Abstract
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 LaCl(3). This procedure makes it possible to control the amount of lanthanum absorbed by the sample by simply varying its initial concentration.