The purpose of this research was to promote the performance of rare earth free oxynitride phosphor (BCNO: boron carbon oxynitride) for next generation of white LED. In particular, I undertook the following research topics, (1) Preparation of spherical BCNO phosphor particle via spray pyrolysis and (2) Enhancement of Photoluminescence intensity of BCNO phosphor using nitrogen containing polymer.
Regarding (1), spherical BCNO phosphor particles were directly synthesized by a modified spray pyrolysis method using water trap. Effect of operating temperature and polymer concentration on the photoluminescence properties were investigated. Scanning electron microscopy revealed that the spherical particles were of size around 1.36 mm. The emission band of the spherical BCNO phosphor prepared at 800℃ was observed at 467 nm under excitation at 365 nm.
Regarding (2), three types of polymers, including polyethyleneimine (PEI), polyallylamine (PAA), and tetraethylene glycol (TEG) were used as carbon sources for the formation of BCNO phosphors. PEI was found to have the highest internal quantum efficiency (IQE) of the three polymers because of its optimum thermal decomposition temperature and high exothermic energy during BCNO formation. The IQE of the BCNO phosphors prepared with PEI was 50%, representing a 130% increase over the value observed when TEG was used as the carbon source. In addition, the emission band of the BCNO phosphors could be tuned from 380 to 490 nm by varying the reaction temperature and polymer concentrations.
We found that mesoporous carbon-silica composites synthesized by tri-constituent co-assembly method exhibit very intense visible photoluminescence excited by low-energy UV light. Now, a class of stable, efficient, inexpensive and less toxic photoluminescent materials which emit white light under long-wavelength UV light is strongly required to replace fluorescent lamps by LED lamps. The composites we synthesized satisfy the required conditions and are the promising materials from the environmental point of view. In this study we tried to control the color of the photoluminescence of the mesoporous carbon-silica composites by changing the synthesis conditions. We also investigated the photoluminescent properties of the graphene-like molecules which were synthesized by fusing pentacenes. Furthermore, we demonstrated in the present investigation that not only the pore-to-pore distance but also the pore diameter of the mesoporous materials having quasi two dimensional hexagonal pore structure can be determined by analyzing the small-angle XRD pattern.
The effect of process parameters in 3D Laser Forming （3DLF） on the forming of density gradient porous structure was investigated. The melted and consolidated parts of metallic powders by laser irradiation （it is called as melted part in this paper） sparsely form along the laser scanning line. The size of melted part strongly depends on the laser input energy. During the direct metal laser sintering, the melted parts conglutinate with each other and made the larger melted part. It was connected to other melted parts in different way by strong laser power and high scan rate. Especially, in the case of same laser energy density, if the scan rate become faster, the connection between melted parts gets stronger and the high density is obtained. With laser sintering condition for similar relative density, the microstructure of material formed by higher scan rate shows more homogeneous microstructure than that of the others formed by slow scan rate.
Recently, an effective removal of environmental pollutants is very important for risk management in our environment. The adsorbents based on an activated carbon and its related membranes or resins are usually utilized for the removal of pollutants. However, these adsorbents provide non-selective and irreversible adsorption, so that high-frequency replacement of the adsorbents and treatment of the waste materials are required.
To overcome the drawbacks, we previously developed a photocatalyst modified with molecular recognition ability by a molecularly imprinted technique. Thehybrid-photocatalyst allowed the selective adsorption and photodegradation of a target compounds in environmental samples.
In this study, we newly developed a magnetic nanoparticle enabling the selective adsorption of a toxic compound, saxitoxin which is one of shellfish toxins. We optimizedthe preparation procedures and evaluated the selective adsorption ability of the prepared materials. The results suggested that the magnetic nano-particle modified with molecular recognition layer was successfully prepared and the selective adsorption ability in the pseudo environmental water sample was achieved.
