神鳥 和彦

The decomposition of protein molecules from a mixed-protein solution on the surface of calcium hydroxyapatite (CaHap) and Ti(IV)-doped CaHap (TiHap) particles with a Ti/(Ca + Ti) atomic ratio (X (Ti)) of 0.10 and 0.20 under UV irradiation of 365 nm in wavelength was investigated. Acidic bovine serum albumin (BSA) and basic lysozyme (LSZ) were employed as a model of pathogenic proteins. The photocatalytic activities of TiHap particles were estimated from the decomposition of BSA and LSZ from the BSA (2.5 mg/cm(3))-LSZ(1.0 mg/cm(3)) mixture under 1 mW/cm(2) UV irradiation dispersed in a 10-mL quartz tube. No change in BSA concentration by UV irradiation was observed for all the unheated original CaHap and TiHap particles without and with low photocatalytic activities, respectively. Similar results were observed for the systems that employed heat-treated particles endowed a high photocatalytic activity by heat treatment at 650 A degrees C for 1 h. On the other hand, a selective photocatalytic decomposition was observed for the LSZ, i.e., only LSZ molecules were decomposed completely from the BSA (2.5 mg/cm(3))-LSZ(1.0 mg/cm(3)) mixture by using heat-treated TiHap particles with X (Ti) = 0.10 and 0.20. This selective decomposition by TiHap particles was interpreted by higher adsorption affinity of positively charged LSZ to highly negatively charged TiHap together with low molecular weight and rigid structure of LSZ molecules.

The effects of polyvinyl alcohol (PVA) molecules on the porosity of disk-like hematite particles produced from the forced hydrolysis reaction using two kinds of PVA molecules with a well-defined molecular weight and a high degree of saponification (PVA-105 and PVA-124) were investigated. It is evident from TEM and field-emission scanning electron microscope (FE-SEM) measurements that a fraction of particles lost their spherical habit and acquired a disk-like shape by the addition of small amounts of both PVA molecules, though no difference in the particle size between the two PVA systems was observed. FE-SEM images of the particles revealed that the disk-like hematite particles are made up of small cluster particles with a diameter of approx. 5-10 nm. The disk-like particles produced a rather lower concentration for PVA-124 with a higher molecular weight than that for PVA-105 with a lower molecular weight. This fact was due to the large number of hydroxy groups in PVA-124 molecules than in PVA-105; hydroxy groups act as adsorption sites onto polynuclear (PN) primary particles and cause pronounced effects on the formation and structure of particles during the aggregation of PN particles. It was clarified from N-2 adsorption measurements at 77 K that the porosity of the hematite particles can be controlled from microporous to mesoporous by changing the concentrations of PVA-105 and PVA-124, as was classified into three groups, i.e., groups 1, 2, and 3. The control particles produced without PVA molecules, classified into group 1, showed type IV adsorption isotherms, and only the voids produced between spherical particles were detected as mesopores. On the other hand, the particles produced with small amounts of PVA produced micropores as classified in group 2. In this group, the particles produced uniform micropores after being outgassed at 100-200 A degrees C. The hematite particles produced with high concentrations of PVAs were classified into group 3. In this group, the particles after being outgassed at lower temperature produced micropores with diameters between 0.6 and 2.0 nm, though the micropores in the particles changed to mesopores after outgassing at 300 A degrees C. This mesopore formation was attributed to the elimination of the PVA-adsorbed layer by evacuation at 300 A degrees C, i.e., the large voids residing in the disk-like hematite particles make the particles mesoporous. This mesopore formation was further confirmed by adsorption experiments of C6H6(benzene) and CCl4 molecules at 298 K.

Calcium hydroxyapatite (Hap) particles were produced using a microreactor, and the relationship between the morphology of the Hap particles and the synthesis conditions using a microreactor was investigated. Sheet-like Hap particles could be produced continuously using a microreactor, whereas only rod-like Hap particles were produced by a batch method. The Ca/P atomic ratio of the Hap particles produced by microreactor processing was 1.40-1.46, which was lower than the stoichiometric value of 1.67. This result suggests that the Hap particles produced by microreactor processing were calcium-deficient. The size of the sheet-like Hap particles increased, and the length of b and c axes of the Hap particles increased as the mixing efficiency of the microreactor increased, whereas the length of a axis remained almost unchanged. The X-ray diffraction patterns revealed that the lattice constant of the c axis increased while that of the a axis decreased as the mixing efficiency of the microreactor increased and they came close to data reported in a previous study. The size and shape of Hap particles produced by microreactor processing significantly depend on the mixing efficiency of the microreactor.