Highly efficient oil–water separation of superhydrophobic cellulose II aerogel based on dissolution and regeneration of cotton in lithium bromide system

• High porosity and superhydrophobic cellulose II aerogel were successfully prepared. • Selective separation of oil-water was achieved by hydrophobized cellulose II aerogels. • Separation efficiency of 98.7% was obtained for toluene/water mixture. • The morphology of hydrophobic cellulose II aerogels can be adjusted by changing the content of aerogel cellulose. In recent years, the frequent occurrence of oil spills and the excessive discharge of oily wastewater have caused serious damage to the environment. Therefore, the development of oil/water separation materials has attracted widespread attention. Here, we have successfully synthesized cellulose aerogels (CAs) based on a green and simple LiBr system and modified the CAs with methyltrimethoxysilane (MTMS) for the fabrication of hydrophobized cellulose II aerogels (HCAs). The prepared HCAs have low density (0.021-0.039 g/cm 3 ), high porosity (97.6-98.7%) and hierarchical porous structure. The water contact angle of the HCAs was 150°±5°, exhibiting the excellent hydrophobic and lipophilic properties of the HCAs. Oil/water separation experiments have shown that HCAs has outstanding separation efficiency of over 96% for a variety of oil/water mixtures. Furthermore, the HCAs also exhibited excellent reusability for long-term use. HCAs are promising for a wide range of practical applications in oil-water separation, including oil/chemical spills and industrial effluent discharge, owing to the green and facile preparation process, excellent separation efficiency and superior reusability.