Facile Synthesis of Highly Stable and Water-Soluble Magnetic MWCNT/α-Fe Nanocomposites Barbara M. Maciejewska,* ,†,‡ L. Emerson Coy, † Krzysztof K. K. Koziol, § and Stefan Jurga †,‡ † NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland ‡ Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University Umultowska 85, 61-614 Poznan, Poland § Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K. * S Supporting Information ABSTRACT: Multiwall carbon nanotubes (MWCNT) were synthesized by the floating catalyst chemical vapor deposition (FCCVD) method. As a result, nanotubes containing metallic iron (α-Fe) were obtained and characterized. The impact of surface modification, on MWCNTs stability in water, was thoroughly studied applying three oxidative protocols. Samples were further characterized and correlated based on scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, Four- ier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA), and the magnetic nature of the embedded nanoparticles was assessed by means of a SQUID magnetometer at room temperature in powder. Finally, precise length segregation of MWCNT/α-Fe nanocomposites was achieved. The studied structures showed excellent quality and unmatched stability in water after more than three months. ■ INTRODUCTION Carbon nanotubes (CNT) are a class of materials undergoing rapid development in recent years. They have attracted a strong interest, mainly due to their extraordinary physical and chemical properties, such as high electrical conductivity and stiffness. 1 A promising material with potential applications in electronics, aerospace, and biomedical applications 2,3 still generates complex questions in contemporary science; for instance, can CNT be incorporated into the human body and used as a potential drug delivery system as well as magnetic resonance contrast agents? 4 Toxicity of these materials is under intensive debate. 5 Many studies indicate that the biocompat- ibility of CNT is influenced by their size, purity, method of synthesis, and functionalization. 6 Moreover, studies have shown a relationship between toxicity and length of multiwall carbon nanotubes (MWCNT). 7,8 This phenomenon is attributed to the needle-like shape of MWCNT which allows them to penetrate the cell membrane without leading to apoptosis. 9,10 However, other studies have reported contradictory results 11 showing the absence of consensus in this matter. An important advantage of MWCNT related to medical applications relies on the possibility of encapsulation of magnetic particles within MWCNT, even during the synthesis procedure. This possibility makes them a perfect candidate for theranostic applications which combines treatments and diagnosis in a single multifunctional particle. However, a further important aspect concerning the use of these structures in medicine is their poor solubility in most organic solvents. As- prepared, not functionalized, MWCNT are hydrophobic 12 which results in a low interaction with polar environment; thus, a very low biocompatibility is observed. Enhancing the chemical reactivity of the outer walls of MWCNT facilitates the attachment of various chemical groups to the outer surface of tubes. The preparation and functionalization method, as well as the purity of MWCNT, are crucial factors that influence the properties and the interaction with other materials. 13 One of the challenges is to develop a synthesis and functionalization protocol that would allow to obtain reproducible, controllable, and high quality CNT samples, giving a much needed ground for a consensus in their applications and properties. On the other hand, magnetic nanoparticles are a promising material for imaging and multimodal applications; 14 in specific, iron-based nanoparticles are used to improve the so-called negative MRI contrast, which provides a more detailed imaging response, sensibility, and effectiveness. 15 Iron particles can be functionalized or encapsulated in diverse structures in order to improve biocompatibility and imaging response. 16 Negative MRI contrast (created mostly by iron oxide particles or iron particles) is induced by local magnetic field disturbance of atom nuclei in their closest surrounding (most common hydrogen nuclei). 17 It results in more effective nuclei relaxation process Received: July 31, 2014 Revised: October 29, 2014 Published: November 5, 2014 Article pubs.acs.org/JPCC © 2014 American Chemical Society 27861 dx.doi.org/10.1021/jp5077142 | J. Phys. Chem. C 2014, 118, 27861-27869