Graphitic Carbon Particles Research Articles

Physicochemical Characterization, and Relaxometry Studies of Micro-Graphite Oxide, Graphene Nanoplatelets, and Nanoribbons

The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn2+ ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

A binderless, covalently bulk modified electrochemical sensor: Application to simultaneous determination of lead and cadmium at trace level

A new type of covalent binderless bulk modified electrode has been fabricated and used in the simultaneous determination of lead and cadmium ions at nanomolar level. The modification of graphitic carbon with 4-amino salicylic acid was carried out under microwave irradiation through the amide bond formation. The electrochemical behavior of the fabricated electrode has been carried out to decipher the interacting ability of the functional moieties present on the modifier molecules toward the simultaneous determination of Pb2+ and Cd2+ ions using cyclic and differential pulse anodic stripping voltammetry. The possible mode of interaction of functional groups with metal ions is proposed based on the pKa values of the modifier functionalities present on the surface of graphitic carbon particles. The analytical utility of the proposed sensor has been validated by measuring the lead and cadmium content from pretreated waste water samples of lead acid batteries.

Porous Graphitized Carbon Monolith as an Electrode Material for Probing Direct Bioelectrochemistry and Selective Detection of Hydrogen Peroxide

For the first time, graphitized carbon particles with a high surface area have been prepared and evaluated as a new material for probing direct electrochemistry of hemoglobin (Hb). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging revealed that the carbon monolithic skeleton was constructed by a series of mesopores with irregular shapes and an average pore diameter of ~5.6 nm. With a surface area of 239.6 m(2)/g, carbon particles exhibited three major Raman peaks as commonly observed for carbon nanotubes and other carbon materials, i.e., the sp(3) and sp(2) carbon phases coexisted in the sample. A glassy carbon electrode modified with carbon monoliths and didodecyldimethylammonium bromide exhibited direct electron transfer between Hb molecules and the underlying electrode with a transfer rate constant of 6.87 s(-1). The enzyme electrode displayed a pair of quasi-reversible reduction-oxidation peaks at -0.128 and -0.180 V, reflecting the well-known feature of the heme [Fe(3+)/Fe(2+)] redox couple: a surface-controlled electrochemical process with one electron transfer. This reagentless biosensing approach was capable of detecting H(2)O(2), a simple molecule but plays an important role in analytical and biological chemistry, as low as 0.1 μM with linearity of 0.1-60 μM and a response time of <0.8 s, comparing favorably with other carbon based electrodes (5 s).

An Optical Fiber Sensor for Measuring Light Absorption in Suspension Solutions

An optical fiber sensor based on attenuated total reflectance (ATR) for extraction chemical information from highly scattering turbid materials has been evaluated. The influence of particles on bulk absorption and ATR transmitted spectra of micron-sized graphite flakes and spherical glassy carbon suspensions were investigated. The ATR transmitted spectra of coiled fiber-optic sensor in those suspensions with various concentrations are insensitive to scattering of suspended particles, especially for graphite flake suspensions. The reason for different influence of graphite flakes and spherical glassy carbon particles suspensions on e ATR spectra analyzed. This study demonstrates that fiber-optic sensor based on ATR technique is a feasible technique in application for monitoring turbid suspensions.

Functionalization/passivation of porous graphitic carbon with di- tert-amylperoxide

