Mossbauer study of magnetic nanoparticles encapsulated in vermiculite

This study reports on the successful preparation of magnetic nanocomposites comprising nanosized magnetic particles encapsulated within thermally expanded vermiculite. The nanosized surface-dressed (with oleic acid) and surface-undressed particles were encapsulated via immersing of the hosting template within magnetic fluid samples. Samples were characterized using transmission electron microscopy, Xray diffraction and Mossbauer spectroscopy. Mossbauer data show that oxidation of the as-precipitated nanosized magnetite to maghemite was not completely accomplished using the employed chemical treatment. Nevertheless, Mossbauer spectra revealed that encapsulation of the nanosized magnetic particles within the hosting template was achieved. In addition, combination of X-ray diffraction and Mossbauer spectroscopy data reveal that the modified clay template size-sorts the nanoparticles while the encapsulation process takes place. Surface-uncoated (coated) magnetic particles presenting average diameter of 9.9 nm (11 nm) while suspended as magnetic fluids experience reduction of average diameter down to 7.2 nm (5.2 nm) within the hosting template.