RESUMO
Ultrafiltration removal of uranium from water, with composite activated carbon cellulose triacetate membranes (AC-CTA), was investigated. The filtrate was provided by uraninite dissolution with pH=6-8. Removal efficiencies were calculated measuring solutions' radioactivities. Membranes were mainly characterized by microscopy analysis, revealing iron after permeation. Uranyl removal was 35±7%. Chemical speciation indicates the presence of (UO(2))(2)CO(3)(OH)(3)(-), UO(2)CO(3), UO(2)(CO(3))(2)(2-) and Fe(2)O(3)(s) as main compounds in the dissolution, suggesting co-adsorption of uranium and iron by the AC during filtration, as the leading rejection path.
RESUMO
Changes in the dielectric properties during the thermochromic transition of commercial VO(2) powders were determined in situ, by analyzing the low-loss region of the electron energy-loss spectroscopy (EELS) spectra in a transmission electron microscope at room temperature (insulator phase) and 100 degrees C (metallic phase). A comparison of experimental EELS spectra and ab initio density-functional theory calculations (WIEN2k code) within the generalized gradient approximation (GGA) is presented. A characteristic peak around 5.6 eV appears in the energy-loss function in metallic phase, which is absent in insulator phase. The origin of the characteristic peak is analyzed by means of energy-band structure calculations.
