133Cs NMR Study of Cs+ Ion Complexes with?Aza-18-crown-6, Diaza-18-crown-6 and?Dibenzyldiaza-18-crown-6 in Binary Acetonitrile?CNitromethane Mixtures

Cesium-133 nuclear magnetic resonance spectroscopy was used as a sensitive probe to investigate the stoichiometry and stability of Cs⁺ ion complexes with aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6) and dibenzylediaza-18-crown-6 (DBzDA18C6) in different binary acetonitrile?Cnitromethane mixtures. In all cases, the exchange between free and complexed cesium ion was fast on the NMR time scale and only a single population average resonance was observed. The ¹³³Cs chemical shift?Cmole ratio data indicated that the cesium ion forms 1:1 cation?Cligand complexes with the investigated aza-crowns in all acetonitrile?Cnitromethane mixtures. The formation constants of the resulting complexes were evaluated from computer fitting of the chemical shift?Cmole ratio data. The stability of the resulting 1:1 complexes with Cs⁺ were found to vary in the order A18C6 > DBzDA18C6 > DA18C6. In all cases, there is the inverse relationship between the complex stability constants and the amount of acetonitrile in the mixed solvent.     

Deposition and photopolymerization of phase-separated perfluorotetradecanoic acid-10,12-pentacosadiynoic acid Langmuir-Blodgett monolayer films

Mixed monolayer surfactant films of perfluorotetradecanoic acid and the photopolymerizable diacetylene molecule 10,12-pentacosadiynoic acid were prepared at the air-water interface and transferred onto solid supports via Langmuir-Blodgett (LB) deposition. The addition of the perfluoroacid to the diacetylene surfactant results in enhanced stabilization of the monolayer in comparison with the pure diacetylene alone, allowing film transfer onto a solid substrate without resorting to addition of cations in the subphase or photopolymerization prior to deposition. The resulting LB films consisted of well-defined phase-separated domains of the two film components, and the films were characterized by a combination of atomic force microscope (AFM) imaging and fluorescence emission microscopy both before and after photopolymerization into the highly emissive "red form" of the polydiacetylene. Photopolymerization of the monolayer films resulted in the formation of diacetylene bilayers, which were highly fluorescent, with the apparent rate of photopolymerization and the fluorescence emission of the films being largely unaffected by the presence of the perfluoroacid.     

Preparation and activity measurement of some low pressure methanol synthesis catalysts

Summary In the present study, twenty four catalysts for low pressure methanol synthesis were prepared according to a pre-designed research program consisting of three stages. In each stage, applying the experimental design techniques, a number of catalysts were synthesized by the co-precipitation method, using different proportions of metal salts solutions. The activities of the catalysts were determined applying a laboratory scale continuous packed bed reactor. It was noted that the calcinations temperature, ageing time and molar ratio of metal nitrates to precipitant, had the highest effects on the activity of the catalysts.     

Verification of Mason and Smythe equations for electrical treeing breakdown at the tip of charged particle tracks in ECE polycarbonate detectors

There are two different equations to describe enhancement of field strength at the track tip in ECE polycarbonate detectors: Mason and Smythe equations. In order to evaluate the equations, PC detectors with different thicknesses were exposed to 1 MeV alpha and/or fast neutron. The response of the detectors was studied as a function of applied voltage and average field strength. The ratio of critical voltages for different detectors was estimated experimentally and compared with calculated values. The experimental results are in good agreement with Smythe's equation. The results show that the track density and mean track diameter in the different detectors have the same behaviour, when the macroscopic field strength increases, and also that the field strength at the tip of tracks is proportional to macroscopic field strength.     

Double-horizon limit, AdS geometry and entropy function

We start from a generic metric which describes four-dimensional stationary black holes in an arbitrary theory of gravity and show that the AdS₂ part of the near-horizon geometry is a consequence of the double-horizon limit and finiteness. We also show that the field configurations of the near horizon are determined if the same conditions are applied to the equations of motion. This is done by showing that in the double-horizon limit field equations at the horizon decouple from the bulk of the space. Solving these equations gives the near-horizon field configurations. It is shown that these decoupled equations can be obtained from an action derived from the original action by applying the double-horizon condition. Our results agree with the entropy function method.     

Comparison between the performance of an immobilized impinging jet stream reactor and a slurry impinging jet stream reactor for photocatalytic phenol degradation

A new immobilized photocatalytic impinging jet stream reactor was designed, and the influences of the effective parameters like jet flow rate, TiO₂ coating disc diameter, nozzle-to-disc distance, and initial concentration on phenol removal were investigated. The reactor was also used as a slurry reactor, and degradation efficiencies in both reactors were compared based on their catalyst loading. The results indicated that the slurry reactor has a higher degradation efficiency than the immobilized reactor at the same TiO₂ loading and other operational conditions. The slurry reactor needs to separate and recover the TiO₂ nanoparticles from the reaction medium which increases the overall process complexity and cost, while the immobilized reactor could be reused at least 4times without any significant decrease in removal efficiency. RTD result indicates that the tank in series model (N?=?5) could properly predict the reactors hydrodynamic behavior.