Kun’ichi Miyazawa

Solvent Engineering for Shape-Shifter Pure Fullerene (C60)

As a highly anticipated technique for bottom-up nanotechnology, i.e., shape control of pure functional molecules, we here report controlled formation of two-dimensional (2D) objects such as hexagons and rhombi and their selective shape shifting into one-dimensional (1D) rods through solvent-dependent changes of crystal lattice, all from pure C(60). Uniformly shaped rhombi and hexagons were obtained at tert-butyl alcohol/toluene and i-propyl alcohol/CCl(4) interfaces, respectively. In addition, exposure of these 2D nanosheets to water induced selective transformation into 1D nanorods. Nanorhombi were converted to short nanorods upon exposure to water. This shape shift is accompanied by changes in crystalline structures from a mixed fcc/hexagonal to pure fcc lattice, the latter of which is almost identical with morphologically similar C(60) nanowhiskers. Metastable nanorhombi which possess a strained mixed crystalline structure metamorphosize into the more stable short nanowhisker (nanorods). In contrast, the stable nanohexagon of a single lattice (and so less strain) does not undergo shape shifting. These results clearly demonstrate controlled formation of 2D nanosheets with various shapes (hexagons, rhombi, etc.) and selective shape shifting to nanorods (short nanowhiskers) all from pure C(60) molecules by very simple solvent treatments.

Fullerene Nanoarchitectonics: From Zero to Higher Dimensions

The strategic design of nanostructured materials, the properties of which could be controlled across different length scales and which, at the same time, could be used as building blocks for the construction of devices and functional systems into new technological platforms that are based on sustainable processes, is an important issue in bottom-up nanotechnology.Such strategic design has enabled the fabrication of materials by using convergent bottom-up and top-down strategies. Recent developments in the assembly of functional fullerene (C60) molecules, either in bulk or at interfaces, have allowed the production of shape-controlled nano-to-microsized objects that possess excellent optoelectronic properties, thus enabling the fabrication of optoelectronic devices. Because fullerene molecules can be regarded as an ideal zero-dimensional (0D) building units with attractive functions, the construction of higher-dimensional objects, that is, 1D, 2D, and 3D nanomaterials may realize important aspects of nanoarchitectonics. This Focus Review summarizes the recent developments in the production of nanostructured fullerenes and techniques for the elaboration of fullerene nanomaterials into hierarchic structures.

Photo-assisted growth and polymerization of C60 ‘nano’whiskers

Abstract C60 nanowhiskers are grown by a liquid–liquid interfacial precipitation method at 21 °C. It is found that the growth of the nanowhiskers is promoted under illumination even with weak room light (fluorescent light). The maximum of their lengths exceeds 1 mm where the diameter is about 250 nm. From Raman scattering measurements, it is shown that C60 molecules in the pristine nanowhiskers are bonded by weak van der Waals forces. The nanowhiskers is easily polymerized under irradiation with laser light. The cross section for this photo-polymerization is much large compared with that for intrinsic C60 bulk crystals.

Fullerene crystals with bimodal pore architectures consisting of macropores and mesopores.

A new class of fullerene (C(60)) crystals with bimodal pore architectures consisting of macropores and mesopores was synthesized by using a liquid-liquid interfacial precipitation (LLIP) method involving an interface between isopropyl alcohol (IPA) and a saturated solution of C(60) in a mixture of benzene and carbon tetrachloride (CCl(4)). By varying the mixing fraction of CCl(4) in benzene, the porosity and electrochemically active surface area can be flexibly controlled.

Structural investigation of the C 60 /C 70 whiskers fabricated by forming liquid–liquid interfaces of toluene with dissolved C 60 /C 70 and isopropyl alcohol

The structure of C 6 0 and C 7 0 whiskers with diameters between submicrometers and micrometers were analyzed by scanning electron microscopy and transmission electron microscopy. The fullerene whiskers were produced by forming liquid-liquid interfaces between toluene solutions of fullerenes and isopropyl alcohol. The growth fronts of C 7 0 whiskers were observed to be crystalline. The C 7 0 whiskers were assumed to be in a state of order-disorder transition. The whiskers of C 6 0 are very flexible, and C 6 0 whiskers bent strongly were torn into finer C 6 0 whiskers. The C 7 0 whiskers showed a higher crystallinity, though a high density of dislocations was observed in the C 6 0 whiskers.

Morphology of C60 nanotubes fabricated by the liquid–liquid interfacial precipitation method

Abstract Single crystalline C60 fullerene nanowhiskers are formed by adding isopropyl alcohol gently to fullerene saturated solutions. The method is called the liquid–liquid interfacial precipitation method. In the present study, observation using transmission electron microscope was made for C60 nanowhiskers with hollow structure, i.e. C60 fullerene nanotubes fabricated by the modification of liquid–liquid interfacial precipitation method using pyridine as solvent. After adding isopropyl alcohol to the C60 solution in the glass bottles, ultrasonic dispersion was applied for 1 min and then the bottles were kept at 10°C. Within 24 h, fibrous solids with the length larger than several millimeters and the diameters ranging from submicrons to 1ΰm were precipitated. For the transmission electron microscope study, the samples were pulverized by the ultrasonic dispersion. Under the transmission electron microscope, tubular morphology was usually observed for the whiskers with the diameters larger than 200 nm and hardly observed for those with the diameters smaller than 200 nm; both the C60 fullerene nanotubes and the fullerene C60 nanowhiskers were in crystalline state. Since partly tubular structures were sometimes observed at the end of the C60 fullerene nanowhiskers, the mechanism for the formation of tubular morphology is suggested to be a dissolution process after the crystal growth. When the samples were kept in the glass bottles for several hours after the pulverization, closing of nanotubes at the ends was observed for relatively smaller nanotubes in diameter. For relatively larger nanotubes in diameter, zigzag thinning of tube wall edges was observed. It is thus expected that subsequent growth or dissolution occurred at the end of the pulverized C60 nanotubes, which may be an effective way to control the shape of tubes. The C60 nanotubes presented here will be useful as adsorbents, catalysts, and membranes.

