Facile One-Pot Synthesis of Mechanically Robust Biopolymer–Silica Nanocomposite Aerogel by Cogelation of Silicic Acid with Chitosan in Aqueous Media

• Published in: ACS sustainable chemistry & engineering Vol. 4; no. 10; pp. 5674 - 5683
• Main Authors: Zhao, Shanyu, Malfait, Wim J, Jeong, Eunho, Fischer, Beatrice, Zhang, Yucheng, Xu, Haixun, Angelica, Emanuele, Risen, William M, Suggs, J. William, Koebel, Matthias M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.10.2016
• Subjects: Cogelation; Hybrid aerogel; Polysaccharides; NMR; Aqueous solution
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.6b01574

A sustainable aqueous-based route is reported for the synthesis of low density mesoporous silica/chitosan nanocomposite aerogels by cogelation of a chitosan biopolymer dissolved in silicic acid. The random “cluster–cluster” aggregate silica structure intertwined at the molecular level with chitosan yields a three-dimensional semi-interpenetrating network with greatly improved mechanical properties when compared to a silica aerogel of similar density. The physical properties of the resulting aerogels depend significantly on the gelation pH. A silica aerogel reference material synthesized at a low pH of 3 features very low density and high porosity resulting in a highly elastic behavior but comparatively weak skeletal structure (final strength <1 MPa). By compounding the acid catalyzed gel with a chitosan coprecursor, an inorganic–organic nanocomposite aerogel is formed that retains high mechanical flexibility (strain at rupture >80%) but with greatly increased yield strength (>7 MPa). Importantly, the reinforcement does not significantly increase density or thermal conductivity. The volume fraction of the biopolymer coprecursor, which has abundant amino and hydroxyl functional groups, can be adjusted to tune the bulk properties of the composite aerogel, enabling the design of nanoscale inorganic/organic biocomposite materials for a wide range of thermal insulation, sorption, catalysis, and other applications where structural integrity is indispensable.