Fabrication of wood-inspired nanocellulose-based aerogels for efficient adsorption and filtration removal of Congo red

Nanocellulose aerogels have received considerable attention as environmentally friendly adsorption materials for dye wastewater treatment. However, it remains challenging to prepare nanocellulose aerogels with excellent mechanical properties, efficient and fast dye separation, and recyclability. Inspired by the wood structure, this study developed an anisotropic aerogel absorbent by modifying nanocellulose using polyethylene glycol diglycidyl ether (PEGDE) and hyperbranched polyethyleneimine (HPEI), and subsequent directional freezing. The double physical-chemical cross-linked and oriented porous structure in the aerogel enhanced the mechanical properties, leading to high compressive strength and rapid resilience. The HPEI modification provided abundant adsorption sites for dye adsorption, and the directional pore structure shortened the flow path of the dye, resulting in a maximum adsorption capacity up to 3149.61 mg/g for Congo red solution at an initial concentration of 400 mg/L, which was considerably higher than the reported adsorption capacities of similar adsorbents. The anisotropic nanocellulose aerogel also exhibited excellent recyclability, maintaining a dye removal rate of 96.88% or higher after eight cycles. Furthermore, a continuous s separation device was designed based on the anisotropic nanocellulose aerogel and real-time purification of dye wastewater was achieved through filtration under gravity. Therefore, the nanocellulose aerogels developed in this study show great potential for efficient purification of textile printing and dyeing wastewater.