Novel Magnetic Nanohybrids: From Iron Oxide to Iron Carbide Nanoparticles Grown on Nanodiamonds

Panagiotis Ziogas,Athanasios B Bourlinos,Ondrej Malina,Jiri Tucek,Alexios P Douvalis

doi:10.3390/magnetochemistry6040073

Abstract

The synthesis and characterization of a new line of magnetic hybrid nanostructured materials composed of spinel-type iron oxide to iron carbide nanoparticles grown on nanodiamond nanotemplates is reported in this study. The realization of these nanohybrid structures is achieved through thermal processing under vacuum at different annealing temperatures of a chemical precursor, in which very fine maghemite (γ-Fe2O3) nanoparticles seeds were developed on the surface of the nanodiamond nanotemplates. It is seen that low annealing temperatures induce the growth of the maghemite nanoparticle seeds to fine dispersed spinel-type non-stoichiometric ~5 nm magnetite (Fe3−xO4) nanoparticles, while intermediate annealing temperatures lead to the formation of single phase ~10 nm cementite (Fe3C) iron carbide nanoparticles. Higher annealing temperatures produce a mixture of larger Fe3C and Fe5C2 iron carbides, triggering simultaneously the growth of large-sized carbon nanotubes partially filled with these carbides. The magnetic features of the synthesized hybrid nanomaterials reveal the properties of their bearing magnetic phases, which span from superparamagnetic to soft and hard ferromagnetic and reflect the intrinsic magnetic properties of the containing phases, as well as their size and interconnection, dictated by the morphology and nature of the nanodiamond nanotemplates. These nanohybrids are proposed as potential candidates for important technological applications in nano-biomedicine and catalysis, while their synthetic route could be further tuned for development of new magnetic nanohybrid materials.

Highlights

Iron carbides (ICs) are among the oldest synthetic materials that are known to, and produced by, humans, arising historically even before the discovery of pure iron [1,2]
A combination of several diffraction peaks characteristic of the orthorhombic Fe3C structure dominate the part of this X-ray diffraction (XRD) diagram between 35 and 90 degrees 2θ, while a careful inspection of the area between 40 and 50 degrees 2θ reveals the presence of the major diffraction peaks of the monoclinic Fe5C2 structure
The characteristic diffraction peaks of the NDs and the Fe3C phase are the only contributions to this diagram, in which a further broadening of the diffraction peaks of this IC phase is clearly shown, indicating a further reduction in its average particle size, relative to the sharper peaks appearing at the XRD diagrams of the higher annealing temperatures samples

Summary

Introduction

Iron carbides (ICs) are among the oldest synthetic materials that are known to, and produced by, humans, arising historically even before the discovery of pure iron [1,2]. They are well known for their prominent structural and mechanical properties and have been used as adjuvant agents in concretes and metal alloys [3]. The presence of the most known member of the family of ICs, cementite (θ-Fe3C), in pearlitic steels, is the main parameter for the development of the exceptional mechanical properties (high strength and ductility) these technologically and economically important materials possess relative to soft iron [3,4,5,6,7,8,9]. IC NPs could be suitable for a diversity of applications, from biomedicine [20,21], to electronics [22,23] and the design of novel catalysts exploiting the magnetically induced heating effect [24,25,26]

Results

Discussion

Conclusion