Search results for "Sorption"
showing 10 items of 4623 documents
Characterization of [Cu]-MCM-41 by XPS and CO or NO adsorption heat measurements
2002
We report the characterization of copper doped MCM-41 prepared by original direct synthesis by XPS and adsorption calorimetry of CO and NO, which are selective molecular probes for Cu(I) and Cu(II) respectively. Investigation of the nature of the copper ions in this particular calcined Cu-MCM-41 by NO adsorption calorimetry shows that two types of energetically distinct adsorption sites exist, meaning the presence of two populations of Cu(II) species differently coordinated to the silica surface in quasi-equimolar concentration, as ascertained by XPS data. A small amount of Cu(I) was also detected, probably stemming from a partial reduction upon the successive vacuum treatments. The respect…
Resonance ionization spectroscopy of fermium (Z=100)
2003
Laser spectroscopy has been applied for the first time to measure resonant transition frequencies of fermium (Zs 100). A number of 2.7=10 atoms was electrodeposited on a Ta filament and covered with a 1 mm Ti layer. Fm 10
Transfer of Water and Active Molecules at the Interfaces in Complex Food Systems: Theoretical and Practical Aspects
2011
Abstract During processing, storage and consumption, mass transfer of various molecules (water, gases, flavour compounds or other solutes) occur between the different phases in complex food products, and/or also between the complex food and its surroundings. These mass transfers can lead to physical and/or chemical changes and thus induce food quality modifications. The objective of this presentation is to better understand the behaviour of small molecules at the interfaces, especially in model heterogeneous food systems. Different techniques have been developed to characterize their properties and their impact on the mass transfers. Particularly, techniques such as rotative diffusion cell …
Electro-optical and laser spectrofluorimetry study of coumarins 7 and 30: evidence for the existence of the close-lying electronic states and conform…
1997
Our experiments and calculations reveal a set of anomalous and interesting properties of coumarin 7 (CU7) and coumarin 30 (CU30) in solution. The spectral dependence of electro-optical coefficients and, consequently, dipole moments indicates that the absorption band is a superposition of several (at least two) electronic transitions. Probably, there are two close-lying π,π* singlet electronic excited states which contribute to the first absorption band. The calculations using the MM2 program show that both dyes in the ground state have two stable plane anti conformers. From time-resolved spectrofluorimetric measurements we obtained evidence for the existence of conformers in paraffin oil so…
Adsorbed CO on group 10 metal fragments: A DFT study
2009
DFT calculations on the helicopter and cartwheel rotations of one CO molecule adsorbed at the bridge site on metal-surface fragments, characterized by two (M(8)) or three (M(14)) metal-atom layers (M = Ni, Pd, Pt) were performed by the B3LYP[LANL2DZ+6-31 g(d,p)] method, to rationalize the adsorption energetics and the steric hindrance characteristics of surface CO molecules. Potential Energy Surfaces were obtained, either fixing the C-O bond-length or allowing it to change. The behavior of the three metals, as obtained from the study of the configurational space characterizing the CO adsorption on the fragments was explained on the basis of the interaction energies involved in the different…
Static and Dynamic Properties of the Nonframework Cations in Na-Mordenites Zeolite
2004
This work consists of exploring the effect of Si/Al ratio and water content on both the static and dynamic properties of the extra-framework cations in a typical zeolite system Na+-Mordenites. Atomistic simulations based on interatomic potentials and minimisation techniques have been used to determine the location of the cations as a function of the Si/Al ratio and the hydration level. Our calculations showed two different cation behaviours depending on the type of channels that they occupy, the positions of the cations in the main channels being substantially perturbed upon the sorption of water molecules whereas those of the cations located in the small side channels being only slightly s…
Three-dimensional orientational colocalization of individual donor--acceptor pairs.
2004
We report on the determination of the three-dimensional orientation of the donor and acceptor transition dipoles in individual fluorescence resonance energy transfer (FRET) pairs by means of scanning optical microscopy with annular illumination. Knowledge of the mutual orientation of the donor and acceptor dipole is mandatory for reliable distance determination based on FRET efficiency measurements. In our model system perylenediimide as the donor and terryelenediimide as the acceptor are coupled via a stiff p-terphenyl linker. The absorption dipoles of the donor and acceptor are selectively addressed by the 488 nm and 647 line of an Ar/Kr mixed gas laser, respectively. A clear deviation fr…
Enhanced nonlinear optical properties and thermal stability of donor-acceptor substituted oligothiophenes
1997
Abstract Linear and nonlinear optical properties of a series of novel donor-acceptor substituted α-oligothiophenes were investigated by means of electrooptical absorption measurements (EOAM) and electric field induced second harmonic generation (EFISH). The second-order polarizabilities β(−2ω; ω, ω) were related to dipole changes Δμ ag and transition dipoles μ ag associated with low-lying charge-transfer (CT) excitations by using the perturbational two-level approximation. Systematic variation of the donor and acceptor groups led to compounds with exceptional nonlinearity and thermal stability. Too strong donor/acceptor pairs, however, yielded structures in the charge-resonance (CR) limit w…
Hartree–Fock study of adhesion and charge redistribution on the Ag/MgO(0 0 1) interface
2001
Abstract Ab initio study of the Ag/MgO(0 0 1) interfaces based on a quantitative analysis of the bonding in the interfacial region is provided in the framework of Hartree–Fock approach. We are describing the way interfacial electronic and other properties evolve as a function of metal coverage. General conclusion that could be drawn from our calculations is that chemical bond formation is not important for the Ag/MgO(0 0 1) perfect interface. Physisorption of Ag atoms over surface O 2− ions associated with atomic polarization and charge redistribution in the metal planes are the dominant effects. The adhesion energy is enhanced by the interaction of the substrate Mg 2+ ions with the surplus…
Adsorption of 3d Transition Elements on a TiO2(110) Surface.
2008
International audience; A first-principles study on the adsorption of 3d transition metal atoms on a stoichiometric TiO2(110) surface is reported. For all 3d elements except Cu, the most stable on-surface adsorption site is a site where the adatom binds to two twofold and one threefold surface oxygen atoms. For Ti, V, and Cr, however, a subsurface site, where the adatom substitutes a sixfold Ti atom, is more stable. The adatoms are oxidized in all cases. The charge transfer to the substrate is larger for the substitutional site than for the on-surface adsorption sites and decreases with atomic number along the 3d series. The relative stabilities of the adsorption sites are discussed in term…