Visible emission from Ag(+) exchanged SOD zeolites.

Broad visible emissions dominant at green or red have been observed for the thermally-treated Ag(+) exchanged SOD zeolites, determined by the Ag(+) loading contents and the excitation wavelengths. Contrary to the notable reversible green/red dominant emission evolution in the Ag(+) exchanged LTA zeolites upon hydration/dehydration in air (or water vapor)/vacuum, emission spectra of the Ag(+) exchanged SOD zeolites are insensitive to the environmental change. This is most probably due to the difficult H2O permeation in SOD zeolites in comparison with LTA zeolites. By combining the environment dependent emission spectra of the Ag(+) exchanged LTA and SOD zeolites, we proposed the following emission mechanisms for Ag(+) exchanged LTA and SOD zeolites: the green emission is due to the transition from ligand-to-metal (framework O(2-)→ Ag(+)) charge transfer state to the ground state and the red emission is due to the transition from the metal-metal (Ag(+)-Ag(+)) charge transfer state to the ground state. The insensitive environment dependent emission characteristics of Ag(+) exchanged SOD zeolites may have potential applications as robust phosphors.

Molecular simulation of nitrogen adsorption in nanoporous silica.

This article reports on a molecular simulation study of nitrogen adsorption and condensation at 77 K in atomistic silica cylindrical nanopores (MCM-41). Two models are considered for the nitrogen molecule and its interaction with the silica substrate. In the "pea" model, the nitrogen molecule is described as a single Lennard-Jones sphere and only Lennard-Jones interactions between the nitrogen molecule and the oxygens atoms of the silica substrate are taken into account. In the "bean" model (TraPPE force field), the nitrogen molecule is composed of two Lennard-Jones sites and a linear array of three charges on the atomic positions and at the center of the nitrogen-nitrogen bond. In the bean model, the interactions between the sites on the nitrogen molecule and the Si, O, and H atoms of the substrate are the sum of the Coulombic and dispersion interactions with a repulsive short-range contribution. The data obtained with the pea and bean models in silica nanopores conform to the typical behavior observed in the experiments for adsorption/condensation in cylindrical MCM-41 nanopores; the adsorbed amount increases continuously in the multilayer adsorption regime until an irreversible jump occurs because of capillary condensation and evaporation of the fluid within the pore. Our results suggest that the pea model can be used for characterization purposes where one is interested in capturing the global experimental behavior upon adsorption and desorption in silica nanopores. However, the bean model is more suitable to investigating the details of the interaction with the surface because this model, which accounts for the partial charges located on the nitrogen atoms of the molecule (quadrupole), allows a description of the specific interactions between this adsorbate and silica surfaces (silanol groups and siloxane bridges) or grafted silica surfaces. In particular, the bean model provides a more realistic picture of nitrogen adsorption in the vicinity of silica surfaces or confined in silica nanopores, where the isosteric heat of adsorption curves show that the nitrogen molecule in this model is sensitive to the surface heterogeneity.

Influence of the hydrothermal treatment on the chromatographic properties of monolithic silica capillaries for nano-liquid chromatography or capillary electrochromatography.

In the last decade, silica monolithic capillaries have focused more and more attention on miniaturized separation techniques like capillary electrochromatography (CEC), nano-liquid chromatography (nano-LC) and chip electrochromatography owing to their unique chromatographic properties and their simplified preparation compared with packed columns. They are synthesized according to a sol-gel multi-step process that includes, after a gelation step at 40 degrees C leading to the formation of the macropores network and the silica skeleton, a post-gelation step (hydrothermal treatment at 120 degrees C in basic medium) that allows to tailor the mesopores and finally a calcination or a washing step to remove remaining polymers. In order to reduce the synthesis time, the number of synthesis steps and above all the temperature synthesis, to adapt the synthesis of such silica monoliths in polymeric microsystem devices, we extensively studied the influence of the hydrothermal treatment and its duration on textural (pore size distribution) and chromatographic properties (retention, efficiency) of in situ-synthesized capillary monoliths in nano-LC and CEC. This study was performed on pure silica and octyl chains grafted silica monoliths. Untreated monoliths show small pores (<6 nm), whereas hydrothermally treated monoliths exhibit medium and large mesopores (8-17 nm). It was demonstrated that the hydrothermal treatment at 120 degrees C was not necessary for pure silica monolithic capillaries dedicated to normal phase liquid chromatography or hydrophilic interaction liquid chromatography (HILIC) and electrochromatography: the suppression of the hydrothermal treatment did not impair efficiencies in CEC and in nano-LC but contributed to increase in retention factors. Minimal plate heights of ca. 5 microm in CEC and 6 microm in nano-LC were obtained with or without hydrothermal treatment with bare silica. In the same way, the hydrothermal treatment was not necessary for grafted silica monoliths only dedicated to CEC. However, the results clearly indicate that the hydrothermal treatment becomes essential before grafting in order to preserve the efficiency of the monolithic silica capillaries dedicated to nano-LC: in this particular case, the suppression of the hydrothermal treatment leads approximately to a loss of a factor two in efficiency.

