Cellulose-based ultralight foam with dual-scale porosity from hybrid fibers for sustainable oil-water separation.

Industrial wastewater and oil spills are increasingly deteriorating the natural environment, driving demands for superhydrophobic oil-water separation materials. However, developing sustainable absorbents for oil spill remediation is challenging due to the typical trade-off between high absorption capacity and low mechanical robustness. Here, we present a biomass-derived ultralight foam using cellulose for environmental remediation, fabricated through integration of vinyltrimethoxysilane-modified Calotropis gigantea fiber (CGF) and microfibrillated cellulose (MFC). The hollow structure of CGF (pore size 8-15 μm) and the nanofibrous network of MFC synergistically combine to achieve ultralow density (6.12 ± 0.21 mg/cm3) and exceptional porosity (99.60 ± 0.14 %). The foam exhibits hydrophobicity (water contact angle of 141.2 ± 0.63°), adsorption capacity of 152.45 ± 5.65 g/g (for chloroform), oil uptake of 139.6 ± 3.17 g/g within 5 s (for dichloromethane), and separation flux of 29,257.9 ± 1491.3 L m-2 h-1 (for dichloromethane). Owing to the incorporation of CGF, it exhibits a 38.2 % higher oil absorption capacity than that of pure foam. The foam possesses temperature stability in a range of -10 °C to 60 °C, and maintains a repetitive separation efficiency of 99.06 ± 0.27 %. Demonstrated in a pump system for continuous oil-water separation, this foam offers a promising sustainable material for environmental remediation.