Synthesis and characterization of mesoporous silica from selectively acid-treated saponite as the precursors

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• 作者：Kiyoshi Okada ; Hisako Yoshizaki ; Yoshikazu Kameshima ; Akira Nakajima ; Chengala D. Madhusoodana
• 关键词：Mesoporous silica ; Saponite ; Acid-treatment ; Cethyltrimethylammonium bromide
• 刊名：Journal of Colloid and Interface Science
• 出版年：2007
• 出版时间：1 October 2007
• 年：2007
• 卷：314
• 期：1
• 页码：176-183
• 全文大小：667 K

文摘

Mesoporous silicas were synthesized by hydrothermal treatment of selectively acid-treated saponite (an ideal structural formula: Na_1/3Mg₃(Si_11/3Al_1/3)O₁₀(OH)₂), having a 2:1 type layered structure as the silica source and its porous properties were examined and compared with that from kaolinite (an ideal structural formula: Al₂Si₂O₅(OH)₄), having a 1:1 type layered structure. Synthetic saponite was selectively leached in H₂SO₄ solutions with various concentrations (0.05–1 M) at 70 °C for 0.5 h. The resulting products (precursors) were mixed with cetyltrimethylammonium bromide (CTABr), NaOH and H₂O, hydrothermally treated at 110 °C and removed the CTABr by calcining at 560 °C. A hexagonal mesoporous phase was obtained with higher Si/(Al(+Mg)) ratios of the resulting precursors. The XRD patterns of these products show the peaks assigned by a hexagonal lattice with ce?_ob=MathURL&_method=retrieve&_udi=B6WHR-4NS2GJ7-7&_mathId=mml10&_user=10&_cdi=6857&_rdoc=22&_acct=C000050221&_version=1&_userid=10&md5=8a23237a161c666a3d80c678cc040085"" title=""Click to view the MathML source"">a₀=4.0–4.6 nm and the crystallinity becomes higher with higher Si/(Al(+Mg)) ratios of the precursors. The specific surface area (ce?_ob=MathURL&_method=retrieve&_udi=B6WHR-4NS2GJ7-7&_mathId=mml11&_user=10&_cdi=6857&_rdoc=22&_acct=C000050221&_version=1&_userid=10&md5=581376ee0152008265bba77c1487d5c4"" title=""Click to view the MathML source"">S_BET) values of the present mesoporous silicas range from 800 to 1100 m²/g at CTABr/precursor = 0.1 and although they are not as high as those from precursors prepared from calcining and acid-treatment of kaolinite (1420 m²/g), they are increased to 1400–1500 m²/g by increasing the ratio CTABr/precursor cedirect.com/scidirimg/entities/2a7e.gif"" alt=""greater-or-equal, slanted"" border=0>0.2. The reason for the difference in the optimum preparation conditions between saponite and kaolinite may be attributed to the difference in the linkage of the SiO₄ tetrahedra in these precursors (i.e. layered or framework structures), which result in great differences in the selective leaching rates and structures of the resulting silica-rich products.