Facile one-step synthesis of magnetic Zeolitic Imidazolate Framework for ultra fast removal of Congo red from water

Nowadays, great efforts have been devoted to combining pure MOFs with functional components, one of which is the preparation of magnetic MOFs. Many cases of preparing magnetic MOFs have been reported, however, the existing strategies are complicated and have poor practicality. Herein, a facile one-step method was developed to endow ZIF-8 with superparamagnetism, where the organic ligand 2-methylimidazole was also used as alkaline source for formation of Fe₃O₄ via coprecipitation in the mixed system containing Zn²⁺, Fe²⁺ and Fe³⁺. The reactions that occurred in succession are formation of Fe₃O₄ and nucleation of ZIF-8. The obtained magnetic ZIF-8 (M-ZIF-8-10) shows high crystallinity, high surface area (958 m² g⁻¹) and superparamagnetism. M-ZIF-8-10 can be used as efficient adsorbent for fast adsorption of Congo Red (CR) from water. The CR adsorption processes follow the pseudo-second-order model and the further fitting results of Langmuir isotherm model show that CR adsorption is monolayer chemisorption with a maximal adsorption capacity of 210.5 mg g⁻¹. Besides, the results demonstrate that both of the two sulfonic groups of CR would simultaneously interact with M-ZIF-8-10. At last, in our opinion, this strategy would be feasible in other alkali-containing systems.