Jun-ichi Minato

Arsenate sorption on schwertmannite

Abstract The sorption mechanism of arsenate [As(V)] on schwertmannite was investigated by means of batch sorption experiments as a function of As(V) concentration in acidic solution at 25 °C. Structural simulation indicated that the surface sites of schwertmannite comprised various O atom (or hydroxyl) and SO4 groups. Sorption experiments showed that the reactive sites for As(V) sorption are surfacecoordinated SO4 groups rather than surface hydroxyl groups, as reported in earlier studies. The As(V) sorption mechanism involves ligand exchange with surface-adsorbed and structural SO4. The results of the sorption experiments also suggested monodentate As(V) coordination at the surface-adsorbed SO4 sites [(Fe1)2SO4] and bidentate As(V) coordination at the structural SO4 sites [(Fe3)2SO4]. The overall ligand-exchange reaction was 0.61 (Fe1)2SO4 + 0.39 (Fe3)2SO4 + 1.61 H2AsO4- → 1.22 Fe1H2AsO4 + 0.39 (Fe3)2HAsO4 + 0.39 H+ + SO42- where the 1 and 3 in Fe1 and Fe3 are coordination numbers. The equilibrium constant derived for the exchange reaction, log KEX = 4.96, describes the observed As(V) sorption behavior. Nanocrystalline materials like schwertmannite are widespread in nature and typically contain significant amounts of anionic impurities, such as sulfate and silicate. Our results indicate that the effects of impurities can be significant and should be considered in order to gain a realistic understanding of sorption processes in natural systems.

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.

Characterization of fullerene nanotubes prepared by the liquid?liquid interfacial precipitation method

Abstract C70 nanotubes were prepared by using pyridine and isopropyl alcohol and heated in air at 250 °C in order to eliminate the contained solvents ‘heat treated C70’. The C70 nanotubes were also successfully prepared by use of pyridine and isobutyl alcohol. The C70 nanotubes heated at 1100 °C in vacuum became amorphous carbon, but retained the tubular structure. The structural characteristics of these C70nanotubes are observed through their high-resolution transmission electron microscopy.

Structure and properties of fullerene nanowhiskers prepared by the liquid-liquid interfacial precipitation method

Fine needle-like crystals of C60, “C60 nanowhiskers”, were found in 2001 in a colloidal solution of PZT ceramics with added C60. Not only the C60 nanowhiskers but also nanowhiskers composed of C70 and C60 derivatives can be synthesized at room temperature by using the liquid-liquid interfacial precipitation method (LLIP method). Tubular nanowhiskers composed of C60 and C70 molecules have been successfully fabricated by using the LLIP method as well. The tubular fullerene nanowhiskers are named “fullerene nanotubes” here. The tubular fullerene nanowhisker is a new form of single crystalline needle-like crystal whose wall is composed of fullerene molecules. In this paper, structural, electrical and mechanical properties of the fullerene nanowhiskers and fullerene nanotubes are discussed.

Synthesis of fullerene nanotubes and microtubes for materials storage, delivery and recovery

Tubular, needle-like crystals of C60 with diameters ranging from micro to nano sizes have been synthesized by the liquid–liquid interfacial precipitation (LLIP) method. The C60 nano- and microtubes can absorb various solutions of alcohol and water, showing that they can be promising containers for materials storage and recovery. Further, C60 microtubes vertically aligned on porous alumina membranes have been successfully prepared for the first time by a modified LLIP method. The vertically aligned C60 microtubes will find a variety of application for bio and environmental uses.

Alkali‐Hydrothermal Modification of Air‐Classified Korean Natural Zeolite and Their Ammonium Adsorption Behaviors

Abstract Korean natural zeolite in which clinoptilolite and mordenite coexisted with feldspar and illite as impurities, was treated with 1.0, 3.0, and 5.0 M NaOH solutions at 100, 150, and 200 °C under autogeneous pressure for 17 hours either with or without an air classification as pretreatment. Phillipsite, analcime, and hydroxycancrinite were identified as reaction products depending on the reaction temperature and NaOH concentration. The air classification of the starting material prior to alkali‐hydrothermal treatment effectively reduced the amount of feldspar, which hardly reacted to zeolite in the hydrothermal reaction. The ammonium adsorption behavior of the treated and untreated samples were investigated in solutions of between 10−3 M and 10−2 M NH4Cl. The amount of adsorbed ammonium ions in alkalihydrothermally treated product from air‐classified material was higher by about two times than was that of corresponding untreated zeolites. The air‐classified zeolite treated in 3 M NaOH solution at 100 °C showed the highest adsorption of ammonium ion among samples. It was explained by both the phase change of clinoptilolite and mordenite to phillipsite with higher cation exchange capacity and the reduction in the amount of feldspar that was less reactive under hydrothermal conditions for the formation of phillipsite. The results indicated that the combination of the air classification and alkali‐hydrothermal treatment effectively improved the adsorption behavior for ammonium ions on natural zeolites with impurities.

Structural, mechanical, and electrical properties of high-pressure sintered C60 nanowhiskers and C60 powder

C60 nanowhiskers fabricated by the liquid-liquid interfacial precipitation method were sintered at 800 °C under 5.5 GPa for 2 h. Structural, mechanical, and electrical properties of sintered C60 nanowhiskers were compared with those of sintered pristine C60 powder under the same conditions. Sintered C60 nanowhiskers showed a relatively high density and a fine texture as compared to sintered pristine C60 powder probably due to the fibrous morphology of starting C60 nanowhiskers. Analysis using four-probe micro manipulator system (SUNYOU, MMS0024-01) revealed low electrical resistivity for the sintered samples. Electrical resistivity of sintered C60 nanowhisker was slightly higher than that of sintered pristine C60 powder. Both of the sintered samples showed high micro-Vickers hardness about 1100 HV. XRD patterns of the sintered samples showed only diffuse peaks that are characteristic of glassy carbon. The peak intensity of glassy carbon in the sintered C60 nanowhiskers was weaker than that of sintered pristine C60 powder, which was consistent with the different electrical resistivity. Characterization by FTIR and Raman spectroscopy confirmed no sign of C60 molecules for both the sintered samples indicating that C60 molecules were significantly reduced by the high temperature and high pressure treatment. The differences of textural and electrical properties between sintered C60 nanowhiskers and sintered pristine C60 powder suggest a good sinterability of the C60 nanowhiskers due to their fibrous morphology as compared with pristine C60 powder.