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PubMed2002

Sorption kinetics of heavy oil into porous carbons.

Sorption kinetics of heavy oil into porous carbons was evaluated by a concept of liquid sorption coefficient obtained from the weight increase of heavy oil with sorption time, which was measured by a wicking test. Exfoliated graphite, carbonized fir fibers and carbon fiber felts were used as porous materials. It was found that the liquid sorption coefficient of fibrous carbons was twice larger than that of exfoliated graphite. Such a difference in the liquid sorption coefficient between the exfoliated graphite and two fibrous carbons was caused by a difference in effective sorption porosity and tortuosity between them. For the exfoliated graphite and carbonized fir fibers, the liquid sorption coefficient and the effective sorption porosity were strongly dependent on their density. The maximum values of both liquid sorption coefficient and effective sorption porosity of the exfoliated graphite were shown at the bulk density around 16 kg/m3. The liquid sorption coefficient of the carbonized fir fibers increased with increasing the density in the range from 6 to 30 kg/m3. When the carbonized fir fibers were densified above 30 kg/m3, the sorption rate was saturated. On the other hand, the sorption kinetics into the carbon fiber felt was almost independent of the bulk density, because the density of the carbon fiber felt is not effective for the pore structure. The effect of bulk density on the sorption kinetics could be supported from an analysis of pore structure of the porous carbons with different densities, which was measured by mercury porosimeter.

Adsorption↗

PubMed2002

Dimensional changes as a function of charge injection in single-walled carbon nanotubes.

Motivated by the central importance of charge-induced dimensional changes for carbon nanotube electromechanical actuators, we here predict changes in nanotube length and diameter as a function of charge injection for armchair and zigzag nanotubes having different diameters. Density functional theory with periodic boundary conditions is used, which we show provides results consistent with experimental observations for intercalated graphites. Strain-versus-charge relationships are predicted from dimensional changes calculated with a uniform background charge ("jellium") for representing the counterions. These jellium calculations are consistent with presented calculations that include specific counterions for intercalated graphite, showing that hybridization between the ions and the graphite sheets is unimportant. The charge-strain relationships calculated with the jellium approximation for graphite and isolated single-walled nanotubes are asymmetric with respect to the sign of charge transfer. The dependence of nanotube strain on charge approaches that for a graphite sheet for intermediate-sized metallic nanotubes and for larger diameter semiconducting nanotubes. However, the strain-charge curves strongly depend on nanotube type when the nanotube diameter is small. This reflects both the dependence of the frontier orbitals for the semiconducting nanotubes on the nanotube type and the pi-sigma mixing when the nanotube diameter is small.

Journal Article↗

PubMed2006

Molecular dynamics simulation study of the structure of poly(ethylene oxide) brushes on nonpolar surfaces in aqueous solution.

The structure of poly(ethylene oxide) (PEO, M(w) = 526) brushes of various grafting density (sigma) on nonpolar graphite and hydrophobic (oily) surfaces in aqueous solution has been studied using atomistic molecular dynamics simulations. Additionally, the influence of PEO-surface interactions on the brush structure was investigated by systematically reducing the strength of the (dispersion) attraction between PEO and the surfaces. PEO chains were found to adsorb strongly to the graphite surface due primarily to the relative strength of dispersion interactions between PEO and the atomically dense graphite compared to those between water and graphite. For the oily surface, PEO-surface and water-surface dispersion interactions are much weaker, greatly reducing the energetic driving force for PEO adsorption. This reduction is mediated to some extent by a hydrophobic driving force for PEO adsorption on the oily surface. Reduction in the strength of PEO-surface attraction results in reduced adsorption of PEO for both surfaces, with the effect being much greater for the graphite surface where the strong PEO-surface dispersion interactions dominate. At high grafting density (sigma approximately 1/R(g)(2)), the PEO density profiles exhibited classical brush behavior and were largely independent of the strength of the PEO-surface interaction. With decreasing grafting density (sigma < 1/R(g)(2)), coverage of the surface by PEO requires an increasingly large fraction of PEO segments resulting in a strong dependence of the PEO density profile on the nature of the PEO-surface interaction.

Journal Article↗

PubMed2006

Raman scattering from high-frequency phonons in supported n-graphene layer films.

