One-step in situ fabrication of a granular semi-IPN hydrogel based on chitosan and gelatin for fast and efficient adsorption of Cu2+ ion

The novel granular semi-IPN hydrogels were in situ prepared in an aqueous solution by the free-radical grafting and crosslinking reactions among chitosan (CTS), acrylic acid (AA), gelatin (GE) and N,N′-methylene-bis-acrylamide. The FTIR spectra and elemental analysis confirmed that the AA monomers were grafted onto CTS backbone, and the GE macromolecular chains interpenetrated through the CTS-g-PAA network. The hydrogels are granular, which are composed of numerous micro-spheres according to the scanning electron microscope observations. The gel strength, adsorption, reuse and recovery properties of the hydrogels for Cu2+ ion were systematically investigated. The results indicate the hydrogel with 2 wt% GE has the highest adsorption capacity of 261.08 mg/g with the recovery ratio of 95.2%. And the incorporation of 10 wt% GE enhanced the storage modulus by 103.4% (ω = 100 rad/s) and 115.1% (ω = 0.1 rad/s), and the adsorption rate by 5.67%. Moreover, the adsorption capacity of the hydrogel is still as high as 153.9 mg/g, after five cycles of adsorption–desorption. It was found that the ion-exchange and complexation interactions between the functional groups (COO− and NH2) of the hydrogels and Cu2+ ion are the predominant adsorption mechanisms.