Abstract
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.
Highlights
Nowadays, the nanoscale/microscale porous particles of transition metal oxides have attracted great attention due to their specific optical, electrical, and magnetic performances derived from the d-layer orbitals with unfilled valence, as well as their unique absorptivity, penetrability, and chemical activity—resulting from their porous structure [1,2,3,4]
The results show that the macroporous Fe3 O4 microparticles, in the micron scale, were prepared by the assembly of the Fe3 O4 open-cell hollow microspheres—in the assembling-first way—whilst the organic monomers of NVP and AMPS played a crucial role in the formation of the
Two kinds of organic monomers, 1-vinyl-2-pyrrolidinone (C6 H9 NO, NVP) with 99.5% purity that is stabilized with 4-Methoxyphenol (MEHQ), and 2-acrylamido-2-methyl propane sulfonic acid (C7 H13 NO4 S, AMPS) with 98% purity, were purchased from J & K Scientific Ltd., Beijing, China
Summary
The nanoscale/microscale porous particles of transition metal oxides have attracted great attention due to their specific optical, electrical, and magnetic performances derived from the d-layer orbitals with unfilled valence, as well as their unique absorptivity, penetrability, and chemical activity—resulting from their porous structure [1,2,3,4]. Depending on the pore size, porous materials can be classified into microporous (pore diameter < 2 nm), mesoporous (2–50 nm), and macroporous materials (>50 nm). There are few studies on macroporous materials, which have larger pore diameters and possess a wider application prospect than mesoporous materials in the field of loading and the transport of large-sized particles, especially organic nanoparticles. Macroporous Fe3 O4 micro/nanoparticles are able to act as carriers for loading and transporting drug-loaded temperature-sensitive micelles in magnetocaloric-responsively controlled drug release systems. Macroporous Fe3 O4 micro/nanoparticles would improve the drawbacks of drug loss in micelles, and on the other hand, they would provide a heat source for the control of temperature-sensitive materials. The colloidal crystal template is usually obtained by the self-assembly of organic microspheres, and the size of the template is far exceeded by the micron scale, leading to the colloidal crystal template method being just as suitable for the preparation of the macroporous bulk materials—rather than the macroporous microparticles [15,16,17]
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