A demonstration model for a selective and recyclable uptake of metals from water: Fe(III) ions complexation and release by a supported natural fluorescent chelator.

We describe here the preliminary stage of development of a process aiming at the selective uptake and release of metal ions from water. The process envisioned involves the encapsulation of highly selective natural chelates secreted by bacteria or other living species in mesoporous solids that could be used as usual resins. To demonstrate the feasibility of the concept, we use a model system involving pyoverdin, a natural Fe(III) ions chelator from a Pseudomonas fluorescens strain, encapsulated in a mesoporous templated silica. For this model study, the native fluorescence of the chelator allows a simpler follow-up and quantification of the uptake and release processes.

Dissipative water intrusion in hydrophobic MCM-41 type materials.

Texture-related features of water intrusion in hydrophobised MCM-41 silicas render these materials especially suitable for energy dissipation in mechanical dampers.

Sorption of hydrophobic molecules by organic/inorganic mesostructures.

During the synthesis of micelle-templated silica an intermediate inorganic/organic mesostructure is obtained with an hexagonal arrangement of channels filled by surfactant molecules. The ability of such a mesostructure to solubilize organic molecules from an aqueous solution was investigated. To that end, silica/cationic surfactant mesostructures were prepared under various conditions and their stability toward surfactant release in water was first compared in order to select materials as stable as possible. Swelled mesostructures were also used. The sorption from solution of hydrophobic molecules was then studied. The affinity of the molecules for the mesostructures is directly related to their hydrophobic character as it is derived from their octanol/water partition coefficient. A cooperative effect between hydrophobic molecules and the cationic surfactant that stabilizes the surfactant inside the mesostructure was observed. Interaction energies between the solutes and the mesostructures were determined by microcalorimetry. They varied in accordance with the hydrophobic character of the molecule and, at low sorption amounts, they were of the same order of magnitude as the solubilization enthalpies in bulk micelles. When the sorption increases, the surfactant layer in the mesostructure is not allowed to swell as the free micelle does, and steric limitations in the headgroup area render sorption less favorable.

Peritonitis in continuous ambulatory peritoneal dialysis: impact of a compulsory switch from a standard to a Y-connector system in a single North American Center.

One hundred one continuous ambulatory peritoneal dialysis (CAPD) patients from a single North American center were analyzed in a retrospective and cross-over study for peritonitis rates using a standard system (Travenol System II) or a Y-shaped disconnect-disinfectant system (Travenol O-set). Twenty-one of 34 patients using the standard set (group I) had 53 episodes of peritonitis in 508 patient-months or one episode per 9.6 patient-months. Nine of 17 patients switching from the standard to the disconnect-disinfectant system (group II) experienced 22 episodes of peritonitis in 275 patient-months or one episode per 12.5 patient-months on the standard set, while six patients had 10 episodes of peritonitis in 275 patient-months or one episode per 27.5 patient-months on the disconnect-disinfectant system (P less than 0.04). Twenty-eight of 67 new CAPD patients starting on the disconnect-disinfectant system (group III) had 37 episodes of peritonitis in 1,086 patient-months or one episode per 29.4 patient-months (P less than 0.01 v group I). Exit-site infections (ESI) occurred in 35.3% of patients using the standard set versus 34.3% of those using the O-set. The presence of an ESI was not associated with a higher risk of peritonitis, but modified the bacteriological profile of subsequent peritonitis episodes in patients using the O-set, favoring the organisms isolated from the exit site. Decreases in peritonitis rates with the O-set were due to a reduction of peritonitis episodes secondary to most bacterial agents and not only to skin organisms. Diabetics using intraperitoneal insulin had similar peritonitis and ESI rates as nondiabetics.(ABSTRACT TRUNCATED AT 250 WORDS)