Masako Yudasaka

High-Power Supercapacitor Electrodes from Single-Walled Carbon Nanohorn/Nanotube Composite

A novel composite is presented as a supercapacitor electrode with a high maximum power rating (990 kW/kg; 396 kW/l) exceeding power performances of other electrodes. The high-power capability of the electrode stemmed from its unique meso-macro pore structure engineered through the utilization of single-walled carbon nanotubes (20 wt %) as scaffolding for single-walled carbon nanohorns (80 wt %). The novel composite electrode also exhibited durable operation (6.5% decline in capacitance over 100 000 cycles) as a result of its monolithic chemical composition and mechanical stability. The novel composite electrode was benchmarked against another high-power electrode made from single-walled carbon nanotubes (Bucky paper electrode). While the composite electrode had a lower surface area compared to the Bucky paper electrode (280 vs 470 m(2)/g from nitrogen adsorption), it had a higher meso-macro pore volume (2.6 vs 1.6 mL/g from mercury porosimetry) which enabled the composite electrode to retain more electrolyte, ensuring facile ion transport, hence achieving a higher maximum power rating (970 vs 400 kW/kg).

Fabrication of ZnPc/protein nanohorns for double photodynamic and hyperthermic cancer phototherapy

Multifunctionalization of carbon nanotubules is easily achieved by attaching functional molecules that provide specific advantages for microscopic applications. We fabricated a double photodynamic therapy (PDT) and photohyperthermia (PHT) cancer phototherapy system that uses a single laser. Zinc phthalocyanine (ZnPc) was loaded onto single-wall carbon nanohorns with holes opened (SWNHox), and the protein bovine serum albumin (BSA) was attached to the carboxyl groups of SWNHox. In this system, ZnPc was the PDT agent, SWNHox was the PHT agent, and BSA enhanced biocompatibility. The double phototherapy effect was confirmed in vitro and in vivo. When ZnPc-SWNHox-BSA was injected into tumors that were subcutaneously transplanted into mice, the tumors almost disappeared upon 670-nm laser irradiation. In contrast, the tumors continued to grow when only ZnPc or SWNHox-BSA was injected. We conclude that carbon nanotubules may be a valuable new tool for use in cancer phototherapy.

Enhancement of In Vivo Anticancer Effects of Cisplatin by Incorporation Inside Single-Wall Carbon Nanohorns

Cisplatin (CDDP) was incorporated inside single-wall carbon nanohorns with holes opened (SWNHox) by a nanoprecipitation method that involved dispersion of CDDP and SWNHox in a solvent followed by the solvent evaporation. The incorporated CDDP quantity increased from the previously reported value of 15 to 46%, and the total released quantity of CDDP also increased from 60 to 100% by changing the solvent from dimethylformamide to water. Concurrently, in vitro anticancer efficiency of CDDP@SWNHox increased to 4-6 times greater than that of the intact CDDP. In vivo, CDDP@SWNHox intratumorally injected to transplanted tumors of mice suppressed the tumor growth more than the intact CDDP. We observed that CDDP@SWNHox adhered to the cell surfaces in vitro and stayed within the tumor tissues in vivo. Therefore, we think that the CDDP released from SWNHox realized high concentrations locally at the cells in vitro and in the tissues in vivo and could efficiently attack the tumor cells. We also found that SWNHox itself had an in vivo anticancer effect, which might increase the anticancer activities of CDDP@SWNHox.

Toxicity of Single-Walled Carbon Nanohorns

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.

Revealing the Secret of Water-Assisted Carbon Nanotube Synthesis by Microscopic Observation of the Interaction of Water on the Catalysts

We elucidated the secret of water-assisted chemical vapor deposition (CVD) by elucidating the influence of water on the catalysts, through ex situ microscopic and spectroscopic analysis. We unambiguously showed that catalyst deactivation readily occurs due to carbon coating and that water acted to remove this coating and revive catalysts activity. This represents the central point of water-assisted CVD.

Nitrogen-containing carbon nanotube growth from Ni phthalocyanine by chemical vapor deposition

Abstract Carbon tubes were obtained by chemical vapor deposition at 700 and 800 °C using Ni phthalocyanine as a starting material. The tubes grew perpendicularly on a quartz glass substrate, and then bent and often coiled as their diameter decreased. Transmission electron microscopy images revealed that the outer and inner diameters of the thin part of the tube were 20 ~ 40 nm and about 10 nm, respectively. X-ray photoelectron spectra indicated that the carbon tubes contained nitrogen. Amorphous carbon films were obtained at 900 and 1000 °C.

Behavior of Ni in carbon nanotube nucleation

A nucleation model was proposed for a carbon nanotube enclosing a Ni bar which was grown by chemical vapor deposition (CVD) at 700 °C using round Ni particles. At an early stage of CVD, each round Ni particle with a diameter of about 30 nm is covered with graphite layers. The graphite-covered Ni particle is considered to be unstable because the graphite layers have a large curvature. This instability is thought to make the graphite-covered Ni particles transform into a Ni bar enclosed within a carbon nanotube. In order to verify this nucleation model, we show that the size of the round Ni particle is a decisive condition for carbon nanotube formation by CVD, and that an intermediate state of the transformation of the graphite-covered Ni particles to the carbon-nanotube-enclosed Ni bar was observed by transmission electron microscopy.

