Mechanism of proton transport in HUP (HUO2.PO4.4H2O)
TL;DR: In this paper, the authors considered the mechanism of proton transport in HUP and examined the crystal structure of the material with respect to the π-charge cloud of the phosphate group and the variation of conductivity with temperature and pressure.
Abstract: Existing theories for the mechanism of proton transport in HUP has been considered and their limitations discussed. The crystal structure of the material has been examined. The transport of protons from one water square to another might take place through the participation of the pi-charge cloud of the phosphate group. A suitable rotation of the water molecule provides the continuous proton pass. The variation of conductivity with temperature and pressure have been interpreted.
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TL;DR: The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2(2+) with the phosphate anions H2PO4(-), HPO4(2-), and PO4(3-) were predicted at the density functional theory and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models.
Abstract: The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO22+ with the phosphate anions H2PO4–, HPO42–, and PO43– were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO43-x in ...
19 citations
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TL;DR: In this article, the authors summarized the results of intercalative ion exchange reactions with guest cationic species spanning the periodic table and showed that the host lattice exhibits highly efficient green photoluminescence (PL) characteristic of the uranyl (UO 2 2+ moiety).
Abstract: Hydrogen uranyl phosphate (HUP), HUO 2 PO 4 ·4H 2 O, is a layered solid that undergoes intercalative ion-exchange reactions with guest cationic species spanning the periodic table. The host lattice exhibits highly efficient green photoluminescence (PL) characteristic of the uranyl (UO 2 2+ moiety. Structural and optical perturbations of the host and guest generally accompany intercalation reactions. Guest metal complexes have afforded an opportunity to study host-to-guest energy transfer, interlamellar acid-base/precipitation chemistry, interlamellar redox chemistry, and host lattice substitution chemistry. These reactions are summarized in this article.
11 citations
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01 Jan 2013
TL;DR: In this paper, a list of ABBREVIATION and SYMBOLS and ACKNOWLEDGMENTS is presented. But the list is limited to ABBVIATIONS and Symbols.
Abstract: ................................................................................................................................... ii DEDICATION ............................................................................................................................... iv LIST OF ABBREVIATIONS AND SYMBOLS ............................................................................v ACKNOWLEDGMENTS ...............................................................................................................x LIST OF TABLES .........................................................................................................................xv LIST OF FIGURES ................................................................................................................... xviii CHAPTER
2 citations
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TL;DR: In this paper, the time-resolved luminescence decays of intercalated compounds of hydrogen uranyl phosphate with p-toluidinium (HUPPT), benzylaminium(HUPBZ), α-methylbenzylaminant amines (HUPMBZ) and hydroxylaminant ammonium cation was studied, showing that the long-range and long-lifetime quenching is hindered.
Abstract: Time-resolved luminescence decays of intercalated compounds of hydrogen uranyl phosphate (HUP) with p-toluidinium (HUPPT), benzylaminium (HUPBZ), α–methylbenzylaminium (HUPMBZ) and hydroxylaminium (HUPHAM) were studied. The prepared compounds belong to the tetragonal P4/ncc space group and showed 00 l reflections shifted to lower angles relative to HUP, indicating that the intercalation increases the c parameter of the unit cell. The luminescence decays of the compounds with 100% of intercalation ratio (HUPHAM and HUPBZ) were analyzed by Global Analysis, assuming Lianos’ stretched exponential as the model function, which can be applied to compounds with restricted geometry and mobile donor and quencher molecules. It was remarkable that the luminescence decays showed that the quenching of the emission of the uranyl ions by the intercalated protonated amines is not restricted by low dimensionality of the host uranyl phosphate, and that a diffusion mechanism occurs. Benzylaminium cation efficiently quenches the excited energy of the uranyl ions at close distance, but the long-range and long-lifetime quenching is hindered. A different situation is found in the case of the small hydroxylaminium cation, where the long distance diffusion of the species is fast, playing an important role in the quenching of the excited uranyl ions at longer times.
1 citations
References
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TL;DR: In this paper, a Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and inter-parallel transfer steps in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by high H-bond vacancies.
Abstract: We have found that hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O has a high proton conductivity. The ac conductivity was 0.4 ohm −1 m −1 at 290°K measured parallel to the faces of sintered disks of the compound. The activation energy was found to be 31 ± 3 kJ mole −1 . The values of conductivity were between 3 and 10 times lower when measured perpendicular to the disk faces due to preferred orientation of the plate-like crystals. Both the powder and sintered disks are stable in air and insoluble in phosphoric acid solution of pH 2.5. Experiments are described which enable possible grain boundary contributions to the conductivity to be determined in such hydrates. The extrinsic grain boundary contribution to the conductivity was found to be small from experiments in which the pH in a solution cell was varied. The abnormally high bulk H + conductivity thus inferred is attributed primarily to the high concentration of H + , which exists as H 3 O + in the interlamellar hydrogen-bonded network. A Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and intramolecular transfer steps, in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by the high concentration of H-bond vacancies.
126 citations
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TL;DR: In this paper, it was shown that the high proton conductivity of hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O (HUP) is sufficient to enable an HUP/H x WO 3 electrochromic cell to function as fast as a cell with an acidic solution electrolyte.
Abstract: We have found that the high proton conductivity of hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O (HUP) is sufficient to enable an HUP/H x WO 3 electrochromic cell to function as fast as a cell with an acidic solution electrolyte. Switching times down to 0.3 s were found. The fabrication procedure to obtain the stable and uniform films of HUP required has been optimized, and dense sintered films up to 6 cm in diameter have been produced.
46 citations
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TL;DR: In this paper, the electrical conductivity of aqueous solution of KOH, NaOH and LiOH was investigated and it was shown that with increasing concentration there is a transition in the primary mechanism of conductance in these solutions from the proton transfer mechanism to the hydrodynamic mechanism.
Abstract: Measurements of the electrical conductivity of aqueous solutions of KOH, NaOH and LiOH are presented within the ranges 25–200°C, 1–3000 atm and 0.1–6.68 molal. These indicate that with increasing concentration there is a transition in the primary mechanism of conductance in these solutions from the proton transfer mechanism to the hydrodynamic mechanism. In LiOH solutions, however, saturation occurs before this transition is established. It is suggested that at high concentrations most of the water molecules are dominated by their proximity to an ion and so cannot participate in the proton transfer mechanism of conductance by the hydroxyl ion. This mechanism is disrupted most by KOH and least by LiOH at a given concentration in excess of 1 molal, and this is related to the greater ionic association of the latter solute.
With increasing concentration of KOH the Walden product becomes more nearly independent of temperature and pressure. Data for the viscosity of water have been surveyed and a table covering the ranges 10–200° and 1–3000 kg cm–1 is presented. The pressure dependence of the conductance of these solutions is virtually independent of concentration to the unexpectedly high value of about 1 molal, but it alters markedly in the range 1–2 molal. The observations are discussed qualitatively.
44 citations