Porous graphitic carbon (PGC) particles were functionalized/passivated in situ in packed beds at elevated temperature with neat di- tert-amylperoxide (DTAP) in a column oven. The performance of these particles for high performance liquid chromatography (HPLC) was assayed before and after this chemistry with the following analytes: benzene, toluene, ethyl benzene, n-propyl benzene, n-butyl benzene, p-xylene, phenol, 4-methylphenol, phenetole, 3,5-xylenol, and anisole. After the first functionalization/passivation, the retention factors, k, of these compounds decreased by about 5% and the number of theoretical plates ( N) increased by ca. 15%. These values of k then remained roughly constant after a second functionalization/passivation but a further increase in N was noticed. In addition, after each of the reactions, the peak asymmetries decreased by ca. 15%, for a total of ca. 30%. The columns were then subjected twice to methanol at 100 °C for 5 h at 1 mL/min. After these stability tests, the values of k remained roughly constant, the number of plates increased, which is favorable, and the asymmetries rose and then declined, where they remained below the initial values for the unfunctionalized columns. Functionalized and unfunctionalized particles were characterized by scanning electron microscopy and BET measurements, which showed no difference between the functionalized and unfunctionalized materials, and X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), where ToF-SIMS suggested some chemical differences between the functionalized and unfunctionalized materials. In particular ToF-SIMS suggested that the expected five-carbon fragments from DTAP exist at higher concentrations on DTAP-functionalized PGC. First principle calculations on model graphitic surfaces suggest that the first addition of a DTAP radical to the surface proceeds in an approximately isothermal or slightly favorable fashion, but that subsequent DTAP additions are then increasingly thermodynamically favorable. Thus, this analysis suggests that the direct functionalization/passivation of PGC with DTAP is plausible. Chemometric analyses of the chromatographic and ToF-SIMS data are also presented.

Thermal Modulation for Multidimensional Liquid Chromatography Separations Using Low-Thermal-Mass Liquid Chromatography (LC)

We report on a proof-of-principle experiment with a novel thermal modulation device with potential use in two-dimensional liquid chromatography (LC × LC) systems. It is based on the thermal desorption concept used in two-dimensional gas chromatography (GC × GC) systems. Preconcentration of neutral analytes eluting from the first dimension column is performed in a capillary "trap" column packed with highly retentive porous graphitic carbon particles, placed in an aluminum low-thermal-mass LC heating sleeve. Remobilization of the trapped analytes is achieved by rapidly heating the trap column, by applying temperature ramps up to +1200 °C/min. Compared to the nonmodulated signal, the presented thermal modulator yielded narrow peaks, and a concentration enhancement factor up to 18 was achieved. With a thermally modulated LC separation of an epoxy resin, it is shown that when the thermal modulation is applied periodically, the trapped and concentrated molecules can be released periodically and that the modulating interface can both serve as a preconcentration device and as an injector for the second dimension column of an LC × LC setup. Because of the thermal modulation, a high-molecular-weight epoxy resin could be adequately separated and the different fractions were identified with a GPC analysis, as well as an offline second dimension LC analysis.

Microwave plasma chemical vapor deposition of graphitic carbon thin films

Thin layers of graphitic carbon were produced from solid organic precursors by a one-step microwave plasma chemical vapor deposition method. Low-pressure Ar-plasma and strong electromagnetic radiation led to the rapid evaporation and pyrolysis of organic precursors at relatively low temperatures, yielding uniform films of nanometer-sized graphitized carbon particles. The structure and morphology of the carbon films were examined using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. A direct correlation between electrical conductivity of graphitic thin films and their structure was established.

Synthesis of graphitic carbon particle chains at low temperatures under microwave irradiation

Chains of graphitic carbon particles were formed by microwave irradiation of polyethylene glycol at temperatures between 160 and 220 °C for 40 min, in the absence of a catalyst. Chains were comprised of individual particles ranging in size from 340 to 620 nm; particle size increased with synthesis temperature. The D/G ratio measured by Raman spectroscopy was 0.91, indicative of a mixture of amorphous and graphitic material. SEM, TEM and TGA measurements confirmed this. Our experiments show that the chains are an intermediate product, which when heated further under hydrothermal conditions, produce MWNTs.

