Interactions of the nitrate ions in various metal nitrate salts with CnH2n+1(CH2CH2O)mOH (CnEOm)-type nonionic surfactants have been investigated both in the solid and in the liquid-crystalline (LC) systems. In the ternary system, the mixture of salt/water/C nEOm has a mesophase up to a certain concentration of salt, and the nitrate ions in this phase are usually in a free-ion form. However, upon the evaporation of the water phase, the nitrate ion interacts with the metal center and coordinates as either a bidentate or unidentate ligand. It is this interaction that makes the AgNO 3 ternary system undergo a phase separation by releasing solid Ag(CnEOm)xNO3 complex crystals. In contrast, the salt/surfactant systems maintain their stable LC phases for months. Note also that the salt/surfactant systems consist of transition-metal aqua complexes in which the coordinated water molecules play a significant role in the self-assembly and organization of the nonionic surfactant molecules into an LC mesophase. Throughout this work, Fourier transform infrared spectroscopy has been extensively used to investigate the interactions of the nitrate ions with a metal center and the metal ions with the surfactant molecules. Polarized optical microscopy and X-ray diffraction techniques have been applied to investigate the nature of the crystalline and LC phases.
A lyotropic AgNO 3 , HAuCl 4 and H 2 PtCl 6 -silica liquid crystalline (LC) phase is used as a supramolecular template for a one-pot synthesis of novel noble metal or complex ion containing nanocomposite materials in the form of a film and monolith. In these structures, Ag 1 , AuCl 4 2 and PtCl 6 22 ions interact with the head group of an oligo(ethylene oxide) type non-ionic surfactant (C 12 H 25 (CH 2 CH 2 O) 10 OH, denoted as C 12 EO 10 ) assembly that are embedded within the channels of hexagonal mesostructured silica materials. A chemical and/ or thermal reduction of the metal or complex ions produces nanoparticles of these metals in the mesoporous channels and the void spaces of the silica. The LC mesophase of H 2 O : X : HNO 3 : C 12 EO 10 , (where X is AgNO 3 , HAuCl 4 and H 2 PtCl 6 ), and nanocomposite silica materials of meso-SiO 2 -C 12 EO 10 -X and meso-SiO 2 -C 12 EO 10 -M (M is the Ag, Au and Pt nanoparticles) have been investigated using polarised optical microscopy (POM), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), Fourier transform (FT) Raman and UV-Vis absorption spectroscopy. Collectively the results indicate that the LC phase of a 50 w/w% H 2 O : C 12 EO 10 is stable upon mixing with AgNO 3 , HAuCl 4 and H 2 PtCl 6 salts and/or acids. The metal ions or complex ions are distributed inside the channels of the mesoporous silica materials at low concentrations and may be converted into metal nanoparticles within the channels by a chemical and/or thermal reduction process. The metal nanoparticles have a broad size distribution where the platinum and silver particles are very small (typically 2-6 nm) and the gold particles are much larger (typically 5-30 nm).
We propose and demonstrate a nanocomposite localized surface plasmon resonator embedded into an artificial three-dimensional construction. Colloidal semiconductor quantum dots are assembled between layers of metal nanoparticles to create a highly strong plasmon-exciton interaction in the plasmonic cavity. In such a multilayered plasmonic resonator architecture of isotropic CdTe quantum dots, we observed polarized light emission of 80% in the vertical polarization with an enhancement factor of 4.4, resulting in a steady-state anisotropy value of 0.26 and reaching the highest quantum efficiency level of 30% ever reported for such CdTe quantum dot solids. Our electromagnetic simulation results are in good agreement with the experimental characterization data showing a significant emission enhancement in the vertical polarization, for which their fluorescence decay lifetimes are substantially shortened by consecutive replication of our unit cell architecture design. Such strongly plasmon-exciton coupling nanocomposites hold great promise for future exploitation and development of quantum dot plasmonic biophotonics and quantum dot plasmonic optoelectronics.
A lyotropic, liquid crystalline (LC) phase of a silver nitrate/ oligo(ethylene oxide), water, and acid mixture was used for onepot synthesis of mesoporous silica materials in which Ag + ions are uniformly distributed. We established that the AgNO 3 -to-surfactant mole ratio is very important in a 50 wt% surfactant/water system to preserve the hexagonal LC phase before and after the addition of the silica source. Below a 0.6 AgNO 3 -to-surfactant mole ratio, the mixture is liquid crystalline and serves as a template for silica polymerization. However, between 0.6 and 0.8 AgNO 3 -to-surfactant mole ratios, one must control the composition of the mixture during the polymerization processes. Above a 0.8 mole ratio, Ag + ions undergo phase separation from the reaction mixture by complexing with the surfactant molecules. The resulting silica materials obtained from AgNO 3 /surfactant ratios above 0.8 have anisotropy but without a hexagonal mesophase. Here, we establish a AgNO 3 concentration range in which the LC phase is preserved to template the synthesis of mesoporous silica, and we discuss the structural behavior of the mixtures at AgNO 3 /surfactant mole ratios of 0.00-2.00, using POM, PXRD, FTIR, and UV-Vis absorption spectroscopy. C 2001 Academic Press
The NO + CO + H2 reaction over CeO2, Au/CeO2 (3 wt% Au), Au/CeO2-Al2O3 (2.9 wt% Au, 20 wt% Al2O3) and CeO2-Al2O3 mixed support prepared by co-precipitation has been studied by FT-IR spectroscopy at elevated temperatures. Formation of NCO species has been detected on all of the samples. The presence of metallic gold is not necessary for the generation of the isocyanates on ceria and the mixed ceria-alumina support. The NCO species are produced by a process involving the dissociation of NO on the oxygen vacancies of the support, followed by the reaction between N atoms lying on the surface and CO molecules. Gold plays an important role in the modification of ceria leading to Ce3+ and oxygen vacancies formation, and causes significant lowering of the reduction temperature of CeO2 and CeO2-Al2O3 enhancing the reducibility of ceria surface layers. The role of H2 is to keep the surface reduced during the course of the reaction. The onset temperature, at which the interaction between the surface isocyanates and NO begins, is low (100 °C). This explains the high activity of the Au/CeO2-Al2O3 catalyst with 100% selectivity in the reduction of NO by CO at low temperature (200 °C) and in the presence of H2. © 2008 Elsevier B.V. All rights reserved
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