Preparation of TEMPO-Oxidized Cellulose Hydrogels Modified with β-Cyclodextrin and κ-Carrageenan for Potential Adsorption Applications

Cellulose-based materials are promising adsorbents for pollutants and other classes of compounds. Here, we report the preparation of hydrogels via chemical cross-linking of microcrystalline cellulose oxidized by the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). The cross-linking process was carried out in the presence of modifiers such as β-cyclodextrin in order to insert hydrophobic cavities or κ-carrageenan due to the presence of negative charges along the molecular chains. Fourier transform infrared spectroscopy (FTIR) characterization evidenced the modification of cellulose chains. Swelling tests showed that all hydrogels reached the swelling equilibrium in the first 10 min of contact, while N₂ adsorption isotherms allowed to evaluate surface areas ranging from 211 to 697 m²/g. Adsorption studies using methylene blue showed the key role of negative charges present in polymer chains favoring interactions with this cationic dye, as hydrogels modified with κ-carrageenan were found to have a high adsorption performance. The kinetic analysis of the adsorption process also suggests contributions from chemical interactions, which may involve electron transfer or electron pairing, as the data from all hydrogels showed high-quality fitting with the pseudo-second-order model.