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X-ray photoelectron spectroscopy (XPS) is among the most utilized analytical methods for nitrogen-doped carbon materials. Clarifying the assignments of nitrogen-doped carbon materials with different degrees of carbonization, which relates to conjugated systems, is essential to correlate structures with the performance of various applications, but such precise assignments were challenging. In this work, precise analyses were conducted to overcome the difficulty to assign the peaks of carbon materials with different degrees of carbonization, different edges, and various nitrogen-containing functional groups in graphene nanoribbons (GNRs), such as nitrile, pyridinic, primary with/without charges, secondary with/without charge, tertiary without charges (graphitic nitrogen), and quaternary nitrogen. Electrons donated from hydrogen and Madelung potentials showed a higher correlation to the peak shift of C1s and N1s XPS spectra than Mulliken charges on nitrogen. Zigzag edges showed a greater influence on the peak shift of tertiary amine (graphitic nitrogen) than armchair edges on XPS spectra. Besides, as the degree of carbonization is increased from aromatic compound-like structures to GNRs, the peak positions of C–N in C1s and N1s XPS spectra shifted to higher binding energies. This research proved that XPS could be applied to the precise structural analyses of nitrogen-containing carbon materials.

Carbonization process of pyromellitic dianhydride (PMDA)-4,4′-diaminodiphenyl ether (ODA)-type polyimide has been studied for decades. However, various reaction mechanisms have been proposed and the detailed mechanisms are still controversial. It is essential to understand the carbonized structures of PMDA-ODA-type polyimide before analyzing the defect structures in graphite. In this work, the carbonization mechanisms of polyimide heated at 1273 K or lower were unveiled and the methodology to analyze carbon materials containing nitrogen, oxygen, pentagons, and heptagons using computational spectral analysis combined with molecular dynamics simulation (ReaxFF) are exhibited. For example, the formations of isoimide and cyclic ether were estimated by ReaxFF, and the presence was supported by experimental and calculated X-ray photoelectron spectroscopy (XPS) and carbon-13 nuclear magnetic resonance (13C NMR) spectra of polyimide heated between 813 and 873 K. The formations of pentagons and heptagon, suggested by ReaxFF, were also supported by Raman and 13C NMR spectra of polyimide heated between 833 and 1273 K. This work also revealed that the previously reported structures were unstable and that amine in the basal plane was the most plausible structure in polyimide heated at 1073 K or higher, as clarified by XPS, ReaxFF, and the energy calculation.

Isotropic pitch-based carbon fiber has been utilized for various applications such as thermal insulation materials for high-temperature furnace and additives for slide member, but the structure of the carbon fiber is still under debate. This is because the precursor pitch contains various aromatic compounds in addition to the complicated oxidation and carbonization reaction during production process of carbon fiber. In this work, oxidation processes of model compounds of pitch such as pyrene (sp2C H with zigzag-like edges), triphenylene (sp2C H with armchair edges), fluorene (pentagon with sp3CH2), and 9-methylanthracene (hexagon with sp3CH3) were analyzed using mass spectrometry, elemental analysis, infrared (IR), Raman, and X-ray photoelectron spectroscopy (XPS) in addition to calculation such as molecular dynamic simulation with a reactive force field (ReaxFF) and simulation of IR, Raman, and XPS spectra (Gaussian09). Combination of calculations and experiments revealed that oxidation proceeded in the order of zigzag-like edges > sp3CH3 > sp2CH2 > armchair edges, and the quinone formed by oxidation worked as a precursor for a crosslinking reaction. It is expected that the results of this work, which revealed the origin of the crosslinking, could lead to improve properties as well as to estimate the detailed structures of isotropic pitch-based carbon fiber.

Edges of carbon materials have been known to work as active sites for various applications such as catalysts, adsorbent, and electrodes, but selecting precursors for carbon materials with controlled edges in the absence of metallic substrate is challenging. This work developed a method to select the superior precursors instantaneously using molecular dynamic simulation. This simulation predicted that hydrogen in precursors gasified and the hydrogen attacked the active sites in precursors upon carbonization, causing the decrement of active sites. Thus, it is essential to reduce the concentration of hydrogen in precursors and it is also necessary to introduce reactive functional groups near the active site to protect the active sites. We indeed synthesized the selected precursors such as diethynyl anthracene, diethynyl chrysene, divinyl naphthyridine, and divinyl phenanthroline and proved that edges in those precursors were maintained even after carbonization at 773 K using diffuse reflectance infrared Fourier transform and X-ray photoelectron spectroscopy with the aid of spectra simulated by density functional theory calculation. Especially, ca. 100% of edge structures of zigzag edges and armchair edges in diethynyl anthracene and diethynyl chrysene was maintained even after carbonization at 773 K.

