Biopolymer-Silica Aerogel Nanocomposites

SiO2 aerogels are attractive materials for a wide range of applications due to their exceptional physical properties. However, despite many decades of research, the use of silica aerogels is still restricted by their poor mechanical properties and limited range in surf"ace chemistry. Because of their flexibility, biocompatibility, hydroxyl reactivity, low density, toughness, and easy formability, biopolymers aerogels have great potential, but they also have inherent limitations related to their high flammability, compressibility, and inherent hygroscopicity. Hybrid biopolymer-silica aerogels can address the limitations of pure silica and pure biopolymer aerogels. The complementarity of the respective material properties has led to a growing interest in the development of biopolymer-silica hybrids with superior properties in three main ways. First, biopolymers can alleviate the inherently fragile structure of silica aerogels and can introduce chemical multi-functionality to the silica surface. Second, the compressibility, flammability and inherent hygroscopicity of pure biopolymer aerogels can be reduced by the incorporation of inorganic components. Third, there are a large number of possible combinations of biopolymers and silica, and there is a large range of functional groups available in biopolymers. Consequently, large variations in structure, surface chemistry, and chemical functionality of aerogels are possible in silica-biopolymer aerogels and this is described in detail for functionalized chitosan-silica aerogels. Thanks to their versatile performance, hybrid biopolymer-silica aerogels are promising candidate materials for thermal insulation, pharmaceutical, biomedical, catalytic, and separation applications.