Seung Bin Park

YAG:Ce phosphor particles prepared by ultrasonic spray pyrolysis

Abstract Spray pyrolysis was applied to the preparation of fine YAG:Ce phosphor particles. The characteristics of particles such as crystallinity, morphology, and photoluminescence were investigated. Phase-pure YAG:Ce particles with high crystallinity were obtained after annealing at lower temperatures than those of conventional preparation processes. The mean size of the particles increased from 0.46 to 1.2 μm when the overall solution concentrations were changed from 0.03 to 1 mol/L. The YAG:Ce particles annealed at 1300°C were nonaggregated and spherical. The particles absorbed excitation energy in the range 403–510 nm, and the maximum excitation wavelength was near 470 nm. The YAG:Ce particles showed broad emission peaks in the range 480–650 nm and had maximum intensity at 528 nm. The photoluminescence intensity of the particles increased monotonically with increasing annealing temperature and showed the maximum value at 1 at% Ce.

Spray Drying Method for Large-Scale and High-Performance Silicon Negative Electrodes in Li-Ion Batteries

Nanostructured silicon electrodes have shown great potential as lithium ion battery anodes because they can address capacity fading mechanisms originating from large volume changes of silicon alloys while delivering extraordinarily large gravimetric capacities. Nonetheless, synthesis of well-defined silicon nanostructures in an industrially adaptable scale still remains as a challenge. Herein, we adopt an industrially established spray drying process to enable scalable synthesis of silicon-carbon composite particles in which silicon nanoparticles are embedded in porous carbon particles. The void space existing in the porous carbon accommodates the volume expansion of silicon and thus addresses the chronic fading mechanisms of silicon anodes. The composite electrodes exhibit excellent electrochemical performance, such as 1956 mAh/g at 0.05C rate and 91% capacity retention after 150 cycles. Moreover, the spray drying method requires only 2 s for the formation of each particle and allows a production capability of ~10 g/h even with an ultrasonic-based lab-scale equipment. This investigation suggests that established industrial processes could be adaptable to the production of battery active materials that require sophisticated nanostructures as well as large quantity syntheses.

Anatase-phase titania: preparation by embedding silica and photocatalytic activity for the decomposition of trichloroethylene

Abstract Nanophase titania particles were prepared by the sol–gel process using two different precursors; titanium isopropoxide(TTIP) and titanium ethoxide (TEOT). Silica-embedded titania particles was also prepared from TEOT and tera-ethyl-ortho-silicate (TEOS). In the case of nanophase titania particles prepared from TTIP, the rutile/anatase mixed phase had higher photoactivity than the pure anatase in the decomposition of TCE. However, in the nanophase titania prepared from TEOT, the photoactivity was increased with the heat treatment temperature until rutile phase began to be formed. The surface area was decreased with the heat treatment temperature. The photoactivity of the pure anatase titania prepared from TEOT was higher than that of Degussa P25 and the anatase/rutile mixed titania prepared from TTIP. Therefore, we concluded that, in order to achieve high photocatalytic activity, it was important to prepare titania particles at high temperature, preferably without forming rutile phase but not necessarily. This conclusion was confirmed by the experimental result that the silica-embedded titania particle of pure anatase phase had higher photoactivity than that of Degussa P25 and the pure anatase titania prepared from TEOT. The embedding of small amount of silica into anatase titania matrix enhanced the thermal stability of nanophase titaina particle resulting in the suppression of the phase transformation from anatase to rutile phase. This thermal stability enables us to calcine the silica-embedded particles at higher temperature without accompanying the phase transformation and to reduce the bulk defects, which are responsible for the low photocatalytic activity.

Recycling rice husks for high-capacity lithium battery anodes.

The rice husk is the outer covering of a rice kernel and protects the inner ingredients from external attack by insects and bacteria. To perform this function while ventilating air and moisture, rice plants have developed unique nanoporous silica layers in their husks through years of natural evolution. Despite the massive amount of annual production near 108 tons worldwide, so far rice husks have been recycled only for low-value agricultural items. In an effort to recycle rice husks for high-value applications, we convert the silica to silicon and use it for high-capacity lithium battery anodes. Taking advantage of the interconnected nanoporous structure naturally existing in rice husks, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.

