Mesoporous silica molecular sieves prepared by ionic and neutral surfactant templating: A comparison of physical properties
Mesoporous silica molecular sieves prepared by ionic and neutral surfactant templating: A comparison of physical properties
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DOI：
10.1021/cm950549a
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发表时间：
1996-08-01
影响因子：
8.6
通讯作者：
Pinnavaia, TJ
中科院分区：
文献类型：
--
作者：
Tanev, PT;Pinnavaia, TJ
分别采用静电组装法和中性组装法制备了一系列介孔MCM-41和HMS硅分子筛，并通过多种物理方法对它们的性能进行了比较。阳离子季铵离子表面活性剂（S+）和阴离子硅酸盐前体（I-）之间的直接S+I-电荷匹配在水热合成条件（100 ℃）下提供长程六方结构，但当在环境温度下进行合成时，长程有序性大大降低。相反，由于较弱的组装力，反离子介导的S（+）X（-）I（+）和中性（SI 0）-I-0途径（其中X（-）是卤素。和S-0是伯胺）提供具有最佳长程有序的煅烧产物。通常，通过静电S+I-或S（+）X（-）I（+）组装形成的MCM-41二氧化硅比通过（SI 0）-I-0组装制备的HMS类似物表现出更大的长程有序性。然而，框架限制的孔结构，虽然依赖于表面活性剂的大小，保持均匀，无论长程六方有序的保真度。通过Si-29 MAS NMR Q（4）/Q（3）Si（O-Si）（4-x）连接性比判断，合成的中性HMS二氧化硅比合成的MCM-41类似物的带电骨架更广泛地交联。HMS框架的中性和广泛交联的特性允许通过溶剂萃取有效和环境友好地回收模板。相比之下，静电模板MCM-41衍生物需要质子离子交换或煅烧从骨架孔中完全除去模板。此外，相对于S+I-和S（+）X（-）I（+）模板化衍生物，HMS介观结构具有更厚的骨架壁、在空气中煅烧时的上级热稳定性和更小的微晶尺寸，这提供了互补的结构中孔性，用于改善对骨架限制的中孔的接近。
A series of mesoporous MCM-41 and HMS silica molecular sieves have been prepared by electrostatic and neutral assembly pathways, respectively, and their properties have been compared by a variety of physical techniques. Direct S+I- charge matching between catioinic quaternary ammonium ion surfactants (S+) and the anionic silicate precursors (I-) affords long-range hexagonal structures under hydrothermal synthesis conditions (100 degrees C), but the long-range order is greatly reduced when the synthesis is conducted at ambient temperature. Conversely, owing to weaker assembly forces, counterion-mediated S(+)X(-)I(+) and neutral (SI0)-I-0 pathways (where X(-) is halide. and S-0 is a primary amine) provide calcined products with the best long-range order when the syntheses are conducted at ambient temperature. In general, MCM-41 silicas formed by electrostatic S+I- or S(+)X(-)I(+) assembly exhibit greater long-range order than the HMS analogues prepared by the (SI0)-I-0 assembly. However, the framework-confined pore structures, though dependent on the size of the surfactant, remain uniform, regardless of the fidelity of the long-range hexagonal order. As-synthesized neutral HMS silicas are much more extensively cross-linked than the as-synthesized charged frameworks of MCM-41 analogues, as judged by the Si-29 MAS NMR Q(4)/Q(3) Si(O-Si)(4-x) connectivity ratios. The neutral and extensively cross-linked character of HMS frameworks allows for the efficient and environmentally benign recovery of the template by solvent extraction. In contrast, electrostatically templated MCM-41 derivatives require proton ion exchange or calcination for the complete removal of template from the framework pores. Also, relative to the S+I- and S(+)X(-)I(+) templated derivatives, HMS mesostructures possess thicker framework walls, superior thermal stability upon calcination in air, and a smaller crystallite size, which affords complementary textural mesoporosity for improved access to the frameswork-confined mesopores.