Graphitic carbon in the Allende meteorite: a microstructural study

Nanoscale Ni-NiO-ZnO Heterojunctions for Switchable Dehydrogenation and Hydrogenation through Modulation of Active Sites

Catalysts consisting of metal-metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel-nickel oxide-zinc oxide (Ni-NiO-ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn-Ni materials (ZN-O), produced by the reaction between hydrazine hydrate and Zn-Ni-acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni-NiO-ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.

Structures and electrical properties of single nanoparticle junctions assembled using LaC2-encapsulating carbon nanocapsules

As the miniaturization of integrated circuits advances, electronics using single molecules and nanosize particles are being studied increasingly. Single nanoparticle junctions (SNPJs) consist of two electrodes sandwiching a single nanoparticle. Nanocarbons with nanospaces in their center, such as fullerenes, carbon nanotubes, and carbon nanocapsules (CNCs), are expected to be elements of advanced SNPJs. In this study, SNPJs were assembled using lanthanum dicarbide (LaC2)-encapsulating CNCs and two gold (Au) electrodes by a nanotip operation inside a high-resolution transmission electron microscope. The atomic configuration and electrical resistance of the SNPJs were investigated in situ. The results implied that the electrical resistance of the SNPJ depended on the interface structures of the contacts between the CNC and Au electrodes, i.e., the contact electrical resistance, and the greatest portion of the current through the SNPJ flowed along the outermost carbon layer of the CNC. Thus, the resistance of the SNPJs using the CNCs was demonstrated and the electrical conduction mechanism of one of the CNC was discussed in this study.

Confined linear carbon chains as a route to bulk carbyne

Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp(1) hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. We report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk production.

Near-field Raman spectroscopy of nanocarbon materials

Nanocarbon materials, including sp² hybridized two-dimensional graphene and one-dimensional carbon nanotubes, and sp¹ hybridized one-dimensional carbyne, are being considered for the next generation of integrated optoelectronic devices. The strong electron–phonon coupling present in these nanocarbon materials makes Raman spectroscopy an ideal tool to study and characterize the material and device properties. Near-field Raman spectroscopy combines non-destructive chemical, electrical, and structural specificity with nanoscale spatial resolution, making it an ideal tool for studying nanocarbon systems. Here we use near-field Raman spectroscopy to study strain, defects, and doping in different nanocarbon systems.

Quenching ilmenite with a high-temperature and high-pressure phase using super-high-energy ball milling

The mass production of highly dense oxides with high-temperature and high-pressure phases allows us to discover functional properties that have never been developed. To date, the quenching of highly dense materials at the gramme-level at ambient atmosphere has never been achieved. Here, we provide evidence of the formation of orthorhombic Fe2TiO4 from trigonal FeTiO3 as a result of the high-temperature (>1250 K) and high-pressure (>23 GPa) condition induced by the high collision energy of 150 gravity generated between steel balls. Ilmenite was steeply quenched by the surrounding atmosphere, when iron-rich ilmenite (Fe2TiO4) with a high-temperature and high-pressure phase was formed by planetary collisions and was released from the collision points between the balls. Our finding allows us to infer that such intense planetary collisions induced by high-energy ball milling contribute to the mass production of a high-temperature and high-pressure phase.

Carbyne forms of carbon: do they exist?

Almost 15 years have passed since carbynes entered the literature as new forms of elemental carbon. They recently attracted attention as possible interstellar dust constituents and as carriers of presolar noble gases in meteorites. Their existence and that of the related mineral chaoite are questioned, and a reevaluation of previous data is suggested.

Purification of Pulsed Laser Synthesized Single Wall Carbon Nanotubes by Magnetic Filtration

Great effort has been expended in the development of methods to purify raw nanotubes by chemical treatment, washing, mechanical filtration, or heat treatment in a vacuum or oxidative environment. These techniques are limited by incomplete removal of catalyst nanoparticles and by the damage to the nanotubes that often results. We have applied a new purification method using filtration in a magnetic field and oxidation and investigated the efficacy using magnetic filtration alone, or combined with chemical-based or annealing-based oxidative treatments. By applying magnetic filtration only, we reduce catalyst content from 11.7 to 3.7 wt %, which is a superior result to oxidation and/or chemical treated samples. By combining chemical and magnetic purification, metal catalyst content is reduced to as much as 0.3 wt %, which is the best result ever for SWNTs synthesized by the laser method. In addition to the reduction of catalyst content, the new purification method increased sample quality, confirmed by Raman spectroscopy and near-infrared absorption. Magnetic filtration is found to be very effective in removing metal catalysts, producing material with high quality and yields.

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.

Carbon onions: carriers of the 217.5 nm interstellar absorption feature

Ultraviolet-visible absorption measurements of high purity and well separated carbon onion samples are reported. The results show that, after purification, absorption features from carbon onions match well with the interstellar UV spectrum. The measurements show that the absorption peak position remains constant at 4.55+/-0.1 microm(-1), and the width varies from 1.2-1.6 microm(-1), a key feature of the interstellar spectrum. The similarities between the experimental and observed absorption spectra indicate that carbon onions are very strong candidates for the origin of the UV interstellar absorption peak at 4.6 microm(-1).

