Nanoassembling of Thixotropically Reversible Alumino-siloxane Hybrid Gels to Hierarchically Porous Aerogel Framework

Abstract

This work describes a versatile strategy for the formation of thixotropically reversible alumino-siloxane hybrid gel suitable for the fabrication of open-porous aerogel like framework. Aminated alumino-siloxane gel was synthesized by pH controlled sol–gel assisted co-condensation of hydrolyzed aluminum isopropoxide with 3-aminopropyltrimethoxy silane. A rare reversible thixotropic flow behavior was noticed for the first time in aminated alumino-siloxane hybrid gel. The hybrid gel was used for preparation of hydrogel microspheres via gel granulation technique. The hydrogel microspheres derived from thixotropic gel showed an open porous network with intercommunicated structure. It was then converted to aerogel microspheres, without the collapse of the transient hybrid porous network by ambient pressure drying technique. The porous framework was tailored to hierarchical domains containing meso/macro porosity, with a dense array of functional amine on internal porous framework. The textural properties of the hybrid alumino-siloxane aerogel microspheres have been characterized by SEM, TEM, FTIR and N2 gas adsorption/desorption analysis and the results are discussed. Hybrid aerogel microspheres exhibit 2–3 times superior properties in terms of surface area and pore features compared to their xerogel counterparts. Thus, open porous aerogel microsphere derived from thixotropic gel could be a new media for controlling host–guest interactions especially when it is intended to be used in adsorption, separation and catalysis/catalyst support.