Root-soil structure inspired hydrogel microspheres with high dimensional stability and anion-exchange capacity

Ion exchange materials show great advantages in water purification, food industry, pharmaceutical industry, etc. However, the ion exchange capacities of ion exchange materials, especially for anion-exchange materials, at present are still relatively low. Hydrogels own abundant functional groups and show high hydrophilicity, and thus are recognized as high-potential ion exchange materials, but may deform and even crush in use due to their low mechanical strength and unavoidable swelling behavior. In this study, inspired by the root-soil structure, novel poly(methacryloxyethyltrimethyl ammonium chloride) composite hydrogel microspheres with ultrahigh ion exchange capacity (more than 3.8 meuqiv/g), low swelling ratio (less than 1.5 g/g under pH = 7), and ultrahigh mechanical strength (more than 28.1 MPa) were prepared. The microspheres showed efficient adsorption for anionic dyes (1491 mg/g for methyl orange, 1693 mg/g for Congo red, and 204.7 mg/g for amaranth, respectively) and great adsorption for bilirubin (131.6 mg/g). Taken together, the hydrogel microspheres were qualified as stable and high-efficiency ion exchange materials. More importantly, the root-soil structure opens up avenues for enhancing the dimensional stability of functional hydrogels.