Synthesis of Macroporous Magnetic Fe₃O₄ Microparticles Via a Novel Organic Matter Assisted Open-Cell Hollow Sphere Assembly Method

Macroporous magnetic Fe₃O₄ microparticles, which might act as both drug carriers and magnetocaloric media, were expected to have broad application prospects on magnetocaloric-responsively controlled drug release systems. A kind of macroporous magnetic Fe₃O₄ microparticle was prepared by an organic matter assisted open-cell hollow sphere (hollow sphere with holes on shell) assembly method in this study. 1-vinyl-2-pyrrolidinone (NVP) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) were selected as the template and the binder, respectively. Ferrous ions were specifically bound to carbonyl groups on NVP and were then reduced by NaBH₄. The reduced irons underwent heterogeneous nucleation and grain growth to form Fe⁰/Fe₃O₄ microspheres consisting of a lot of nano-Fe⁰ grains, and were then assembled into Fe⁰/Fe₃O₄ microparticles wrapped by AMPS. Results indicate that NVP binding with ferrous ions can promote a self-polymerization process and the formation of Fe⁰/Fe₃O₄ microspheres, while AMPS enwrapping around the resultant microspheres can facilitate their assembly into larger aggregates. As a result, macroporous Fe₃O₄ microparticles composed of several open-cell hollow Fe₃O₄ microspheres can be obtained under a Kirkendall-controlled oxidation. Moreover, these as-prepared macroporous Fe₃O₄ microparticles possess a narrow particle size distribution and exhibit ferromagnetism (Ms = 66.14 emu/g, Mr = 6.33 emu/g, and Hc = 105.32 Oe). Our work, described here, would open up a novel synthesis method to assemble macroporous magnetic Fe₃O₄ microparticles for potential application in magnetocaloric-responsively controlled drug release systems.