Preparation of magnetic metal-organic framework for adsorption of microcystin-RR

Microcystins produced during the outbreak of cyanobacteria are a serious threat to human beings and the ecological environment, so it's important to remove microcystins from water. In this study, the magnetic metal-organic framework (MOFs) Fe3O4@ZIF-8 was prepared to adsorb microcystins. The characterization of the structure, morphology and properties of the material showed that the material had high specific surface area, great paramagnetism and obvious core-shell structure. At the same time, the effects of pH, contact time, initial concentration of microcystin-RR, temperature, coexisting ions, real water and reusability were investigated and the kinetic models and isotherm models were established. The results showed that the adsorption processes were well described by the pseudo-second-order kinetic model and Freundlich isotherm model, indicating that the adsorption process was chemical heterogeneous multi-layer adsorption process. In addition, when pH = 6.0 and temperature was 298 K, the theoretical maximum adsorption capacity of Fe3O4@ZIF-8 was calculated to be 6.055 mg·g−1 for microcystin-RR. Most importantly, Fe3O4@ZIF-8 could be separated from aqueous solution under external magnetic field easily, and maintained good adsorption performance after three cycles. The adsorption mechanism analyzed by FTIR and XPS showed that the adsorption process involved π-π accumulation, complexation reaction and electrostatic interaction. Therefore, the Fe3O4@ZIF-8 is a kind of potential material which aims to provide a new idea in the field of removing microcystins.