Environmental Applications of Biobased Polydopamine-β-Cyclodextrin-Epichlorohydrin Supramolecular Hydrogel with Tuneable Swelling and Selective Adsorption Behaviors

Supramolecular hydrogels have been extensively studied for environmental applications owing to their biocompatible, nontoxic, and cost-effective properties. Herein, a polydopamine-β-cyclodextrin-epichlorohydrin (PDA-β-CD-EP) supramolecular hydrogel was facilely prepared through one-pot polymerization using a molar ratio of dopamine (DA)/β-cyclodextrin (β-CD)/epichlorohydrin (EP) of 1/2/50. Compared with other hydrogels, the (PDA-β-CD-EP) supramolecular hydrogel can selectively adsorb malachite green from mixed dyes. The structure, surface morphology, and thermostability of the PDA-β-CD-EP supramolecular hydrogels were illustrated by FT-IR, SEM–EDX, and TGA-DTG, respectively. Interestingly, the PDA-β-CD-EP-2 supramolecular hydrogel exhibited excellent pH-responsive swelling behavior. The influences of the pH, adsorption time, dosage, and initial concentration were systematically studied. Under optimal conditions, the maximum adsorption capacity of the PDA-β-CD-EP-2 supramolecular hydrogel was 652.1 mg/g for MG according to the Langmuir fitting results, much higher than those of the other adsorbents. More importantly, the PDA-β-CD-EP-2 supramolecular hydrogel possessed good reproducibility, reusability, and biodegradability. Besides, the selective adsorption mechanism was proposed and proved, such as hole size and shape effect, electrostatic force, and host–guest interaction. Overall, this study could provide a method to prepare a PDA-β-CD-EP-2 supramolecular hydrogel as a biosorbent for wastewater remediation.