Catalytic Activity of Nonaggregating Cu Nanoparticles Supported in Pores of Zeolite for Aerobic Oxidation of Benzyl Alcohol.

Cu nanoparticles (NPs) as catalysts have the good advantage of being more abundant than noble metal NPs. In this study, we synthesized nonaggregating Cu NPs supported in Y-type zeolite by the photoreduction method. In this method, Cu ions in pores of zeolite can be slowly reduced with a small amount of reductant at room temperature. The high-resolution transmission electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction patterns, and UV-Vis spectra supported that nonaggregating Cu NPs existed in the pores of zeolite. Catalytic activities of Cu NP-zeolite were investigated for the aerobic oxidation of benzyl alcohol. Our Cu NP-zeolite had a large turnover frequency of 17 h-1. The yield of benzaldehyde increased in proportion to the amount of Cu loading at ≤0.5 wt %, indicating that Cu NPs in pores of zeolite work as catalysts for selective aerobic oxidation of benzyl alcohol. The high catalytic activity was brought by nonaggregating Cu NPs in pores of zeolite. The catalytic reaction for other aromatic alcohols with electron-donating groups proceeded, whereas it did not proceed for the aromatic alcohols with electron-withdrawing groups or aliphatic alcohols, indicating that the interaction between zeolite and the benzene ring also contributed to the reaction. This study would be expected to contribute to the development of Cu NP catalysts.

Role of constituents for the chirality isolation of single-walled carbon nanotubes by the reversible phase transition of a thermoresponsive polymer.

The simple sorting procedure and continuous use of poly(N-isopropylacrylamide) (PNIPAM), a well-known thermoresponsive polymer, have a high potential for the mass production of single-walled carbon nanotubes (SWCNTs) with a specific electronic structure. However, knowledge of efficient single-chirality sorting methods with mixed surfactant systems is not applicable. In this work, we explored experimental conditions by controlling the interaction among PNIPAM, sodium cholate (SC) and SWCNTs. An optimization of the PNIPAM and SC concentrations as well as the addition of sodium borate achieved the selective release of (6,4) nanotubes into the liquid phase after the PNIPAM phase transition. The sorting mechanism with PNIPAM was explained by the difference in the micelle configuration on the SWCNTs and the hydrophobic collapse of PNIPAM in the presence of a sodium salt. The one-step sorting procedure for obtaining SWCNTs with a single chirality via PNIPAM will help promote their widespread application.

Quantum Yield Enhancement in Graphene Quantum Dots via Esterification with Benzyl Alcohol.

The quantum yield of graphene quantum dots was enhanced by restriction of the rotation and vibration of surface functional groups on the edges of the graphene quantum dots via esterification with benzyl alcohol; this enhancement is crucial for the widespread application of graphene quantum dots in light-harvesting devices and optoelectronics. The obtained graphene quantum dots with highly graphene-stacked structures are understood to participate in π-π interactions with adjacent aromatic rings of the benzylic ester on the edges of the graphene quantum dots, thus impeding the nonradiative recombination process in graphene quantum dots. Furthermore, the crude graphene quantum dots were in a gel-like solid form and showed white luminescence under blue light illumination. Our results show the potential for improving the photophysical properties of nanomaterials, such as the quantum yield and band-gap energy for emission, by controlling the functional groups on the surface of graphene quantum dots through an organic modification approach.

Aqueous synthesis of protectant-free copper nanocubes by a disproportionation reaction of Cu2O on synthetic saponite.

Here, we report a synthesis of Cu nanocubes by photoreduction of CuSO4. Because synthetic saponite (one of the layered clay minerals) was used as the adsorbent, the nanocubes contained no capping agents or protectants, and the disproportionation reaction of Cu2O with H2SO4 was found to be the key for morphological control.

Selective extraction of semiconducting single-walled carbon nanotubes with a thermoresponsive polymer.

The extraction of single-walled carbon nanotubes by exploiting the phase transition of poly(N-isopropylacrylamide), a thermoresponsive polymer, was performed to obtain homogenous electronic properties. The semiconducting single-walled carbon nanotubes were selectively extracted into the aqueous phase of a PNIPAM solution above the lower critical solution temperature.

Mass and Charge Measurements on Heavy Ions.

The relationship between mass and charge has been a crucial topic in mass spectrometry (MS) because the mass itself is typically evaluated based on the m/z ratio. Despite the fact that this measurement is indirect, a precise mass can be obtained from the m/z value with a high m/z resolution up to 105 for samples in the low mass and low charge region under 10,000 Da and 20 e, respectively. However, the target of MS has recently been expanded to the very heavy region of Mega or Giga Da, which includes large particles and biocomplexes, with very large and widely distributed charge from kilo to Mega range. In this region, it is necessary to evaluate charge and mass simultaneously. Recent studies for simultaneous mass and charge observation and related phenomena are discussed in this review.

