Iron Pyrite (FeS₂), which has received much attention as an earth abundant semiconductor material, has relatively low bandgap of 0.95 eV. Downsizing to present quantum confinement effect enables us to increase the bandgap. This report proposed the electro-spray deposition (ESD) method to downsize the nanoparticle (NP) of FeS₂. It is found that the fabricated FeS₂ contained Marcasite which is impurity phase of FeS₂. The TEM observation revealed the NPs of 5-nm diameter were produced by the ESD method. We suggested that the NPs were produced via Rayleigh fission since the distribution of NP’s diameter were scattered, resulting in poor fitting with logarithmic normal distribution.

In this research project, we attempted to prepare the novel catalyst for steam reforming process by chemical solution deposition. Perovskite material such as barium titanate (BTO) has been widely incorporated into the long life catalyst for steam reforming process. However, this material is well known as the low surface area, resulting in the low catalytic activity. In our previous study, BTO hollow particles with high surface area was prepared by template method, and this material has relatively good catalytic activity. However, the preparation method for the BTO hollow particle was quite complicate process for mass production. To solve this subject, we attempted to prepare the barium titanate with high surface area be one step chemical solution deposition in this research. We selected SiO₂ nano-particle as a core particle, and barium titanate was nano-coated on a core-particle using double alkoxide precursor solution. As a result, BTO/SiO₂ core-shell hybrid particle with 33 m²/g surface area was obtained by one step chemical solution deposition. Subsequently, metal component such as Ni and Co was loaded on a obtained BTO/SiO₂ hybrid particle to estimate the catalytic activity for the ethanol steam reforming process. As a result, the catalytic activity of the obtained hybrid materials was nearly equal to that of the BTO hollow particle.

Single-phase nanoparticles of brookite, a less common polymorph of TiO₂ than rutile and anatase, were successfully synthesized using a water-soluble titanium glycolate complex as the precursor and nanoparticle growth by an oleate-modified hydrothermal growth method. The synthesized particles were approximately 30 nm in size, had high crystallinity, and were highly dispersible in water. The morphology of the synthesized particles was a pseudocube surrounded mainly with four {210} and two {001} faces, accompanying truncation with small {111} facets. It is considered that the preferential absorption of oleate molecules on {210} and {001} faces resulted in the pseudocubic crystal shape. The brookite TiO₂ nanoparticles had amphiphilic properties. The ~20–40 nm TiO₂ nanoparticles were highly dispersible in both water and cyclohexane. The activity of the brookite nanoparticles for the degradation of acetaldehyde under UV irradiation was higher than that of Degussa P-25 TiO₂ powder.

This research aims to develop a method to realize anisotropic surface modification of metal oxide nanoparticles. The anisotropic surface modification can be realized under the condition that the interaction with organic molecules largely depends on the crystal faces. In order to evaluate the interaction between organic molecules and crystal faces of metal oxide nanoparticles, we placed rutile and anatase phases of TiO₂ single crystal substrate in high-temperature and high-pressure water with various organic molecules. After this hydrothermal treatment, substrates were rinsed and analyzed by contact angle measurement and X-ray photoelectron spectroscopy. The results showed that rutile (110) face had higher affinity with phosphoric acid and anatase (101) also had higher affinity with amines. These results are indispensable to realize anisotropic surface modification of metal oxide nanoparticles during their synthesis.

The use of magnetic nanoparticles in biomedical applications has been studied for a long time. When magnetic nanoparticles are exposed to a magnetic field they exhibit various responses. We have been focusing on the phenomenon by which magnetic nanoparticles dispersed in a liquid emit sonic waves when they are exposed to an AC magnetic field. We term this phenomenon as sonic wave emission by stimulated magnetic nanoparticles (SWESMAN). SWESMAN is a very recent phenomenon as it was first discovered in 2008. Magnetic nanoparticles exposed to an alternating magnetic field of frequency f emit a sonic wave of frequency 2f. In this paper, we demonstrate that the positions of magnetic particles embedded in a polymer gel can be determined from the acoustic pressure of the sonic waves that they emit, since the acoustic pressure is proportional to the distance between the magnetic particles and the detection point. We also propose other potential applications of SWESMAN. A delay between the SWESMAN signal and the excitation current was found. We conjecture that this delay originates from the propagation distance of sonic waves emitted by magnetically stimulated particles. We examine the possibility of using the signal delay in practical applications.

In this project, we conducted molecular dynamics simulations of penetration/permeation behaviors of alkanethiol-functionalized gold nanoparticles into/across a model biological membrane (phospholipid bilayer). In particular, effects of surface charge, length of a carbon chain of the alkanethiol, and composition and structure of the lipid bilayer were analyzed. As a result, effects of surface properties of the gold nanoparticles on their adhesion and penetration mechanism into the model cell membrane at molecular level were elucidated. It was also found that more realistic structure of the lipid bilayer can highly induce spontaneous permeation of nanoparticles across the model cell membrane.

