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.

Single-wall carbon nanohorns (SWNHs) are recently discovered nanostructured spherical aggregates of graphitic tubes. The unique physicochemical properties of SWNHs, including their large surface area, suggest their possible utility as carriers in drug delivery systems. Here we investigated the in vitro binding and release of the antiinflammatory glucocorticoid dexamethasone (DEX) by as-grown SWNHs and their oxidized form, oxSWNHs. Adsorption analyses using [3H]-DEX determined the amount of DEX adsorbed by oxSWNHs to be 200 mg for each gram of oxSWNHs in 0.5 mg/mL of DEX solution, which was approximately 6 times larger than that obtained for as-grown SWNHs. Adsorption kinetics indicated that oxSWNHs had higher affinity for DEX than as-grown SWNHs. Treatment of oxSWNHs at 1200 degrees C under H2, which removed the oxygen-containing functional groups on oxSWNHs, did not diminish the high affinity for DEX, suggesting that oxygen-containing functional groups have little contribution for the affinity. DEX-oxSWNH complexes exhibited sustained release of DEX into phosphate-buffered saline (pH 7.4) at 37 degrees C and more rapid biphasic release into culture medium. The biological integrity of the released DEX form was confirmed by activation of glucocorticoid response element-driven transcription in mouse bone marrow stromal ST2 cells and induction of alkaline phosphatase in mouse osteoblastic MC3T3-E1 cells. Notably, synthesis of SWNHs does not require a metal catalyst, the toxicity of which could become problematical in clinical use, and no cytotoxicity was observed in cells cultured in the presence of oxSWNHs under our conditions. Taken together, these observations highlight the potential utility of SWNHs in drug delivery systems.

A hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN), in which the graphene layers distributed inside the CNT inner cavities, is designed to support noble metal (e.g. PtRu) nanoparticles efficiently. Well-dispersed PtRu nanoparticles with diameters of 2-4 nm are immobilized onto NCNT-GHN supports by a low-temperature chemical reduction method without requiring any pretreatment. Compared with conventional CNTs and commercial catalyst, much enhanced catalytic performance is achieved by a synergistic effect of the hierarchical structure (graphene-CNT hybrid) and electronic modulation (N-doping) during the methanol electrooxidation reaction. An improved singlecell performance with long-term stability is also demonstrated by using NCNT-GHN as catalyst support. These results explain previously reported findings on highly dispersed gold nanoparticles, in which the peripheral atoms are positively charged

We extensively investigated in vitro and in vivo the toxicities of as-grown single-walled carbon nanohorns (SWNHs), a tubular nanocarbon containing no metal impurity. The SWNHs were found to be a nonirritant and a nondermal sensitizer through skin primary and conjunctival irritation tests and skin sensitization test. Negative mutagenic and clastogenic potentials suggest that SWNHs are not carcinogenic. The acute peroral toxicity of SWNHs was found to be quite low--the lethal dosage for rats was more than 2000 mg/kg of body weight. Intratracheal instillation tests revealed that SWNHs rarely damaged rat lung tissue for a 90-day test period, although black pigmentation due to accumulated nanohorns was observed. While further toxicological assessments, including chronic (repeated dose), reproductive, and developmental toxicity studies, are still needed, yet the present results strongly suggest that as-grown SWNHs have low acute toxicities.

Due to the simplicity of the process, holes in the graphene walls of single-wall carbon nanotubes (SWNTs) and single-wall carbon nanohorns (SWNHs) have often been opened using O2 gas at high temperatures, even though this contaminates the nanotubes with carbonaceous dust (C-dust). To open holes with less C-dust contamination, we found that a slow temperature increase of 1 degrees C/min or less, in air, was effective. We also found that SWNHs having little C-dust could store a large quantity of materials inside the tubes. We infer that the local temperature increase due to the exothermic reaction of combustion may have been suppressed in the slow combustion process, which was effective in reducing the C-dust.

Single-wall carbon nanohorn (SWNH), which is a tubular particle with a cone cap, was oxidized in an oxygen flow at various temperatures. N(2) adsorption at 77 K, thermogravimetry (TG), differential thermal analysis (DTA), transmission electron microscopy, and Raman spectroscopy measurements were carried out on the oxidized SWNHs. The specific surface area of the oxidized SWNHs can be controlled by oxidation temperature, giving the maximum value of 1420 m(2)/g. The pore size distribution by the BJH method and the comparison plot of the N(2) adsorption isotherms of SWNH oxidized at different temperatures against that of as-grown SWNH revealed the minimum oxidation temperature for opening internal nanopores. TG-DTA analyses determined the components of as-grown SWNH: amorphous carbon 2.5 wt %, defective carbon at the cone part 15 wt %, tubular carbon 70 wt %, and graphitic carbon 12 wt %. These systematic analyses provided the exact internal nanopore volume of 0.49 mL/g for pure SWNH particles.

Selective synthesis of particles of angstrom to nanometer size consisting of one to many metal atoms is instrumental in various applications, but it has been hampered by the tendency of the metal atom to form large clusters. We found, as studied by the state-of-the-art electron microscopic technique, a strategy to produce metal-containing nanoparticles isolated from each other by depositing metal atoms in a hydrophilic hole on or in the interior of a carbon nanotube as demonstrated by the reaction of Gd(OAc) 3 with oxidized single-wall nanohorns. Besides the potential utilities of the deposited metal clusters, the metal deposition protocol provides a method to control permeation of molecules through such openings.carbon nanotube ͉ metal nanoparticle ͉ self-assembly ͉ metal deposition A s has been amply demonstrated in chemistry by way of metal-catalysis, metal-complexation should immensely widen the scope of carbon cluster science (1-5). Thus, metalcontaining hollow carbon clusters, such as endohedral metallofullerenes (6, 7) and carbon nanotube (NT) filled with metal atoms (3,4,(8)(9)(10)(11)(12), have been suggested as promising materials. However, the methodology to rationally control the size and the location of the metal clusters and to ensure high-yield production of the material on a large scale has been lacking. We report here a method for forming a one-to multiatom metal cluster specifically at the hydrophilic hole opening of a NT (8,13,14) as demonstrated by deposition of Gd(OAc) 3 in single-wall carbon nanohorns (NHs), a new variety of single-wall NTs (15). The hole-selective deposition of the Gd atoms allows atomic-scale detection of the structural defect in the graphitic materials, and, on a bulk scale, controls the permeability of molecules through the holes. The result would find use for modulation of the electronic properties of NTs (16).Attachment of one atom or a multiatomic cluster onto a selected location of the surface of materials is intellectually challenging and practically useful. Because the oxidized edge of NT is rich in hydrophilic functional groups, such as hydroxy and carboxyl groups (8,13,14,(17)(18)(19), and hence creates a ''locally amphiphilic'' structure (20) on a graphene sheet, we considered that selective accumulation of hydrophilic metal ions, one by one through self-assembly, onto a small hole of a partially oxidized graphene sheet should be possible. We report that treatment of single-wall NH possessing hole openings of several angstroms to Ϸ2-nm diameter with methanolic Gd(OAc) 3 ⅐(H 2 O) 4 permits selective deposition of one to several Gd(III) atoms in an opening at the tip of the tube, or a cluster of an average 1.6-nm diameter in the interior of an opening on the sidewall. The valence and the number of the deposited metal atoms were determined by high-resolution transmission electron microscopy (TEM) and quantitative electron energy-loss spectrometry (EELS) with atomic sensitivity in a dedicated scanning TEM (STEM) with 0.5-nm spatial resolution. With this analytical ...

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