柴 史之

The unique morphology was spontaneously constructed during precipitation under acidic conditions without specific growth modifiers.

One-dimensional hydroxyapatite (1D-HAP) particles were synthesized via a hydrothermal process using calcium sodium nitrilotriacetate (CaNa-NTA) as a Ca2+ reservoir. CaNa-NTA dissolved slowly at 150°C to enable Ca2+ to be supplied to the aqueous phase to react with phosphate and hydroxide ions. The average length and width of the 1D-HAP particles were 6.0μm and 60 nm, respectively the former depended on the amount of CaNa-NTA loaded but the latter did not. We investigated the formation of 1D-HAP particles by powder X-ray diffraction measurement and electron microscopy observation.

Synthesis procedures of monodisperse Prussian blue nanoparticles have been investigated to control their size in a citric acid reduction system. Two different procedures, enforced-nucleation and additional-growth ones, are applied to decrease and to increase the particle size, respectively. In the former, small amount of ascorbic acid is added in the citric acid solution as the enforced-nucleation agent, which varies the number of nuclei and thus the particle size depending on its amount. In the latter, a part of Prussian blue dispersion preliminarily prepared is introduced into the reactant solution that provides additional reaction resources for the further growth. As a result, Prussian blue nanoparticles are prepared in the range of 20-100nm in the mean size with narrow size distribution.

One-dimensional yttrium hydroxide particles of hexagonal crystal structure were selectively synthesized through a hydrothermal reaction of yttrium chloride solution that was alkalized by two-step addition of sodium hydroxide solution. Keeping the YCl3 solution at pH similar to 6.8 for a few minutes before raising the pH to the sufficient level (pH similar to 13) was concluded to be the practical requirement for the one-dimensional Y(OH)(3) particle formation. This requirement was successfully achieved by the two-step addition procedure that was applicable to adjust the pH values independently. The size distribution of one-dimensional particles was changed depending on the interval time between alkali-additions and on the pH of the hydrothermal reaction. The formation mechanism of the one-dimensional particles was also discussed.

This report proposes a procedure to synthesize monodisperse Au nanoparticles of different mean sizes (6-15 nm) under a constitute reaction condition only by altering the interval time between additions of citric acid and NaOH solutions into boiling HAuCl4 solution without any growth modifiers.

A procedure to obtain monodisperse nanoparticles of cobalt(1) hexacyanoferrate(III) was investigated. To prevent a reaction with [Fe(CN)(6)](3-), Co2+ was stored in the form of a citrate complex at pH 7.8. By lowering the pH to 3.4 by the addition of acid, part of the Co2+ was released and reacted with [Fe(CN)(6)](3-) to form nuclei, followed by their growth via mass-transfer of Co2+ from the citrate complex to the solid. Here, gelatin was employed as a protective colloid. The particles obtained were cubic and fairly monodisperse. The mean particle size was typically 160 nm and varied from 30 to 450 nm, depending on the reactant contents. The formation mechanism associated with equilibrium shifts was supported by a calculated estimation of free Co2+ on the basis of the equilibrium relationships involved in the preparation system.