Highly porous silica networks derived from gelatin/siloxane hybrids prepared starting from sodium metasilicate

The formation of polymeric hybrid materials of siloxanes with gelatin (GE) starting from sodium metasilicate as the silica source, and their transformation into silica under different conditions have been studied. Gelatin/silicate hybrid nanocomposites were obtained by acid precipitation of mixed gelatin and sodium silicate solutions. Porous xerogels with large BET areas (452 m(2)/g) constituted by closed packed microspheres (1 mum diameter) containing residual gelatin in microporous domains were obtained after thorough extraction of gelatin with water from the nanocomposites. By calcination at 550 degreesC the residual gelatin occluded in the micropores was eliminated and a highly microporous silica (BET area 834 m(2)/g) with microspherical morphology was produced. Blanks were prepared in order to establish the role of GE in the process. Silica samples obtained under the same conditions but without gelatin also have large BET areas but they are mesoporous (40-100 Angstrom), presenting an irregular morphology on a micron scale. The morphological and textural differences between both silica types demonstrate the nanocomposite structure of the hybrids, making evident the templating role of gelatin in the formation of the silica network. (C) 2004 Elsevier B.V. All rights reserved.