Adsorption and Diffusion of Na+, Cs+ and Ca+2 Ions in C-S-H and C-a-S-H Nanopores

Cementitious materials act as a diffusion barrier, immobilizing liquid and solidradioactive waste and preventing their release into the biosphere. The retention capability of hydratedcement paste and its main hydration product, C-S-H gel, has been extensively explored experimentallyfor many alkali and alkaline earth cations. Nevertheless, the retention mechanisms of these cations atthe molecular scale are still unclear. In this paper, we have employed molecular dynamics simulationsto study the capacity of C-S-H to retain Cs, Ca and Na, analyzing the number of high-affinity sites onthe surface, the type of sorption for each cation and the diffusivity of these ions. We have also exploredthe impact of aluminum incorporation in C-S-H at a constant concentration of the ions in the gel pore.We found strong competition for surface sorption sites, with notable differences in the retention of thecations under study and a remarkable enhance of the adsorption in C-A-S-H with respect to C-S-H

New Analogues of the BODIPY Dye PM597 : Photophysical and Lasing Properties in Liquid Solutions and in Solid Polymeric Matrices

New tailormade BODIPY dyes have been synthesized by a simple protocol to reach wavelength finely tunable laser action from 540 to 625 nm while maintaining highly efficient and photostable laser emission. The new dyes are analogues of the commercial dye PM597 with the eight position free (PTH8) or substituted by the groups acetoxymethyl (PTAlk) or p-acetoxymethylphenyl (PTAr). The photophysical properties strongly depend on the geometrical distortion from planarity of the indacene core generated by the presence of the bulky 2,6-di-tert-butyl groups and the eight substituent. In both liquid and polymeric solid solutions, lasing efficiencies of up to 63 and 48%, respectively, were observed under transversal pumping at 532 nm with high photostabilities. In the case of PTAlk incorporated into silicon-containing solid organic matrices, the laser emission remained at 92% of its initial intensity value after 100 000 pumping pulses in the same position of the sample at 30 Hz repetition rate. The laser action of the new dyes enhances that of the parent dye PM597 and outperforms the lasing behavior of dyes considered to be benchmarks over the green-yellow to red spectral region.This work was supported by projects MAT2007-65778-C02-01 and -02 of the Spanish Ministerio de Investigacio´n, Ciencia e Innovacio´n (MICIN). M.P.-S. thanks MICIN for a predoctoral scholarship (cofinanced by Fondo Social Europeo). M.L. was a recipient of a Juan de la Cierva contract (MICIN)Peer reviewe

New Analogues of the BODIPY Dye PM597 : Photophysical and Lasing Properties in Liquid Solutions and in Solid Polymeric Matrices

New tailormade BODIPY dyes have been synthesized by a simple protocol to reach wavelength finely tunable laser action from 540 to 625 nm while maintaining highly efficient and photostable laser emission. The new dyes are analogues of the commercial dye PM597 with the eight position free (PTH8) or substituted by the groups acetoxymethyl (PTAlk) or p-acetoxymethylphenyl (PTAr). The photophysical properties strongly depend on the geometrical distortion from planarity of the indacene core generated by the presence of the bulky 2,6-di-tert-butyl groups and the eight substituent. In both liquid and polymeric solid solutions, lasing efficiencies of up to 63 and 48%, respectively, were observed under transversal pumping at 532 nm with high photostabilities. In the case of PTAlk incorporated into silicon-containing solid organic matrices, the laser emission remained at 92% of its initial intensity value after 100 000 pumping pulses in the same position of the sample at 30 Hz repetition rate. The laser action of the new dyes enhances that of the parent dye PM597 and outperforms the lasing behavior of dyes considered to be benchmarks over the green-yellow to red spectral region.This work was supported by projects MAT2007-65778-C02-01 and -02 of the Spanish Ministerio de Investigacio´n, Ciencia e Innovacio´n (MICIN). M.P.-S. thanks MICIN for a predoctoral scholarship (cofinanced by Fondo Social Europeo). M.L. was a recipient of a Juan de la Cierva contract (MICIN)Peer reviewe

Adsorption and Diffusion of Na+, Cs+ and Ca+2 Ions in C-S-H and C-a-S-H Nanopores

Cementitious materials act as a diffusion barrier, immobilizing liquid and solid<br>radioactive waste and preventing their release into the biosphere. The retention capability of hydrated<br>cement paste and its main hydration product, C-S-H gel, has been extensively explored experimentally<br>for many alkali and alkaline earth cations. Nevertheless, the retention mechanisms of these cations at<br>the molecular scale are still unclear. In this paper, we have employed molecular dynamics simulations<br>to study the capacity of C-S-H to retain Cs, Ca and Na, analyzing the number of high-affinity sites on<br>the surface, the type of sorption for each cation and the diffusivity of these ions. We have also explored<br>the impact of aluminum incorporation in C-S-H at a constant concentration of the ions in the gel pore.<br>We found strong competition for surface sorption sites, with notable differences in the retention of the<br>cations under study and a remarkable enhance of the adsorption in C-A-S-H with respect to C-S-H

Synthesis and functionalization of new polyhalogenated BODIPY dyes. Study of their photophysical properties and singlet oxygen generation

A theor. and exptl. study on the iodination of BODIPY dyes with different degrees of substitution has been developed. Polyhalogenated BODIPYs synthesized in this work are the first examples of this type of dyes with more than two halogen atoms in the BODIPY core and they can be selectively functionalized. Surprisingly, the position in which halogen is attached has a marked effect in the photophys. properties and modulates the fluorescence capacity of the resulting BODIPY. These iodinated BODIPYs are efficient singlet oxygen generators.Spanish Ministerio de Economia y Competitividad (MINECO)UCM/BSCHBasque GovernmentDepto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu

Benchmark of ReaxFF Force Field for Subcritical and Supercritical Water

Water in the subcritical and supercritical states has remarkable properties that make it an excellent solvent for oxidation of hazardous chemicals, waste separation, and green synthesis. Molecular simulations are a valuable complement to experiments in order to understand and improve the relevant sub- and super-critical reaction mechanisms. Since water molecules under those conditions can act not only as solvent but also as reactant, dissociative force fields are specially interesting to investigate theseprocesses. In this work, we evaluate the capacity of the ReaxFF force field to reproduce the microstructure, hydrogen bonding, dielectric constant, diffusion, and proton transfer of sub- and super-critical water. Our results indicate that ReaxFF is able to simulate water properties in these states in very good quantitative agreement with existing experimental data, with the exception of the static dielectric constant which is reproduced only qualitatively.</div

Benchmark of ReaxFF Force Field for Subcritical and Supercritical Water

<div><div><div><p>Water in the subcritical and supercritical states has remarkable properties that make it an excellent solvent for oxidation of hazardous chemicals, waste separation, and green synthesis. Molecular simulations are a valuable complement to experiments in order to understand and improve the relevant sub- and super-critical reaction mechanisms. Since water molecules under those conditions can act not only as solvent but also as reactant, dissociative force fields are specially interesting to investigate theseprocesses. In this work, we evaluate the capacity of the ReaxFF force field to reproduce the microstructure, hydrogen bonding, dielectric constant, diffusion, and proton transfer of sub- and super-critical water. Our results indicate that ReaxFF is able to simulate water properties in these states in very good quantitative agreement with existing experimental data, with the exception of the static dielectric constant which is reproduced only qualitatively.</p></div></div></div