Functional ceramics were synthesized using ceramic powders activated by mechanochemical processing. The activated powders were dispersed in an alkali-containing solvent to dissolve the metallic ions at the powder surface and effect re-precipitation between the grains. The“ non-firing ceramic process” afforded high-strength ceramic solids without the need for calcination. The key step in this technique is surface activation of the ceramic powders through mechanochemical processing. We investigated the bonding and activity of the atoms near the surface by spectroscopic analysis of desorption of the adsorbed water molecules, a convenient and quantitative method. The powder surface contained an increased number of uncoordinated defects after mechanochemical processing, and powders with high compact strength showed high activity and had high surface AlV content. Diffuse reflectance infrared Fourier transform measurements of the desorption of water molecules allowed for easy and rapid determination of differences in the surface activity, which was not possible when using alternative analysis methods.
We have successfully immobilized a single giant vesicle onto the chemically modified surface of a cantilever for atomic force microscopy (AFM). The giant-vesicle-immobilized probes allowed us to measure the surface forces between soft interfaces. Additionally, we have carried out the simulations of the corresponding systems using the computational micro-fluid dynamics to reproduce successfully the force-distance curves, which were in qualitative agreement with those from the AFM measurements.
We have developed submicron-sized liposomes modified with a mucoadhesive polymer to enhance peptide drug absorption after oral and pulmonary administration. Liposomal behavior in the gastrointestinal tract is a critical factor for effective peptide drug delivery. The purpose of this study was to prepare quantum dot- (QD-) loaded submicron-sized liposomes and examine liposomal behavior in the body after oral administration using in vivo fluorescence imaging. Two types of CdSe/CdZnS QDs with different surface properties were used: hydrophobic (unmodified) QDs and hydrophilic QDs with glutathione (GSH) surface modifications. QD- and GSH-QD-loaded liposomes were prepared by a thin film hydration method. Transmission electron microscopy revealed that QDs were embedded in the liposomal lipid bilayer. Conversely, GSH-QDs were present in the inner aqueous phase. Some of the GSH-QDs were electrostatically associated with the lipid membrane of stearylamine-bearing cationic liposomes. QD-loaded liposomes were detected in Caco-2 cells after exposure to the liposomes, and these liposomes were not toxic to the Caco-2 cells. Furthermore, we evaluated the in vivo bioadhesion and intestinal penetration of orally administered QD-loaded liposomes by observing the intestinal segment using confocal laser scanning microscopy.Indocyanine green (ICG) was also used as a near-infrared label of liposomes and was used to observe their dynamic behavior using non-invasive in vivo imaging (IVISR imaging system) after pulmonary administration to rats.
Synthesis of barium zirconate (BaZrO3) nanocubes with perovskite structure was carried out by the composite-hydroxide-mediated (CHM) approach. The synthesis was conducted using zirconium dioxide (ZrO2) as a zirconium-source starting material and barium hydroxide［Ba(OH)2］ as a barium-source starting material. Through the use of these starting materials, BaZrO3 was prepared with a mixture of anhydrous sodium hydroxide (NaOH) and potassium hydroxide (KOH) as the reaction medium at 170～230℃ for 0～72h. Measurement by X-ray diffraction (XRD) confirmed the presence of perovskite BaZrO3 and indicated that the lattice of the obtained BaZrO3 was cubic. The amount of BaZrO3 increased as the reaction temperature increased. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation revealed BaZrO3 nanocubes. The results showed that BaZrO3 nanocubes could be shaped from ZrO2 and Ba(OH)2. In order to clarify the formation mechanism of the BaZrO3 nanocubes, various reaction conditions such as the processes of increasing, maintaining, and decreasing the temperature were investigated. BaZrO3 nanocubes with sharp-edged corners were formed via the CHM approach when the temperature was maintained at 230℃ for increasing periods of time.
In order to fabricate the high performance permanent magnet, we had prepared the following materials as the precursor of nanocomposite magnet by using core-shell structure with Fe phase as soft phase and ε-Fe2O3 phase as hard phase. In order to prepare air-stable metallic Fe nanoparticles, iron-oxide nanoparticles as precursors were reduced in a hydrogen atmosphere and then their surfaces were oxidized under low concentration of oxygen. To obtain Fe2O3 phase, we treated iron oxide nanoparticles with silica shell at several temperature. The size of magnetic nanoparticles affects their magnetism. We had also controlled the particle size and crystal structure.