Near-Infrared Photoluminescence Properties of Endohedral Mono- and Dithulium Metallofullerenes.

The optical properties of endohedral metallofullerene molecules can be tuned by changing the fullerene size as well as the number of metal atoms inside the fullerene cages. In this work we have synthesized and isolated a series of mono- and dithulium metallofullerenes, including Tm@C82 (isomers I, II, III, IV), Tm@C88 (I-IV), Tm2@C82 (I-III), and (Tm2C2)@C82 (I-III). Near-infrared photoluminescence is observed from the thulium metallofullerenes. By changing the number of Tm ion in the fullerene cage, we have found that one can vary and tune the photoluminescence from 1200 to 1300-2000 nm observed for Tm(2+) (4f(13)) in Tm@C88 and Tm(3+) (4f(12)) in (Tm2C2)@C82, respectively. The photoluminescence intensity depends sensitively on the fullerene cages. (Tm2C2)@C82 (III) exhibits the highest photoluminescence intensity among the three structural isomers because of its large HOMO-LUMO energy gap.

Synthesis and UHV-STM observation of the T(d)-symmetric Lu metallofullerene: Lu2@C76(T(d)).

The first T(d)-symmetric lutetium metallofullerene, Lu(2)@C(76), has been synthesized, isolated, and characterized. Because of the charge transfer from the encapsulated Lu atoms to the T(d)-C(76) fullerene cage, the otherwise unstable T(d)-C(76) fullerene can be significantly stabilized as a Lu(2)@C(76) fullerene. Both STM and STS results are consistent with a charge state of (Lu(2))(6+)@C(76)(6-)(T(d)).

Determining exact molar absorbance coefficients of single-wall carbon nanotubes.

A new spray technique coupled with atomic force microscopy is developed to obtain the absolute number of carbon nanotubes in a unit volume. By using the present technique, the absolute molar absorbance coefficient of single-wall carbon nanotubes (SWNTs) has been determined and found to be ca. 2-5 x 10(7) L mol(-1) cm(-1). This molar absorbance coefficient enables us to deal with carbon nanotubes as individual "molecules" and to adequately compare them with other related compounds such as fullerenes. The absorbance coefficient of SWNTs is found to be only 100 times as large as those of fullerenes. This indicates that the large aspect ratio, random orientation in dispersion solution and anisotropic absorption properties of SWNTs substantially reduce their absorption probability.

A new AFM-HRTEM combined technique for probing isolated carbon nanotubes.

A new technique has been developed for characterizing individual carbon nanotubes (CNTs). This technique combines atomic force microscopy (AFM) measurements with an independent determination of the CNT structure obtained by using thin carbon grid membranes for high-resolution transmission electron microscopy (HRTEM) measurements. The membrane grids are easily transferred onto silicon oxide substrates, where they are observed by AFM and an optical charged-coupled device. Electrostatic force microscopy measurements are also performed on single- and double-walled CNTs whose structures had previously been determined by HRTEM. The results reveal that the diameter and outer tube length have a greater effect on determining the capacitance of the nanotubes than the presence of the inner tube of double-walled CNTs.

An efficient fabrication of vertically aligned carbon nanotubes on flexible aluminum foils by catalyst-supported chemical vapor deposition.

An efficient and versatile growth of thin-layer carbon nanotubes on a flexible aluminum foil (for kitchen use) by catalyst-supported chemical vapor deposition is reported. The aluminum foil used in the present experiment is commercially available for kitchen use. The electron-beam vapor deposition and dip-coating have been used for preparing catalysts on the aluminum foil. Vertically aligned thin-layer CNTs with typical diameters of 2.5-6.0 nm and lengths up to 90 µm are obtained when ethanol is used in combination with Fe and Co catalyst particles at a growth temperature of around 650 °C under an Ar/H(2) gas flow. Thermo-gravimetric analyses together with HR-TEM observations indicate that the purity of the CNTs synthesized by the current technique is very high.

Magnetic properties and crystal structure of solvent-free Sc@C82 metallofullerene microcrystals.

Magnetic properties of solvent-free crystals of the endohedral Sc@C82 are investigated by SQUID and X-ray powder diffraction. We find that the crystal is a paramagnet and the magnetic susceptibility decreases from 150 K with evidence of antiferromagnetic-like interactions by slow cooling. X-ray crystal analysis reveals the presence of a phase transition at 150 K, which is attributed to an orientational ordering transition of the fullerene molecules. At low temperatures we find a magnetic metastable state that can be controlled by the cooling rate. The metastable state can be formed by rapid cooling. The direction of Sc@C82 molecular axis in the crystals is disordered in the metastable state, and the susceptibility is higher than that in the slow cooling case at low temperature.