Results of room-temperature Raman scattering studies of ultrathin graphitic films supported on Si (100)/SiO2 substrates are reported. The results are significantly different from those known for graphite. Spectra were collected using 514.5 nm radiation on films containing from n = 1 to 20 graphene layers, as determined by atomic force microscopy. Both the first- and second-order Raman spectra show unique signatures of the number of layers in the film. The nGL film analogue of the Raman G-band in graphite exhibits a Lorentzian line shape whose center frequency shifts linearly relative to graphite as approximately 1/n (for n = 1 omegaG approximately 1587 cm-1). Three weak bands, identified with disorder-induced first-order scattering, are observed at approximately 1350, 1450, and 1500 cm-1. The approximately 1500 cm-1 band is weak but relatively sharp and exhibits an interesting n-dependence. In general, the intensity of these D-bands decreases dramatically with increasing n. Three second-order bands are also observed (approximately 2450, approximately 2700, and 3248 cm-1). They are analogues to those observed in graphite. However, the approximately 2700 cm-1 band exhibits an interesting and dramatic change of shape with n. Interestingly, for n < 5 this second-order band is more intense than the G-band.

Journal Article↗

PubMed2003

Reconstructed mass-spectrometric pattern for characterization of carbon compounds in smoker's lung in situ.

BACKGROUND: Cigarette smoke is a major anthropogenic pollutant and contributes to the permanent load of ambient particulate matter in the air, particularly indoors. It is the leading risk factor for premature loss of life due to chronic bronchitis, emphysema and lung cancer. Smoker's lung and graphite pneumoconiosis are pathological states characterized by the deposition of carbonaceous particles. METHODS: Mass spectrometry was used to evaluate unstained lung sections obtained in vivo from a heavy smoker and a patient with occupationally acquired graphite pneumoconiosis. RESULTS AND DISCUSSION: The composition of carbon compounds deposited in lung tissue samples is demonstrated here for the first time. Thirty carbonaceous-containing microareas from ten biopsies (three areas per biopsy) of lung tissues were analyzed mass-spectrometrically. In each case, the samples were taken from a smoker's lung or those demonstrating a graphite pneumoconiosis. The lung-tissue samples were selected by light microscopy before they were evaporated for mass spectrometry. First-order criteria were anionic and cationic mass peaks which occur within the mass patterns in lung tissues of smoker's lung, although not in graphite pneumoconiosis. Second-order criteria were mass peaks from smoker's lung with standard deviations SD < or = 14% of the mean value. First and second-order mass peaks matched the mass peaks of experimental cigarette-smoke condensate in 9 out of 11 peaks. A software program was developed that enabled fast, automated recognition of the typical mass peaks, and thereby confirmed the histological diagnosis of smoker's lung. CONCLUSIONS: The analysis of carbonaceous particles within lung biopsies from a heavy smoker corresponded to the spectra of tobacco condensate and not to the investigated biopsies of graphite peneumoconiosis. RECOMMENDATION AND OUTLOOK: The analyses were performed in order to find out whether mass-spectrometric criteria exist for the differentiation of carbonaceous lung-tissue deposits. Mass spectrometry may be a valuable tool in determining the composition of carbon compounds deposited in human lung tissue. So far, qualitative assessment of the composition of deposits in lung tissue is only possible after the patient is deceased (autopsy).

Aged↗

PubMed2004

Formation and transformation of carbon nanoparticles under electron irradiation.

This article reviews the phenomena occurring during irradiation of graphitic nanoparticles with high-energy electrons. A brief introduction to the physics of the interaction between energetic electrons and solids is given with particular emphasis on graphitic materials. Irradiation effects are discussed, starting from microscopic mechanisms that lead to structural alterations of the graphite lattice. It is shown how random displacements of the atoms and their subsequent rearrangements eventually lead to topological changes of the nanoparticles. Examples are the formation of carbon onions, morphological changes of carbon nanotubes, or the coalescence of fullerenes or nanotubes under electron irradiation. Irradiation-induced phase transformations in nanoparticles are discussed, e.g. the transformation of graphite to diamond, novel metal-carbon phases in nanocomposite materials or modified phase equilibria in metal crystals encapsulated in graphitic shells.

Biocompatible Materials↗

PubMed1995

Atomic absorption spectrometric determination of cadmium and lead in human and artificial teeth by direct atomization technique.

