Functionalization of Silica Surfaces
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Imparting desired properties to silica surfaces to obtain functionalized silica surfaces is usually effected in different directions. In some cases, it is necessary to moderate interactions between surrounding molecules and surface sites, while in other cases, such interactions should be enhanced to prepare modified matrices with high specificity and selectivity. Besides, functionalization of silica surfaces is often carried out to immobilize diverse compounds to make them heterogeneous. A description is provided for chemical reactions, which are used to modify surfaces and to produce functionalized silica surfaces. A consideration is given to basic principles that should be adhered to when applying functionalized silica surfaces to various types of chromatographic separation [in such cases as stationary phases in gas and liquid chromatography, reversed and normal phases in high-performance liquid chromatography (HPLC) and affinity chromatography, chiral stationary phases for separating optical isomers]. Examples are presented which are intended to illustrate the production of highly specific and complexing adsorbents based on silicas with functionalized surfaces and their application in solid-phase extraction (SPE) of ions and molecules. A general outline is made of methods for activating surfaces of silica matrices with a view to heterogenize metal complex catalysts, to immobilize enzymes and other biologically active compounds. Also included is a brief analysis of the practical experience acquired in the sphere of application of functionalized silicas in the capacity of chemically active fillers of polymeric compositions and effective thickeners of dispersion media. Some consideration is also given to the state of the art and scope for research into the application of functionalized silica surfaces in formation of nanostructures in various fields of modern materials science (sensitive elements of sensing devices, organically modified silicates, organically modified ceramics, etc.).