Microporous cationic nanofibrillar cellulose aerogel as promising adsorbent of acid dyes

Cellulose aerogel based on cationic cellulose nanofibrils (Q-CNF) with surface rich in trimethylammonium chloride functional groups was prepared by freeze drying and chemical crosslinking with an aliphatic triisocyanate. The aerogel, in the form of a rigid porous material, was shown to be an efficient adsorbent for anionic dyes and exhibited strong resistance to disintegration in water. The adsorption capacity for red, blue, and orange dyes was 250, 520, and 600 µmol g⁻¹ (about 160, 230, and 560 mg g⁻¹), respectively. Zeta potential measurements confirmed the main contribution of electrostatic interactions between positive sites on the CNF surface and dye sulfonate groups. The adsorption capacity was shown to be related to the specific surface area of the nanocellulose aerogel and the cationic content of the CNF. Spent Q-CNF adsorbent could be regenerated by extraction with KCl solution in ethanol–water mixture and reused for multiple adsorption–desorption cycles without significant loss of adsorption capacity. Such Q-CNF aerogels show great promise for application as reusable adsorbents from a renewable resource for treatment of dye-loaded water.