A method of graphite furnace atomic absorption spectrometry (GFAAS) with a direct atomization technique has been developed for the determination of trace amounts of Cd and Pb in human teeth and artificial teeth. The samples were ground to a particle size of less than 10 microns and mixed with the same amount of graphite powder. One-half to 2 mg of mixed sample was weighed in a tared graphite cup and atomized in a cup-type graphite furnace according to the heating program that was established. Absorbances were determined by integration of the spectral lines in the absorbance vs time spectrum. Calibration was affected using aqueous standard solutions. The results for six human tooth samples and two artificial tooth samples were in good agreement with the values obtained by GFAAS for dissolved samples. The relative standard deviations were 3.1-12% (n = 10) for Cd (19-95 ng g-3) and 0.9-8.1% (n = 10) for Pb (1.43-6.32 micrograms g-3). The determination limits corresponding to twice the standard deviation (sigma, n = 10) for blank measurements were 13 pg for Cd and 53 pg for Pb.

Cadmium↗

PubMed2006

New redox mediator-modified polysulfone composite films for the development of dehydrogenase-based biosensors.

This work presents polysulfone membranes as new materials for the development of compact dehydrogenase-based biosensors. Composite films were prepared by mixing polysulfone with graphite and were deposited on epoxy-graphite composite electrodes. Redox mediators were successfully immobilized in the composite film leading to highly reproducible biosensors, without leakage of the immobilized species. This results in a more reliable analytical system as, at the same time, problems of electrode fouling related to the detection of the coenzyme nicotinamide adenine dinucleotide (NADH) on which is based the amperometric detection of dehydrogenase-based biosensors are avoided. Scanning electron microscopy was used to study the morphological characteristics of the surface and the cross-section of the polysulfone-graphite composite films. Several procedures to immobilize enzymes in these membranes were demonstrated. Glutamate dehydrogenase (GlDH) was immobilized as an example of dehydrogenase enzyme, in this case for the development of an ammonium biosensor. High sensitivity, good selectivity, wide linear ranges and short response times were obtained for the optimized sensors and biosensors. Their good performance combined with the simplicity of the construction method, make the polysulfone-graphite composite films attractive matrices for the development of new enzyme-based biosensors, especially those based on dehydrogenase enzymes.

Biosensing Techniques↗

PubMed2006

Substrate and surfactant effects on the glass-liquid transition of thin water films.

Temperature-programmed time-of-flight secondary ion mass spectrometry (TP-TOF-SIMS) and temperature-programmed desorption (TPD) have been used to perform a detailed investigation of the adsorption, desorption, and glass-liquid transition of water on the graphite and Ni(111) surfaces in the temperature range 13-200 K. Water wets the graphite surface at 100-120 K, and the hydrogen-bonded network is formed preferentially in the first monolayer to reduce the number of nonbonding hydrogens. The strongly chemisorbed water molecules at the Ni(111) surface do not form such a network and play a role in stabilizing the film morphology up to 160 K, where dewetting occurs abruptly irrespective of the film thickness. The surface structure of the water film formed on graphite is fluctuated considerably, resulting in deweting at 150-160 K depending on the film thickness. The dewetted patches of graphite are molecularly clean, whereas the chemisorbed water remains on the Ni(111) surface even after evaporation of the film. The abrupt drop in the desorption rate of water molecules at 160 K, which has been attributed to crystallization in the previous TPD studies, is found to disappear completely when a monolayer of methanol is present on the surface. This is because the morphology of supercooled liquid water is changed by the surface tension, and it is quenched by termination of the free OH groups on the surface. The surfactant methanol desorbs above 160 K since the hydrogen bonds of the water molecules are reconstructed. The drastic change in the properties of supercooled liquid water at 160 K should be ascribed to the liquid-liquid phase transition.

Adsorption↗

PubMed2003

The effect of the reinforcing carbon on the microstructure of pitch-based granular composites.

Carbon composites were prepared with four pitches (a commercial impregnating coal-tar pitch, two thermally treated pitches and an air-blown pitch) and four granular carbons (anthracite, graphite, green petroleum coke and foundry coke). Granular carbon/pitch proportions were optimized for each composite and differed in the characteristics of the single components. Interactions of the pitch with the granular carbons during pyrolysis and their subsequent effects on the microstructure of the final composite were monitored by light microscopy. The results show that the light texture of the matrix and the porosity of the composite depend not only on the chemical composition of the pitch but also on the specific granular carbon used as reinforcing material. The same pitch may generate different light textures depending on the characteristics of the carbon. Composites from thermally treated pitches and graphite show highly ordered matrices orientated in the direction of graphite planes. Graphite particles seem to exert a huge influence on mesophase development during the pyrolysis of the treated pitches, affecting not only the orientation of the mesophase, but also reducing the rate of mesophase formation. On the other hand, when green petroleum coke is used with the thermally treated pitches, matrices show a small size light texture, due to the high reactivity of the pitch in the presence of this granular carbon. The porosity of the composites is controlled by both the pitch and the granular carbon.

