Synthesis of nanoparticles of feroxyhyte doped with lanthanum by a sonochemical method

This work deals with the sonochemical synthesis of colloidal dispersions of magnetic nanoparticles formed by lanthanum-doped iron oxyhydroxides coated with citrate. Our aim is to obtain bimodal contrast agents with magnetic properties that allow their use in both resonance and X-ray techniques. For this purpose, three synthesis strategies have been developed using a combination of ultrasound and co-precipitation methods. Three ultrasound frequencies were used in the synthesis: 581, 861 or 1141 kHz. The structural characterization of the prepared materials was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, total reflection X-ray fluorescence (TXRF) and Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDX) In the presence of lanthanum, magnetite cannot be formed. Instead, an orange-brown magnetic compound is obtained. Both XRD diffraction patterns and Raman spectra confirmed that the obtained compound is a feroxyhyte containing an amorphous lanthanum compound in its structure. The size of the feroxyhyte nano-discs remained almost constant when the ultrasound frequency was increased. The La/Fe molar ratio of the samples obtained increases when La(OH)₃, which is prepared in the preliminary stages, is added rather than LaCl₃. This procedure makes it possible to control the amount of lanthanum absorbed by the sample by simply varying its initial concentration.