We attempted to prepare sustained release fine particles using a two-step mechanical powder processing method; particle-shape modification and dry particle coating. First, particle shape of bulk drug was modified by mechanical treatment to yield drug crystals suitable for the coating process. Drug crystals became more rounded with increasing rotation speed, which demonstrates that powerful mechanical stress yields spherical drug crystals with narrow size distribution. This process is the result of destruction, granulation and refinement of drug crystals. Second, the modified drug particles and polymer coating powder were mechanically treated to prepare composite particles. Polymer nanoparticle agglomerate obtained by drying poly(meth)acrylate aqueous dispersion was used as a coating powder. The porous nanoparticle agglomerate has superior coating performance, because it is completely deagglomerated under mechanical stress to form fine fragments that act as guest particles. As a result, spherical drug crystals treated with porous agglomerate were effectively coated by polymeric powder, showing sustained release after curing process. From these findings, particle-shape modification of drug crystals and dry particle coating with nanoparticle agglomerate using a mechanical powder processor is expected as an innovative non-aqueous technique for preparing controlled-release coated particles having high drug content and size smaller than 100 μm.

Inorganic phosphors that have luminescence switching function are expected to visualize changes in surrounding media. In this study, an attempt has been made to develop a novel phosphor based on CeO₂ with such function using its excellent redox responsibility. The Sm³⁺ ion has been chosen as a dopant in CeO₂ because it shows a relatively strong visible emission due to allowed magnetic-dipole transitions in a cubic CeO₂ host. Since the redox responsibility was thought to depend largely on the structure of CeO₂:Sm³⁺ particles, three kinds of synthetic methods have been employed, namely, the solid-state reaction, the spray drying, and the hydrothermal method, to obtain samples of different microstructures. The sample from the solid-state reaction was composed of micrometer-sized particles and it showed very poor luminescence switching function. On the other hand, the sample from the spray drying was a nano-sized powder and exhibited luminescence quenching in response to Ce⁴⁺→Ce³⁺ reduction by an aqueous L(+)-ascorbic acid solution at room temperature. The samples from the hydrothermal reaction had three kinds of morphologies as cube-like, sphere-like, and rod-like nanoparticles. The luminescence quenching behavior also depended on such the morphologies and only the rod-like sample showed appreciable quenching. The reduced rod-like sample could be oxidized by H₂O₂, followed by luminescence recovery. Thus the CeO₂:Sm³⁺ phosphor has been proven to have luminescence switching function, depending on its microstructure, and is promising as an inorganic imaging powder.

In order to explore whether lunar regolith induce airway hyperreactivity or bronchial asthma or not, we examined cellular influences of lunar regolith simulant whose component are similar to that of the lunar regolith. Particularly, we focused chemical component and particle size because the difference in the gravity between earth and moon, affect the different in the particle size of respirable dusts. The regolith simulant was fractionated to <10 μm, <25 μm and 10–25 μm by gravitational sedimentation in suspensions. The particle size with less than 10 μm means the respirable dust in earth, and particle size with less than 25 μm means respirable dusts in moon by calculating the one sixth of gravity of earth. Additionally, we also examined cellular influences of fine regolith simulant. Human lung carcinoma A549 cells were incubated at concentration of 0.1 and 1.0 mg/ml of these regolith simulants. After 24 h exposure, cytotoxicity, oxidative stress and immune response were examined. When the concentration was 1.0 mg/ml, cell membrane damage, mitochondrial dysfunction and induction of IL-8 were observed. Compared with crystalline silica which is positive control, cellular influences of the regolith simulant at concentration of 0.1 mg/ml were little. Secretion of IL-1β and TNF-α was observed at concentration of 1.0 mg/ml, however, induction of their gene expression did not observed at 24 h after exposure. Induction of cellular oxidative stress was small. Although the cell influence tended to be strong in the <10 μm particles, there was no remarkable difference. These results suggest that influence of chemical components and particles size on the cellular influence of lunar regolith simulant is small.

We developed a unique numerical method for direct numerical simulations (DNS) of dense colloidal dispersions. This method, called the smoothed profile method (SPM), enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electro- hydrodynamic couplings can be fully taken into account. We have applied the SPM successfully for simulating the dynamics of various particle dispersions including the following problems.

1) electrophoresis of charged colloids (DC/AC fields)

2) thermal diffusion of colloidal particles

3) rheology of colloidal dispersions

4) motions of a chain in shear flow

5) hindered settling of particles

6) the motions of colloidal particles in a compressible fluid

Recently, the SPM is extended for dispersions of self-propelled particles (squirmer) and also for dispersions of rigid particles. One can download an open software called KAPSEL, which implements the SPM, from the website.

In this study, we propose polymerization of monodisperse silica particles using organic reactions between the particle surfaces. The “monomer” particles are prepared by modified Stöber synthesis and contain organic functional group on their surface. The “polymerization” can theoretically be carried out between the same kind of organic groups or between two kinds of reactive functional groups. The latter reaction will result in the formation of “alternating copolymer,” which allows the formation of mesoporous solids with various pore size distributions. We have optimized the combination of silanes, reaction conditions for the formation of monomer and polymerization. The structure has been analysed by nitrogen and water adsorptions, SEM, DLS and Raman spectroscopy.