Mesostructured Silica Films with Metal Oxide Doped Pore Walls
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1007-S04-12
Mesostructured Silica Films With Metal Oxide Doped Pore Walls Joachim Koehler1, Jun Cai2, Rolf Juergen Behm2, and Nicola Huesing1 1 Institute of Inorganic Chemistry I, Ulm University, Ulm, 89081, Germany 2 Institute of Surface Chemistry and Catalysis, Ulm University, Ulm, 89081, Germany ABSTRACT In this work, novel approaches towards mixed metal oxide mesostructured films by a combination of evaporation-induced self-assembly and sol-gel processing of deliberately designed precursor molecules (from single source precursors to metal-surfactant complexes) are reported. The focus lies on Ti-oxide doped silica films with in a wide range variable Ti to Si ratios. The ligand-assisted templating based on metal-coordinated surfactants allows a selective positioning of the metal species in the silica wall which is advantageous for many catalytic applications. For the synthesis of these metal doped silica films, a non-ionic polyether-based surfactant (Brij56) was simultaneously used as the structure-directing agent and ligand for the respective metal-alkoxide, such as titanium isopropoxide. These metalcoordinated surfactants were mixed with a prehydrolyzed silica-solution based on tetraethoxysilane and ethanol and spin- or dip coated. In the second approach, a single source precursor for network formation based on 3-acetyl-6-trimethoxysilylhexane-2-one that was coordinated to titanium isopropoxide was synthesized. This precursor was either used as network forming agent in the presence of tetraethoxysilane and a surfactant (Brij56) or in combination with the metal-coordinated surfactant to broaden the accessible range of the Si:Ti ratios. The final films were characterized by XRD, XPS, nitrogen porosimetry and TEM.
INTRODUCTION Despite the great advantages offered by variations in pore sizes and structures, the main handicap that limits the range of applications of silica-based mesostructured materials lies in their inert chemical character. The insertion of metal oxides into porous silica materials by several different approaches such as direct synthesis[1], post treatment[2] or by one-pot synthesis to prepare, i.e. mesoporous doped silica films[3] is well known. However, the main problem – how to obtain a homogeneous final material without phase separation, clustering of one species or pore blocking – is not sufficiently remains unsolved so far. The preparation of mesoporous films with a structure directing agent such as the non-ionic surfactant Brij56 via evaporation-induced self-assembly processes (EISA)[4], allows for an integration of a large variety of metal oxides directly into the pore walls (more or less isomorphically substituting silicon in the amorphous network), assuming that the metalalkoxide can be complexed to the ethylenglycol moiety of the surfactant, as it was already shown for Fe-Brij56[5] or Ti-, Zr-Brij56[6,7]. The use of inorganic-organic single source precursors for network formation in which silicon and i.e. titanium centers are linked coordinatively in a stable way within one molecule li
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