ZIF-67 grows in chitosan-rGO hydrogel beads for efficient adsorption of tetracycline and norfloxacin

Abstract

In this study, a novel hydrogel bead (rGO@ZIF-67@CS) was synthesized by integrating ZIF-67 into a chitosan and reduced graphene oxide (rGO) dual-network system. This hydrogel was designed for efficient removal of tetracycline (TC) and norfloxacin (NOR) in single- and binary-solute systems. The adsorption experiments revealed that TC and NOR can be effectively removed over a wide range of pH (4–8), achieving maximum adsorption capacities of 1685.26 mg·g−1 at pH = 4 for TC and 1890.32 mg·g−1 at pH = 5 for NOR. The pseudo-second-order kinetic and Langmuir models better fitted the kinetic and isotherm data of both antibiotics, indicating a homogeneous adsorption process dominated by monolayer chemisorption. Even after five adsorption–desorption cycles, the adsorption efficiency of the two antibiotics remained above 80 %. In the binary systems, rGO@ZIF-67@CS simultaneously removed 92.68 % of TC and 82.46 % of NOR. Additionally, in practical applications, the fixed-bed system treated 320 mL of the TC solution and 290 mL of the NOR solution. Microscopic characterization suggested that the adsorption mechanisms were likely attributed to pore filling, π-π stacking, hydrogen bond interactions, and complexation.