Seong-Ho Yoon

Preparation of Nitrogen-Doped Graphene Sheets by a Combined Chemical and Hydrothermal Reduction of Graphene Oxide

Nitrogen-doped graphene sheets were prepared through a hydrothermal reduction of colloidal dispersions of graphite oxide in the presence of hydrazine and ammonia at pH of 10. The effect of hydrothermal temperature on the structure, morphology, and surface chemistry of as-prepared graphene sheets were investigated though XRD, N(2) adsorption, solid-state (13)C NMR, SEM, TEM, and XPS characterizations. Oxygen reduction and nitrogen doping were achieved simultaneously under the hydrothermal reaction. Up to 5% nitrogen-doped graphene sheets with slightly wrinkled and folded feature were obtained at the relative low hydrothermal temperature. With the increase of hydrothermal temperature, the nitrogen content decreased slightly and more pyridinic N incorporated into the graphene network. Meanwhile, a jellyfish-like graphene structure was formed by self-organization of graphene sheets at the hydrothermal temperature of 160 °C. Further increase of the temperature to 200 °C, graphene sheets could self-aggregate into agglomerate particles but still contained doping level of 4 wt % N. The unique hydrothermal environment should play an important role in the nitrogen doping and the jellyfish-like graphene formation. This simple hydrothermal method could provide the synthesis of nitrogen-doped graphene sheets in large scale for various practical applications.

A study on the effect of heat treatment on functional groups of pitch based activated carbon fiber using FTIR

Abstract Pitch based active carbon fibers (ACFs) were analyzed by a FTIR micro-ATR technique by introducing a very thin KBr layer on their surfaces. The ACFs were thermally treated at 600, 1100, and 1200 °C respectively, to investigate the change of their surface functionalities. As the heat treatment temperature increased, the amount of oxygen containing surface functional groups were reduced and the ACFs became more hydrophobic. When the ACFs were thermally treated, the decrease of carboxylic acid groups occurred first and ketone or quinone groups subsequently disappeared at higher heat treatment temperatures. The degree of graphitization of the ACF was increased significantly when it was treated at 1100 and 1200 °C and this was partially attributed to the release of the CO groups in the conjugated ketone or quinone structures.

Chemoselective hydrogenation of nitroarenes with carbon nanofiber-supported platinum and palladium nanoparticles.

Platinum and palladium nanoparticles supported on three types of carbon nanofibers (CNFs) are synthesized and used as catalysts in the hydrogenation of nitroarenes. Nanosized platinum particles dispersed on platelet-type CNF efficiently catalyze the reduction of functionalized nitroarenes to the corresponding substituted anilines in high turnover numbers with other functional groups remaining intact.

Cure Behavior of the Liquid-Crystalline Epoxy/Carbon Nanotube System and the Effect of Surface Treatment of Carbon Fillers on Cure Reaction

The FT-IR spectra of carbon nanotubes (CN) and oxidated carbon nanotubes were obtained using diffuse reflection Fourier-transform infrared (DRIFT) spectroscopy. The cure behavior of the liquid-crystalline epoxy (LCE)/CN and the LCE/carbon black (CB) systems were investigated. The effect of surface treatment of the carbon nanotube on the cure behavior in the LCE/CN system was investigated with differential scanning calorimetry (DSC), and was compared with those of the CB. The heat of cure in the LCE/CN system was higher than that in the LCE/CB system. The activation energy was dependent on the concentration of the curing agent. The activation energies for the cure reaction were decreased as a result of surface treatment of carbon materials. It was possible to promote the curing reaction by the surface treatment of the carbon nanotube without decreasing the heat of cure. The isothermal kinetic parameters were obtained from the Kamal equation. TEM images of carbon nanotube: carbon nanotube bundle.

Formation of hydrogen-capped polyynes by laser ablation of graphite particles suspended in solution

Laser ablation of graphite particles suspended in benzene, toluene, or hexane solution has been studied using a Nd:YAG laser (355, 532, and 1064 nm). Product analyses using HPLC coupled with UV and visible absorption spectroscopy and GC/MS showed that linear hydrogen-capped polyynes (CnH2: n ¼ 10, 12, 14, and 16) were formed in benzene and toluene, while those of n ¼ 8, 10, 12, and 14 were produced in hexane. The formation rates of polyynes increased with increasing particle concentration from 0.5 to 4 mg/ml, then decreased above that until 10 mg/ml. The formation rates of polyynes decreased with increasing wavelength of the Nd:YAG laser, 355 nm > 532 nm > 1064 nm. 2002 Elsevier Science B.V. All rights reserved.

Microstructure of mesophase pitch-based carbon fiber and its control☆

The macro as well as microscopic structure of four mesophase pitch-based carbon fibers of typical textures is observed using optical, scanning electron, transmission electron, and scanning tunneling microscopes. The four fibers had transverse textures of radial, radial-skin/random-core, random and quasi-onion. High resolution SEM clarified the domains to have typical shapes of linear, bent, multi-fold bent and loop. The shapes and alignment of the domains depended upon the spinning conditions and mesophase pitch properties, which defined the texture in a rather complex manner, varying in the transverse locations of the fibers of any overall textures. Each domain appeared to possess micro-domains which were arranged to define the size and shape of the domain. The shape of the micro-domains was basically unchanged by carbonization and graphitization, while the carbon plane cluster, or graphitic unit grew during carbonization and graphitization within the micro-domain. Such crystal growth brings about shrinkage of the micro-domain to change the size of the domains, strongly influencing overall structure and the properties of the carbon and graphitized fibers. The unique pleat shaped structural units, which are aligned in a zig-zag manner in the longitudinal section of the carbon and graphitized fibers, were found by high resolution SEM and STM. Such structures were formed in the spinning step with the fiber of liquid crystal polymers and mesophase pitch-based carbon fiber. Neither PAN, isotropic pitch-based fibers nor needle coke exhibited such a structure. The size and alignment in the pleat-like structure were also dependent upon the nature of mesophase pitch and spinning conditions, although the formation mechanism is not clarified yet. Such overall structure is briefly compared to the properties of the carbon fiber to find guidelines for the preparation of carbon fibers with better performances.

