Dual-charged cryogels for efficient removal of dyes and oil-water separation in wastewater treatment

With the development of modern industry, water pollution has become an urgent environmental issue, so it is very urgent to find one-step strategy to treat with complicated wastewater. In this paper, poly (vinyl imidazole - co - methacrylic acid) cryogels were prepared with freezing polymerization for the treatment of complicated wastewater containing not only cationic dyes and anionic dyes but also common organic solvents. For the preparation of cyrogels, with the increase of the molar ratio of methacrylic acid to vinyl imidazole, the adsorption capacity of dyes varied as 271.33–187.09 mg·g −1 for methyl blue, 342.96–150.16 mg·g −1 for methyl orange, 7.76–85.72 mg·g −1 for methylene blue, and 19.19–110.10 mg·g −1 for crystal violet. Thus, by adjusting the molar ratio of monomers, a variety of versatile cryogels could be designed to treat with dye solutions of different type and concentration. Adsorption mechanism was then investigated through kinetics and isotherm, which showed single-layer chemical adsorption. Moreover, the surface hydrophilicity of porous cryogels made it possible for the separation of oil-water mixtures with over 95 % separation efficiency by selective water permeation. This study provides a quite new approach to prepare cryogels with both positive and negative charges.