Levofloxacin Synergistic Capture Using a "Memory-Effect" Layered Double Oxides Loaded with ZIF-67 Nanoparticles

Layered double hydroxides (LDHs) are limited by a lack of adsorption active sites and low porosity, leading to a suboptimal performance in antibiotic adsorption. In this study, LDH was used as templates to obtain LDO through high-temperature calcination, creating rapid mass transfer channels for LVX, thereby enhancing adsorption capacity and reducing adsorption time. Subsequently, small ZIF-67 crystals were grown in situ between the layers and on the surface of LDOs, providing additional adsorption active sites and surface area to the LDO@ZIF-67 composite material. In the LVX removal process, the synergistic effect between LDO and ZIF-67 mainly depends on the "memory effect" and the interaction of various mechanisms such as metal complexation, hydrogen bonding, and electrostatic attraction. LDO@ZIF-67 exhibits a rapid adsorption rate toward LVX, reaching adsorption equilibrium within 40 min, with an adsorption capacity as high as 268 mg/g, surpassing values reported in some literature. The adsorption process was more consistent with the Langmuir (R² = 0.992) and pseudo-second-order kinetic model (R² = 0.991). The analysis of adsorption thermodynamics results showed that the adsorption capacity gradually decreased with the increase of temperature, which belonged to the adsorption process of spontaneous exothermicity and reduced degree of freedom. In addition, LDO@ZIF-67 still maintains a good porous crystal structure after 5 cycles of adsorption-desorption, and the adsorption capacity can reach 214 mg/g. This study highlights the significant potential of LDO@ZIF-67 for removal of LVX from aqueous solutions and its promising application in wastewater treatment.