Single-Walled Carbon Nanotubes Prepared by Large-Scale Induction Thermal Plasma Process: Synthesis, Characterization, and Purification

Characterization and purification studies have been performed on the single-walled carbon nanotubes (SWNTs), prepared by the large-scale (i.e., at production rates of ∼100 g h−1) induction thermal plasma process. The main impurities present in the as-produced soot materials are first identified by various material analyses and turn out to be amorphous carbon, graphitic carbon particles, and metal/metal−oxide catalysts, but without significant content of fullerenes. In particular, the amounts of graphitic particles present were high in comparison with those of other plasma arc or laser-grown SWNTs, and it is believed that these graphitic particles mainly originate from the remains of the feedstock materials. On the basis of this observation, different purification protocols have been explored by combining the two-step processes of thermal oxidation in air and liquid oxidation in a variety of acids. At each step of the purification, the changes in the SWNT samples are monitored by various analytical techniques, and the results reveal that the air oxidation at 350 °C for 1 h, followed by refluxing in 7 M HNO3 for 6 h, provides for the best efficiency in conducting the purification of the thermal plasma-grown SWNT. The material properties of the purified samples, such as the electrical resistivity and the specific surface area (SSA), have also been analyzed by using the Brunauer−Emmett−Teller (BET) and the four-probe methods, the measured values being ∼500 m2 g−1 and ∼2 × 10−3 Ω cm, respectively.

Reaction of graphite fluoride with NaOH–KOH eutectic

Graphite fluoride has been generally considered chemically inert against strong alkalis under ambient conditions. In the present study we demonstrate that treatment of graphite fluoride with eutectic NaOH–KOH mixture at 250 °C induces dramatic structural and textural changes in the solid as evidenced by XRD, FT-IR, Raman, UV–vis absorption and fluorescence and microscopy techniques (TEM, AFM). The reaction proceeds in the molten state leading to water-soluble, graphitized carbon particles which unlike graphite fluoride, adopt a variety of morphologies, like platy, tetragonal, triangular, discoid and spherical. The resulting carbon particles are dispersible in water and fluoresce under UV excitation.

Dielectric Properties of PMMA/Soot Nanocomposites

Dielectric analysis (DEA) of relaxation behavior in poly(methyl methacrylate) (PMMA) soot nanocomposites is described herein. The soot, an inexpensive material, consists of carbon nanotubes, amorphous and graphitic carbon and metal particles. Results are compared to earlier studies on PMMA/multi-walled nanotube (MWNT) composites and PMMA/single-walled nanotube (SWNT) composites. The beta relaxation process appeared to be unaffected by the presence of the soot, as was noted earlier in nanotube composites. The gamma relaxation region in PMMA, normally dielectrically inactive, was "awakened" in the PMMA/soot composite. This occurrence is consistent with previously published data on nanotube composites. The dielectric permittivity, s', increased with soot content. The sample with 1% soot exhibited a permittivity (at 100 Hz and 25 degrees C) of 7.3 as compared to 5.1 for neat PMMA. Soot increased the dielectric strength, deltaE, of the composites. The 1% soot sample exhibited a dielectric strength of 6.38, while the neat PMMA had a value of 2.95 at 40 degrees C. The symmetric broadening term (alpha) was slightly higher for the 1% composite at temperatures near the secondary relaxation and near the primary relaxation, but all samples deviated from symmetrical semi-circular behavior (alpha = 1). The impact of the soot filler is seen more clearly in dielectric properties than in mechanical properties studies conducted earlier.

Carbon films grown on Pt(1 1 1) as supports for model gold catalysts

Carbon films were grown on a Pt(1 1 1) single crystal by ethylene decomposition at elevated temperatures (1000–1300 K). Depending on the preparation conditions, different carbon structures formed on the metal surface such as flat and curved graphitic layers, carbon particles and carbon nanowires. Although these carbon films exhibited a high density of surface defects, gold interacted only weakly with the carbon surface. CO adsorption on the Au/carbon systems was very similar to that observed for various Au/oxide systems previously studied. This finding strongly indicates that CO adsorption on gold is essentially independent of the nature of support.

