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UID:5504-1569335400-1569340800@www.is2m.uha.fr
SUMMARY:Séminaire Diane Rebiscoul  (CEA ICSM)
DESCRIPTION:The role of nanoconfinement on water properties and specific ion\neffects on the evolution of porous silica\nProcesses taken place at the solid/aqueous solution interface have a strong impact on\nthe evolution of materials in the fields of construction\, environment\, geochemistry\, membranes\,\ncatalysis\, and nuclear wastes. Since many materials in these application fields are completely\nor partially nanoporous (cementitious materials\, biominerals\, clay\, secondary minerals…) and\nfilled with aqueous solutions\, the processes and chemical reactions occurring in this\nnanoconfinement has a major impact on the materials evolution on a macroscopic scale. The\nstudy of such processes and chemical reactions occurring in nanometer-sized porosities in\ncontact with aqueous solutions (ions sorption\, electrolyte diffusion\, phase precipitation\, pore\nwall dissolution and the recondensation of dissolved species) is important since it differs from\nthe ones occurring in dense materials. Since water takes part in most of these processes and\nchemical reactions\, the understanding of water molecules behavior in such media is essential to\nbe able to predict the behavior of such materials.\nGenerally\, the macroscopic evolution of materials in solution is described or predicted\nusing modelling. Thermodynamic models and rate laws developed and integrated in computer\nprograms (PHREEQC\, JChess…) generally take into account some data arising from\nmeasurements performed in diluted media (concentration of dissolved ions\, pH\, kinetics and\nthermodynamic constants…). For nanoporous materials\, the validity of these models and rate\nlaws are still not proven yet\, thus prediction can be defective. Indeed\, under confinement and\nin presence of ions\, the water behavior is modified by the strong interactions between the pore\nsurfaces and the ions structuring water\, and slowing down its dynamics/transport from\nnanoscale to macro-scale. Such effects modify the electrostatic interactions in the system and\nthus the ions free energy landscape. Since chemical reactions such as silica\nhydrolysis/recondensation processes are controlled by the solution-silica interfacial layer\, the\nstudy of the modification of this interfacial layer in nanoconfinement is of paramount\nimportance to describe the evolution of nanoporous materials in aqueous solution. In-fine\, this\nwill allow the improvement of the thermodynamic models and rate laws of processes occurring\nin nanoconfinement.\nIn this study\, we investigated the water properties (structure and dynamics) in the\npresence of ions in silica nanoconfinement and relate it to the evolution of silica mesoporous\nmaterials in aqueous solutions. We used an original approach\, consisting in the use of\nelectrolyte solutions having ions with various kosmotropic property XCl2 (X = Ba\, Ca\, Mg)\nconfined in model systems such as two parallel and plane silica surfaces spaced of 3 and 5 nm\n(nanochannels) and highly ordered mesoporous silica materials represented by SBA-15 (6 nm\npore size and microporous pore wall) and MCM-41 (3 nm pore size and dense pore wall).
URL:https://www.is2m.uha.fr/event/seminaire-diane-rebiscoul/
LOCATION:Amphithéâtre 5 de l’ENSCMu
ATTACH;FMTTYPE=image/png:https://www.is2m.uha.fr/wp-content/uploads/2019/09/dianerebiscoul.png
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