes, and formation of additional nanorods have been observed. Transmission electron microscopy study revealed typical nanorods of 20 nm in diameter and with amorphous structure. The direct observation of the synthesis of nanorods under electron microscopy manifests the possibility of nano-machining of such nanomaterials using electron beams. This may lead to future integration and networking of nanostructures of different functionalities, which is crucial for nanotechnology. 相似文献
5.
A novel continuous process is used for production of carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CVD) of methane on iron floating catalyst in situ deposited on MgO in a fluidized bed reactor. In the hot zone of the reactor, sublimed ferrocene vapors were contacted with MgO powder fluidized by methane feed to produce Fe/MgO catalyst in situ. An annular tube was used to enhance the ferrocene and MgO contacting efficiency. Multi-wall as well as single-wall CNTs was grown on the Fe/MgO catalyst while falling down the reactor. The CNTs were continuously collected at the bottom of the reactor, only when MgO powder was used. The annular tube enhanced the contacting efficiency and improved both the quality and quantity of CNTs.The SEM and TEM micrographs of the products reveal that the CNTs are mostly entangled bundles with diameters of about 10-20 nm. Raman spectra show that the CNTs have low amount of amorphous/defected carbon with IG/ID ratios as high as 10.2 for synthesis at 900 °C. The RBM Raman peaks indicate formation of single-walled carbon nanotubes (SWNTs) of 1.0-1.2 nm diameter. 相似文献
6.
Shuyan Gao Hao Fan Xianjun Wei Liang Li Yoshio Bando Dmitri Golberg 《Particle & Particle Systems Characterization》2013,30(10):864-872
Electrocatalysts for the oxygen reduction reaction (ORR) present some of the most challenging vulnerability issues reducing ORR performance and shortening their practical lifetime. Fuel crossover resistance, selective activity, and catalytic stability of ORR catalysts are still to be addressed. Here, a facile and in situ template‐free synthesis of Pt‐containing mesoporous nitrogen‐doped carbon composites (Pt‐m‐N‐C) is designed and specifically developed to overcome its drawback as an electrocatalyst for ORR, while its high activity is sustained. The as‐prepared Pt‐m‐N‐C catalyst exhibits high electrocatalytic activity, dominant four‐electron oxygen reduction pathway, superior stability, fuel crossover resistance, and selective activity to a commercial Pt/C catalyst in 0.1 m KOH aqueous solution. Such excellent performance benefits from in situ covalent incorporation of Pt nanoparticles with optimal size into N‐doped carbon support, dense active catalytic sites on surface, excellent electrical contacts between the catalytic sites and the electron‐conducting host, and a favorable mesoporous structure for the stabilization of the Pt nanoparticles by pore confinement and diffusion of oxygen molecules. 相似文献
7.
Novel three-dimensional porous carbon network (3D-PC) anode was developed by a facile in situ NaCl-template method utilizing citric acid as carbon source. The synthesis process involves the dissolution of NaCl and citric acid in deionized water, citric acid coated on NaCl template during freeze-drying process, carbonization of the composites, and removal of the template with water. The resultant 3D-PC presents high electrical conductivity, large specific surface area, sufficient active sites, large interlayer distance, and high mechanical flexibility, which are contributed to the efficient Na-storage. Therefore, the 3D-PC anode displays enhanced rate performance of 101 mAh g?1 at 1000 mA g?1 and extremely long cycle life of 138 mAh g?1 after 2000 cycles at 200 mA g?1. The unique synthesis strategy coupled with the excellent Na-storage performance ensures 3D-PC a promising anode material for low-cost sodium-ion batteries. 相似文献
8.
