Browsing by Author "Lee, Jae Eun"

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    Biodiesel production by sulfated mesoporous titania–silica catalysts synthesized by the sol–gel process from less expensive precursors
    (Chemical Engineering Journal, 2012-11-21) Shao, Godlisten N.; Sheikh, Rizwan; Hilonga, Askwar; Lee, Jae Eun; Park, Yeung-Ho; Kim, HT
    A sulfated titania–silica composite (S-TSC) was obtained through surface modification of mesoporous titania–silica composite synthesized using less expensive precursors; titanium oxychloride and sodium silicate as titania and silica sources respectively. A pre-formed titania sol facilitated the synthesis of a mesoporous composite with a high BET surface area (520 m2/g), suitable for surface modification using sulfuric acid to improve its catalytic performance. The materials synthesized via this process were examined by XRD, XRF, FTIR, SEM, TEM, TGA, and N2 physisorption studies. FTIR analysis showed the vibration band of the TiAOASi bond at 943 cm 1, suggesting the incorporation of titania into silica to form a composite. This vibration band was substantially shifted to 952 cm 1 after the attachment of the sulfate group. The catalytic activity of a series of as-prepared TSC, S-TSC calcined samples and pure H2SO4 were evaluated for esterification of oleic acid and transesterification of waste oil with methanol to yield methyl esters. It was observed that at these reaction conditions, S-TSC-450 and S-TSC-550 possessed high catalytic activity comparable to that of pure H2SO4 implying that surface modification of the titania–silica composite improves its acidic properties.
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    Characterization of Calcium-Doped Silica Gel Prepared in an Aqueous Solution
    (Resources Processing, 2012-02-20) Quang, Dang Viet; Park, Jin Koo; Kim, Jong-gil; Elineema, Gideon; Shao, Godlisten N.; Lee, Jae Eun; Kim, Hee Taik
    In this study, calcium-doped silica was prepared by modifying sodium silicate-based silica gel in an aqueous solution of Ca(OH)2. Silica gels with less than 1 mm in size with different pH values were treated in Ca(OH)2 solution at concentrations ranging from 2 to 20 g/L and aged at 25, 60, and 90°C for 40 min. The BET surface area of the silica gel decreased while its pore size increased considerably after modification in Ca(OH)2 solution. The pH of 5% calcium-doped silica in water ranged from about 8.5 to 10, depending on the pH of silica gel, the aging temperature, and the concentration of the Ca(OH)2. When the concentration of the Ca(OH)2 solution was 20%, needle-like crystals of calcium silicate hydrate formed over the surface of silica gel.
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    A Gentle Method to Graft Thiol-Functional Groups onto Silica Gel for Adsorption of Silver Ions and Immobilization of Silver Nanoparticles
    (2012-10-22) Quang, Dang Viet; Lee, Jae Eun; Kim, Jong-gil; Kim, You Na; Shao, Godlisten N.; Kim, Hee Taik
    Thiol-functionalized silica that has been used to remove heavymetal from an aqueous solution and supportmetallic nanoparticles is usually synthesized by reflux in an organic solvent containing 3-mercaptopropyltrimethoxysilane (MPTMS). In this paper, we report a gentle method for grafting thiol-functional groups onto silica gel by an aging process that does not require mixing and refluxing in an organic solvent. Silica gel was synthesized by a sol–gel method from H2SO4 (40%) and sodium silicate, which was crushed into beads with sizes ranging from 180 to 450 μm. Silica beads (50 g) were mixed with 75 mL of a functionalization solution consisting of MPTMS, H2O, and C2H5OH and aged at 50 °C for 36 h in a box dryer. The success of the functionalization process was confirmed by FT-IR, BET, SEM and elemental analyses. The functionalization solution was percolated into pores and thiolfunctional groups were grafted onto the surface and pore walls of the silica beads. The ability of these functionalized silica beads to adsorb silver ionswas determined by the Langmuir isotherm equationwith amaximumadsorption of 75.8 mg/g. Silver nanoparticles with sizes ranging from 2 to 6 nmformed by chemical reductionwere located inside the pores and on the surfaces.
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    Influence of titania content on the mesostructure of titania–silica composites and their photocatalytic activity
    (Powder Technology, 2012-08-28) Shao, Godlisten N.; Hilonga, Askwar; Jeon, Sun Jeong; Lee, Jae Eun; Elineema, Gideon; Quang, Dang Viet; Kim, Jong-Kil; Kim, Hee Taik
    Titania–silica composites (TSC) with various Ti/Si ratios were synthesized via sol–gel process using less expensive precursors; sodium silicate solution as a silica source and titanium oxychloride as a titania source. The influence of varying Ti content in the composites was examined by FTIR, SEM, TEM, DTA/TGA, N2 physisorption studies, XRF and XRD. The BET surface area of the raw materials increased with increasing Ti/Si ratio up to 2.9 (461 m2/g) but further increase of Ti content beyond that ratio yielded compositeswith decreased surface area. The effect of aging evaluated in the samplewith Ti/Si=2.9 revealed that aging the composite for 2 h yields titania–silica powderwith the highest surface area (461 m2/g). The FTIR analysis displayed the presence of a vibration band at 945 cm−1, assignable to hetero linkage of the Si–O–Ti depicting the incorporation of TiO2 into SiO2 to form a composite.Moreover, photodegradation of methyl orange (MO) by the samples calcined at 800 °C showed that the TSC-5-800 (Ti/Si=5.6) exhibited the highest maximum photocatalytic activity of all the composites.