Silver confined within zeolite EMT nanoparticles: preparation and antibacterial properties.

The preparation of pure zeolite nanocrystals (EMT-type framework) and their silver ion-exchanged (Ag(+)-EMT) and reduced silver (Ag(0)-EMT) forms is reported. The template-free zeolite nanocrystals are stabilized in water suspensions and used directly for silver ion-exchange and subsequent chemical reduction under microwave irradiation. The high porosity, low Si/Al ratio, high concentration of sodium and ultrasmall crystal size of the EMT-type zeolite permitted the introduction of a high amount of silver using short ion-exchange times in the range of 2-6 h. The killing efficacy of pure EMT, Ag(+)-EMT and Ag(0)-EMT against Escherichia coli was studied semi-quantitatively. The antibacterial activity increased with increasing Ag content for both types of samples (Ag(+)-EMT and Ag(0)-EMT). The Ag(0)-EMT samples show slightly enhanced antimicrobial efficacy compared to that of Ag(+)-EMT, however, the differences are not substantial and the preparation of Ag nanoparticles is not viable considering the complexity of preparation steps.

New aluminate with a tetrahedral structure closely related to the c84 fullerene.

A new aluminate Sr33Bi(24+delta)Al48O(141+3delta/2), having an F3m cubic structure (a = 25.090 angstroms, Z = 4) and forming a close packed face centered cubic array of "Al84" fullerene geometry, has been discovered. This original structure consists of corner-sharing AlO4 tetrahedra forming "Al84O106" cubic units whose assemblage delimits five types of cages, three of them being empty, one being occupied by strontium, and the fifth one forming the huge spheric fullerene-type cavity. In the latter, strontium, oxygen, and bismuth ions form concentric spheres, with an onion-skin-like configuration. The latter ions are disposed into a compact "Bi16O(52-n[]n)" anion whose the exceptional geometry is characterized by a strong stereoactivity of the 6s2 lone pair of Bi3+.

Designing fast oxide-ion conductors based on La2Mo2O9

The ability of solid oxides to conduct oxide ions has been known for more than a century, and fast oxide-ion conductors (or oxide electrolytes) are now being used for applications ranging from oxide fuel cells to oxygen pumping devices. To be technologically viable, these oxide electrolytes must exhibit high oxide-ion mobility at low operating temperatures. Because of the size and interaction of oxygen ions with the cationic network, high mobility can only be achieved with classes of materials with suitable structural features. So far, high mobility has been observed in only a small number of structural families, such as fluorite, perovskites, intergrowth perovskite/Bi2O2 layers and pyrochlores. Here we report a family of solid oxides based on the parent compound La2Mo2O9 (with a different crystal structure from all known oxide electrolytes) which exhibits fast oxide-ion conducting properties. Like other ionic conductors, this material undergoes a structural transition around 580 degrees C resulting in an increase of conduction by almost two orders of magnitude. Its conductivity is about 6 x 10(-2) S cm(-1) at 800 degrees C, which is comparable to that of stabilized zirconia, the most widely used oxide electrolyte. The structural similarity of La2Mo2O9 with beta-SnWO4 (ref. 14) suggests a structural model for the origin of the oxide-ion conduction. More generally, substitution of a cation that has a lone pair of electrons by a different cation that does not have a lone pair--and which has a higher oxidation state--could be used as an original way to design other oxide-ion conductors.