A study on the effect of surface treatment of carbon nanotubes for liquid crystalline epoxide–carbon nanotube composites

Chemical surface oxidation of carbon nanotubes was employed to modify the interfaces between liquid crystalline epoxide (LCE) molecules and carbon nanotubes (CNs). Polar functional groups are formed on the surfaces of the carbon nanotubes as a result of the treatment. The thermotropic behavior of the nematic liquid crystalline (LC) phase in liquid crystalline epoxide–carbon nanotube (LCE–CN) composites has been examined using polarized optical microscopy. The LC phase in the LCE–surface oxidized CN composite evolves at a lower temperature compared to that for LCE–CN, due to polar interactions. The mechanical properties of LCE–CN composites tend to increase with increasing CN content. The electrical conductivity of LCE–CN composites was found to increases dramatically compared to that of pristine LCE resin, up to 5 wt% CN loading, and then increase linearly with increasing CN content at high CN loadings. An investigation of the thermal properties of LCE–CNs in relation to the surface treatment of CNs was also undertaken. Surface oxidation of CNs was found to improve the mechanical durability and thermal stability of LCE–CN composites.

Platinum Nanoparticles Supported on Nitrogen‐doped Carbon Nanofibers as Efficient Poisoning Catalysts for the Hydrogenation of Nitroarenes

Carbon-supported metal nanoparticles are widely used as sensors, electrocatalysts for fuel cells and Li ion batteries, or heterogeneous catalysts for various organic transformations. Since the catalytic properties of these materials are highly dependent on the supports, numerous studies have been performed to modify the carbon supports to improve their catalyst performances. 2] One method to tailor the chemical and/or physical properties and stabilize metal nanoparticles–support interactions involves the chemical modification of the carbon surface by introduction of functional groups or the doping of heteroatoms. For example, the addition of sulfur, nitrogen, phosphorous, or halogen containing compounds as a catalyst poison to the original catalyst often retards the reaction rate, but sometimes also suppresses possible side reactions, thereby leading to highly selective organic transformations. 6] Another way to improve the catalyst performance is the use of carbon nanomaterials as a support, because their nanolevel controlled surface structures lead to the immobilization of highly dispersed metal nanoparticles with narrow size distributions and high conductivity. We previously reported the synthesis and application of metal nanoparticles supported on carbon nanofibers (CNFs) in hydrogenation catalysts. CNFs are classified into three types, in which the graphite layers are perpendicular (platelet: CNFP), parallel (tubular : CNF-T), or stacked obliquely (herringbone: CNF-H). Among these metal-supported CNFs (M/CNF; M = Ru, Rh, Pd, and Pt), Pt/CNF-P and Pt/CNF-H were proven to act as reusable catalysts for the nitro-selective reduction of halonitrobenzenes to the corresponding haloanilines with high turnover numbers in the presence of n-octylamine (OctNH2) as a catalyst poison. Because of these results, we were interested in nitrogen-doped CNF as a support for metal nanoparticles. The combination of carbon nanostructures and the doping of nitrogen atoms are expected to offer an efficient poisoning catalyst for chemoselective catalytic reactions. In this paper, we report that platinum nanoparticles can be immobilized on the surface of nitrogen-doped, herringbone-type carbon nanofibers (N-CNFH), and the formed Pt/N-CNF-H compounds are highly efficient reusable catalysts for the nitro-selective hydrogenation of functionalized nitroarenes. N-CNF-H was synthesized by using chemical vapor deposition over a MgO supported Ni–Fe catalyst using acetonitrile and hydrogen at 530 8C, as reported previously. Elemental analysis of N-CNF-H revealed the amount of nitrogen incorporated into N-CNF-H to be approximately 5 wt %. Immobilization of platinum particles (metal loadings of ca. 1 and 3 wt %) on NCNF-H was performed by applying the same method as for Pt/ CNF, that is, by thermally decomposing [Pt(dba)2] (dba = dibenzylideneacetone) in toluene in the presence of N-CNF-H under an argon atmosphere (Scheme 1).

Rhodium nanoparticles supported on carbon nanofibers as an arene hydrogenation catalyst highly tolerant to a coexisting epoxido group.

Rhodium nanoparticles supported on a carbon nanofiber (Rh/CNF-T) show high catalytic activity toward arene hydrogenation under mild conditions in high turnover numbers without leaching the Rh species; the reaction is highly tolerant to epoxido groups, which often undergo ring-opening hydrogenation with conventional catalysts.

Li+ storage sites in non-graphitizable carbons prepared from methylnaphthalene-derived isotropic pitches

Abstract The reversible Li+ storage sites and storage–de-storage mechanisms are studied with the carbonaceous materials prepared from methylnaphthalene-derived isotropic pitches. Results of the electrochemical studies indicate that these carbons have at least three different Li+ storage sites: Li+ ions are de-stored from site I at 0.0–0.12 V (vs. Li/Li+), from site II at 0.12–0.8 V, and from site III at >0.8 V. Site III is the most prosperous among the three when the preparation temperature is