RESUMEN
The photocatalytic activity of Bismuth-codoped Sr4 Al14 O25 : Eu2+ , Dy3+ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a postannealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase Sr4 Al14 O25 : Eu2+ , Dy3+ , Bi3+ phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micrograins with sizes in the range of 0.5-20 µm. The samples present an intense greenish-blue fluorescence and persistent emissions at 495 nm, attributed to the 5d-4f allowed transitions of Eu2+ . The fluorescence decreases as Bi concentration increases; that suggest bismuth-induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation, whereas only 62.49% MB degradation is achieved under UV irradiation. Our results suggest that codoping the persistent phosphors with Bi3+ can be an alternative to enhance their photocatalytic activity.
RESUMEN
The photocatalytic activity, of undoped and Europium-doped LaSr2 AlO5 powders, has been investigated by degrading methylene blue dye in water solutions. Those powders were fabricated by a combustion method and an annealing treatment in air. All samples showed a tetragonal single phase according to by X-ray diffraction measurements (XRD). Scanning electron microscopy (SEM) revealed irregular semi-oval grains with sizes in the range of 3.5-4.27 µm. Photoluminescence spectrum showed sharp emission peaks at 588 nm and at 617 nm which are associated with (7) F1 ,(7) F2 â (5) D0 Eu(3+) ion forbidden transitions, respectively, under UV light excitation of 322 nm. The methylene blue (MB) degradation under UV light (254 nm) was studied by monitoring changes in the absorbance peak of MB at 665 nm. Finally, LaSr2 AlO5 :Eu powders were used three times and the efficiency for the degradation of MB decreased from 100 to 61% after the third cycle of use.
RESUMEN
Silver nanocrystals (Ag NCs) hold promising antibiotic and antiviral properties in biological systems. The biodistribution of silver nanostructures injected into animals in vivo is currently unknown, remaining as a fundamental issue for potential therapeutic applications. Here, we injected Ag NCs capped with bovine serum albumin (BSA) in live rats to elucidate their fate in several organs including liver, heart and brain. Very significant accumulations of nanoparticles were confirmed by inductively coupled plasma mass spectroscopy (ICPMS) and transmission electron microscopy (TEM) techniques on the liver and heart. In contrast, the brain tissue did not reveal evidence of particles content. Our results suggest that Ag+ permeated across the blood-brain barrier (BBB), and followed swift clearance from the organ.