Surface‐enhanced Raman scattering studies on chemically transformed carbon nanotube thin films

AbstractWe review our experimental data obtained by Raman spectroscopy on single‐walled carbon nanotubes (SWNTs) using surface‐enhanced Raman scattering (SERS). We focused on the study of the dependence of the SERS spectra of SWNTs on both the rough metallic substrate type and the film thickness. In particular, we show that degradation of the nanotubes, mainly metallic, occurs for very thin films with the formation of graphitic, fullerene‐like or amorphous carbon particles. We show also that SWNTs reacting with H2SO4 form a salt of the hydrogensulfate type similar to that resulting from graphite–H2SO4 interaction. SWNTs exhibit a complicated spectroelectrochemical behavior in aqueous and non‐aqueous H2SO4 solutions that depends also on the sweep potential range. We demonstrate that the oxidation–reduction processes have a quasi‐reversible or irreversible character. Finally, SERS studies on compressed SWNTs in different host matrices, inorganic and organic, reveal nanotube breaking and that tube fragments may react or not with the host matrix used. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Growth of Single-Walled Carbon Nanotubes by the Rapid Heating of a Supported Catalyst

Single-walled carbon nanotubes (SWNTs) have been synthesized by the rapid injection of a nickel formate/silica gel catalyst/support into a hot fluidized-bed reactor. The initial rapid heating of the catalyst in the hydrocarbon feedstock was found to be essential for the nucleation of SWNTs since only amorphous or graphitic carbon particles were formed without it. These results suggest that the rapid heating of the catalyst precursor enables the formation of the small metal particles required for SWNT growth, probably due to the accelerated thermal decomposition of the catalyst precursor and enhanced nucleation rate. The growth of the SWNTs was investigated by the adoption of different methods for introducing the catalyst, and by varying the synthesis parameters including the catalyst loading, hydrocarbon gas flow rate, and concentration. The results found that SWNTs formed only under certain reaction conditions. The nanotubes produced were characterized by electron microscopy and Raman spectroscopy.

Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints

We present new interstellar dust models which have been derived by simultaneously fitting the far-ultraviolet to near-infrared extinction, the diffuse infrared (IR) emission and, unlike previous models, the elemental abundance constraints on the dust for different interstellar medium abundances, including solar, F and G star, and B star abundances. The fitting problem is a typical ill-posed inversion problem, in which the grain size distribution is the unknown, which we solve by using the method of regularization. The dust model contains various components: PAHs, bare silicate, graphite, and amorphous carbon particles, as well as composite particles containing silicate, organic refractory material, water ice, and voids. The optical properties of these components were calculated using physical optical constants. As a special case, we reproduce the Li & Draine (2001) results, however their model requires an excessive amount of silicon, magnesium, and iron to be locked up in dust: about 50 ppm (atoms per million of H atoms), significantly more than the upper limit imposed by solar abundances of these elements, about 34, 35, and 28 ppm, respectively. A major conclusion of this paper is that there is no unique interstellar dust model that simultaneously fits the observed extinction, diffuse IR emission, and abundances constraints.

Three nanostructured graphitic particles and their growth mechanisms from high-temperature carbon vapor confined by Ar gas

CO 2 laser vaporization of graphite was carried out in the presence of high pressure Ar gas up to 0.8 MPa. We compared transmission electron microscope images and Raman spectra of deposited particles and luminous laser plumes of vaporized and clustered carbon species. We discuss the growth mechanisms of three graphitic carbon particles, a single-wall carbon nanohorn aggregate, a platelet graphite particle, and a polyhedral graphite particle, grown depending on the confinement of the Ar atmosphere. The formation of graphitic sheet or shell structures, dependent on resident carbon densities and their temperature gradient, is thought to begin from supersaturated hot carbon vapor up to about 3000 °C and leads to the growth of the three graphitic particles.

