Dynamical Properties of Confined Water Nanoclusters: Simulation Study of Hydrated Zeolite NaA: Structural and Vibrational Properties

• Published in: ACS nano Vol. 2; no. 8; pp. 1603 - 1614
• Main Authors: Demontis, Pierfranco, Gulín-González, Jorge, Jobic, Hervé, Masia, Marco, Sale, Roberto, Suffritti, Giuseppe B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.08.2008
• Subjects: Catalysis; Chemical Sciences; Colloids - chemistry; Computer Simulation; Crystallization - methods; Macromolecular Substances - chemistry; Materials Testing; Models, Chemical; Models, Molecular; Molecular Conformation; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology - methods; Particle Size; Surface Properties; Vibration; Water - chemistry; Zeolites - chemistry; molecular sieves; molecular dynamics simulations; zeolites; nanoclusters; confined water
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/nn800303r

Water nanoclusters confined to zeolitic cavities have been extensively investigated by various experimental techniques. We report a series of molecular dynamics simulations at different temperatures and for water nanoclusters of different sizes in order to attempt an atomistic interpretation of the properties of these systems. The cavities of zeolite NaA are spherical in shape and about 1 nm in diameter and can host nanoclusters of water containing nearly up to 24 water molecules. A modified interaction potential, yielding a better reproduction of experimental hydration energy and water diffusivity across a number of different zeolites, is proposed. Molecular dynamics simulations reproduce the known experimental structural features obtained by X-ray diffraction. Variations of simulated vibrational IR and IINS spectra with temperature and size of nanoclusters are in good agreement with experiment. The simulated water nanoclusters in zeolite NaA are found to be too small to crystallize and, at low temperature, behave as amorphous ice, in agreement with recent experimental results for similar water nanoclusters in reverse micelles.