Multiscale kapok/cellulose aerogels for oil absorption: The study on structure and oil absorption properties

[Display omitted] •An efficient and economic kapok/cellulose aerogel for oil cleanup was prepared.•The dimension of cellulose showed a great impact on property of aerogels.•KNAs exhibited better oil absorption and mechanical property than KMAs.•All aerogels owned a dual-scale hierarchically porous structure at micro-level.•By silanization, these aerogels possessed great hydrophobicity and lipophilicity. An efficient and economic kapok/cellulose aerogel for waste oil treatment was successfully fabricated via simple freeze-drying and surface modification. To investigate their oil absorption performance, various aerogels by multi-scale cellulose and different lengths of kapok fibers were characterized. The use of cellulose nanofibers (CNF) enabled aerogels to possess remarkably uniform pore size and structural integrity, while the introduction of kapok improved their mechanical property, oil absorption and retention performance. For kapok/microfibrillated cellulose (MFC) aerogels, an excessively enlarged porous structure caused by long fibers would damage the structural stability of aerogels and reduce their oil absorption capability. Compared with the sheet-like structure formed by self-aggregated MFC, filamentous CNF exhibited better entanglement characteristics and possessed a more positive impact on enhancing the structural integrity and mechanical properties of aerogels. These aerogels presented ultra-low density (4.9 mg/cm3), desirable hydrophobicity (147.6°), outstanding oil absorption (141.9 g/g) and retention (97.7 %) capacity, and excellent selective sorption property, making them ideal absorbents for oil spill cleaning.