Structural and magnetic studies of monophasic maghemite (γ-Fe2O3) magnetic nanocrystallites (MNCs) synthesized by the co-precipitation chemical route are reported in this paper. For the synthesis, a starting precursor of magnetite (Fe3O4) in basic medium was oxidized at room temperature by adjusting the pH = 3.5 at 80˚C in an acidic medium without surfactants. X-ray diffraction (XRD) pattern shows widened peaks indicating nanometric size and Rietveld Refinement confirms only one single-phase assigned to γ-Fe2O3 MNCs. High Resolution Transmission Electron Microscopy (HR-TEM) demonstrates the formation of nanoparticles with diameter around D ≈ 6.8 ± 0.1 nm which is in good agreement with Rietveld Refinement (6.4 ± 1 nm). A selected area electron diffraction pattern was carried out to complement the study of the crystalline structure of the γ-Fe2O3 MNCs. M(H) measurements taken at different temperatures show almost zero coercivity and remanence indicating superparamagnetic domain and high magnetic saturation.

The AC susceptibility of [Y 0.8 Ca 0.2 ](Ba 0.5 Sr 0.5 ) 2 Cu 3 O 7−δ was investigated as a function of frequency and amplitude of AC magnetic field. The susceptibilities of the sample display the field amplitude dependence. The peak temperature (T p ) of its imaginary part shows not frequency dependence but field amplitude dependence. The frequency effect on AC susceptibility was negligible. As the field amplitude increases, T p shifts to lower temperature.

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En el presente trabajo se evaluó experimentalmente la degradación del colorante azul, Cibacron Navy-H2G a través de la acción fotocatalítica de nanopartículas industriales de TiO2 de la empresa española Avanzare. Las nanopartículas corresponden a la fase anatasa caracterizada por DR-X, tienen un tamaño aproximado de 26,6 nm, medidos con TEM y 20,4 nm, medidos con DLS. La degradación fotocatalítica se evaluó en función a la masa del fotocatalizador desde 0,1 g hasta 1,0 g; a la concentración del colorante desde 20 ppm hasta 100 ppm; y a pH desde 2 hasta 10. El tiempo de degradación fotocatalítica del colorante se monitoreo con espectrofotometría UV-Visible. Los mejores resultados del proceso se obtuvieron con una masa de 0,6 g de nanopartículas de TiO2 , concentración de colorante de 20 ppm y a un pH de 4.