Development of chitosan-poly(ethyleneimine) based double network cryogels and their application as superadsorbents for phosphate

The fabrication of novel chemically cross-linked double network cryogels (DNC), with an abundant number of amine groups, based on chitosan (CS) cross-linked with glutaraldehyde (GA), as the first network, and poly (ethyleneimine) (PEI), with a concentration up to 15% cross-linked with ethyleneglycol diglycidyl ether (EGDGE), as the second network, and their enhanced sorption capacity for phosphate ions are presented here. The phosphate sorption was fast (equilibrium in three hours) and well modeled by the pseudo-second-order kinetic model. The experimental sorption isotherms were fitted with Langmuir, Freundlich, Sips and Dubinin-Radushkevich isotherm models. The Langmuir and Sips isotherms were the best in modeling the sorption process. The maximum sorption capacity given by the Langmuir isotherm for the DNC having the highest content of GA and the highest concentration of PEI was about 343 mg phosphate/g, which placed this novel sorbent among the best sorbents for phosphate recently reported in literature.