Enhanced photoluminescence, Raman spectra and field-emission behavior of indium-doped ZnO nanostructures

Indium-doped (In-doped) ZnO nanostructures with four different morphologies, namely nanochips, nanotripods, nanorods, and nanodisks, have been successfully synthesized by a simple hydrothermal method. The effects of indium dopant and various morphologies on the structural, optical and field-emission properties of these ZnO nanostructures were investigated. The XRD patterns demonstrated that the In-doped ZnO nanostructures exhibited the hexagonal wurtzite structure with preferential orientation along the (0 0 2) crystal plane, and a slight difference in lattice parameters was detected among the samples with various morphologies. The doped nanostructures were found to be single crystals grown along the c-axis. The composition of the doped ZnO nanostructures was confirmed by X-ray diffraction (XRD), X-ray photospectroscopy (XPS), and energy-dispersive spectroscopy (EDS). The photoluminescence (PL) spectra of doped ZnO nanostructures having a blue-shift in the UV region show a prominent tuning in the optical band gap, without any significant peak relating to intrinsic defects. From Raman spectra, the 437 cm−1 mode corresponds to the E2 mode for wurtzite ZnO crystals with very sharp features which revealed the better crystallinity of samples. The lowest turn-on field of the field-emission was found to be ∼2.5 V μm−1 and the highest emission current density of 1.13 mA cm−2 was also obtained for In-doped ZnO nanochips under a field of 6.3 V μm−1. The field enhancement factor β was estimated to be 10 640 ± 3 in the case of doped nanochips, which was much higher than that of any previous report. Moreover, the doped ZnO nanostructures exhibit good long period emission current stability with a variation of less than 5% during 25 h under a field of 6.3 V μm−1. The superior field-emission properties were attributed to the better morphologies, In-doping and better crystallinity of In-doped ZnO nanostructures.

Preparation of nonaggregated Y2O3 : Eu phosphor particles by spray pyrolysis method

Ministry of Education, Culture and Science of Japan, Hiroshima Industrial Technology Organization, KOSEF (Korea Science and Engineering Foundation)

Linear relationship between the crystallite size and the photoactivity of non-porous titania ranging from nanometer to micrometer size

The dependency of the photoactivity on the crystallite size of anatase titania for the decomposition of trichloroethylene (TCE) was investigated. The crystallite size of anatase-phase was controlled at a fixed surface area and particle size by the spray pyrolysis. The surface area was also changed by the gas-phase decomposition of titanium-tetra-iso-propoxide (TTIP) by keeping the crystallite size in a similar range. The photoactivity of titania particles of the same surface area and particle size increased linearly with increasing the crystallite size of anatase-phase as long as no significant rutile phase was formed. It was proved that the photoactivity of titania is supposed to be enhanced by increasing the surface area while keeping a similar crystallite size. The lab-made titania particles of nanometer size and pure anatase-phase had higher photoactivity than that of Degussa P25 due to the larger crystallinity, although their surface area was smaller than that of Degussa P25. For all titania samples, the photoactivity normalized by the surface area was linearly increased with increasing the crystallite size of anatase-phase, regardless of the preparation method; the particle size ranging from nanometer to micrometer.

A high-volume spray aerosol generator producing small droplets for low pressure applications

Abstract A high-volume spray aerosol generator capable of producing small droplets for lowpressure applications, hereafter named filter expansion aerosol generator (FEAG), is described and characterized. The potential applications of this spray generator are thin film deposition, aerosol etching, and ultrafine particle preparation by spray pyrolysis at reduced pressure. The FEAG is mainly composed of a pneumatic nozzle for dispersing liquid, a porous glass filter with 80 mm diameter, and a vacuum pump (6001min −1 ). The liquid flow rate through the filter was 3 cm 3 cm −2 h −1 . The mean droplet size was estimated to be 2.1 μm with a geometric standard deviation 1.76. In principle, this generator can be scaled up by increasing vacuum pump capacity and filter area.

Design and Fabrication of New Nanostructured SnO2-Carbon Composite Microspheres for Fast and Stable Lithium Storage Performance

One-pot method for metal oxide-carbon composite microsphere with three-dimensional ordered macroporous (3DOM) structure is first introduced. The 3DOM structured SnO2 -carbon microspheres prepared as the first target material show superior electrochemical properties as anode material for lithium ion batteries. The newly developed process can be applied to the preparation of 3DOM-structured metal oxide-carbon composite microspheres for wide applications.

The crystalline phase stability of titania particles prepared at room temperature by the sol-gel method

Titania particles having anatase, brookite and rutile phase were prepared at various H+/TTIP (Titaniumtetraisopropoxide) mole ratios and room temperature by the sol-gel method. The crystalline phases according to the variation of the post heat treatment temperature were observed. The crystalline phase and the phase transformation, morphology, and crystallite size were identified by using XRD, TG/DTA, Raman spectroscopy and TEM. The brookite phase of titania particles prepared at the H+/TTIP mole ratio of 0.02 and room temperature was not transformed into anatase or rutile even with the heat treatment at 750°C, and also the anatase phase was stable at the temperature as high as 850°C. However, the titania particles prepared at the H+/TTIP mole ratio of 0.67, which contained the mixed phases of anatase, brookite, and rutile at room temperature, showed only rutile phase at temperature of 750°C. It was thus shown that the initial crystalline phase of the primary particles prepared at room temperature had an important effect on the phase transformation behavior upon post heating. Phase transformation from brookite to anatase and subsequently to rutile occurred with heating.