Transparent and thermally super-insulating κ-carrageenan aerogels

•Zirconium-ion crosslinking effectively reinforced the κ-carrageenan gel network. • •A polarity-gradient solvent-exchange strategy significantly reduced gel shrinkage. • •SAXS revealed the structural evolution of κ-carrageenan fibers during aerogel formation. • •The obtained aerogel combined high transparency with ultralow thermal conductivity. This study presents a facile strategy for fabricating transparent κ-carrageenan aerogels via multivalent metal-ion crosslinking, polarity-gradient solvent exchange, and supercritical carbon dioxide drying. The structural evolution of the κ-carrageenan gel network toward a nanofibrous architecture was further elucidated by SAXS. The resulting aerogels exhibited a unique combination of high optical transparency (up to 79.4%), high specific surface area (442.9–504.9 m 2  g −1 ), ultralow thermal conductivity (14.84–17.22 mW m −1  K −1 ), and low bulk density (54.42–77.33 mg cm −3 ). In addition, the crosslinking-induced structural and chemical changes in κ-carrageenan were systematically investigated by FT-IR, XRD, and XPS, while the thermal stability and compressive mechanical performance of the aerogels were also comprehensively evaluated. Owing to their highly transparent nanostructure and excellent thermal insulation capability, the κ-carrageenan aerogels developed in this work demonstrate a highly competitive property profile among polysaccharide-based aerogels reported to date and hold considerable promise for transparent thermal insulation applications. This study reports a strategy for preparing a transparent nanofibrous κ-carrageenan aerogel through steps including tetravalent metal ion crosslinking, polarity-gradient solvent exchange, and supercritical carbon dioxide drying. The resulting aerogel exhibits high transparency, low haze, ultra-low thermal conductivity, and low density. Its overall performance shows significant competitiveness among currently reported polysaccharide-based aerogels, and it also holds outstanding application potential in the field of transparent thermal insulation. Download: Download high-res image (176KB) Download: Download full-size image