From crystallites to columns: Hierarchical Zn/Ni bimetallic MOF-biopolymer composite beads as high-capacity adsorbents for 17β-estradiol in water

17β-Estradiol (E2) is a potent endocrine-disrupting chemical (EDC) that exists in aquatic environments and poses serious risks to human and ecological health. In this study, we synthesized a Zn/Ni bimetallic metal–organic framework (MOF) using a continuous-flow reactor and embedded it within a κ-carrageenan/NH 4 A matrix to prepare composite beads for efficient E2 removal from water. The anisotropic MOF crystallites exhibited a hierarchical structure and assembled into the lamellar superstructures, forming accessible adsorption sites. Small angle x-ray scattering analysis showed a radius of gyration parameter of R g = 13.6 nm, providing an estimate of crystallite size. X-ray photoelectron spectroscopy (XPS) further confirmed the bimetallic surface composition of the Zn/Ni MOF. Batch adsorption experiments were performed to evaluate the effects of adsorbent dosage, initial E2 concentration, and solution pH. Under optimized conditions, the composite beads achieved 99.2% E2 removal with an adsorption capacity of 409.3 mg g −1 . Fixed-bed column studies further showed that the Thomas model satisfactorily described the breakthrough behavior, with a maximum column capacity of 623.82 mg g −1 at a flow rate of 2 mL min −1 , influent concentration of 40 mg L −1 , and bed height of 20 cm. Molecular dynamics simulations further supported the strong and stable interaction of E2 with the Zn/Ni MOF framework. These results demonstrate that Zn/Ni MOF@κ-car/NH 4 A is an efficient, robust, and sustainable adsorbent for removing steroidal estrogens from aqueous systems.