The electron transport properties of two types of carbon-polyimide (C-PI) nanocomposite thin films have been evaluated. Conductive nanocomposites formed by incorporation of 30 nm carbon particles prior to polymer cross linking (ex situ formation) has been compared to high energy ion beam irradiation in situ formation of nanoscale carbon clusters within the polymer composite. Addition of carbon nanoparticles were able to reduce the resistivity by 13 orders of magnitude for 8 vol% carbon content. The irradiated in situ formed film showed a comparable resistivity to this 8% C-PI film. All the films exhibited negative temperature coefficient of resistance (NTCR) behaviour. While in the ex situ films the NTCR decreased progressively with increasing temperature above 350 K, the in situ film exhibited a constant NTCR value at ambient as well as elevated temperatures indicating that films formed by ion beam irradiation eliminate possible clustering of nanoparticles prior to crosslinking seen in the ex situ films. The optimum hop energies for the ex situ films ranged from 23.1 to 8.05 meV when carbon content increased from 1 to 8 vol% and the corresponding value for the in situ formed film was 34.94 meV. These films had appreciable NTCR values, and were evaluated for their thermistor behaviour as a class of material with potential for temperature sensing devices. 相似文献
9.
We report on the synthesis of tubular composite of doped polyaniline (PANI) with carboxylic groups contained multi-walled carbon nanotube (MWNTs) by in situ polymerization. Based on the interaction between aniline monomers and c-MWNTs , aniline molecules were adsorbed and polymerized on the surface of c-MWNTs . The structural characterization showed that tubular composites are core (c-MWNTs )-shell (doped-PANI) structures with diameters of several tens of nanometers, and lengths of up to several hundreds of nanometers. The conductivities of these tubular composites are several times higher than that of PANI without MWNT, which will offer new application possibilities. PACS 81.05.Qk; 81.05.Tp 相似文献
10.
《Current Applied Physics》2005,5(4):302-304
Multi-walled carbon nanotube (MWNT) nanocomposites with poly(methyl methacrylate) were prepared via both an in situ bulk polymerization and a suspension polymerization using a radical initiator of 2,2-azobisisobutyronitrile (AIBN). Prior to the synthesis, the MWNT was purified in an acidic solution to remove impurities such as metallic catalysts and amorphous carbons. The AIBN induced PMMA was grafted on the MWNT, which was confirmed by a Fourier transform infrared spectrometer (FT-IR). The composite morphology of the MWNT was observed by scanning electron microscopy (SEM). Electrical characteristics were further examined via both a four-probe method and a rotational rheometer equipped with a high voltage generator. 相似文献
11.
Cumulative and continuous laser vaporization synthesis of single wall carbon nanotubes and nanohorns
A. A. Puretzky D. J. Styers-Barnett C. M. Rouleau H. Hu B. Zhao I. N. Ivanov D. B. Geohegan 《Applied Physics A: Materials Science & Processing》2008,93(4):849-855
The conditions for the scaled synthesis of single wall carbon nanotubes (SWNTs) and single wall carbon nanohorns (SWNHs) by
laser vaporization at high temperatures are investigated and compared using in situ diagnostics. An industrial Nd:YAG laser
(600 W, 1–500 Hz repetition rate) with tunable pulse widths (0.5–50 ms) is utilized to explore conditions for high-yield production.
High-speed videography (50000 frames/s) of the laser plume and pyrometry of the target surface are correlated with ex situ
high resolution transmission electron microscopy analysis of the products for pure carbon targets and carbon/catalyst targets
to understand the effects of the processing conditions on the resulting nanostructures. Carbon is shown to self-assemble into
single-wall nanohorn structures at rates of ∼1 nm/ms, which is comparable to the catalyst-assisted SWNT growth rates. Two
regimes of laser ablation, cumulative ablation by multiple pulses and continuous ablation by individual pulses, were explored. Cumulative ablation with spatially overlapping 0.5-ms pulses is favorable for
the high yield and production rate of SWNTs at ∼6 g/h while continuous ablation by individual long laser pulses (∼20 ms) at
high temperatures results in the highest yield of SWNHs at ∼10 g/h. Adjustment of the laser pulse width is shown to control
SWNH morphology. 相似文献
12.