Site Identification of Carboxyl Groups on Graphene Edges with Pt Derivatives

Although chemical functionalization at carboxyl groups of nanocarbons has been vigorously investigated and the identities and quantities of the carboxyl groups have been well studied, the location of carboxyl groups had not previously been clarified. Here, we show that site identification of carboxyl groups is possible by using Pt-ammine complex as a stain. After Pt-ammine complexes were mixed with graphenes in ethanol, many Pt-ammine complex clusters with an average size of about 0.6 nm were found to exist at edges of graphene sheets, indicating that the carboxyl groups mainly existed at the graphene edges. These results will make it easier to add functionalities by chemical modifications for various applications of nanotubes and other nanocarbons.

Light-assisted oxidation of single-wall carbon nanohorns for abundant creation of oxygenated groups that enable chemical modifications with proteins to enhance biocompatibility.

We show that light-assisted oxidation with hydrogen peroxide effectively and rapidly opens holes in carbon nanohorn walls and, more importantly, creates abundant oxygenated groups such as carboxylic groups at the hole edges. These oxygenated groups reacted with the protein bovine serum albumin. The obtained conjugates were highly dispersed in phosphate-buffered saline and were taken up by cultured mammalian cells via an endocytosis pathway.

Coaxially Stacked Coronene Columns inside Single-Walled Carbon Nanotubes†

One of the most interesting features of molecular materials is the fact that their physical properties change with the arrangement of the molecules as well as with the properties of the molecules themselves. Self-organization is an efficient pathway through which organic molecules assemble to form well-ordered nanometer-scale objects that are hardly synthesized by conventional chemical reactions. In these systems, two or more molecules are held together and are assembled by means of intermolecular (noncovalent) bonding such as ion–dipole or dipole–dipole interactions, hydrogen bonding, hydrophobic interactions, or p–p stacking. Such molecular self-organization and recognition processes are among the most practical and effective means to facilitate a “bottom-up” approach in nanotechnology. In general, however, fabrication of well-defined organic nanowires or other types of onedimensional (1D) nanostructures with controllable size and morphology is not as far advanced as for their inorganic counterparts. 2] Single-walled carbon nanotubes (SWCNTs) can offer a suitable interior space for the accommodation of molecules. Nanostructures produced by the incorporation of such molecules into SWCNTs are expected to exhibit several superior features. For example, because the diameter of SWCNTs can be adjusted to the size of the molecules, wellordered molecular arrangements more than a micrometer in length can be easily produced. The synthesized molecular arrangements are also expected to be strong and flexible under mechanical strain because the nanotube templates sustain the structure. Furthermore, the already synthesized nanostructures are isolated from reactive species by the tube wall, which leads to the superior durability of the encapsulated molecules. Herein we demonstrate such a 1D SWCNT-templated nanostructure using planar p-conjugated molecules (coronenes). Encapsulated coronenes form nano-scale columns in a way that differs from 3D solid coronenes, thus resulting in electronic and optical properties peculiar to the 1D structure. The production of well-ordered molecular assemblies in SWCNTs can be expected to inspire novel approaches for the synthesis of low-dimensional molecular materials with unique physical properties. The self-organized 1D structure of coronenes inside SWCNTs (coronenes@SWCNTs) was achieved through vapor-phase doping (Figure 1). Coronene confinement in nanometer spaces produces a characteristic columnar structure. Figure 1b,d and Figure S2a (see the Supporting Information) show high-resolution TEM (HRTEM) images of the coronene columns inside SWCNTs; coronene molecules are positioned along the tube axis at almost regular intervals. The formation of the columnar structure is due to two dominant factors: p–p stacking between coronenes and the interaction between the encapsulated coronene and the host SWCNT. In the monoclinic crystal, coronenes have an interplanar distance of 0.34 nm with a tilt angle of about 468 relative to the stacking axis. On the other hand, within SWCNTs, statistical analysis of the HRTEM images shows that the distance between the molecular planes is 0.35 0.03 nm (Figure S2b) and the angle between the molecular plane and the tube axis (q) is approximately 778 (Figure S2c, 1c). Although the interplanar distances are identical between 1D and solid coronenes within the experimental error, a substantial difference is observed for the tilt angle. The observed structure that involves coronene columns was supported by total energy calculations for zig-zag (n, 0) SWCNTs. Figure 1e shows the stabilization energy (DE) of coronenes inside SWCNTs as a function of tube diameter (d), where the molecular plane of coronenes was set to be [*] Prof. T. Okazaki, Y. Iizumi, Dr. S. Okubo, Dr. Z. Liu, Dr. K. Suenaga, Y. Tahara, Dr. M. Yudasaka, Prof. S. Iijima Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba 305-8565 (Japan) Fax: (+ 81)29-861-6241 E-mail: toshi.okazaki@aist.go.jp