Freeze-dried cellulose-based aerogel with unidirectional pore structure for anionic dyes and oils adsorption

Abstract

Carboxylated nanocellulose (CNC)-based aerogels were prepared based on optimized freeze-drying (FD) for anionic dyes and oils adsorption. Wood powders were used as the raw material to extract the CNC. Polyethyleneimine (PEI) and methyltrimethoxysilane (MTMS) were physically crosslinked with CNC to improve water treatment performance. Directional freezing was employed for constructing unidirectional pore structure to enhance mass transfer and dielectric was utilized for aiding microwave heating to enhance heat transfer. This optimized method could reduce the FD time of aerogels by over 40 %. Dyes adsorption experiments revealed that CNC/PEI aerogel by optimized FD possessed high adsorption performance and selectivity for anionic dyes, with the highest adsorption capabilities of 882.09 mg·g⁻¹ for Congo red (CR) and 550.95 mg·g⁻¹ for Sunset yellow (SY). Following liquid-phase modification, CNC/PEI/MTMS aerogel exhibited great hydrophobicity, and adsorption capabilities of six selected oils reached 21.53–30.74 times its own weight. The directional freezing also enhanced the mechanical property of the aerogels, increasing compressive moduli by more than 2.7 times. The aerogels demonstrated excellent recyclability, retaining over 90 % and 87 % of initial adsorption capability for dyes and oils, respectively, after 20 adsorption–desorption cycles. The FD optimization method proposed in this work not only improved the water treatment performance of CNC-based aerogels but also reduced their preparation cost. The prepared aerogels showed significant potential for efficient treatment of dyeing and oily wastewater.