Organic-Containing Mesoporous Silicas with a Variety of Mesophases and a Periodic Pore Wall Structure
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Organic-Containing Mesoporous Silicas with a Variety of Mesophases and a Periodic Pore Wall Structure Shinji Inagaki and Shiyou Guan Toyota Central R&D Labs., Inc. Nagakute, Acihi 480-1192, Japan ABSTRACT In this report we introduce new types of organic-inorganic hybrid mesoporous materials, in which organic and inorganic moieties are distributed homogeneously at the molecular level in the framework, forming a covalently bonded network. Possessing unique surfaces on which both organic and inorganic components are exposed, these materials are expected to have applications in various areas as catalysts, adsorbents and separators, and as hosts for nano-cluster synthesis. The hybrid mesoporous materials showed not only unique surface properties but also unique structural features in micron- or angstrom-scales. Mesoporous materials containing ethylene groups in the main framework formed a variety of particle morphologies of hexagonal rod, spherical, and decaoctahedral shapes in the sizes of 1-10 µm. Mesoporous material containing phenylene groups showed novel crystal-like 7.6 Å periodicity in the pore walls. The mesoporous material has periodically arranged hydrophobic-hydrophilic surfaces, which is a great advantage for use as catalyst and host material for inclusion chemistry. INTRODUCTION Beginning with the synthesis of highly ordered mesoporous materials such as MCM-41 [1] and FSM-16 [2,3], the number of researchers working with these materials has grown rapidly, with over a thousand papers published annually on this subject. During this time, remarkable advances have occurred in the area of synthesis, and it is now possible to synthesize mesoporous materials with various compositions, structures, and morphologies. Because the composition of a material directly affects its catalytic and adsorption functions, as well as its physical properties such as electromagnetic behavior, particular effort is being made to expand into the development of non-SiO2 mesoporous materials. As a result, development has expanded to include inorganic substances in general, including metasilicates containing various heteroatoms, non-silicon oxides [4], sulfides [5], phosphates [6], platinum [7] and carbon [8]. Furthermore, from around 1996, development has expanded to include systems containing not just inorganic substances but organic components as well [9-15]. The fact that it is now possible to exploit the various specialized functions of organic groups within uniformly distributed and stable inorganic nanopores has led to an abrupt expansion in the functionality of mesoporous materials. Conventional organic surface-grafted mesoporous materials have uniform structures in which the surface of the inorganic main framework is covered by an organic group. In such a structure, the inorganic and organic components are separated at the molecular level (Figure 1a), and while the surface characteristics are controlled by the properties of the organic groups, the only role played by the inorganic framework is to provide the support structure. Acc
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