In situ one-pot construction of MOF/hydrogel composite beads with enhanced wastewater treatment performance

Abstract

Metal-organic framework (MOF)-based composite hydrogel microspheres (MOF/hydrogel) are one of the most promising adsorbents for high-efficiency wastewater treatment. However, conventional MOF/hydrogel synthesis methods involve simple blending, which inevitably results in poor particle-polymer matrix interactions and particle agglomeration. In this work, inspired by the symbiotic relationships in nature, we successfully constructed a three-dimensional zeolitic imidazolate framework-8 (ZIF-8)/polysaccharide (sodium alginate-kappa-carrageenan, SC) hydrogel beads, denoted a ZIF-8/SC, via phase inversion based on an in situ one-pot method for nanosized ZIF-8 assembly with polysaccharide matrices. Notably, our adsorbent demonstrated excellent mechanical performance with a stress and an elastic modulus of 1.14 MPa and 1.70 MPa respectively, as well as exhibited the good stability after immersed in water at room temperature for 7 days. Furthermore, benefiting from the uniform distribution and interfacial compatibility of ZIF-8, ZIF-8/SC exhibited a good adsorption capacity value of 2887 mg g−1, resulting in better removal performance than most MOF-based or natural polymer-based ciprofloxacin adsorbents. Moreover, the adsorption processes followed the pseudo-second-order and Langmuir isotherm models. In addition, we fabricated a ZIF-8/SC column for practical dynamic separation, which could treat 1500 mL of CIP solution in tap water. The experimental characterization results revealed that the adsorption mechanism involved electrostatic, π-π stacking, and hydrogen-bonding interaction, as well as coordination effects between CIP and the adsorbent. This study could offer a promising strategy for designing uniform MOF-based composite hydrogel adsorbents for pharmaceutical wastewater treatment with appealing application prospects.