알림마당
특별초청 세미나
미래를 창조하는 포스텍 화학공학과
Functional Mesoporous Materials Using Organic Templates: Preparation o…
- 일자
- 2013.10.25
- 시간
- 16:30
- 연사
- 조은범 교수
- 장소
- 환경동 112호
- 소속
- 서울과학기술대학교
Abstract
1. Periodic mesoporous thiophene-silicas with hexagonal (p6mm) symmetry were synthesized using 2,5-bis(triethoxysilyl)thiophene (BTET) precursor in the presence of Pluronic P123 (EO20PO70EO20) and PLGE (EO17(L28G7)EO17) triblock copolymers at different acidic conditions. P123-templated mesoporous thiophene-silicas with p6mm ordered structure were prepared in the presence of hydrochloric acid and iron(III) chloride hexahydrate used as acid catalysts. However, it was found that a relatively large fraction of the Si-C bonds in thiophene-bridging groups were decomposed during synthesis process. On the other hand, thiophene-silicas synthesized at lower acidic conditions were disordered and non-porous structures. In contrast, PLGE-templated thiophene-silicas with p6mm ordered mesostructure were prepared using copper(II) perchlorate hexahydrate and boric acid as well as hydrochloric acid. Importantly, up to 97.3% of the Si-C bonds in mesoporous thiophene-silica prepared in the presence of boric acid were retained. Solid state 29Si MAS NMR clearly showed that the structural stability of Si-C bond is dependent on the acidity and the stirring time of the synthesis. Also, thermal stability of thiophene-bridging groups was shown to be dependent on the acidity of the synthesis gel.
2. Ordered mesoporous silica/ceria-silica composites were synthesized using cerium(IV) hydroxide and tetraethyl orthosilicate (TEOS) co-precursors in the presence of hexadecyltrimethylammonium bromide (CTAB) under basic conditions. These composites consisted of Ce-doped mesoporous silica particles (about 500 nm) with highly ordered 2D hexagonal (p6mm) and 3D bicontinuous cubic (Ia3d) symmetries and irregular ceria-rich silica-ceria particles. Wide angle XRD, diffuse reflectance UV-vis, and XPS analysis showed that 10 – 24 % of cerium was at the Ce3+ oxidation level and the remaining predominant fraction of Ce was at the Ce4+ oxidation level. The cerium loading was varied in these composite materials up to 43 wt% (~ 3.1 mmol/g). The specific surface areas of the mesoporous silica/ceria-silica composite samples obtained on the basis of nitrogen adsorption isotherms were higher than 350 m2 g-1 and their pore widths were between 3.3 and 3.5 nm. The mesoporous silica/ceria-silica samples were reduced at 850 oC under flowing H2 in N2 environment. The crystal structure of the reduced samples changed to hexagonally structured phase with the oxidation state of Ce3+, while the ordered mesostructure of silica was preserved.
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