Origin of graphitic carbon and pentlandite in matrix olivines in the Allende meteorite

Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials.

Fullerenes, fulleranes and polycyclic aromatic hydrocarbons in the Allende meteorite

In this paper, we confirm our earlier observations of fullerenes (C60 and C70) in the Allende meteorite (Becker et al., 1994a, 1995). Fullerene C60 was also detected in two separate C-rich (approximately 0.5-1.0%) dark inclusions (Heymann et al., 1987) that were hand picked from the Allende sample. The amounts of C60 detected were approximately 5 and approximately 10 ppb, respectively, which is considerably less than what was detected in the Allende 15/21 sample (approximately 100 ppb; Becker et al., 1994a, 1995). This suggests that fullerenes are heterogeneously distributed in the meteorite. In addition, we present evidence for fulleranes, (C60Hx), detected in separate samples by laser desorption (reflectron) time-of-flight (TOF) mass spectrometry (LDMS). The LDMS spectra for the Allende extracts were remarkably similar to the spectra generated for the synthetic fullerane mixtures. Several fullerane products were synthesized using a Rh catalyst (Becker et al., 1993a) and separated using high-performance liquid chromatography (HPLC). Polycyclic aromatic hydrocarbons (PAHs) were also observed ppm levels) that included benzofluoranthene and corannulene, a cup-shaped molecule that has been proposed as a precursor molecule to the formation of fullerenes in the gas phase (Pope et al., 1993).

Elemental carbon as interstellar dust

C 60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in cireumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature—low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented.

Soot morphology: an application of image analysis in high-resolution transmission electron microscopy

Interest in the fine structure of soots and carbon blacks is motivated by a variety of possible applications. The structure provides information on the origins of the particles and on their adsorptive and reactive properties. This paper describes a method for quantification of the structure of soots and carbon blacks based on direct electron microscopic observation followed by image analysis of these materials. High-resolution transmission electron microscopy (HRTEM) provides a very detailed observation of particle structure. The differences in soot structure, because of its complexity, may not be easily quantifiable with the human eye; therefore, high-level computer software has been used to manipulate HRTEM images. This technique involves the application of fast Fourier transforms (FFT) to single particles and the measurement of characteristic parameters such as interplanar spacings and crystallite sizes from these particles. The methodology and application of this characterization technique are presented here. Results are shown for different samples obtained from soot and carbon black particles selected to illustrate the capabilities of the methodology. Quantitative information can be obtained on structural characteristics, e.g., interplanar spacing, circularity, orientation, elongation, and length distribution of lattice fringes, as well as on the fractional coverage of the extracted pattern.

Characteristics and formation of amino acids and hydroxy acids of the Murchison meteorite

Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the alpha-amino acids and alpha-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.

13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites

13C NMR spectra have been obtained of the insoluble carbon residues resulting from HF-digestion of three carbonaceous chondrites, Orgueil (C1), Murchison (CM2), and Allende (CV3). Spectra obtained using the cross polarization magic-angle spinning technique show two major features attributable respectively to carbon in aliphatic/olefinic structures. The spectrum obtained from the Allende sample was weak, presumably as a consequence of its low hydrogen content. Single pulse excitation spectra, which do not depend on 1H-13C polarization transfer for signal enhancement were also obtained. These spectra, which may be more representative of the total carbon in the meteorite samples, indicate a greater content of carbon in aromatic/olefinic structures. These results suggest that extensive polycyclic aromatic sheets are important structural features of the insoluble carbon of all three meteorites. The Orgueil and Murchison materials contain additional hydrogenated aromatic/olefinic and aliphatic groups.

Carbon Compounds in Interplanetary Dust: Evidence for Formation by Heterogeneous Catalysis

Associations of carbonaceous material with iron-nickel alloy, carbides, and oxides were identified by analytical electron microscopy in ten unmelted chondritic porous micrometeorites from the earth's stratosphere. These associations, which may be interpreted in terms of reactions between a carbon-containing gas and catalytically active dust grains, suggest that some of the carbon in the chondritic porous subset of interplanetary dust was emplaced through heterogeneous catalysis.

Interstellar Carbon in Meteorites

The Murchison and Allende chondrites contain up to 5 parts per million carbon that is enriched in carbon-13 by up to + 1100 per mil (the ratio of carbon-12 to carbon-13 is approximately 42, compared to 88 to 93 for terrestrial carbon). This "heavy" carbon is associated with neon-22 and with anomalous krypton and xenon showing the signature of the s-process (neutron capture on a slow time scale). It apparently represents interstellar grains ejected from late-type stars. A second anomalous xenon component ("CCFXe") is associated with a distinctive, light carbon (depleted in carbon-13 by 38 per mil), which, however, falls within the terrestrial range and hence may be of either local or exotic origin.