In order to use carbon nanotube (CNT)-supported catalyst as fuel cell electrodes, Pt-Ni-Fe/CNT/carbon paper (CP) electrode was prepared using an ethylene glycol reduction method. CNTs were directly synthesized on Ni-impregnated carbon paper, plain carbon cloth, and Teflonized carbon cloth using chemical vapor deposition. FESEM and TEM images and thermogravimetric analysis indicated that in situ CNT on carbon paper (ICNT/CP) possesses more appropriate structural quality and stronger adhesion to the substrate than other substrates. The contact angle analysis demonstrated that the degree of ICNT/CP surface hydrophobicity encountered a 24% increase in comparison to CP and promoted to superhydrophobicity from hydrophobicity. The polarization curves and electrochemical impedance spectroscopy results of the loaded Pt-Ni-Fe on in situ and ex situ CNT/CP illustrated that the power density increased and charge transfer resistance reduced compared to commercial Pt/C loaded on CP. The results can be attributed to the outstanding properties of CNTs and high catalytic activity of triple catalysts causing alloying of Pt with Ni and Fe, which makes them a proper candidate to be used as cathode electrodes in proton exchange membrane fuel cells. 相似文献
13.
A.A. Puretzky D.B. Geohegan X. Fan S.J. Pennycook 《Applied Physics A: Materials Science & Processing》2000,70(2):153-160
The key spatial and temporal scales for single-wall carbon nanotube (SWNT) synthesis by laser vaporization at high temperatures are investigated with laser-induced luminescence imaging and spectroscopy. Graphite/(Ni, Co) targets are ablated under typical synthesis conditions with a Nd:YAG laser at 1000 °C in a 2-in. quartz tube reactor in flowing 500-Torr Ar. The plume of ejected material is followed for several seconds after ablation using combined imaging and spectroscopy of Co atoms, C2 and C3 molecules, and clusters. The ablation plume expands in stages during the first 200 7s after ablation and displays a self-focusing behavior. Interaction of the plume with the background gas forms a vortex ring which segregates and confines the vaporized material within a ~1-cm3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 7s) and cobalt (2 ms) at 1000 °C. This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs over several seconds in a plume of mixed nanoparticles. By adjusting the time spent by the plume within the high-temperature zone using these in situ diagnostics, single-walled nanotubes of controlled (~100 nm) length were grown and the first estimate of a growth rate on single laser shots (0.2 7m/s) was obtained. 相似文献
14.
Hye Jin Yoo Yong Chae Jung Nanda Gopal Sahoo 《Journal of Macromolecular Science: Physics》2013,52(4):441-451
In‐situ polymerization was employed to achieve well‐dispersed carbon nanotube‐reinforced polyurethane composites. In‐situ polymerization showed predominant as primarily dispersal of carbon nanotubes in the matrix polymer according to scanning electron microscopy (SEM) observation and atomic force microscopy (AFM) images. Differential scanning calorimetry (DSC) results suggested that the addition of multi walled nanotubes (MWNTs) into polyurethane increased the rate of crystallization, this effect being more significant in polyurethane (PU)‐MWNT composite, which was prepared by an in‐situ polymerization process. The composites obtained by in‐situ polymerization showed enhanced mechanical properties as well as good electroactive shape memory. The original shape of the sample was almost recovered with bending mode when an electric field of 50 V was applied. 相似文献
15.
The synthesis of diamond at high pressure and high temperature and the discovery of fullerenes and carbon nanotubes are among the most important achievements in carbon science. In the present work, we report the synthesis of diamond from carbon nanotubes at 4.5 GPa and 1300°C. Under these conditions, no diamond crystals were obtained when graphite was used as the starting material. The detailed investigation shows that at high pressure and high temperature carbon nanotubes first transform into quasi-spherical onion-like structures and then into diamond crystals. Our work suggests that carbon nanotubes can be used for the synthesis of high-quality diamond crystals at lower pressure and temperature. 相似文献
16.
