Alternative chemical route to mesoporous titania from a titanatrane complex
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High-purity, mesoporous titania was prepared by reaction of dimethylaminotitanatrane, [NMe2–Ti(OCH2CH2)3N] in the presence of micellar aggregates as templating agents followed by thermal treatments in the temperature range 350–450 °C. The powders were characterized by nitrogen adsorption–desorption isotherms, thermogravimetry– differential thermal analysis, Fourier transform infrared, field-emission scanning electron microscopy, and x-ray diffraction. Analysis of the morphological characteristics of titanium oxide powders calcined at 350 °C for 120 h and at 450 °C for 6 h showed the presence of a mesoporous structure, with an average pore size of about 3.5 nm. Firing temperatures above 450 °C caused the collapse of the mesoporous structure. Composite Nafion-based membranes, containing 5 wt% mesoporous titania fired at 450 °C as a filler were successfully prepared. Preliminary tests in a prototype direct methanol fuel cell demonstrated that the composite membrane allowed cell operation up to 145 °C, thus showing a significant performance improvement over pure Nafion.
I. INTRODUCTION
The recent discovery of mesostructured materials has given new perspectives in a large number of environmentally friendly applications. A very interesting material for those applications is titania that has been widely used for such as sensors, catalysis, and energy production and storage.1–3 The control of grain size and porosity is paramount for such applications. Therefore, the tailoring of pore size and distribution of oxide materials has attracted wide attention from researchers. A widely applied method to obtain mesostructured or mesoporous metal oxides involves micellar aggregates of surfactants as templating agents. The method was first described by Mobil’s researchers to obtain mesoporous silica.4 The synthesis of mesostructured phases of a variety of metal oxides such as Fe, W, Pb, Sb, and Zr, was studied by Stucky et al.5–8 as an extension of the original approach. The successful preparation of mesostructured oxides of different transition metals, such as V,9,10 Ti,11–14 Nb, Ta, Zr, and Y,15 has also been reported. However, the complete success of this method has been limited and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0007 128
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 1, Jan 2005 Downloaded: 19 Mar 2015
infrequent. The procedure may, in fact, yield lamellar organic–inorganic composites, and the breakdown of mesopores or mesostructure occurs after the removal of the surfactant.16 Moreover, the formation of crystalline phases within the pore walls might also disrupt the mesostructure. The control of the various competitive reactions between and within organic and inorganic phases is a key point to achieve mesoporous metal oxides. Behrens16 and Fröba et al.17 identified three types of interactions driving the reactions involved in the synthesis of mesoporous metal oxides: organic–organic, inorganic–inorganic, and organic–inorganic interactions. The
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