Dissolution and Reaction Catalysis Strategy Using Alkaline Solvent for Mild Fabrication of Chitin Composite Hydrogel for Dye Adsorption

Abstract

As the most abundant natural amino polysaccharide, chitin remains among the least exploited polymers due to its poor solubility, which restricts its research and utilization. In this study, a new chitin composite hydrogel was prepared by a mild process at 25 °C within a short time. To enhance the adsorption capacity, sodium carboxymethyl cellulose and attapulgite were introduced into the structure of a hydrogel by chemical reaction and physical interaction, respectively. Alkaline solution was used as a solvent to dissolve chitin and used as a catalyst to accelerate the cross-linking reaction between chitin and sodium carboxymethyl cellulose. This solvent (8 wt% NaOH/6 wt% urea solution) has dual functions: to dissolve chitin and to accelerate the cross-linking reaction of chitin with carboxymethyl cellulose by epichlorohydrin. The cross-linking reaction occurred at room temperature (25 °C) within a short time (4 h).  Fourier transform infrared spectroscopy (FTIR) indicated that chitin and sodium carboxymethyl cellulose has been successfully cross-linked. X-ray diffraction results showed that the cross-linked structure was amorphous and that attapulgite kept its crystal structure in the hydrogel. Scanning electron microscopy showed the coarse surface of composite hydrogel with attapulgite. The adsorption capacity for methylene blue reached 167 mg g^-1.