Forming multiwalled carbon nanotubes by the thermal decomposition of Mo(CO) 6

Multiwalled carbon nanotubes (MWCNTs) have been obtained by decomposing molybdenum hexacarbonyl under air or argon in a closed cell. In addition to the carbon nanotubes (CNTs), Mo 2C was obtained. A high percentage of CNT was obtained from only a few graphitic carbon particles. Our proposed mechanism suggests that CNT is formed via the Boudard reaction as well as by the reduction of CO by Mo.

In situ nuclear magnetic resonanceinvestigations of lithium ions in carbon electrode materialsusing a novel detector

The reversible electrochemical process (insertion/extraction) oflithium ions in graphitic carbon was monitored in situ for the firsttime by 7Li nuclearmagnetic resonance (NMR) spectroscopy using a novel NMR apparatus. Thecompression coin cell battery imager is a simple devicethat combines the functions of an electrochemical cell and an NMRdetector. A series of 7Li NMR spectra obtained for a blend ofspherical and flaky disordered graphitic carbon particles revealedtwo distinct chemical shift signatures for the lithium ions thatwere inserted and extracted in the first electrochemical cycle. Thelithium signal at ~50 ppm is consistent with the interplanesites for lithium ions on the sixfold axis between two stackedaromatic carbon rings aligned in registry. The second predominantlithium signal at ~12 ppm occurs in the chemical shift regionreported for high-stage lithiated graphite and a dispersion oflithium-ion sites found in disordered carbon matrices. In addition,we observed chemical shift signatures similar to those assignedto Li-7 nuclei in lithium oxide, lithium carbonate, lithium alkyls,and lithium alkoxides that occur near 0 ppm and represent lithiumnuclei that are irreversibly bound in the electrode/electrolyteinterphase. An increase in intensity in the spectral region that isnormally associated with irreversibly bound lithium was observedduring the first discharge cycle, as anticipated. However, the samepeaks in the spectrum unexpectedly diminished during the subsequentcharge cycle, suggesting that the interphase between the carbonelectrode and the electrolyte is built up over several cycles.

Field emission from polymer-converted carbon films by ultraviolet radiation

A polymer, poly(phenylcarbyne) (PPC), was converted to carbon film by ultraviolet pulsed-laser (KrF, λ=248 nm) irradiation in nitrogen atmosphere at room temperature. The irradiated PPC consisted of fine graphitic carbon particles of several tens of nm in size, and exhibited good field emission properties. Low turn-on emission field of 2 V/μm (at 1 nA/cm2), high emission current density of 20 mA/cm2 (at 12 V/μm), and high emission luminescent spots density of 104/cm2 were observed for the polymer film irradiated by a pulsed-laser fluence of 40 mJ/cm2. We demonstrate multiple-lines and 2×5 array field emission patterns using the laser irradiation of PPC.

Emission Imaging Spectroscopic and Shadowgraphic Studies on the Growth Dynamics of Graphitic Carbon Particles Synthesized by CO2 Laser Vaporization

Emission imaging spectroscopy and shadowgraphy were applied to study the growth of carbon particles synthesized by 20-ms CO2 laser-pulse irradiation at 0.5−1.5 × 105 W/cm2 onto a graphite target in an Ar gas atmosphere (300−760 Torr). Emission images of growing carbon clusters and/or particles in a vaporization plume, measured with a temporal resolution of 1.67 ms, showed a constricted structure near the target that expanded widely into the Ar gas environment. On the other hand, the emission images of C2, not showing the constricted structure, indicated its presence close to the target and expansion in a narrow region. When directly ejected and/or formed carbon species (C, C2, and C3 , respectively) with velocities of 0.3−2.6 × 103 cm/s depart from the graphite surface, the formation of hot carbon clusters and/or particles begins and continues in the expanding plume. In shadowgraph images, the formation of a mushroom cloud containing darkened areas and black spots (size < 1 mm), probably corresponding to ...