Carbon↗

PubMed2003

Fullerenes and interplanetary dust at the Permian-Triassic boundary.

We recently presented new evidence that an impact occurred approximately 250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a (3)He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earth's surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for (3)He vs. giant impact for fullerene).

Dust↗

PubMed2005

Surface characteristics of spacecraft components affect the aggregation of microorganisms and may lead to different survival rates of bacteria on Mars landers.

Layers of dormant endospores of Bacillus subtilis HA101 were applied to eight different spacecraft materials and exposed to martian conditions of low pressure (8.5 mbar), low temperature (-10 degrees C), and high CO(2) gas composition and irradiated with a Mars-normal ultraviolet (UV-visible- near-infrared spectrum. Bacterial layers were exposed to either 1 min or 1 h of Mars-normal UV irradiation, which simulated clear-sky conditions on equatorial Mars (0.1 tau). When exposed to 1 min of Mars UV irradiation, the numbers of viable endospores of B. subtilis were reduced three to four orders of magnitude for two brands of aluminum (Al), stainless steel, chemfilm-treated Al, clear-anodized Al, and black-anodized Al coupons. In contrast, bacterial survival was reduced only one to two orders of magnitude for endospores on the non-metal materials astroquartz and graphite composite when bacterial endospores were exposed to 1 min of Mars UV irradiation. When bacterial monolayers were exposed to 1 h of Mars UV irradiation, no viable bacteria were recovered from the six metal coupons listed above. In contrast, bacterial survival was reduced only two to three orders of magnitude for spore layers on astroquartz and graphite composite exposed to 1 h of Mars UV irradiation. Scanning electron microscopy images of the bacterial monolayers on all eight spacecraft materials revealed that endospores of B. subtilis formed large aggregates of multilayered spores on astroquartz and graphite composite, but not on the other six spacecraft materials. It is likely that the formation of multilayered aggregates of endospores on astroquartz and graphite composite is responsible for the enhanced survival of bacterial cells on these materials.

Bacillus subtilis↗

PubMed2004

[Probe into the platelets adhesion to carbonaceous biomaterials].

In order to clarify the mechanism of blood coagulation for carbonaceous biomaterials, the plasma rich in platelet was obtaining through the centrifugation of fresh human blood containing anticoagulant. Adhesive tests of platelets to surfaces of DLC, diamond film(DF) and graphite was carried out at 37 degrees C. Then, morphology observation, counting and deformation index calculation of the platelets adhering to surfaces of the three kinds of materials were analyzed by SEM. It has been shown that there is no any platelet on the surface of DLC, but on DF and graphite, a lot of platelets are observed with serious deformation of type III-V. The adhesive amounts of platelet on the surface of graphite are more than those on DF, but deformation index of platelets on the surface of DF is more than that on graphite. Three major conclusions have been obtained through comparative analyses with our previous researches and related literatures: (1) Adhesion, deformation and collection of platelets occurred in succession on material surfaces resulting from protein adsorption are the major mechanism of blood coagulation of carbonaceous materials; (2) Deformation degree of platelets is more important hemocompatibility index than consumption ratio of platelets for carbonaceous materials; (3) The purer the DLC, the better is the hemocompatibility. These conclusions possess important directive function for improving and designing carbonaceous materials used in artificial mechanical heart valves.

Biocompatible Materials↗

PubMed2006

[Analysis of FT-IR-ATR spectra of serum proteins adsorbed on carbonaceous materials].

To clarify the reason causing difference of serum proteins adsorbability on different carbonaceous materials, FT-IR-ATR spectra of human serum albumin (HSA) and human serum fibrinogen(HFG) before and after adsorbing on diamond like carbon film (DLC),diamond film (DF) and graphite were analyzed. It has been shown that there are hydrogen bond because of -NH at the interfaces of HSA-DLC, HFG-DF and HFG-graphite. Based on the results, earlier research conclusion that the adsorbability of HSA on DLC higher than that on DF and graphite, but on DF and graphite the adsorption of HFG takes precedence can be explained rationally.