Placing and imaging individual carbon nanotubes on Cu(111) clean surface using in situ pulsed-jet deposition-STM technique.

We report pulsed-jet deposition of single-wall and double-wall carbon nanotubes (SWNTs and DWNTs; CNTs) onto a clean Cu(111) surface and their scanning tunneling microscopy (STM) observations under ultra-high vacuum (UHV). The clean Cu(111) surface prepared by a repeated Ar-sputtering and annealing is introduced into a load-lock chamber kept at a 10(-5)-Pa range vacuum, and the CNTs dispersed in a chloroform solution by ultrasonication are pulse-injected onto the surface. Since the substrate is annealed at 700 K to remove the residual solvent molecules, high resolution lattice images of the CNTs are successfully observed by STM. High-resolution chirality-resolved images of the two SWNTs with a metal cluster are also observed, supporting the well accepted growth mechanism of the CNTs from the metal-catalyst cluster. The present pulsed-jet deposition in high-vacuum is superior to the conventional spin-coating or drop-coating techniques for preparing clean and well-defined CNTs on clean surfaces for high-resolution and contamination-free UHV-STM observation.

Enhanced 1520 nm photoluminescence from Er3+ ions in di-erbium-carbide metallofullerenes (Er2C2)@C82 (isomers I, II, and III).

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.

Enhanced photoluminescence from very thin double-wall carbon nanotubes synthesized by the zeolite-CCVD method.

Photoluminescence (PL) from purified (>90%) double-wall carbon nanotubes (DWNTs), which have been synthesized by zeolite catalyst-supported chemical vapor deposition (zeolite-CCVD), of very small diameters (0.8-nm average inner tube) is reported. The PL contour mappings for various ratios (1-90%) of double- versus single-wall carbon nanotubes by thermal oxidation have enabled us to unambiguously identify the chirality of inner tubes for the DWNTs synthesized. After the extensive high-temperature oxidation at 700 degrees C, high-purity (>90%) DWNTs of approximately 0.8 nm inner diameter are obtained, and most of these correspond to the DWNTs having inner tubes with chiralities of (7,5), (7,6), and (9,4).

High-resolution analysis of (Sc3C2)@ C80 metallofullerene by third generation synchrotron radiation X-ray powder diffraction.

The X-ray structure of Sc(3)C(82) is redetermined by the MEM/Rietveld method by using synchrotron radiation powder data at SPring-8, where the C(2) encapsulated structure available to discuss the Sc-Sc interatomic distances has been determined. The encapsulated three scandium atoms form a triangle shape. A spherical charge distribution originating from the C(2) molecule is located at the center of the triangle. Interatomic distances between Sc and Sc are 3.61(3) A in the triangle. The distance between Sc and the center of the C(2) molecule is 2.07(1) A.

High-yield synthesis of single-wall carbon nanotubes on MCM41 using catalytic chemical vapor deposition of acetylene.

High-quality single-wall carbon nanotubes (SWNTs) with narrow diameter distribution have been grown on Fe/Co-loaded MCM41 by using acetylene as the carbon source within a short reaction period, typically 10 min or less. The optimum temperature for SWNTs synthesis is 850 degrees C. Longer reaction time (i.e., 30 min) favors the formation of multiwall carbon nanotubes (MWNTs) and graphitic carbon. When the reaction time is reduced to less than 10 min, formation of MWNTs and graphitic carbon is greatly suppressed, and high-quality SWNTs dominates the yield. The surface of the as-grown SWNTs is found to be free from amorphous carbon, as observed from high-resolution transmission electron microscope (HRTEM) analysis. Raman spectral data show a G/D ratio above 10, indicating that the as-grown SWNTs have very few defects. Furthermore, radial breathing mode (RBM) analysis reveals that the diameter distribution of the current SWNTs is narrow and ranges from 0.64 to 1.36 nm.

Entrapping of exohedral metallofullerenes in carbon nanotubes: (CsC60)n@SWNT nano-peapods.

Exohedral C60-based metallofullerenes, CsC60, have been synthesized and successfully encapsulated into single-wall carbon nanotubes (SWNTs) in high yield by reducing C60 molecules into anions. High-resolution transmission electron microscopy (HRTEM) images and in situ electron energy loss spectroscopy (EELS) indicate that Cs atoms and C60 molecules align within SWNTs as CsC60 exohedral metallofullerenes, and that the formal charge state of encaged CsC60 is expressed as Cs+1C60-1. The present peapods with the exohedral metallofullerenes provide a new insight and the possibility to fine-tune the electronic and transport properties of carbon nanotubes.