Junichi Hojo

Sonochemical synthesis of monodispersed magnetite nanoparticles by using an ethanol-water mixed solvent

The magnetite nanoparticles were synthesized in an ethanol-water solution under ultrasonic irradiation from a Fe(OH)(2) precipitate. XRD, TEM, TG, IR, VSM and UV/vis absorption spectrum were used to characterize the magnetite nanoparticles. It was found that the formation of magnetite was accelerated in ethanol-water solution in the presence of ultrasonic irradiation, whereas, it was limited in ethanol-water solution under mechanical stirring. The monodispersibility of magnetite particles was improved significantly through the sonochemical synthesis in ethanol-water solution. The magnetic properties were improved for the samples synthesized under ultrasonic irradiation. This would be attributed to high Fe(2+) concentration in the magnetite cubic structure.

ORGANIC GELS ARE USEFUL AS A TEMPLATE FOR THE PREPARATION OF HOLLOW FIBER SILICA

A novel mesoporous silica with a tubular structure has been prepared using organic gel fibers as a template.

Formation of fine silicon carbide powders by a vapor phase method

Abstract The formation of silicon carbide powders by the vapor phase reaction of SiCl4 + CH4 (1400–1500°C), CH3SiCl3 (800–1400°C) and (CH3)4Si (800–1400°C) was studied. The effectiveness of the silicon sources was in the sequence (CH3)4Si > CH3SiCl3 > SiCl4, in accordance with the thermodynamic parameters. Fine β-SiC powders were produced by the pyrolysis of (CH3)4Si in hydrogen above 900°C. The crystallinity of the products increased with increasing reaction temperature. The particles were spherical and had average sizes of 0.02–0.12μm which decreased with increasing reaction temperature and with decreasing (CH3)4Si concentration. A reaction process consisting of the formation of particles of organosilicon polymers and their subsequent decomposition was proposed for the formation of SiC particles by the pyrolysis of (CH3)4Si.

Properties of magnetic nanoparticles in the Brownian relaxation range for liquid phase immunoassays

Properties of magnetic nanoparticles in the Brownian relaxation region were studied. Using the magnetic nanoparticles that exhibit remanence, we measured the magnetic properties, such as static magnetization, magnetic relaxation, and alternating current susceptibility, in a solution. Comprehensive comparisons were made between the experimental results and the theoretical ones predicted from the Brownian relaxation. From the comparison, the distributions of the particle parameters, i.e., the magnetic moment and the relaxation time, were estimated. It was shown that all the magnetic properties can be well explained when we take into account the parameter distributions in the sample.

Sonochemical coating of magnetite nanoparticles with silica

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating.

A pH-responsive carboxylic β-1,3-glucan polysaccharide for complexation with polymeric guests

The helix-forming nature of β-1,3-glucan polysaccharides is a characteristic that has potential for producing gene carriers, bio-nanomaterials and other chiral nanowires. Herein, carboxylic curdlan (CurCOOH) bearing the β-1,3-polyglucuronic acid structure was successfully prepared from β-1,3-glucan polysaccharide curdlan (Cur) by one-step oxidation using a 4-acetamido-TEMPO/NaClO/NaClO(2) system as the oxidant. The resulting high-molecular-weight CurCOOH was proved to bear the 6-COOH group in 100% purity. The optical rotatory dispersion (ORD) spectra indicated that the obtained CurCOOH behaves as a water-soluble single-strand in various pH aqueous media. This advantage has allowed us to use CurCOOH as a polymeric host to form various macromolecular complexes. For example, complexation of CurCOOH with single-walled carbon nanotubes (SWNTs) resulted in a water-soluble one-dimensional architecture, which formed a dispersion in aqueous solution that was stable for several months, and much more stable than SWNTs complexes of the similar negatively-charged polyacrylic acid (PAA) and polymethacrylic acid (PMAA). It was shown that in the complex, SWNTs are effectively wrapped by a small amount of CurCOOH, enabling them to avoid electrostatic repulsion. This pH-responsive CurCOOH formed a very stable complex with cationic water-soluble polythiophenes (PT-1), which was stabilized not only by the hydrophobic interaction but also by the electrostatic attraction between trimethylammonium cations in PT-1 and dissociated anionic COO(-) groups in CurCOOH. The included PT-1 became CD-active only in the neutral to basic pH region, and the positive Cotton effect suggested that the conjugated main chain is twisted in the right-handed direction. We also found that CurCOOH can interact with polycytidylic acid (poly(C)) only under high NaCl concentrations, the binding and release of which could be controlled by a change in the salt concentration. We believe, therefore, that CurCOOH bearing a dissociable COOH group can act as a new potential polymeric host to construct novel polymeric complexes applicable for gene carriers, biosensors, chiral polymer assemblies, etc.

Size Distribution of Magnetic Marker Estimated from AC Susceptibility in Solution for Biosensor Application

The ac susceptibility of magnetic markers in solution was studied for biosensor application, where the marker consisted of magnetic nanoparticles and a coating material. From the frequency dependence of the susceptibility caused by the Brownian rotation of the marker, we estimated the distribution of marker size, which is an important parameter for biosensor application. For this purpose, we analyzed the experimental data by the singular value decomposition (SVD) method. Using this method, we can directly estimate the size distribution without assuming any distribution function. The estimated distributions were also compared with those obtained from optical dynamic light scattering (DLS) measurements. It was shown that the size distribution estimated by magnetic measurement (SVD) slightly shifts to a size lower than that estimated by the optical measurement (DLS). It was also shown that the frequency dependence of the susceptibility can be better explained by the size distribution estimated by the SVD method than by the distribution estimated with DLS. The difference between the magnetic and optical measurement results was discussed in terms of aggregation of the markers.

Synthesis of mesoporous silica modified with titania and application to gas adsorbent

Abstract Three kinds of silica-based mesoporous materials were synthesized and subjected to adsorption study. Firstly is pure silica involving >1000 m 2 /g of specific surface area (PS; pure silica). Secondly, titania was deposited onto the surface of pure silica (TDS; titania-deposited silica). Thirdly, titania was incorporated into silica network by a partial hydrolysis method (STM; silica–titania mesoporous composite). Acidity and adsorbability for water were enhanced by the addition of titania, especially in STM.

The sinterability of ultrafine WC powders obtained by a CVD method

The sintering behaviour of ultrafine WC powders produced by a CVD method (particle size <0.3μm) and commercial WC powders (particle size ~ 1μm) is investigated in hydrogen and in vacuum. It has been found that ultrafine WC powders have an extremely high sinterability and give a sintered body with a relative density of 100% by sintering at a considerably lower temperature than normal, such as 1750° C. Also WC powders with a large particle size and a wide-size distribution have a high sinterability caused by the presence of fine particles and the sinterability of WC powders is influenced significantly by the sintering atmosphere. The atmospheric effect is discussed in connection with the heating behaviour of a surface oxide layer and free carbon.

Incorporation of oxide nanoparticles into barrier-type alumina film via anodic oxidation combined with electrophoretic deposition

The incorporation of metal oxide nanoparticles into a barrier-type anodic alumina film on an Al substrate was investigated using a one-step anodic oxidation combined with electrophoretic deposition. Basically, the electrolysis was carried out in an oxide nanoparticle dispersed ammonium pentaborate solution using an Al substrate as the anode. As a result, the TiO2 and SiO2 nanoparticles with a negative surface charge could be introduced into the alumina film grown on the Al anode, and the film thickness increased by the dispersion of the nanoparticles inside the alumina layer. The measurement of the capacitance and corrosion potential demonstrated that the present method was valid for enhancing the characteristics of the barrier-type alumina film.