Sol-Gel Methods for Materials Processing Focusing on Materials for P
Sol-gel processing is a soft-chemistry method to obtain functional materials at low temperatures. This route can be used to produce very sophisticated nanomaterials and to tailor the materials to very specific applications. Adsorption and detection of pol
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Abstract. Here we consider the routes of synthesis (which is performed by use of sol-gel method) of a new class of sorbents, namely: polysiloxane xerogels functionalized with nitrogen-, oxygen-, phosphorus- and sulfur content ligand groups. Applying a number of physical methods (SEM, TEM, AFM, IR and Raman spectroscopy, 1ɇ, 13C, 29Si and 31P CP/MAS NMR, EPR spectroscopy, ERS, thermal analysis) we established the structure of both: the xerogels and their surface. An influence of some factors on the structural-adsorption characteristics of such xerogels and their sorption properties is analyzed. Keywords: Sol-gel method, functionalized polysiloxane xerogels, synthesis, structure, sorption properties.
1. Introduction Modification of silicas surface by trifunctional silanes, R3SiRc (R – ɋl or AlkO; Rc – functional group)1–4; realization of hydrolytic polycondensation of alkoxysilanes5–9 (the sol-gel method10); accomplishment of hydrolytic polycondensation of alkoxysilanes in the presence of surfactants (the tamplate method)11 – these are the most widly used approaches which are applied for synthesis of polysiloxane adsorbents that contain functional groups in their surface layer. Here we consider the sol-gel method which recently had received wide practice. Usually, the most applied one is its variation which is based on reaction of joint hydrolytic polycondensation of alkoxysilanes (Scheme 1). Introduction of water and catalyst (e.g., ɇ+, Ɉɇ–, F–) in the initial system leads to hydrolysis of alkoxysilanes with a formation of silanol groups, {Si–OH. _ *To whom correspondence should be addressed: Dr. Yu.L. Zub, Head of Surface Chemistry of Hybrid Materials Department, O.O. Chuiko Institute of Surface Chemistry, NAS of Ukraine, 17 General Naumov Str., Kyiv 03164 Ukraine; e-mail: [email protected] P. Innocenzi, Y. L. Zub and V. G. Kessler (eds.), Sol-Gel Methods for Materials Processing © Springer Science + Business Media B.V. 2008
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+ H2O (Solv), catalyst xSi(OAlk)4 + y(AlkO)3SiRc + z(AlkO)3SiRcc –o –o (SiO4/2)x · (O3/2SiRc)y · (O3/2SiRcc)z –AlkOH Scheme 1 These groups start to interact with each other(or with alkoxysilyl groups, AlkO–Si{) immediately, which leads to a creation of siloxane bounds ({Si–O– Si{), causing occurrence of oligomers. The results of further condensation of these oligomers are the occurrence of polymers of a various structure. The growth of polymers conducts to occurrence of colloidal particles which consequently leads to occurrence of sol. The further integration of these particles and creation of aggregates causes transaction of sol into gel. The following treatment of formed gel (its ageing, washing, drying, etc.) results in a xerogel. The presence of trifunctional silanes (AlkO)3SiRc (functionalizing agents) in abovementioned systems allows one to obtain xerogels (adsorbents) which contain necessary functional groups in their surface layer. Most of alkoxysilanes are liquids, which are mixed up together, however, nonaqueous solvents often are used during synthesis – as wi
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