Papers by Author: Jin Koo Park

Abstract: Silver-doped silica gel was prepared by the reaction of colloidal silica and AgNO3. In the synthetic process, aluminum ions promote the chemical durability of silver-doped silica gel with dramatically decreasing the elusion of silica ions at the aqueous solution. Especially, aluminum ions induce slow release silver ion of silver-doped silica gel over a long period of time. Also, antimicrobial effects evaluated using a shake flask method resulted in a disinfection ratio of Staphylococcus aureus(ATCC 6538) and Escherichia coli(ATCC 25922) of over 99.9%, indicating high anti-microbial properties.

Abstract: Homogeneous precipitated calcium carbonate(PCC) was synthesized by calcinations, hydration and carbonation of limestone which has been deposited in Danyang, Korea. In the reaction process, shapes(scalenohedral and cubic) and sizes(0.2~0.3μm and 2.0μm) of the powder were controlled by reaction temperature. Synthesized PCC was applied to hand-made paper as filler and coated paper. For the prepared papers, physical/optical properties(brightness, whiteness, opacity, roughness, gloss, tensile strength, internal tearing strength, stiffness, bursting strength) and printability(ink gloss, ink set-off, dry pick, wet pick) were characterized

Abstract: A process for the recovery of nanoporous silica and sodium fluoride from hexafluorosilicic acid and sodium silicate under the different molar ratios was studied. In order to prepare the appropriate solutions of initial compounds 25% of hexafluorosilicic acid and the 18% of sodium silicate were used. Obtained nanoporous silica and sodium fluoride have been characterized by XRD, BET, TGA, EDX and SEM.

Abstract: The purpose of this work is to influence of CaO concentrations of 5.0 wt.% and 10.0 wt.%, slurry feeding rate of 200~400
/min, rotating rate of drum of 5,000 and 10,000 rpm, inlet and outlet temperature on the synthesis of Ca(OH)2 powder, and the synthesis of precipitated calcium carbonate by carbonation process using Ca(OH)2 prepared by spray drying method. As the feeding rate of slurry was increased, the particle size of Ca(OH)2 was decreased. Regardless of rotating rate of drum, when the concentration of CaO was 5.0 wt.% and 10.0 wt.%, the morphology of Ca(OH)2 showed spherical shape of 10~30 μm and 20~60 μm, respectively. The specific surface area of synthesized Ca(OH)2 was 27~30 m2/g. When the initial reaction temperature was 11 °C and 30 °C, the shape and particle size of precipitated calcium carbonate synthesized in the carbonation process showed the rectangular shape of 0.1~0.4 μm and the spindle shape of 0.5~1.0 μm, respectively.

Abstract: A process for the recovery of nanoporous silica and sodium fluoride from hexafluorosilicic acid and sodium silicate under the different molar ratios was studied. In order to prepare the appropriate solutions of initial compounds 25% of hexafluorosilicic acid and the 18% of sodium silicate were used. Obtained nanoporous silica and sodium fluoride have been characterized by XRD, BET, TGA, EDX and SEM.

Abstract: Transparent TiO2, WO3-TiO2, and MoO3-TiO2 films were prepared by spin-coating each colloidal suspension. The monolayer coverage of WO3 on the surface of TiO2 greatly increased the photocatalytic activity in the decomposition of gaseous 2-propanol, whereas the addition of MoO3 considerably decreased the photocatalytic reaction of TiO2. For the estimation of superhydrophilicity, the change of contact angles between the water drop and the film surface was measured as a function of UV-irradiation time. The measured contact angle of WO3-TiO2 film was considerably lower than that of TiO2 before the UV-irradiation, and it decreased to the minimum value about 4 times faster than that of pure TiO2 films with the irradiation of UV light. On the other hand, MoO3-TiO2 films showed a low contact angle at initial point, but their contact angle was very slowly decreased under the UV light. The initial low contact angles suggest the high hydrophilic character of WO3-TiO2 and MoO3-TiO2 films with high Lewis surface acidities. The observed trend suggests that the superhydrophilicity is closely related to the photocatalytic activity.