Magnetic Hyperthermia Enhancement in Iron-based Materials Driven by Carbon Support Interactions

Abstract

Magnetic hyperthermia (MH) shows great potential in clinical applications because of its very localized action and minimal side effects. Because of their high saturation magnetization values, reduced forms of iron are promising candidates for MH. However, they must be protected in order to overcome their toxicity and instability (i. e., oxidation) under biological conditions. In this work, a novel methodology for the protection of iron nanoparticles through confinement within graphitic carbon layers after thermal treatment of preformed nanoparticles supported on carbon is reported. We demonstrate that the size and composition of the nascent confined iron nanoparticles, as well as the thickness of their protective carbon layer can be controlled by selecting the nature of the carbon support. Our findings reveal that a higher nanoparticle-carbon interaction, mediated by the presence of oxygen-containing groups, induces the formation of small and well-protected α-Fe-based nanoparticles that exhibit promising results towards MH based on their enhanced specific absorption rate values.

Keywords: carbon supports; iron magnetic nanoparticles; magnetic hyperthermia; nanoparticle-carbon interactions; specific absorption rates.

Scheme 1

Schematic representation of the synthetic methodology to obtain Fe₃C@C/CNF from thermal treatment of Fe₃O₄NP/CNF under vacuum.

Figure 1

HRTEM images of a) Fe₃O₄NP/CNF and b) Fe₃O₄NP/CNF_AC, and size distribution of Fe₃O₄NPs. HRTEM images of c) Fe₃C@C/CNF and d) Fe₃C@C/CNF_AC and size distribution of Fe₃C@C. e)–g) HRTEM images of the three characteristic types of nanoparticles found in Fe₃C@C/CNF_AC hybrid material with high magnification images showing interplanar distances for the different iron crystallographic phases.

Figure 2

a) Powder XRD of samples before and after thermal treatment. CNF and CNF_AC controls are shown for comparison and Fe₃C, α‐Fe and Fe₃O₄ as references. b) Raman spectra of all the samples before and after thermal treatment with a λ=514 nm laser. c) Raman spectra of Fe₃C@C/CNF and Fe@Fe₃C@C/CNF_AC using a λ=785 nm laser. d) TGA in air of samples before and after thermal treatment, with CNF and CNF_AC as controls.

Figure 3

CV measurements of Fe₃C@C/CNF a) during 50 CV cycles and b) after a stability test increasing the potential window, showing the appearance of a Fe₃C redox peak. CV measurements of Fe₃C@C/CNF_AC c) during 50 CV cycles and d) after a stability test increasing the potential window, showing the appearance of a Fe₃C redox peak.

Scheme 2

Schematic representation of the proposed mechanism for the transformation of Fe₃O₄NP/CNF precursors into Fe₃C@C/CNF materials and the influence of the different carbon supports on the final morphology and composition of the nanoparticles.

Figure 4

HRTEM images and size distribution of Fe₃C@C/CNF_AC with iron contents of 45.8 and 15.7 %.

Figure 5

a) Frequency dependence of SAR values at a constant AC magnetic field of 20 kA m⁻¹ and b) field dependence of SAR values at a constant frequency of 250 kHz of Fe₃C@C/CNF and Fe₃C@C/CNF_AC and Fe₃C@C/CNF_AC after purification in HCl acid (Fe₃C@C/CNF_AC_HCl).