Large pore mesoporous M1-xSixO2 thin films (M = Ti, Zr; 0.1≤ x ≤0.9) with homogeneous framework

PAULA C. ANGELOMÉ; LEANDRO ANDRINI; FÉLIX G. REQUEJO; M. CECILIA FUERTES; GALO J. A. A. SOLER-ILLIA

Conferencia; XV International Sol Gel Conference (Sol Gel’09); 2009

Mesoporous oxide thin films (MOTF) derived from the combination of sol-gel and self-assembly techniques are potentially useful for advanced coatings, sensors, optoelectronic devices or catalysts. Synthesis of these materials by Evaporation Induced Self Assembly (EISA) pathway has been demonstrated for many different systems, including Si and transition metal oxides. However, very few reports of mixed oxide-based MOTF exist to date. Mixed oxide transparent matrices are interesting in order to obtain tuned refractive index, tunable acidity or surface charge (catalysts), retention of amorphous phases, diminished reactivity or selective functionalization. These effects have been extensively studied for applications such as catalysis, ultra low expansive glasses (ULE®), optical fibers, waveguides, graded refractive index optics, etc . If the interesting properties of mixed oxides are combined with a high specific area as in mesoporous thin films, the range of possible applications is even wider. One of the challenges of mixed oxide phases is to obtain homogeneous compositions without phase separation or zones enriched in one component. Control of the reaction rates is essential in order to achieve this goal. In this work, we report the synthesis and thorough characterization of highly homogeneous M-Si mesoporous mixed oxide thin films in a wide compositional range (from 10% to 90% of M=Ti or Zr), using block copolymers as pore templates. A detailed structural characterization of the obtained films was performed by means of TEM, 2D-SAXS, FTIR, UV and XANES spectroscopy. The composition effect on the mesoporous film final characteristics was studied in detail at meso and microscopic level, and correlated with solution variables. Environmental Porosimetry Analysis (EPA) permits to determine pore volume and size. The adequate choice of the inorganic precursor (TEOS and transition metal chlorides or alkoxides) leads to obtaining MOTF with excellent interdispersion of the cations, as assessed by FTIR, UV-Visible and XANES spectroscopy. These mixed oxide phases remain amorphous and mesoporous after thermal treatment up to 1000ºC.