Hollow nanofibers with mesoporous silica walls have been fabricated using electrospun polymer nanofibers and surfactant micelles as templates. The nanofibers are the possible candidates for insulating materials due to their high porosity. We aimed to remedy the fragility of the nanofibers by introducing the organo-siloxane into the silica framework. However, the introduction of organosiloxane hindered the formation of ordered mesoporous structure. Also the flexibility of the nanofibers was not sufficiently enhanced. The fabrication of silica nanofibers with hierarchical pore structure was also studied by forming the surfactant-templated silica in the continuous pore structure of polymer nanofibers prepared by electrospinning a polymer blend solution. The silica nanofibers possessed the bimodal internal pore structure originating from the phase separation of polymer blend and surfactant micellar structure.
The biological denitrification process is widely used in waste water treatment due to the low operational cost compared with that in physicochemical treatment. However, two different reactors are required in this process because ammonia nitrogen is converted into harmless nitrogen gas through two different biological steps （nitrifying and denitrifying steps） required for different environment （aerobic and anaerobic conditions). The purpose of our research is to design a composite biofilm of denitrifying bacteria and nitrifying bacteria that imitate a biofilm in the nature from the viewpoint of fine particle technology. Five different types of denitrifying bacteria and two different types of nitrifying bacteria were used as model bacteria. Surface physicochemical properties can be treated as an indicator of the adhesive properties of microbial cells. The electrophoretic mobility was measured as a function of ionic strength using the laser Doppler method and the surface potential was estimated using the soft particle theory. The microbial cells used in this study were charged negatively. The contact angle between a microbial lawn and a droplet of a specified fluid was measured using the sessile drop technique and the change in the free energy of interaction, ΔG, between one species of microbial cells, between different species of microbial cells. This result indicated that denitrifying bacteria and nitrifying bacteria could not be aggregated thermodynamically because ΔG was positive in all combinations. To promote the microbial adhesion, disrupted microbial cell suspension, chitosan, polyethyleneimine and dopamine were added to the mixed cell suspension, respectively. It was found that polydopamine was effective to aggregate denitrifying bacteria and nitrifying bacteria artificially. Finally, the formation of the composite biofilm of denitrifying bacteria and nitrifying bacteria were succeeded.
A monolayer of particles at an air/water interface was used to model a Pickering emulsion, in order to determine the effect of the size of the particles in a monolayer at an air/water interface and their packing density on the physico-chemical properties of a model Pickering emulsion (a monolayer), e.g., stiffness, adhesive ability, and change in particle packing, after a collision by a particle in the water phase. A Langmuir trough was used to obtain surface pressure-area per molecule isotherms of bare TiO2 particulate monolayers at an air/water interface and the Monolayer Particle Interaction Apparatus (MPIA) to directly study the forces between the TiO2 monolayers at an air/water interface and a micro-sized TiO2 particle in the subphase. The effect of the packing density of the particles in the monolayer on its stability was observed by optical microscopy, while the forces were being measured by bringing the micro-sized TiO2 particle in the subphase in and out of contact with the TiO2 monolayer. Langmuir monolayers of bare, hydrophilic TiO2 particles were directly formed at the air/water interface by using a subphase with a pH below the isoelectric point of TiO2. The effects of the particle size on the physical properties of the monolayer were then investigated by using particles with a diameter of 75 nm, 300 nm, 3μm and 10 μm. The packing density influence was determined by measuring the forces and by imaging the air/liquid interface in the presence of the monolayer at different surface pressures. We found that the particulate monolayer became more deformable and instable as the size of the particle decreased. Large particles (micro-sized) gave the least deformable monolayer, where monolayers of a high particle packing density gave stable monolayers even upon contact by a micro-sized particle.
In the point of a demonstration of its fundamental properties compared with bulk water,a single water molecule within a confined subnano space is one of the important topics in both material and life sciences. However, a single molecule of H2O, that is completely isolated without any hydrogen bonds, is rare so far because water usually exists in hydrogen-bonded environments.The inner space of the fullerene C60 is suitable to entrap a water molecule.It would be possible to control the properties of the outer carbon cage as well as to study the isolated specieswhen atoms or molecules are encapsulated in fullerenes.Endohedral fullerenes encapsulating a wide variety of species, such as metal ions and rare gases, have been synthesized with physical methods under harsh conditions. However, these methods are not suitable to obtain endohedral fullerenes encapsulating small molecules.
