Satoshi Motozuka

Synthesis and luminescence properties of Eu(III)-doped nanoporous silica spheres.

Europium (III) (Eu(3+))-doped nanoporous silica spheres were synthesized, and the states of Eu(3+) ions in the silica framework structure were investigated. The ordered nanopores were preserved with the doping at the Eu(3+) molar concentration to Si up to 10 mol%, and the O-Si-O and Si-OH groups in the structures were clearly rearranged with the doping, indicating the interaction of Eu(3+) with the O atoms. The significant morphological changes in the spheres were observed with the doping. The photoluminescence spectral shapes due to the transitions of (5)D(0)-(7)F(1) and (5)D(0)-(7)F(2) were indicative of the presence of the Eu(3+) in an environment of a low symmetry. It was found that the Eu(3+) was located inside the silica framework to electrostatically interact with the environmental O atoms, which would prevent the aggregation among Eu(3+) ions to show the efficient luminescence. Therefore, the interactions between the Eu(3+) ions and silica framework structures in the spheres were successfully clarified.

Efficient incorporation of monomeric anthracene into nanoporous silica/surfactant nanocomposite spheres using a mechanochemical solid state reaction

The incorporation of anthracene (Ant) into nanoporous silica/surfactant nanocomposite spheres was successfully achieved using a mechanochemical solid state reaction. The Ant molecules were incorporated into the nanopores while preserving the silica nanostructures, indicating the effective hydrophobic interactions with the alkyl chains of the surfactant. The blue photoluminescence intensity due to the monomer state was enhanced by increasing the mechanochemical milling force, suggesting this is an efficient preparation method for a luminescent medium by monomeric assembly of the Ant molecules.

Formation of stacked luminescent complex of 8-hydroxyquinoline molecules on hydroxyapatite coating by using cold isostatic pressing.

Cold isostatic pressing successfully formed a chelate complex of 8-hydroxyquinoline (8 Hq) molecules on plasma-sprayed hydroxyapatite (HAp) coating by solid-state reaction. The complex emits a fluorescence peak at approximately 500 nm by UV irradiation. The red shift of the fluorescence was newly observed in the cases of highly compressed complex due to π - π stacking of aromatic ring in the molecular structure of 8 Hq. The immersed complex coating in Simulated Body Fluid (SBF) demonstrated amorphous apatite precipitation and kept its fluorescence property.

Preparation of copper–graphite composite particles by milling process:

The fabrication of copper–graphite composites by a milling process was investigated using a centrifugal ball mill. The copper particles were homogeneously milled in a graphite vessel, and the reaction time was varied. Scanning electron microscopy images clearly revealed that a fragment of graphite ground by the copper particle adheres to the copper particle surface, indicating the formation of a copper–graphite composite. The composite graphite amount per 1 g of copper particles increased to 0.46 mg at the milling time 5 min, and subsequently decreased to 0.25 mg at 60 min, indicating the suitable milling-time for the interfacial adhesion. When using only the copper particles, the naturally oxidized layer on the surface decreased with milling. On the other hand, when using only the graphite, the characteristic graphite structure is disrupted and the defect structure increased with milling. Thus, the new copper surface generated by milling strongly reacts with the defect structure of the graphite. It is suggested that the interfacial bonding between the copper and graphite was attributed to a Van der Waals attraction and/or binding force due to oxygen atoms located at the interface.

Mechanochemical fabrication of iron–graphite composites

The fabrication of iron–graphite composites was investigated using a milling process. Based on the milling time of the process, the average particle size of the host iron particles decreased to 10 µm. The size of the graphite particles decreased to a nanometer scale, resulting in the graphite strongly adhering to the iron surfaces. Raman spectra revealed that the graphite aromatic ring structure disappeared and the iron near-surface layer was changed to iron oxide phases. The dangling bond of the fragmented graphite combined with the oxidized iron surface by interfacial binding to efficiently form the interfacial composites.

