A novel hybrid hydrogel bead of sodium alginate/attapulgite/zeolitic imidazolate framework-8 for efficient adsorption of norfloxacin from water

Sodium alginate (SA) hydrogels have been extensively utilized for pollutant removal from wastewater due to the distinct properties of hydrophilicity, biocompatibility and reusability. However, the limited functional groups and poor adsorption capacity have hindered their applications. In this study, a novel hybrid hydrogel bead, composed of sodium alginate, attapulgite, and zeolitic imidazole framework-8 (SA/ATP/ZIF-8), was synthesized using a one-pot blending and ion cross-linking method for adsorptive removal norfloxacin (NOR) from aqueous solutions. The incorporation of ATP and ZIF-8 significantly enhanced the thermal stability and anti-swelling properties of the SA hydrogel beads. The effects of solution pH, contact time, initial NOR concentration, temperature, and the presence of coexisting substances on NOR uptakes were systematically investigated. The results demonstrated that the NOR uptake on SA/ATP/ZIF-8 hybrid hydrogel beads was significantly higher than that of the pure SA and SA/ATP hydrogel beads, and the maximum theoretical adsorption capacity of SA/ATP/ZIF-8 for NOR was 1360.67 mg/g at pH 5.0. Furthermore, the adsorption kinetic was well-described by a pseudo-second-order model, while the adsorption isotherm was most accurately represented by the Langmuir-Freundlich model. In tests conducted with Nandu River water, the SA/ATP/ZIF-8 exhibited removal efficiencies of 100 % for NOR at an initial concentration of 0.0015 mmol/L and 71 % at 0.015 mmol/L. Spectroscopic characterization and adsorption performance experiments indicated that the adsorption of NOR onto SA/ATP/ZIF-8 involved multiple mechanisms, including hydrogen bonding, electrostatic adsorption, cation exchange, π-π electron donor-acceptor interaction (EDA), and coordination. Consequently, the remarkable features of SA/ATP/ZIF-8 hydrogel beads highlight their great potential and promising practicability for separation and removal of lower-concentration antibiotics from wastewater.