Preparation of\nTEMPO-Oxidized Cellulose Hydrogels\nModified with β‑Cyclodextrin and κ‑Carrageenan\nfor Potential Adsorption Applications

Cellulose-based materials are promising adsorbents for\npollutants\nand other classes of compounds. Here, we report the preparation of\nhydrogels via chemical cross-linking of microcrystalline cellulose\noxidized by the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO).\nThe cross-linking process was carried out in the presence of modifiers\nsuch as β-cyclodextrin in order to insert hydrophobic cavities\nor κ-carrageenan due to the presence of negative charges along\nthe molecular chains. Fourier transform infrared spectroscopy (FTIR)\ncharacterization evidenced the modification of cellulose chains. Swelling\ntests showed that all hydrogels reached the swelling equilibrium in\nthe first 10 min of contact, while N<sub>2</sub> adsorption isotherms\nallowed to evaluate surface areas ranging from 211 to 697 m<sup>2</sup>/g. Adsorption studies using methylene blue showed the key role of\nnegative charges present in polymer chains favoring interactions with\nthis cationic dye, as hydrogels modified with κ-carrageenan\nwere found to have a high adsorption performance. The kinetic analysis\nof the adsorption process also suggests contributions from chemical\ninteractions, which may involve electron transfer or electron pairing,\nas the data from all hydrogels showed high-quality fitting with the\npseudo-second-order model.