Polyaniline-coated multi-walled carbon nanotubes were prepared by in situ chemical polymerization method for the novel sensing materials of ammonia gas. The thickness of the polyaniline coatings was controlled by the oxyfluorination treatment on the multi-walled carbon nanotubes. The oxyfluorination with higher oxygen content produced the more hydrophilic functional groups on the surface of multi-walled carbon nanotubes. Both the resistivity change and the response time were significantly improved with high repeatability using the more hydrophilic multi-walled carbon nanotubes which were modified with oxyfluorination. 相似文献
17.
Epitaxial Growth of Urchin‐Like CoSe2 Nanorods from Electrospun Co‐Embedded Porous Carbon Nanofibers and Their Superior Lithium Storage Properties
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Jinkai Wang Hongkang Wang Daxian Cao Xuan Lu Xiaogang Han Chunming Niu 《Particle & Particle Systems Characterization》2017,34(10)
A facile synthesis of porous graphitic carbon nanofibers (CNFs) with encapsulated Co nanoparticles (denote as Co@CNFs) via electrospinning and subsequent annealing is reported. The in situ generated Co nanoparticles (NPs) promote the CNF graphitization under a low temperature of 700 °C, which simultaneously results in the porous structure of the Co@CNFs with a large surface area (416 m2 g?1). Furthermore, urchin‐like CoSe2 nanorods are epitaxially grown from the Co@CNFs via a facile hydrothermal selenation, in which the embedded Co NPs serve as directing seeds and sacrificial Co‐source, and CoSe2 nanorods are rooted into the CNFs (denote as CoSe2@CNFs). When used as anode materials for lithium ion batteries, the CoSe2@CNFs demonstrate superior lithium storage properties, delivering a high reversible capacity of 1405 mA h g?1 after 300 cycles at a current density of 200 mA g?1. The enhanced lithium storage performance can be attributed to the novel hybrid structure, namely, the porous and graphitic CNFs can not only facilitate the charge/ion transfer but also buffer the volume changes of the electrode during lithiation/delithiation processes. More importantly, a general strategy is provided to graphitize amorphous carbon materials via the use of in situ generated transition metal nanoparticles as catalyst. 相似文献
18.
P. R. Raimann N. S. Hochgatterer C. Korepp K. C. Möller M. Winter H. Schröttner F. Hofer J. O. Besenhard 《Ionics》2006,12(4-5):253-255
This paper introduces a novel in situ method for monitoring electrode reactions in lithium-ion batteries parallel to the electrochemical experiment (in situ electrochemical environmental scanning electron microscopy). Alloy and alloy/carbon composite electrodes suffer from large volume changes followed by cracking and loss of electronic contact of the particles. The measurement setup and the cell principle are described. Reactions occurring on the surface of a Sn/carbon/binder composite electrode during the lithiation process are presented for illustration. The new method provides insight into the dynamics of electrode reactions, shape changes of particles, spatial distribution of solid electrolyte interphase reactions, etc. 相似文献
19.
The procedure of aperture synthesis by an incoherent source during displacement of the receiving system in space is considered.
The advantages of the method are the possibility of aperture synthesis with the help of antenna arrays consisting of two receivers
and its applicability to both the source of a quasimonochromatic signal and that possessing a continuous spectrum. The method
is applicable with the same limitations as the known methods using the procedures of signal phasing. The results of mathematical
simulation of the synthesis upon location of two sources with close frequencies at different distances and in the presence
of noise, as well as the results of the in situ experiment with a reverberation interference, are given. The algorithm for
decreasing the time of aperture synthesis without resolution deterioration is proposed and tested in situ. 相似文献
20.
A. V. Zaikovskii V. A. Mal’tsev S. A. Novopashin 《Journal of Engineering Thermophysics》2010,19(2):94-101
The possibilities of plasma-chemical synthesis of carbon and composite nanomaterials in a dc electric arc are demonstrated
in experiments. Synthesis of tungsten carbide nanoparticles is implemented, along with the known processes of synthesis of
carbon nanostructures and metal nanoparticles. 相似文献