Carbon nanotubes filled with continuous ferromagnetic -Fe nanowires and surface- functionalized with paramagnetic Gd(III): A candidate magnetic hyperthermia structure and MRI contrast agent

Abstract

The main goal of this project was the development of carbon nanotubes as a candidate for dual-functioning magnetic hyperthermia structure and magnetic resonance imaging contrast agent. This was achieved by lling carbon nanotubes with continuous ferromagnetic -Fe nanowires and surface functionalized with paramagnetic Gd(III). Also, length control of both nanotube and nanowire was investigated. Firstly, a low vapour flow-rate and constant evaporation temperature chemical vapour deposition method based on the thermal decomposition of ferrocene was employed which achieved continuous -Fe nanowires on the same scale as the nanotube for lengths >10 m without the necessity of post-synthesis heat-treatment or introduction of other precursor elements. The low vapour flow-rate regime has the advantage of sustaining the intrinsic temperature gradient at the tip of the forming structure which drives the vapour feedstock to the growth front to guarantee continuous nanowire formation. For initially mixed-phase nanowires of length less than 10 m, the continuous -Fe nanowires were achieved by postsynthesis heat treatment. Secondly, a simple wet chemical method involving only sonication in aqueous GdCl3 solution was used for surface functionalization of iron-fi lled multiwalled carbon nanotubes with gadolinium. Functional groups on the sidewalls produced by the sonication provide active nucleation sites for the loading of Gd3+ ions. Characterization by electron paramagnetic resonance, electron energy loss spectroscopy, and high-resolution transmission electron microscopy con rmed the presence of Gd3+ ions on the sidewall surface. The ferromagnetic properties of the encapsulated iron nanowire maintained after surface functionalization. At room temperature a saturation magnetization of 40 emu/g and a coercivity of 600 Oe were observed. Heating functionality in an alternating applied magnetic eld was quanti ed through the measurement of speci c absorption rate: 50 W/gFe and the intrinsic loss power: 1.12 nHm2kg��1 at magnetic eld strength 8 kA/m and frequency of 696 kHz. These structures exhibited an extremely high relaxivity r1 200 mM��1 s��1 at high magnetic field (9.4 T).