Synthesis of Fe3O4@ZIF-8 magnetic core–shell microspheres and their potential application in a capillary microreactor

A facile synthesis strategy for preparing Fe3O4@ZIF-8 magnetic core–shell microspheres has been successfully developed. The procedure involves first pre-treating the magnetic cores with an anionic polyelectrolyte to alter the surface charge of the particles and adsorb Zn2+ cations to initiate nucleation and then growing a thin layer of ZIF-8 to form a highly reactive, magnetic core–shell microsphere (Fe3O4@ZIF-8). The characterization by various techniques indicates that ZIF-8 shell is continuous and has an average thickness of around 100 nm. The Fe3O4@ZIF-8 microspheres as catalysts could be easily filled into a capillary microreactor with the help of an external magnetic field. The microreactor demonstrates excellent catalytic activity at a shorter residence time for Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate.