The Experts below are selected from a list of 168 Experts worldwide ranked by ideXlab platform
Dominique Costa - One of the best experts on this subject based on the ideXlab platform.
-
insight into the bonding of silanols to oxidized aluminum Surfaces
Journal of Physical Chemistry C, 2018Co-Authors: Matic Poberžnik, Dominique Costa, Anne Hemeryck, Anton KokaljAbstract:In the context of elucidating the mechanism by which siloxane-based sol–gel coatings adhere to the Surface, the adsorption of a model silanol molecule, CH3Si(OH)3, and its oligomers (up to the trimer) on oxidized and fully Hydroxylated aluminum substrates is described using density functional theory (DFT). To link our calculations with the synthesis of siloxane-based sol–gel coatings, the focus is given on the condensation mechanism. We find that the formation of a monodentate bonding mode with the Hydroxylated Surface via the condensation mechanism is exothermic by ≥0.5 eV in all considered cases. In contrast, the formation of a bidentate bonding mode is exothermic only for the trimer. However, taking entropic contributions into account, we find that the formation of the bidentate bonding mode is exergonic already for the dimer due to favorable entropic effects of a liberated water molecule during the reaction. In contrast, the reaction entropy is unfavorable for the monodentate formation because the eff...
-
insight into the bonding of silanols to oxidized aluminum Surfaces c
The Journal of Physical Chemistry, 2018Co-Authors: Matic Poberžnik, Dominique Costa, Anne Hemeryck, Anton KokaljAbstract:In the context of elucidating the mechanism by which siloxane-based sol–gel coatings adhere to the Surface, the adsorption of a model silanol molecule, CH₃Si(OH)₃, and its oligomers (up to the trimer) on oxidized and fully Hydroxylated aluminum substrates is described using density functional theory (DFT). To link our calculations with the synthesis of siloxane-based sol–gel coatings, the focus is given on the condensation mechanism. We find that the formation of a monodentate bonding mode with the Hydroxylated Surface via the condensation mechanism is exothermic by ≥0.5 eV in all considered cases. In contrast, the formation of a bidentate bonding mode is exothermic only for the trimer. However, taking entropic contributions into account, we find that the formation of the bidentate bonding mode is exergonic already for the dimer due to favorable entropic effects of a liberated water molecule during the reaction. In contrast, the reaction entropy is unfavorable for the monodentate formation because the effects of the immobilized silanol molecule counteract and surpass those of the liberated water molecule. The monodentate to bidentate transformation is therefore determined by the interplay between entropy and energy, and we find that the longer the oligomer chain, the more likely is the bidentate formation due to increasingly favorable reaction energies. These results further reveal that for the silanol monomer, additional molecule–Surface chemical bonds do not form via the condensation mechanism due to the strained configuration it has to adopt in the bidentate bonding mode.
-
dft study of the adsorption of microsolvated glycine on a hydrophilic amorphous silica Surface
Physical Chemistry Chemical Physics, 2008Co-Authors: Dominique Costa, Frederik Tielens, Asma Tougerti, Christel Gervais, Lorenzo Stievano, Jean-françois LambertAbstract:Density functional theory (DFT) periodic ab initio molecular dynamics calculations are used to study the adsorption of gaseous and microsolvated glycine on a Hydroxylated, hydrophilic silica Surface. The silica model is presented and the interaction of water with Surface silanols is studied. The heat of interaction of water is higher with the associated silanols (be they terminal or geminal ones) studied here than with isolated silanols presented in past works. Glycine is stabilized in a parallel mode on the Hydroxylated Surface. Terminal silanols do not allow the stabilization of the zwitterionic form, whereas geminal silanols do. Molecular dynamics (MD) first-principle calculations show that microsolvated zwitterion glycine directly binds through the carboxylate function to a Surface silanol rather than through water molecules. The adsorption mode, whether with or without additional water molecules, is parallel to the Surface. The ammonium function does not interact directly with the silanol groups but rather through water molecules. Thus, the carboxylate and ammonium functions exhibit two different reactivities towards silanols. The calculated free energies, taking into account the chemical potentials of water and glycine in the gas phase, suggest the existence of a thermodynamic domain in which the glycine is present in the gas phase as well as strongly adsorbed on specific sites of the Surface.
-
Ab initio study of the Hydroxylated Surface of amorphous silica: A representative model
Chemistry of Materials, 2008Co-Authors: Frederik Tielens, Jean-françois Lambert, Christel Gervais, Francesco Mauri, Dominique CostaAbstract:A new complete, representative model for the Hydroxylated Surface of amorphous silica is presented and characterized by means of periodic DFT calculations. This model accounts for the experimentally encountered ring size distribution, Si-O-Si and O-Si-O angles, silanols density, and distribution (isolated, associated, geminals). Properties such as NMR shifts, dehydrogenation energies, OH vibrational frequencies, and the interaction with water are investigated. The results are compared with former experimental and theoretical results. This new representative model for this complex Surface would probably help the investigation of its reactivity toward amino acids or other organic molecules, opening new perspectives in the understanding of the chemistry of amorphous materials.
Peter T Cummings - One of the best experts on this subject based on the ideXlab platform.
-
Molecular Investigation of Oxidized Graphene: Anatomy of the Double-Layer Structure and Ion Dynamics
2019Co-Authors: Yu Zhang, Boris Dyatkin, Peter T CummingsAbstract:We investigated the influence of Surface oxidization of planar graphene electrodes on charge storage and ion dynamics of supercapacitors. Our approach compared two distinct ionic liquid (IL) electrolytes: tetraethylammonium tetrafluoroborate solvated in acetonitrile (TEA-BF4/ACN) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide solvated in acetonitrile (EMIm-TFSI/ACN). Both experimental electrochemical tests and molecular dynamics (MD) simulations showed positive, electrolyte-specific influences of hydroxyl-free electrode interfaces on capacitance. In the EMIm-TFSI/ACN system, the Hydroxylated Surface, because of its strong interaction with anions, impeded Surface charge storage. On the other hand, in the case of TEA-BF4/ACN, the distribution and orientation of ACN across the system exerted vital influence on the capacitance, especially on the positive hydroxyl-free electrode. Furthermore, MD simulations of ion mobility with respect to the electrode Surface in the lateral and perpendicular directions revealed significantly slower diffusion performance on the oxidized Surface. Our efforts enhanced the level of fundamental understanding of the effects of hydroxyl groups on electrode–electrolyte interfaces and resulting supercapacitor performance
-
electric double layer at the rutile 110 Surface 2 adsorption of ions from molecular dynamics and x ray experiments
Journal of Physical Chemistry B, 2004Co-Authors: Milan Předota, Zheng Zhang, Paul Fenter, And D J Wesolowski, Peter T CummingsAbstract:Molecular dynamics (MD) simulations were conducted to characterize the microstructure of the interface between aqueous solutions and the (110) Surface of rutile (R-TiO2) for Hydroxylated and nonHydroxylated Surfaces, each either neutral or negatively charged. The fully atomistic description of the rutile Surface and its interactions with the fluid phase was based on ab initio calculations, while the aqueous phase was described by the SPC/E model and existing parametrizations for Rb + ,N a + ,S r 2+ ,Z n 2+ ,C a 2+ , and Cl - ions. Formation of inner-sphere complexes of cations with Surface oxygens was identified for all cations studied. On negatively charged Surfaces, Zn 2+ is shown to sorb at two bidentate sites, between a bridging and terminal oxygen, and between two terminal oxygens (Hydroxylated Surface only), while all other cations occupy a tetradentate site, in contact with two terminal and two bridging oxygens in adjacent rows on the crystal Surface, and directly above an additional triply coordinated oxygen in the Ti-O Surface plane. These differences in inner-sphere binding configuration appear to be related to the bare ionic radii of the cations. Simulation results agree very well with X-ray standing wave and crystal truncation rod studies of the inner-sphere adsorption sites of the cations Rb + and Sr 2+ . MD and X-ray results for Zn 2+ adsorption are qualitatively consistent, but important differences in adsorption heights are discussed. Both MD simulations and X-ray studies indicate that, on rutile (110), interaction of Cl - with neutral and negatively charged Surfaces and with sorbed, multivalent cations is minimal. The Hydroxylated Surface gives better agreement with experiments than the nonHydroxylated Surface and is therefore inferred to be the dominant Surface in contact with aqueous solutions at ambient conditions. At the negative, Hydroxylated Surface, the MD results indicate that Sr 2+ and Ca 2+ also form outersphere species that are laterally ordered with respect to the crystal Surface structure, though these are much less abundant than the inner-sphere species. At positively charged Hydroxylated Surfaces, MD simulations indicate Cl - adsorption in the tetradentate site 4.3 A above the Surface, with longer-range ordering of ions and water molecules than was observed on neutral or negatively charged Surfaces. The adsorption geometries of ions are not sensitive to an increase of temperature to 448 K.
Jean-françois Lambert - One of the best experts on this subject based on the ideXlab platform.
-
dft study of the adsorption of microsolvated glycine on a hydrophilic amorphous silica Surface
Physical Chemistry Chemical Physics, 2008Co-Authors: Dominique Costa, Frederik Tielens, Asma Tougerti, Christel Gervais, Lorenzo Stievano, Jean-françois LambertAbstract:Density functional theory (DFT) periodic ab initio molecular dynamics calculations are used to study the adsorption of gaseous and microsolvated glycine on a Hydroxylated, hydrophilic silica Surface. The silica model is presented and the interaction of water with Surface silanols is studied. The heat of interaction of water is higher with the associated silanols (be they terminal or geminal ones) studied here than with isolated silanols presented in past works. Glycine is stabilized in a parallel mode on the Hydroxylated Surface. Terminal silanols do not allow the stabilization of the zwitterionic form, whereas geminal silanols do. Molecular dynamics (MD) first-principle calculations show that microsolvated zwitterion glycine directly binds through the carboxylate function to a Surface silanol rather than through water molecules. The adsorption mode, whether with or without additional water molecules, is parallel to the Surface. The ammonium function does not interact directly with the silanol groups but rather through water molecules. Thus, the carboxylate and ammonium functions exhibit two different reactivities towards silanols. The calculated free energies, taking into account the chemical potentials of water and glycine in the gas phase, suggest the existence of a thermodynamic domain in which the glycine is present in the gas phase as well as strongly adsorbed on specific sites of the Surface.
-
Ab initio study of the Hydroxylated Surface of amorphous silica: A representative model
Chemistry of Materials, 2008Co-Authors: Frederik Tielens, Jean-françois Lambert, Christel Gervais, Francesco Mauri, Dominique CostaAbstract:A new complete, representative model for the Hydroxylated Surface of amorphous silica is presented and characterized by means of periodic DFT calculations. This model accounts for the experimentally encountered ring size distribution, Si-O-Si and O-Si-O angles, silanols density, and distribution (isolated, associated, geminals). Properties such as NMR shifts, dehydrogenation energies, OH vibrational frequencies, and the interaction with water are investigated. The results are compared with former experimental and theoretical results. This new representative model for this complex Surface would probably help the investigation of its reactivity toward amino acids or other organic molecules, opening new perspectives in the understanding of the chemistry of amorphous materials.
Ch Woll - One of the best experts on this subject based on the ideXlab platform.
-
water adsorption on the Hydroxylated h 1 1 o zno 000 Surface
Physical Chemistry Chemical Physics, 2006Co-Authors: M Schiek, K Alshamery, M Kunat, Franziska Traeger, Ch WollAbstract:The adsorption of water multilayers on a well defined single crystal, hydroxyl-terminated ZnO-Surface, H(1 × 1)-O-ZnO(000) Surface has been investigated using infrared (IR) spectroscopy, helium atom scattering (HAS) and X-ray photoelectron spectroscopy (XPS). The results reveal the formation of well ordered mono-, bi- and multilayers of D2O and H2O on this substrate. On the bare hydroxyl-covered H(1 × 1) Surface the OH-stretch vibration could be clearly identified in the IR-spectra. The water adsorption and desorption kinetics on this Hydroxylated Surface were studied by monitoring the reflectivity of the Surface for helium atoms. The analysis of the data yielded activation energies for desorption of H2O from the H(1 × 1) O-ZnO Surface of 55.2 kJ mol−1. The results reveal the formation of ordered mono- and bilayers. Further exposure to water at 113 K results in the formation of amorphous 3-D islands.
Sandra Isabel Simonetti - One of the best experts on this subject based on the ideXlab platform.
-
density functional theory based study of 5 fluorouracil adsorption on β cristobalite 1 1 1 Hydroxylated Surface the importance of h bonding interactions
Applied Surface Science, 2015Co-Authors: Sandra Isabel Simonetti, Estela Pronsato, A Juan, G Brizuela, A LamAbstract:Abstract Silica-based mesoporous materials have been recently proposed as an efficient support for the controlled release of a popular anticancer drug, 5-fluorouracil (5-FU). Although the relevance of this topic, the atomistic details about the specific Surface-drug interactions and the energy of adsorption are almost unknown. In this work, theoretical calculations using the Vienna Ab-initio Simulation Package (VASP) applying Grimme's—D2 correction were performed to elucidate the drug–silica interactions and the host properties that control 5-FU drug adsorption on β-cristobalite (1 1 1) Hydroxylated Surface. This study shows that hydrogen bonding, electron exchange, and dispersion forces are mainly involved to perform the 5-FU adsorption onto silica. This phenomenon, revealed by favorable energies, results in optimum four adsorption geometries that can be adopted for 5-FU on the Hydroxylated silica Surface. Silanols are weakening in response to the molecule approach and establish H-bonds with polar groups of 5-FU drug. The final geometry of 5-FU adopted on Hydroxylated silica Surface is the results of H-bonding interactions which stabilize and fix the molecule to the Surface and dispersion forces which approach it toward silica (1 1 1) plane. The level of hydroxylation of the SiO 2 (1 1 1) Surface is reflected by the elevated number of hydrogen bonds that play a significant role in the adsorption mechanisms.
