Papers by Author: Jun Ho Ji

Abstract: A generation method of in-situ gold nanoparticles using a small-sized ceramic heater with a local heating area is presented. The heater surface temperature was maintained uniformly. Gold nanoparticles with high concentration (> 107 particles/cm3) were produced and were stably generated for several hours because the heater surface temperature was maintained uniformly. Higher surface temperature yielded higher geometric mean diameter (GMD), geometric standard deviation (GSD), and total number concentration. Using this generator particle size distribution was easily controlled. Spherical and non-agglomerated nanoparticles were observed from TEM images, even at high concentration and high temperature. Although air was used as a carrier gas, the generated gold nanoparticles displayed pure crystallinity of the gold element, as determined by XRD analysis.

Abstract: A pulsed spark-discharge aerosol generator using air as a carrier gas was successfully applied to the titania nanoparticle production. The titanium vapor evaporated by spark discharge was subsequently supersaturated and condensed to titania nanoparticles by nucleation and condensation. The size and concentration of the particles can be controlled easily using air as a carrier gas by altering the repetition frequency, capacitance, gap distance, and flow rate of the spark-discharge system. TEM observation shows that the generated particles were aggregates, which primary particle sizes are a few nanometers. The element composition of the nanoparticles was titanium and the crystal phase was amorphous. XPS analysis shows that oxidation state of generated particles corresponded to TiO2. These XPS data indicates that some fraction of the evaporated titanium vapor could be oxidized in an air atmosphere by the oxidation with oxygen. However, enough time for crystallization was lacked because of raid cooling.

Abstract: Even though activated carbon fibers (ACF) have been attractive due to high specific surface area and uniform micropore structure, there are only a few reports about the photocatalyst immobilization on ACF or their photodegradation behavior for removal of organic pollutants. In this study, ACF were selected as adsorptive support for photocatalyst immobilization. As photocatalysts, TiO2 nanoparticles were synthesized by using a N2-diluted and oxygen-enriched co-flow hydrogen diffusion flame. The visible flame length of 150mm was obtained by direct photographs. Flame temperature was measured by rapid insertion measurement technique with a R-type (Pt/Pt-13%Rd) thermocouple which was in wire shape (127μm diameter). TiO2 particles were sampled by using a high temperature particle sampler and then were coated on ACF filters. The sampling was carried out at 70mm and 110mm above the burner. The structure of TiO2 particles was analyzed by XRD. TiO2 coated ACF filters were characterized by FESEM-EDX and BET analyses. TiO2 particles on ACF filters were found to be agglomerated particles and the size of primary particles was approximately 50nm. The structure of TiO2 particle was anatase-phase crystalline structure. The specific surface area of TiO2 coated ACF filter was enhanced to be 1700~1860m2/g, depending on the sampling location, and the pores were micropores, regardless of the sampling location.