Tailoring of organically-modified silica MCM-41 type materials with dye molecules
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Tailoring of organically-modified silica MCM-41 type materials with dye molecules Bénédicte Lebeau1, Christabel E. Fowler2, Stephen Mann2 1 Laboratoire de Matériaux Minéraux, ENSCMu, Mulhouse, France 2 School of Chemistry, University of Bristol, Bristol, United Kingdom. ABSTRACT Micelle templated co-condensation of tetraethoxysilane and 3-(2,4-dinitrophenylamino)propyltriethoxysilane was used to covalently attach an organic chromophore into silica materials with MCM-41 architecture. Hexagonally highly-ordered mesoporous dye-functionalized silica materials with various dye contents (up to 43 wt%) were precipitated from alkaline and acidic aqueous solutions containing cetyltrimethylammonium bromide (C16TMAB) surfactant. These materials were obtained in the form of powders, excluding their use in thin film applications, such as required for membrane and optical devices. Therefore, an evaporation-induced self assembly process was used to prepare transparent mesostructured dye-functionalized silica thin films and monoliths. Analogous materials with increased pore channel sizes were fabricated by addition of the micelle swelling agent 1,3,5-trimethylbenzene to the reaction mixture or by replacing C16TMAB surfactant by an amphiphilic triblock copolymer (poly(ethylene oxide)block-poly(propylene oxide)-block-poly(ethylene oxide)). This synthetic route was also used to produce bimodal mesostructured dye-modified silica materials using both latex spheres and C16TMAB micelles as organic structure-directing agents. INTRODUCTION The discovery of the M41S family of mesoporous solids has stimulated research in the area of supramolecular assembly templated, ordered porous materials [1,2]. The increase of the pore size of periodic porous materials offers new opportunities for large molecules in fields such as catalysis, separation and adsorption processes. Tailoring of these materials for specific applications requires both structural and compositional control. Various strategies have been developed to functionalize the surface of these materials [3]. The attachment of organic groups to the backbone of the inorganic matrix can modify the pore surface characteristics (hydrophilichydrophobic balance, polarity,…), provide specific surface sites for metal-ion binding, catalysis or controlled sorption, and also contribute to a particular physical or chemical property (optical or electrical properties, electrochemical reactions, chemical or biochemical reactivity,…). The one-pot synthesis route involving the co-condensation of siloxane and organosiloxane in the presence of supramolecular surfactant templates was pioneered by Burkett et al. [4]. In comparison to the post-grafting process, this method allows a higher organic content and a more homogeneous organic dispersion in the material [5]. This strategy, which leads to an intimate coupling of functional groups into the silica network was used to produce a wide range of organically-modified silica MCM-41-type materials [4,6-9] and ordered mesoporous multicomponent inorganic-organic hybri
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