Flexible and crack-free bacterial cellulose (BC)–silica composite aerogels (CAs) are prepared through a sol–gel process followed by freeze drying, in which the BC matrix and silica gel skeleton form an interpenetrating network microstructure. The BC–silica CAs exhibit low density (0.02 g cm⁻³), high specific surface area (734.1 m² g⁻¹) and low thermal conductivity (0.031 W m⁻¹ K⁻¹), almost the same as pure silica aerogels. Due to the synergic effects of the BC matrix and silica gel skeleton, the obtained CAs show excellent robustness and flexibility which overcome the inherent fragility of traditional inorganic aerogels. Furthermore, the dried CAs can withstand a huge capillary force and keep their integrity and flexibility even upon being immersed in a liquid phase again. Hence, the CAs can be functionalized conveniently in a liquid phase to extend their applications. The hydrophobization modified CAs have potential to be used as adsorbents for water purification and show excellent oil absorption capability on the surface of water, and can be removed from water conveniently.

Bacterial cellulose (BC)–silica composite aerogels (CAs) with interpenetrating network (IPN) microstructure are prepared through a permeation sol–gel process followed by freeze drying. The IPN structure is constructed by diffusing the precursor into a three-dimensional (3D) BC matrix followed by permeating the catalyst into the BC network gradually to promote the in situ condensation of precursor to form a SiO₂ gel skeleton from outside to inside. The precursor used here is Na₂SiO₃ instead of traditional tetraethoxysilane. This IPN structure could offer excellent mechanical properties to aerogels, and is essential to prepare flexible aerogels by freeze drying. The compression modulus of CAs could be adjusted in the range of 0.38 MPa to 16.17 MPa. The BC–silica CAs exhibit low density (as low as 0.011 g cm⁻³), high specific surface area (as high as 534.5 m² g⁻¹) and low thermal conductivity (less than 0.0369 W m⁻¹ K⁻¹). Furthermore, the contact angle of the hydrophobization modified CAs is as high as 145°. The outstanding hydrophobicity and the large specific surface area endow the hydrophobic CAs with excellent oil absorption capability on the water surface. Moreover, the hydrophobic CAs that had absorbed oil could be washed and recycled.

Aerogels are nanoporous materials with excellent properties, especially super thermal insulation. However, owing to their serious high brittleness, the macroscopic forms of aerogels are not sufficiently rich for the application in some fields, such as thermal insulation clothing fabric. Recently, freeze spinning and wet spinning have been attempted for the synthesis of aerogel fibers. In this study, robust fibrous silica-bacterial cellulose (BC) composite aerogels with high performance were synthesized in a novel way. Silica sol was diffused into a fiber-like matrix, which was obtained by cutting the BC hydrogel and followed by secondary shaping to form a composite wet gel fiber with a nanoscale interpenetrating network structure. The tensile strength of the resulting aerogel fibers reached up to 5.4 MPa because the quantity of BC nanofibers in the unit volume of the matrix was improved significantly by the secondary shaping process. In addition, the composite aerogel fibers had a high specific area (up to 606.9 m²/g), low density (less than 0.164 g/cm³), and outstanding hydrophobicity. Most notably, they exhibited excellent thermal insulation performance in high-temperature (210 °C) or low-temperature (−72 °C) environments. Moreover, the thermal stability of CAFs (decomposition temperature was about 330 °C) was higher than that of natural polymer fiber. A novel method was proposed herein to prepare aerogel fibers with excellent performance to meet the requirements of wearable applications.