Adsorption↗

PubMed1981

Mechanical properties of poly(methyl methacrylate) bone cements.

Samples of low viscosity poly(methyl methacrylate) (PMMA), graphite reinforced PMMA, and graphite reinforced low viscosity PMMA were evaluated for their compression strength and fracture toughness. These results were compared with two currently used plain PMMA bone cements. There were no statistically significant differences in compression strength between the five cements. Graphite reinforcement of plain cement produced a 32% increase in fracture toughness over plain cement. Graphite reinforcement of low viscosity cement also produced a significant increase in toughness (31%) over low viscosity cement with fiber reinforcement. However, low viscosity cement demonstrated significantly less fracture toughness than plain PMMA.

Analysis of Variance↗

PubMed2004

Dilatometric and mass spectrometric investigations on lithium ion battery anode materials.

Lithium ion batteries operate beyond the thermodynamic stability of the aprotic organic electrolyte used. In 1 M LiClO(4) propylene carbonate electrolyte, with and without the addition of ethylene sulfite as a film forming electrolyte additive, we have used in situ electrochemical dilatometry and on-line electrochemical mass spectrometry to study the volume expansion/contraction of graphitic anodes and the formation of propylene gas, which both can occur during the graphite anode reduction (charge) process. The combination of both methods allows us to get insights into the respective electrolyte reduction mechanisms. The results indicate that the major failure mechanisms of graphitic anodes in pure PC electrolyte can be attributed to the intercalation of solvated lithium ions and the formation of propylene gas, which causes the graphite particles to exfoliate and crack.

Journal Article↗

PubMed1996

Studies of critical factors in the determination of arsenic in Standard Reference Materials of Marine origin by ETAAS:;NMKL(*) interlaboratory study.

A study to determine factors which are known to influence the electrothermal atomic absorption (ETAAS) determination of As has been performed. The study has been carried out using five sample solutions of marine Standard Reference Materials distributed to four participating laboratories. Uncoated and pyrolytically coated graphite tubes with L'vov platform and Ni and Pd/Mg as chemical modifiers have been tested. No differences in results have been obtained between AAS instruments equipped with Zeeman correction or deuterium arc background correction. Small differences in concentration levels of arsenic as well as in characteristic mass were found when chemical modifiers were compared. Pd/Mg will be recommended in order to avoid a contamination of the graphite furnace with nickel. The characteristic mass was improved by using pyrolytically coated graphite tubes with the L'vov platform compared with uncoated graphite tubes with the L'vov platform. In the interlaboratory study, the standard addition procedure will be recommended.

Journal Article↗

PubMed2005

Adsorption of water vapour from humid air by selected carbon adsorbents.

The water uptake by carbon molecular sieves (CMS) and graphitized carbons, all of which are used to determine volatile organic compounds in air, was investigated using a direct experimental approach. CMS, e.g. Carboxen 1002, Carboxen 1003 and Anasorb CMS adsorb substantial amounts of water, in the range 400 to 450 mg per gram of adsorbent. Graphitized carbons, e.g. Carbrogaph 5TD and Carbopack X show low water trapping, less than 30 mg g(-1) and Carbopack Y as little as 5 mg g(-1) or less. The water sorption capacity for graphitized carbons is strongly dependent on the relative humidity (RH). The change of RH from 95 to 90% decreases the amount of adsorbed water by more than a factor of 2. Two different water adsorption mechanisms are operative: adsorption on polar centers and micropore volume filling. For graphitized carbons and CMS at low RH, adsorption on polar centers is involved. For CMS, once the threshold value of relative humidity (RHth) is surpassed, micropore volume filling becomes predominant. RHth is 44 +/- 3 and 42 +/- 3% for Carboxen 1002 and 1003, respectively, and 32 +/- 3% for Anasorb CMS. The CMS mass in the trap was found not to affect the mass of retained water under condition of incomplete saturation of adsorbent bed with water. Thus, the restrictions commonly imposed on the CMS mass are not necessary. The dry purging technique is suggested to remove adsorbed water. Carbograph 5TD and Carbopack X require only a few hundred ml of dry air to remove adsorbed water entirely. Water can also be purged out from CMS; however, much larger volumes of dry air are needed.

Adsorption↗