Facile synthesis of high-swelling cyclodextrin polymer for sustainable water purification

Porous materials are widely used in the adsorption field to sequester pollutants to address the global sustainable water security and water scarcity concerns. However, there are still challenges that limit their industrial application, especially the required rational design and construction of porous structures. Here, we report a high-swelling cyclodextrin polymer (His-CDP) that is facilely synthesized without additional design and templates, to achieve high affinity, non-specific and rapid adsorption of pollutants. His-CDP rapidly swells in water with high swelling ratio (706 %), and swelling results in a significant increase in the specific surface area (from 38 m²∙g⁻¹ of dry state to 562 m²∙g⁻¹ of wet state) and abundant adsorption sites. The adsorption rates of His-CDP for methylene blue (MB), bisphenol A (BPA), and copper ion (Cu²⁺) are 0.304 g∙mg⁻¹∙min⁻¹, 0.370 g∙mg⁻¹∙min⁻¹, and 0.117 g∙mg⁻¹∙min⁻¹, respectively, which are 106–571 times, 5–15 times, and 36–58 times higher than those of activated carbons and low-swelling cyclodextrin polymer. The maximum adsorption capacities of His-CDP for MB, BPA, and Cu²⁺ are 1.06 mol∙g⁻¹, 0.35 mol∙g⁻¹, and 1.95 mol∙g⁻¹, respectively. His-CDP has high stability, good reproducibility, cost-effective regeneration, and is expected to be produced on a large scale. As a demonstration application, we demonstrate that His-CDP outperforms activated carbons in rapid, high-capacity purification of tap water, treatment of industrial wastewater and remediation of polluted surface water. Our findings open the way for the application of high-swelling polymers in sustainable water purification.