Synthesis of carbon nano-onions filled with γ-Fe and Gd/GdCl3: A candidate multifunctional system

Stabilization of high-spin high-volume ferromagnetic gamma-Fe nanocrystals inside carbon nano-onions (CNOs) has recently attracted an important attention for possible applications in magnetic hyperthermia cancer therapy. Here we report an advanced investigation of the chemical vapour synthesis (CVS) fabrication methodology of the filled CNOs, with focus on 1) the stabilization of the gamma-Fe nanocrystals in presence of larger concentration of Cl radicals and 2) the structural functionalization, through simultaneous encapsulation of both ferromagnetic gamma-Fe and paramagnetic GdCl3 phases. By employing HRTEM we demonstrate an anomalous structural configuration of the CNOs, involving the coexistence of defect-rich concentrical-like and radially-oriented graphitic layers. XPS and Raman spectroscopy evidence the presence of C-S bond-formation and defect nucleation as key parameters for the growth of the radially-oriented graphitic layers. This unusual structural arrangement of the CNO is found to stabilize the gamma-Fe phase at room temperature. We highlight the absence of FCC to BCC structural relaxation within timescales of 8 months from sample-fabrication. XRD, Rietveld refinements, together with magnetometry confirm the presence of a ferromagnetic transition arising below T similar to 70 K within gamma-Fe. This interpretation is further corroborated through extended characterization with ESR spectroscopy. Structural manipulation and functionalization of the CNOs is demonstrated by including tris(tetramethyl-cyclopentadienyl)gadolinium(III) as a precursor in the pyrolysis experiments. The functionalized CNO (filled with ferromagnetic gamma-Fe/Fe3C and paramagnetic Gd/GdCl3) can be visualized as a multifunctional-container and a candidate for magnetichyperthermia-cancer-therapy and MRI contrast applications.

Automated summary

An investigation of chemical vapour synthesis (CVS) fabrication methodology of filled carbon nano-onions (CNOs) with stabilized high-spin high-volume ferromagnetic gamma-Fe nanocrystals and functionalized with paramagnetic GdCl3 phases is reported. The anomalous structural configuration of CNOs, consisting of defect-rich concentrical-like and radially-oriented graphitic layers, is observed. The stabilization of gamma-Fe phase at room temperature is attributed to this unusual structural arrangement. Furthermore, the functionalized CNOs show potential applications in magnetic hyperthermia cancer therapy and MRI contrast.