Novel amphoteric cryogels for Cd²⁺ ions removal from aqueous solutions

In this work, amphoteric cryogels based on N,N-dimethyl acrylamide, methacrylic acid and allylamine, crosslinked by N,N-methylenebisacrylamide were synthesized by free-radical polymerization in cryo-conditions. The synthesized cryogels were used for the removal of cadmium ions from aqueous solutions under different pH values. The chemical structure was studied by FTIR, porosity by nitrogen adsorption and morphology by scanning electron microscopy and texture analyzer. The amphoteric properties of cryogels were studied by zeta potential measurements. Adsorption tests revealed that cryogels exhibit 3 times higher adsorption capacity at pH 6.0 than at pH 4.0. The maximum adsorption capacity of the amphoteric cryogels for Cd²⁺ was 113 mg/g, at pH 6.0 and initial Cd²⁺ concentration 100 ppm. The results suggest that the predominant removal mechanism is ion exchange between sodium, which initially presents in the structure of the cryogel, and cadmium from the aqueous phase. Recovery studies suggested that the cryogels used can be regenerated and efficiently reused.