Environmental Applications of Biobased Polydopamine--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-beta-cyclodextrin-epichlorohydrin (PDA-beta-CD-EP) supramolecular hydrogel was facilely prepared through one-pot polymerization using a molar ratio of dopamine (DA)/beta-cyclodextrin (beta-CD)/epichlorohydrin (EP) of 1/2/50. Compared with other hydrogels, the (PDA-beta-CD-EP) supramolecular hydrogel can selectively adsorb malachite green from mixed dyes. The structure, surface morphology, and thermostability of the PDA-beta-CD-EP supramolecular hydrogels were illustrated by FT-IR, SEM-EDX, and TGA-DTG, respectively. Interestingly, the PDA-beta-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-beta-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-beta-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-beta-CD-EP-2 supramolecular hydrogel as a biosorbent for wastewater remediation.