Abstract:

Objective In order to solve water pollution problem caused by lipids and coloring substances, cellulose nanofibers (CNF) is employed as the substrate material, and CNF aerogels are utilized as carriers for hydrophobic modification to prepare highly elastic cellulose nanofiber aerogel (CNF-Xs) with excellent oil absorption properties for practical applications.
Method Cellulose nanofibers were selected as the substrate material, with a low dosage of the hydrophobic component methyltrimethoxysilane (MTMS) serving as the modifier. Utilizing a freeze-drying method, low-cost and high-performance hydrophobic-oleophilic cellulose nanofiber aerogels were fabricated, and the oil-water separation performance and mechanical properties of these aerogels were characterized. Furthermore, the relationship between the dosage of MTMS and micro-morphology, chemical structure, surface roughness, and compressive properties of the aerogels were explored. The influences of MTMS incorporation on the properties of the aerogels was investigated, so as to guide the development of highly elastic CNF-based aerogels with superior oil absorption capabilities for practical applications.
Results The CNF-Xs aerogel was found to feature a three-dimensional network skeleton composed of microfibers and nanofibers, exhibiting an orderly layered structure and porous cellular architecture. The results showed that these structural characteristics endowed the aerogel with an ultra-low density of 0.08 g/cm³ and superior structural stability, which was recoverable from deformation even at a strain as large as 80%, demonstrating good compressive properties. The aerogel exhibited an absorption capacity of 39.41 g/g for hexane stained with Oil Red and maintained an ultra-high separation efficiency of 98% after 10 cycles of use. Additionally, the siloxane network structure of MTMS provided the CNF-Xs aerogel with exceptional hydrophobicity. Even at a low dosage (the molar ratio of CNF and MTMS is 1:3), the water contact angle of the composite aerogel reached 133°.
Conclusion Using cellulose nanofibers as the raw material and the hydrophobic component MTMS as the modifier, hydrophobic and oleophilic CNF-Xs were successfully prepared through a green and low-cost one-step process under conditions of low MTMS dosage. The water contact angle of the CNF-Xs reached 133° (the molar ratio of CNF and MTMS is 1:3), and they exhibited excellent oil-selective adsorption properties. MTMS enhances the elastic potential energy of CNF-Xs through its hydrolysis, condensation, and crosslinking to form a three-dimensional network structure, which results in good mechanical properties even at a strain of 80%. After 100 cycles, the retention rates of the maximum relative height and maximum stress are above 90% and 73%, respectively, indicating high structural stability. The CNF-Xs can recover to their original height within 3 s after removing external strain, demonstrating excellent compressive performance and mechanical strength. The adsorption capacity of CNF-Xs for cyclohexane, n-hexane, hexadecane, and edible oils ranges from 17.82 to 39.41 g/g, exhibiting high efficiency in adsorbing oily dyes. After 10 oil-water separation cycles, the oil-water separation efficiency remains above 98%. The aerogel not only has a simple preparation process and low raw material cost but also exhibits excellent performance in treating oily dye wastewater.

Key words: cellulose nanofiber aerogel, methyltrimethoxysilane, hydrophobic modification, oil-water separation, wastewater treatment