Fabrication of hierarchical composite microspheres of copper-doped Fe3O4@P4VP@ZIF-8 and their application in aerobic oxidation

Abstract

Novel hierarchical magnetic composite microspheres of copper-doped Fe₃O₄@poly(4-vinylpyridine-co-divinylbenzene)@ZIF-8 (Cu-FPZ, Cu stands for copper doped) were successfully fabricated. The core–shell Fe₃O₄(PAA)@P4VP magnetic microspheres were first synthesized by a polymerization approach, in which the 4-vinylpyridine (4-VP) monomer interacted with a –COOH group of poly(acrylic acid) modified Fe₃O₄ by means of a hydrogen-bond interaction. Then Zn²⁺ was adsorbed on the surface of the P4VP shell, followed by the formation of a ZIF-8 porous shell with 2-methylimidazolate. Finally, nearly 5.45 wt% of copper content was incorporated with the ZIF-8 framework to form a magnetic core–shell copper-doped Fe₃O₄@P4VP@ZIF-8. The obtained copper-doped Fe₃O₄@P4VP@ZIF-8 catalyst was applied in the selective oxidation of alcohols and epoxidation of olefins using molecular oxygen as the oxidant. The results demonstrated that the magnetic core–shell copper-doped Fe₃O₄@P4VP@ZIF-8 catalyst showed better catalytic activity with significantly improved turnover number and turnover frequency (up to 8.25 h⁻¹) than other copper MOFs. Furthermore, this heterogeneous catalyst could be cycled at least 15 times without significant loss of activity.