Construction of physically crosslinked chitosan/sodium alginate/calcium ion double-network hydrogel and its application to heavy metal ions removal

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2020-08, Vol.393, p.124728, Article 124728
• Main Authors: Tang, Shuxian, Yang, Jueying, Lin, Lizhi, Peng, Kelin, Chen, Yu, Jin, Shaohua, Yao, Weishang
• Format: Article
• Language: English
• Subjects: Calcium ion; Chitosan; Double-network; Heavy metal ions adsorption; Physical hydrogel; Sodium alginate
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.124728

[Display omitted] •A novel eco-friendly physically-crosslinked double-network hydrogel was prepared.•Semi-dissolution acidification sol–gel transition and internal gelation methods were combined.•The mechanical property of the hydrogel was significantly improved.•The hydrogel showed excellent adsorption capacities for Pb2+, Cu2+ and Cd2+.•The adsorption mechanism, kinetics, isotherms and thermodynamics were studied. Chemical hydrogels have been extensively applied to the removal of heavy metal pollutants. However, most of chemical hydrogels inevitably contain toxic chemical crosslinker residues, which impose serious threats on the environment. Herein, a novel eco-friendly physically-crosslinked double-network hydrogel of chitosan/sodium alginate/calcium ion (CTS/SA/Ca2+ PCDNH) was prepared by the combination of the semi-dissolution acidification sol–gel transition method with the internal gelation method. The PCDNH is formed via the physical crosslinking of sustainable biopolymers, which avoids the excessive use of toxic chemical reagents. In addition, the PCDNH exhibits significantly better mechanical properties than the single-network physical hydrogel crosslinked via electrostatic interactions, which overcomes the weak mechanical properties of physical hydrogels. The formation mechanism and structure of the hydrogel were determined by Fourier-transform infrared spectroscopy (FTIR), 13C solid state nuclear magnetic resonance spectroscopy (13C-SSNMR) and scanning electron microscopy (SEM). The heavy metal ions adsorption mechanism was explored by X-ray photoelectron spectroscopy (XPS) analysis. The adsorption kinetics, isotherms and thermodynamics were further studied to understand the adsorption mechanism. Our work has provided a new method for the fabrication of natural polymers-based eco-friendly, low-cost and robust physical hydrogels for the heavy metal ions removal.