Structural and magnetic properties of titanate nano-heterostructures decorated with iron based nanoparticles

Titanate nano-heterostructures have been prepared by a microwave-assisted hydrothermal method and then modified by replacing the Na+ ions present in the outer walls of the nanotubes (NT) by Fe3+ ions. The structural and magnetic properties of the product have been investigated in detail. It was observed that the titanate nanostructures are decorated with anatase (An) nanoparticles of size ca. 2 nm, producing TiNT@AnNP nano-heterostructures and that substitution with Fe3+ generates β-FeOOH and α-Fe2O3 phases, furnishing Fe-TiNT@AnNP. HAADF-STEM analysis revealed a complex nano-heterostructure with nanoparticles of β-FeOOH of size ca. 5 nm in the interlayer spaces and nanoparticles of α-Fe2O3 of size ca. 10–12 nm on the outer walls. Magnetic measurements at 300 K showed a ferromagnetic contribution in combination with a paramagnetic component for both the pristine and ion-exchanged samples. To the best of our knowledge, such iron-exchanged TiNT nano-heterostructures with α-Fe2O3 and β-FeOOH phases have not been reported previously. The key feature of this work is that ion-exchange of titanate nanotubes with iron ions generates a complex nano-heterostructure, the optical and magnetic properties of which are systematically modified. As titanate nanotubes and their derivatives are well known for their low toxicity and good biocompatibility, the additional magnetic behavior shown by the nanostructures reported here may make them potentially applicable in biomagnetic sensing.