Highly compressible and hydrophobic anisotropic cellulose-based aerogel fabricated by bidirectional freeze-drying for selective oil absorption

Cellulose-based aerogels have become a great potential for oil absorption applications due to their wide range of sources, low density, and good adsorption properties. However, many reported cellulose-based aerogels to have the drawbacks of low oil recovery rate and poor mechanical, which limit their application. In this study, high reusable and excellent mechanical properties silylated TEMPO-oxidized nanofibers/polyvinyl alcohol aerogels (STPA) were fabricated through a three-step process of aqueous silylation, bidirectional freezing, and freeze-drying. A bidirectional freezing technique was employed to obtain two unique structural aerogels by adjusting the methyltrimethoxysilane concentration. The STPA possessed many excellent physical properties, such as ultralight (9.79 mg/cm3), hydrophobicity (136°), and compressibility; as an adsorbent, STPA showed high adsorption capacity (51–111 g/g) for various types of organic solvents. Furthermore, the excellent compressibility enables STPA fast and highly efficient recovery of the absorbed oil by simple mechanical squeeze. It possesses an excellent oil recovery rate of 80% and maintains around 90% of its initial saturated absorption capacity after 50 cycles of absorption–squeezing. Therefore, the successful microstructure design of the biomass-aerogel through bidirectional freezing could provide new thoughts for the design of multifunctional oil absorbents and STPA with good mechanical properties and reusability showing promising prospects in the field of water treatment.