Ryoo R, Park I S, Jun S, Lee C W, Kruk M, Jaroniec M
Department of Chemistry, School of Molecular Science-BK21, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea.
J Am Chem Soc. 2001 Feb 28;123(8):1650-7. doi: 10.1021/ja0038326.
Silica molecular sieves with uniform pores on the borderline between micropore (diameter <2 nm) and mesopore (from 2 to 50 nm) ranges were synthesized by a novel method using judiciously chosen mixtures of short double-chain alkylammonium surfactants. These silicas were characterized using X-ray diffraction (XRD), thermogravimetry, and nitrogen and argon adsorption. The calcined materials exhibited either 2-dimensional (2-D) hexagonal or disordered structures with XRD interplanar spacing from 2.51 to 2.93 nm, including the value of as small as 2.69 nm for highly ordered 2-D hexagonal silica. The dependence of the pore size and surfactant content on the surfactant chain length provided strong evidence for supramolecular templating being operative in the formation of small-pore silicas, even for the surfactant chain length of six carbon atoms. Both hexagonally ordered and disordered calcined samples were shown to exhibit narrow pore size distributions with maxima in the range from 1.96 to 2.61 nm (reliably evaluated on the basis of the unit-cell dimension and pore volume for 2-D hexagonal materials, and calculated using a properly calibrated procedure), tailored by the surfactant chain length. The samples exhibited primary pore volumes from 0.28 to 0.54 cm(3) g(-1) and specific surface areas from 730 to 930 m(2) g(-1). Because of their small yet uniform pore size and large specific surface area, the silicas reported herein promise to be useful in applications in adsorption and catalysis. Adsorption studies of these materials provided a unique new insight into the pore-filling mechanism for small-pore materials. Moreover, the approach proposed herein is expected to facilitate the synthesis of not only small-pore silicas but also materials with other framework compositions, thus largely contributing to bridging the gap in attainable pore sizes between micropore and mesopore ranges.
采用一种新颖的方法，通过精心选择短双链烷基铵表面活性剂的混合物，合成了孔径均匀、处于微孔（直径<2nm）和介孔（2至50nm）范围边界的二氧化硅分子筛。使用X射线衍射（XRD）、热重分析以及氮气和氩气吸附对这些二氧化硅进行了表征。煅烧后的材料呈现出二维（2-D）六方或无序结构，XRD晶面间距为2.51至2.93nm，对于高度有序的二维六方二氧化硅，该值小至2.69nm。孔径和表面活性剂含量对表面活性剂链长的依赖性为超分子模板作用在小孔径二氧化硅形成过程中的发挥提供了有力证据，即使对于六个碳原子的表面活性剂链长也是如此。结果表明，六方有序和无序的煅烧样品均呈现出窄的孔径分布，最大值在1.96至2.61nm范围内（基于二维六方材料的晶胞尺寸和孔体积可靠评估，并使用适当校准的程序计算），由表面活性剂链长定制。样品的初级孔体积为0.28至0.54cm³ g⁻¹，比表面积为730至930m² g⁻¹。由于其孔径小且均匀以及比表面积大，本文报道的二氧化硅有望在吸附和催化应用中发挥作用。对这些材料的吸附研究为小孔径材料的孔填充机制提供了独特的新见解。此外，本文提出的方法有望促进不仅小孔径二氧化硅的合成，还能促进具有其他骨架组成的材料的合成，从而在很大程度上有助于弥合微孔和介孔范围可达到的孔径之间的差距。
