Papers by Author: Gun Dae Lee

Abstract: The photo-catalytic hydroxylation of phenol with hydrogen peroxide was carried out over TS-1 and Ti-MCM-41 catalysts. For comparison, the dark (thermal)-catalytic hydroxylation of phenol was also performed. The difference in catalytic behaviors of TS-1 and Ti-MCM-41 and product distribution in both the reactions were investigated. The TS-1 and Ti-MCM-41 catalysts having the Si/Ti ratio of 50 were prepared by in-situ crystallization and characterized using XRD, UV-DRS. In the all reactions, the main products were catechol (CAT), hydroquinone (HQ) and benzoquinone (BQ). In dark (thermal)-reaction, TS-1 showed a higher catalytic activity than Ti- MCM-41. In photo-reaction, however, the activity of Ti-MCM-41 was comparable to that of TS-1. The conversion of phenol and the selectivity to CAT in the photo-catalytic reaction were higher than those in dark (thermal)-reaction. In the all reactions, the selectivity to CAT increased remarkably when the selectivities to HQ and BQ decreased with reaction time.

Abstract: The TiO2/mica pearlescent pigments were prepared by the hydrolysis of TiOCl2 on the natural mica (muscovite) followed by a calcinations process. The phase transformation of anatase to rutile during calcination and their proportion in the TiO2 thin layer have been analyzed by XRD measurements. The pH controlling during the initial stage of hydrolysis of TiOCl2 showed a pronounced effect on the phase transformation of TiO2 on the substrate. This result may be due to the fact that the pH controlling during the hydrolysis affects the crystal structure and size of TiO2. The decrease in crystallinity and crystallite size of TiO2 resulted in lowering the temperature of phase transformation from anatase to rutile.

Abstract: Ni nanosheet has been prepared at various temperature and time with anion surfactant by chemical reduction of the nickel ion complexes formed from complexing reagent in a pressurized vessel. Sample was characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS), a selected-area electron diffraction (SAED) and a high sensitive magnetometer (HSM). The use of SDBS and sodium tartrate could be a key factor for the formation and growth of Ni nanosheet.

Abstract: TiO2 nanoparticles were prepared using the hydrolysis of titanium tetraisopropoxide (TTIP) using TENOH as a peptizing agent in the hydrothermal method. The physical properties of prepared nanosized TiO2 particles were investigated. The photocatalytic degradation of orange II has been studied using a batch reactor in the presence of UV light. The crystallite size of the anatase phase is increased from 15 to 30 nm as the molar ratio of TENOH/TTIP increases from 0.1 to 1.0. The titania particle prepared at TENOH/TTIP molar ratio=0.1 shows the highest activity on the photocatalytic decomposition of orange II and the photocatalytic activity decreases according to an increase in TENOH/TTIP molar ratio. In addition, the titania particles prepared at 160oC shows the highest activity on the photocatalytic decomposition of orange II

Abstract: Mesoporous MCM-41 materials were prepared using the conventional thermal and microwave heating method. Both in conventional thermal and microwave heating synthesis of MCM-41, tetraethyl orthosilicate (TEOS) and cetyltrimethyl ammonium bromide (CTAB) were used as Si source and template, respectively. Microwave heating was carried out in a modified 400 W, 2.45 GHz microwave oven. In both methods, the crystallization temperatures was 70 °C and crystallization time was 3~12 h. The prepared MCM-41 samples were characterized by XRD, TEM and SEM. The XRD patterns of MCM-41 samples prepared from both the methods were typical of a relatively well ordered material. TEM results also revealed that the MCM-41 samples prepared from both the methods possess the regular hexagonal array of mesoporous channels. On the contrary, SEM has shown the difference in morphologies of the MCM-41 samples prepared from both the methods. The samples prepared by conventional thermal heating method mainly consist of irregular and small particles, whereas the samples prepared by microwave heating method have elongated rope-like structure and their length extends longer than 10 μm.

Abstract: Freeze casting is a useful forming technique to produce complex-shaped ceramic parts. The colloidal processing stage is an essential step for preparation of freeze casting slurries. In order to optimize freeze casting slurries, several processing additives, such as dispersant, binder, surfactant, and cryo-protectant are usually employed. Dispersion and suspension rheology of aqueous alumina/ zirconia slurries with 55 and 60 vol.% solid loading have been characterized in terms of the effect of organic additives, and the resulting microstructures of the freeze cast green and sintered materials examined.

Abstract: The sedimentation density significantly decreased after addition of dispersant; the effect was more pronounced with pure alumina, as compared with SiC-containing slurry. With further addition of surfactant, the sedimentation density increased somewhat, but decreased with binderadditions. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e., low sedimentation density gave high low-shear viscosity, indicative of high structure formation in the suspended particles. Shear rate rheological measurements showed continuous shear thinning behavior.

Abstract: Nanocrystalline nickel powders were prepared by chemical reduction of nickel chloride hydrate with different surfactant at moderate temperature in a pressurized vessel. Nickel nanosheets were generated successfully through reducing the nickel ion complexes, formed by sodium tartrate, at alkaline condition by hydrazine hydrate. The nanosheets and nanowires were characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS) and a high sensitive magnetometer (HSM).

Abstract: Symmetrically and unsymmerically substituted bis-dithiobenzil nickel complexes containing four substituted and unsubstituted methoxy groups were synthesized from a benzoin compound using phosphorous pentasulfide under the conventional thermal and microwave processing. The efficiency of microwave synthesis over the conventional thermal synthesis was illustrated by the yield of bisdithiobenzil nickel complex dyes. The samples were characterized by the means of elemental analyzer, 1HNMR, IR spectroscopy, Uv-vis spectroscopy and DSC.