Synthesis and characterization of ZIF-8@SiO2@Fe3O4 core@double-shell microspheres with noble metal nanoparticles sandwiched between two shell layers

•A new ZIF-8@Pd/SiO2@Fe3O4 microsphere with core@double-shell structure was prepared.•Well-dispersed Pd nanoparticles were sandwiched between the two kinds of shells.•Surface modification by using PSS solution was the key to obtain the ZIF-8 shell.

We demonstrate the preparation of sandwich structured microspheres containing Fe3O4 cores, inner silica shells, supported Pd nanoparticles and outer ZIF-8 shells. The synthesis involved first deposition of silica layer on magnetic cores through traditional Stöber method and subsequent immobilization of Pd nanoparticles on the silica surface via grafting techniques, followed by the assembly of ZIF-8 shells over the Pd nanoparticles. Uniquely, the noble metal nanoparticles are sandwiched between the silica shell and porous ZIF-8 shell and such a configuration allows the metal nanoparticles to remain stable against aggregation and leaching while at the same time they are selectively accessible to the external environment outside of the ZIF-8 shells. Also, the resulting core@double-shell microspheres exhibit a superparamagnetic behavior with a high saturation magnetization of ~36.7 emu/g inheriting from the magnetic Fe3O4 cores. It is believed that the designed microspheres could find potential uses in heterogeneous catalysis and adsorption fields with excellent reusability and high efficiency.

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