Ionically cross-linked sodium alginate/κ-carrageenan double-network gel beads with low-swelling, enhanced mechanical properties, and excellent adsorption performance

Double-network gel is composed of two kinds of crosslinked organic/inorganic networks, which has a good prospect of environmental application and its application in the antibiotic removal has important practical significance. Novel polysaccharide-based double-network gel bead (SK) with low-swelling, enhanced mechanical properties and excellent adsorption capacity of ciprofloxacin hydrochloride (CIP) was prepared via a facile ionically cross-linking method. Mechanical properties tests and swelling experiments showed that the sorbent has an enhanced mechanical property with stress of 1.07 MPa and an elastic modulus of 1.3 MPa at 90% strain and a reduced swelling property compared to a single kappa-CG/Ca2+ network. The adsorption performances of SK gel for CIP were investigated by changing the ratio of raw materials, crosslinking agent concentration, adsorbent dosage, contact time, temperature, pH, and pollutant concentration systematically. The above studies indicated that the maximum adsorption capacity of 291.6 mg/g was obtained at pH = 5.1. The kinetic datas were well fitted to the pseudo-second-order model, indicating that chemical sorption was the rate-limiting step. The isotherm of adsorption could be described by the Langmuir-Freundlich model well, which showed that SK gel had heterogeneous surface and different binding sites. By analyzing FT-IR spectroscopy and the adsorption changes under different pH, the adsorption mechanism may be explained by hydrogen bonding and the electrostatic interactions between CIP and the adsorbent. This study highlighted that SK gel beads could be used as a promising adsorbent for the large-scale removal of CIP in aqueous solutions, and the research will be conducive to address CIP pollution efficiently.