Nitrogen-doped carbon materials such as graphene and activated carbon have been studied as solid base catalysts. However, active sites of carbon catalysts have long been ambiguous because of the presence of various functional groups. This work clarified the dependence of positions of nitrogen atoms in aromatic hydrocarbons on catalytic activities of well-known Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate to produce ethyl cyanocinnamate (ECC) as one of the examples for catalytic reactions. Catalytic activities of 30 kinds of aromatic hydrocarbons composed of one, two, and three aromatic rings with zero, one, two, and three nitrogen atoms were compared. Phenazine with zigzag edges and pyridinium ion with quaternary nitrogen showed low catalytic activities. On the other hand, 1,10-phenanthroline with armchair edges showed a high ECC selectivity of 99.3% and a high ECC yield of 59.0%. Among various aromatic hydrocarbons carbonized on silica, 1,10-phenanthroline carbonized at 923 K exhibited the highest ECC selectivity of 89.5% and the highest ECC yield of 10.2% because of the highest percentage of 1,10-phenanthroline-like N after carbonization. We believe that this work can serve as a perfect example to examine the performance of carbon catalysts at a molecular level in the future.

Interactions of metal cations such as Li + , Na + , K + , Mg 2+ , Ca 2+ , Sr 2+ , Cr 3+ , Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ with ammonia-treated graphene sheets (G) and thermal stability of metal cations coordinated with oxygen- and nitrogen-containing functional groups on G were investigated by rinsing G coordinated with metal cations (G-Metal) in 2-propanol using sonication and by heating G-Metal at 773 K, respectively. Monovalent alkali metal cations, divalent alkaline-earth metal cations, divalent transition metal cations such as Mn 2+ , and the other metal cation such as Zn 2+ were removed by rinsing because of either no interaction or weak interactions between metal cations and G including various thermally stable nitrogen- and oxygen-containing functional groups. Trivalent transition metal cations such as Cr 3+ and Fe 3+ were agglomerated by heat treatment at 773 K, whereas divalent transition metal cations such as Co 2+ , Ni 2+ , and Cu 2+ remained without severe agglomeration. Phenanthroline-like groups on edges of graphene showed the strongest interaction with Ni 2+ among all of investigated nitrogen- and oxygen-containing functional groups as results of density functional theory calculation. The thermal stability of N Ni bonding was confirmed as above 873 K as results of heat treatment of a standard compound (Ni phthalocyanine) in a glass ampoule.

Carbon-based films (0.8–13 μm thick) with good bonding to the substrate and high processability were produced at 650 °C on an alumina substrate, using SU 2.5 bisphenol-A type novolac epoxy (plus triethyleneteramine curing agent) as the carbon precursor. This precursor gave crack-free and scratch resistant carbon films. Interconnected filamentary nickel nanoparticles were more effective for conductivity enhancement than silver nanoparticles or multiwalled carbon nanotubes at 5 vol.% or below, in spite of the high conductivity of silver and the high aspect ratio of nanotubes. The carbon film with 2.5 vol.% nickel showed resistivity 6 × 10−3 Ω cm.

The three-dimensional microstructuring of carbon is useful for microelectromechanical devices and electrode arrays. A microstructure in the form of a microscale bridge (consisting of a girder and two adherent substructures) on an alumina substrate with a surface roughness of 1–2 μm (which allowed bonding by mechanical interlocking) was attained by using a novel low-cost process that involved thermoplastic spacer (paraffin wax) evaporation during pyrolysis of an epoxy-based film that coated the spacer and parts of the substrate. Fillers were chosen to reduce the shrinkage during pyrolysis and to increase the electrical conductivity. Multiwalled carbon nanotube as a filler was particularly effective for reducing the cracking tendency. Carbon black and silver nanoparticles as sole fillers were ineffective, producing cracked bridges. The total filler content (nanotube, optionally along with silver nanoparticles) had to exceed 3 vol.% in order to attain good control of the shape of the bridge. The method used a novolac epoxy resin in combination with an amine curing agent (without ultra-violet curing). The epoxy was chosen for low viscosity and strong bonding to the substrate. A bridge with a girder of length 90–300 μm, separated from the substrate by a height of 5–15 μm, was attained.

