Magnetic induction heating as a new tool for the synthesis of Fe3O4-TiO2 nanoparticle systems

A novel method for the synthesis of Fe3O4-TiO2 nanoparticles is described, where the magnetic induction heating of Fe3O4 nanoparticles is employed to calcine a metal oxide precursor gel. Magnetite Fe3O4 nanoparticles were mechanically dispersed in the as-prepared TiO2 gel and subsequently submitted to the action of an ac magnetic field (frequency 313 kHz, amplitude 340 Oe, induction times, t = 10, 20, and 30 min). The magnetic heating of the magnetic nanoparticles is able to calcine the precursor gel and thus to produce the TiO2 crystallization in the anatase phase, as supported by TGA analysis. The calcined structure, magnetically filtered to select the Fe3O4-TiO2 nanostructure, was analyzed by X-ray diffraction and transmission electron microscopy. The results show that the Fe3O4-TiO2 nanostructure basically consists of an ensemble of Fe3O4 cores surrounded by tiny TiO2 aggregates (crystallite size <5 nm) forming an effective shell. The synthesis route and the TiO2 environment do not introduce significant changes in the magnetic response of the magnetite nanoparticles. Thus, magnetic induction heating of magnetic nanoparticles appears as a new tool to reach a versatile calcination process to obtain Fe3O4-TiO2 nanostructures.