Microporous Semicrystalline Silica Materials
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W.T. Lim, N.H. Heo, and J. Choi Departments of Industrial Chemistry and Agricultural Chemistry, Kyungpook National University, Teagu, Korea 701-702 (Received 15 October 1999; accepted 25 April 2000)
A new family of microporous semicrystalline silica materials (MSSMs) were developed at room temperature from acidic mixtures of alkyl-substituted silane and tetramethylalkoxysilane. Hydrolyzed alkyl-substituted silica precursors, having hydrophilic silanol groups and hydrophobic alkyl groups, presumably act not only as templates but also as sol stabilizers for continuous pore engineering of silica materials in the micropore region. Depending on the substituted alkyl (SUA) groups in initial sols, MSSMs have distinct broad x-ray diffraction peaks in low 2 range of 2° to 12°, distinguishable thermal behavior of SUA groups, highly flexible processability, and discrete micropore size with good thermal stability of micropores after the removal of SUA groups. These designer microporous silicas are expected to be useful for molecular sieving applications. Precise pore-size control in processed silicas has been a great challenge. Although various silica materials were developed with a wide range of morphologies, crystallinities, and pore-size properties, there is still a great need for the development of new and cost-effective silica materials. Especially important is the development of microporous processed materials that can be used for molecular sieving in various technologies such as gas separation, catalysis, membrane reactors, sensors, and adsorbents.1–4 Recently, precise pore-size control was achieved in the mesoporous range (2–50 nm) by the syntheses of the M41S family of porous materials through the sol-gel technique.5–8 However, precise control is still not accomplished for silica gels or films in the microporous range (
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