Heat dissipation from aircraft is important. Carbon fiber polymer–matrix structural composites have high in-plane thermal conductivity, but low through-thickness conductivity. A nanostructuring method involving carbon black at the interlaminar interface was developed to improve the through-thickness conductivity. Ethylene glycol monoethyl ether (EGME) was used for dispersing the carbon black and to partially dissolution of the epoxy resin on the fiber-epoxy prepreg surface. EGME evaporated from the prepreg surface prior to composite fabrication. The optimum carbon black content in EGME for attaining high through-thickness conductivity was 0.8 wt.% for both unidirectional and crossply configurations. Applying EGME without carbon black improved the conductivity by up to 36%, but in the case with carbon black, the improvement was up to 210%. For the same interlaminar interface modification (except for EGME with 1.2 wt.% carbon black), the conductivity and its fractional increase were higher for the crossply configuration than the corresponding unidirectional configuration. The through-thickness compressive modulus and the flexural modulus were increased by up to 14% and 11%, respectively by using EGME with carbon black. The average thickness of the interlaminar interface increased with increasing carbon black content, but it was decreased by the use of EGME alone.

Electrochemical behavior of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) separated by agarose gel chromatography was analyzed as electrodes of electric double-layer capacitor (EDLC). Due to the doping of ions to semiconducting SWCNTs, the cyclic voltammogram of semiconducting SWCNTs showed amphoteric behavior, which is analogous to that of dopable conducting polymers. As the potential was increased or decreased from the flat band potential, the capacitance of semiconducting SWCNTs was increased, but that of metallic SWCNTs was slightly increased. The high capacitance of semiconducting SWCNTs at the high potential is beneficial for EDLC due to the possible limitation of capacitance.

Mesophase spherules separated from pitches and asphalt by quinoline (mesocarbon microbeads) were heat-treated under a pressure of 5 kbar at 1300–2000°C for 1 hr. The as-separated microbeads gave a bulk density of 1.8–1.9 g/cm3 after heat treatments at high temperatures. The pre-heated microbeads gave high bulk density above 2.0 g/cm3 after high temperature heat treatment. The mesocarbon microbeads were found to have low graphitizability under pressure. The as-separated microbeads showed a heterogeneous process of graphitization, but the maximum amount of the graphitic component was only 60% even after 2000°C-treatment under 5 kbar. On the pre-heated microbeads, almost no graphitization was observed. The spherical shape of the as-separated microbeads was lost even after the heat treatments at low temperatures under 5 kbar. However, the pre-heated microbeads showed the tendency to keep the original spherical shape even after heat treatment at 1900°C.

The influence of organic sulfur compounds and metals on the texture of the mesophase formed in pitch during the carbonization process was investigated by the addition of organic sulfur compounds and organometallic compounds to the cracked oil obtained from Khafji asphalt and polyvinyl chloride (PVC) pitch. These pitches, containing sulfur and metals, have been examined by polarised light microscopy, and quinoline insolubles (QI), sulfur and metal contents were determined. The existence of either organic sulfur compounds or organometallic compounds in the pitch has no effect on mesophase texture. However, the coexistence of sulfur and metals (such as vanadium or nickel) has a great effect on mesophase texture. From these results, sulfur and metals coexisting in the pitch have a catalytic effect which activates the thermal decomposition and the thermal polymerization reactions of the pitch. Furthermore, the precursors of mesophase (β resin) are formed abundantly in the pitch by these reactions. These precursors promote the nucleation of mesophase spherules, and a large number of mesophase spherules are formed in the pitch at the same time. Therefore, these spherules coalesce with each other before growing to large spheres and lead to a fine mosaic texture.

Carbonaceous mesophase spherules of a new-type have been found in the heat-treated products of quinoline-soluble portion of coal-tar pitch containing carbon black. Their spherules have molecular orientation different from that proposed by Brooks and Taylor. The effect of a magnetic field is discussed on the orientation of the spherules formed during carbonization processes using a polarization microscope.

The invention provides carbon fibers having mechanical properties equival to or even better than those of the polyacrylonitrile-based carbon fibers from a bituminous material, e.g. coal tar pitch, as the starting material. The starting pitch is first partially hydrogenated in tetrahydroquinoline under specific conditions followed by a heat treatment to give a pitch composition suitable for spinning which can be characterized by several parameters including the proportions of the carbons and hydrogens having different chemical shifts in the NMR analysis. The pitch composition for spinning is then subjected to spinning under specific conditions including the temperature condition for controlling the viscosity behavior of the molten pitch composition determined by use of the Andrade's equation and the pitch filament is then infusibilized in an oxidative atmosphere and carbonized in an inert atmosphere into carbon fibers having a tensile strength of at least 200 kg/mm2 and a tensile modulus of at least 10 tons/mm2.