The molecular surgical approach is a promising method to synthesize yet-unknown endohedral fullerenes, which consists of creation of an opening on the empty fullerene cage, insertion of a small guest through the opening, and closure of the opening with retention of the guest.To realize endohedral fullerenes encapsulating a water molecule, creation as well as restoration of a larger orifice is needed. With the concept of dynamic control of opening size, an open-cage C60 derivative was synthesized, whose opening can be enlarged in situ, resulting in quantitative encapsulation of a molecule of H2O under the high-pressure conditions. The easy method to restore the opening was developed to realize the organic synthesis of water-encapsulating C60. The structure of H2O@C60 was clearly determined by the single crystal X-ray analysis, and the properties of the single H2O molecule as well as the spherical π-system encapsulating the water molecule were studied.
A new method for the surface deactivation of zeolite catalyst was tested via a mechanochemical approach using powder composer. Post-synthetic mechanochemical treatment of ZSM-5 zeolite causes a selective deactivation of catalytically active sites only existing on the external surface, giving a unique ZSM-5 zeolite catalyst without acid sites on the external surface, as a potentially useful catalyst for highly selective production of p-xylene.
Nanoparticles and their applications in the biomedical research fields have attracted increasing interest over the past decade. Previous in vitro studies have demonstrated that synthetic nanoparticles could be incorporated into living cells mainly via endocytotic pathways depending on their size, shape, surface charge, and surface chemistry. It is thus important to investigate the effects of surface properties of nanoparticles on the possible interactions between nanoparticles and biomolecules for understanding the mechanisms of cellular uptake and the subsequent clearance from the cells. In the current research, we have examined chemical conversion of the surface structures of nanoparticles in living cells with the aim to directly observe intracellular uptake and localization of the nanoparticles before and after the conversion. We have developed （1） gold nanorods （GNRs） coated with coumarin-protected alkylamino-linkers and （2） silicananoparticles（SNPs） covered with dibenzylcyclooctyne（DBCO） structures. By using the former nanoparticles, we have accomplished esterase-catalyzed conversion of their surface chemical structures in living cells. On the other hand, DBCO structures on SNPs can be modified with various azido compounds via the bioorthogonal Huisgen [3+2] cycloaddition. We prepared phospholipids bearing an azido group and investigated intracellular localization of SNPs after the addition of the azido lipids. As expected, accumulation of nanoparticles on the plasma membrane was observed right after the addition of azido lipids, demonstrating that chemical conversion of their surface could alter the interactions between nanoparticles and cell membrane.
Thin films of sheet-like powder were fabricated by using flow assisted electrophoretic deposition method (flow assisted EPD). Effects of slurry properties and EPD conditions on the microstructure of fabricated thin film were investigated. It was shown that the film had a relatively homogeneous microstructure when the slurry flow rate was high, even though the amount of deposited powder was small. It was also found that the films fabricated from slurries with different pH value had almost the same microstructure by using flow assisted EPD. The particle dispersion and flocculation state should be changed when changing slurry pH, however, assisted slurry flow with an appropriate flow rate may break the aggregates and maintain relatively well dispersion of particles, resulting in homogeneous structure of fabricated films.
The purpose of the present study was development of novel technique for separation, classification and surface modification of particles dispersed in the dry system using dry-cyclone with mist. It was clear that classification performance was improved using a cyclone with water mist supplied from a upper part of dust box and a cut size was able to be controlled changing the flow rate of the entrainment gas. The ratio of the mass of the powders collected by the upper part of the cyclone to the mass of the total feeding powder was enhanced because of the attractive force, which was attributed to the static electricity that appeared between the silica particle and the wall of the cyclone under the condition of the existence of water mist. However, this type of attractive force was expected to be weaker between silica particles with a small contact area within the cyclone thereby maintaining the dispersion stability of the particles. Hence, the classification performance of the cyclone was enhanced during the supply of the water mist. As similarly, this method using mist was applicable to the classification of particles by Louver type classifier. Mist generated from dry ice and hot water was supplied to the separator from the bottom of the classifier to make the cut size smaller. About surface modification of particles using dry-cyclone and mist of silane coupling agent solution, it was effective that the entire of the surface of the particles was modified in the smaller time dry-system from the measurement of the contact angle and the surface tension.