Hybrid Inorganic-Organic Mesoporous Silicates—Nanoscopic Reactors Coming of Age

Abstract

This review describes methods of preparing hybrid inorganic–organic mesoporous silicates with uniform channel structures, as well as some of their applications. Both reactive and passive organic groups can be incorporated in the porous solids by grafting methods or by co‐condensation under surfactant control. Functional groups have been placed selectively on the internal or external pore surfaces or even within the walls of the mesoporous solids. Organic functionalization of these solids permits tuning of the surface properties (hydrophilicity, hydrophobicity, binding to guest molecules), alteration of the surface reactivity, protection of the surface from attack, and modification of the bulk properties (e.g., mechanical or optical properties) of the material. Recent applications of hybrid mesoporous silicates are highlighted, including catalysis, sorption of metals, anions, and organics, reactors for polymerization, fixation of biologically active species, and optical applications.

Surfactant‐Assisted Synthesis of Alumina with Hierarchical Nanopores

“…[3] Use of the mesoporous materials in these applications will require the ability to control their nanostructure. Systematic control of the diameter of the mesopores has been amply demonstrated, but control of pore length, which is manifest in the shape of the material particles, is less well developed.…”

Heterogeneous Catalysis and Solid Catalysts

“…Silica, MCM-41, and polymers can be functionalized for application as supports for the preparation of immobilized or hybrid catalysts [119], [122], [199][200][201][202][203][204][205]. The functional groups may serve as anchoring sites (surface bound ligands) for complexes and organometallic compounds.…”

“…There are several routes for the synthesis of immobilized homogeneous catalysts: 1) Anchoring the catalytically active species via covalent bonds on the surface of suitable inorganic or organic supports such as SiO 2 , mesoporous MCM-41, zeolites, polystyrenes, and styrene -divinylbenzene copolymers [199][200][201], [205]. The polymerization or copolymerization of suitably functionalized monomeric metal complexes is also known.…”

“…The reagents for covalent bonding on siliceous materials (SiO 2 , MCM-41) are often alkoxy-or chlorosilanes which are anchored to the surface by condensation reactions with surface hydroxyl groups [199][200][201], [205]. Functional groups thus created on the surface can include phosphines, amines etc., which serve as anchored ligands for active species that undergo ligand-exchange reactions.…”

Nanoporous Catalytic Materials with Organic Frameworks

“…Modification of reaction environment inside zeolites is primarily limited to counter-ion exchange. [1] Researchers have recently been able to graft different reactive groups into the pores of MCM-41 sieves, [7] but the number of examples of this postsynthesis modification for catalytic applications is small. The ideal solution would be nanostructured materials with the chemical tunability, mechanical properties, and processability of an organic system, coupled with the high surface area, stability, and reactivity of an inorganic, supercage material.…”