Nanoporous Carbon Tubes from Fullerene Crystals as the π‐Electron Carbon Source

Here we report the thermal conversion of one-dimensional (1D) fullerene (C60) single-crystal nanorods and nanotubes to nanoporous carbon materials with retention of the initial 1D morphology. The 1D C60 crystals are heated directly at very high temperature (up to 2000 °C) in vacuum, yielding a new family of nanoporous carbons having π-electron conjugation within the sp(2)-carbon robust frameworks. These new nanoporous carbon materials show excellent electrochemical capacitance and superior sensing properties for aromatic compounds compared to commercial activated carbons.

Vortex-Aligned Fullerene Nanowhiskers as a Scaffold for Orienting Cell Growth

A versatile method for the rapid fabrication of aligned fullerene C60 nanowhiskers (C60NWs) at the air-water interface is presented. This method is based on the vortex motion of a subphase (water), which directs floating C60NWs to align on the water surface according to the direction of rotational flow. Aligned C60NWs could be transferred onto many different flat substrates, and, in this case, aligned C60NWs on glass substrates were employed as a scaffold for cell culture. Bone forming human osteoblast MG63 cells adhered well to the C60NWs, and their growth was found to be oriented with the axis of the aligned C60NWs. Cells grown on aligned C60NWs were more highly oriented with the axis of alignment than when grown on randomly oriented nanowhiskers. A study of cell proliferation on the C60NWs revealed their low toxicity, indicating their potential for use in biomedical applications.

Surfactant-assisted assembly of fullerene (C60) nanorods and nanotubes formed at a liquid-liquid interface.

Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcrystals at the liquid-liquid interface. C60 crystals were grown using a liquid-liquid interfacial precipitation (LLIP) method by layering surfactant solution in butanol with a saturated solution of C60 in benzene. In the LLIP method, it is suggested that the crystal formation mechanism is driven by supersaturation related to the low C60 solubility in alcohol. We found that the dimensions of the synthesized C60 flowers depend on the concentration and surfactant type. In the absence of surfactant (i.e., in the butanol/benzene system), 1D C60 nanowhiskers (nanorods) and C60 nanotubes (diameter 400 nm-2 μm and length 5-20 μm) are obtained. However, when surfactants are incorporated into the system flowerlike microcrystals consisting of C60 nanotubes are observed. For instance, crystals grown at the interface of a 0.01% diglycerol monolaurate (C12G2) nonionic surfactant in butanol with benzene lead to the formation of flower-shaped microcrystals of average sizes in the range of 10-35 μm. To the best of our knowledge, this is the first example of the surfactant-assisted assembly of C60 crystals. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have shown that fullerene flowers have a hexagonal structure with cell dimensions of a = 2.539 nm and c = 1.021 nm, which differ from that of pristine C60. Mixtures of flower-shaped C60 crystals and free-standing C60 nanotubes are found in the 0.1% C12G2/butanol system. However, clusters or giant aggregates of nanowhiskers lacking any specific shape are observed in the 1% C12G2/butanol system although these crystals exhibit hexagonal close-packed structures. Flower-shaped C60 microcrystals are also observed with anionic surfactants cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC). C60 flowers obtained from 0.01% CTAB and 0.01% CTAC also exhibit hexagonal structures with cell dimensions of a = 2.329 nm and c = 1.273 nm, a = 2.459 nm and c = 0.938 nm, respectively. Our C60 flowers exhibit intense photoluminescence (PL) and a blue-shifted PL intensity maximum compared to the same parameters for pristine C60, demonstrating the potential to control the optoelectronic properties of fullerene-based nanostructures.

Structural characterization of the C60[C(COOC2H5)2] whiskers prepared by the liquid-liquid interfacial precipitation method

Fine whiskers of a C 6 0 derivative, i.e., C 6 0 monosubstituted by ethyl ester of malonic acid, C 6 0 [C(COOC 2 H 5 ) 2 ], were fabricated for the first time using a system of toluene with concentrated C 6 0 [C(COOC 2 H 5 ) 2 ] and isopropyl alcohol. The center-to-center distance of C 6 0 [C(COOC 2 H 5 ) 2 ] molecules along the close-packed direction of the C 6 0 [C(COOC 2 H 5 ) 2 ] whiskers was in the same range as that of the C 6 0 nanowhiskers prepared by the same method. The C 6 0 [C(COOC 2 H 5 ) 2 ] whiskers were assumed to take body-centered tetragonal or hexagonal close-packed crystal structures. The C 6 0 [C(COOC 2 H 5 ) 2 ] whiskers showed a high density of stacking faults. The C 6 0 [C(COOC 2 H 5 ) 2 ] whiskers with the growth direction different from the C 6 0 whiskers were observed.