Surface-engineered mesoporous silica particles with luminescent, cytocompatible and targeting properties for cancer cell imaging

To develop a novel cancer cell imaging approach, we fabricated surface-engineered mesoporous silica (MPS) particles with multi-functionalities. Specifically, mechanochemically-treated europium(III)-doped MPS (Eu:MPS) particles were prepared, and a folate N-hydroxysuccinimidyl ester (FA-NHS) molecule was immobilized on the particle surface as a targeting ligand for specific types of cells. With the mechanochemical treatment, the siloxane bonds were changed to show better luminescence quantum efficiency as revealed by 29Si-NMR and photoluminescence spectroscopy, suggesting interaction changes between the silica framework structures and the doped Eu ions. Furthermore, the mechanochemically-treated particles immobilized with FA-NHS specifically bind to the cancer cells and the subsequent uptake by the cells was in situ observed using time-lapse optical microscopy. The particles did not exhibit any toxicity in the cellular proliferation stages. The particles after the binding and uptake also showed intense luminescence from the cells at a culture time of 24 h, demonstrating a clear imaging ability along with all the cellular shapes. Therefore, the present surface-engineered luminescent particles will be used for specific cancer targeting and imaging purposes.

Texture formation in iron particles using mechanical milling with graphite as a milling aid

Crystallographically anisotropic platelet iron particles were successfully prepared using a conventional ball mill with addition of graphite (Gp) particles. The morphological and structural changes resulting from the milling were investigated using scanning electron microscopy and X-ray diffraction. The spherical iron particles were plastically deformed into platelet shapes during the milling. Simultaneously, it is suggested that the size of the Gp particles decreased and adhered as nanoparticles on the surface of the iron particles. The adhered Gp particles affected the plastic deformation behavior of the iron particles: the {001} planes of α-iron were oriented parallel to the particle face, and no preferred in-plane orientation was observed. This study not only details the preparation of soft magnetic metal particles that crystallographically oriented to enhance their magnetic properties but also provides new insight into the activities of the well-established and extensively studied mechanical milling ...

Effects of compression on orientation of ligands in fluorescent complexes between hydroxyapatite with amino acids and their optical properties

This study aims to reveal the effects of pressure during cold isostatic pressing (CIP) on the microstructure and optical properties of fluorescent HAp complexes. Although the microsturucture-dependent properties of fluorescent HAp complexes have been reported to improve the antibacterial properties of photocatalyst coating layers, the mechanism behind the changes in the fluorescence properties of highly compressed HAp complexes has not yet been unveiled. CIP was successfully used to fabricate fluorescent HAp - amino acid complexes, and their fluorescence intensities increased with increasing fabrication pressure. Peak wavelength of fluorescence emitted by the HAp - amino acid complexes exhibited yellow to red shift. Although the thickness of the amino acid layer was saturated in higher pressure cases, the concentration of amino acids increased proportionally with pressure, which suggests changes in the packing structures of the ligands in the HAp- amino acid complexes. Polarized Raman spectroscopy measurements clearly detected ligands normally arranged to the HAp layer under high pressure fabrication conditions, which can provide the tightly packed ligand structure in the HAp- amino acid complexes. These tightly packed ligand structure in the HAp- amino acid complexes could emit stronger fluorescence owing to the increased density of complexations. This newly found pressure dependency in the optical properties of HAp-amino acid complexes is beneficial for developing biocompatible fluorescence materials or enhancement agents for antibacterial coating layers.

Mechanochemical surface modification of carbon fibers using a simple rubbing method

A simple rubbing treatment was used to mechanochemically modify the surface of polyacrylonitrile-based carbon fibers and its effect on their surface structure and functional groups was studied using several surface characterization techniques. To control the mechanochemical effect, the shear forces accompanying rubbing were kept constant. Scanning electron microscopy tests and the peak positions and widths of the main Raman spectroscopy bands indicated that there were no morphological changes to the carbon fibers following rubbing. In contrast, X-ray photoelectron spectroscopy showed an increase in oxygen-containing functional groups; in addition to hydroxyl species, the main groups introduced were alkoxide, carbonyl, and carboxyl groups. The ratio of carboxyl groups on the carbon fiber surface increased with the shear force magnitude, indicating carbon surface oxidation. The difference between the Raman and X-ray photoelectron spectroscopy results indicates that the modification was confined to the first few atomic layers; therefore, this rubbing method is capable of producing efficient mechanochemical surface modification of carbon fibers. This technique is simple, is relatively inexpensive, and is applicable to carbon fiber-reinforced plastic processing techniques.