Structure and Dynamics of Confined Water in AlPO₄-5 Zeolite

Abstract

The structural and dynamic properties of confined water in AlPO 4 -5 zeolite (Ø ) 7.3 Å) have been investigated by neutron scattering experiments during the adsorption process. Our aim is to elucidate the peculiar behavior of confined water at the nanoscopic confinement range. Confined water presents unusual properties in comparison with other sorbate species such as deuterium or methane. Even in the nanoporous diameter range, the water sorption phenomenon looks like the so-called "capillary condensation" phase transition or the "drywet" transition. Furthermore, the sorbed water quantity in AlPO 4 -5 channels is exceptionally large. Our structural and dynamic results clearly show that the so-called "capillary condensation" step observed in the sorption isotherm is the signature of a crystallization phenomenon at room temperature (T ) 300 K). It corresponds to the growth of two helices of ice of high density (d ) 1.2) that is driven by structural commensurability with the AlPO 4 -5 channel structure.

Confinement effects on water structure in membrane lyotropic phases

“…At such mesoscopic scale, numerous studies have shown that the structure and the physical properties of confined liquids in cavities differ strikingly from the bulk system [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The experiments on the confinement of water or associated liquid such as alcohol in mesoporous materials (aerogels, controlled pore glass, MCM-41.…”

“…Numerous investigations have been devoted on the understanding of confined water and other liquids into mesoporous materials such as MCM-41, Vycor, clay and porous silicon [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These studies have revealed effects of confinement which affect both the structure and dynamics of the confined system of which properties differ strictly from these-ones of bulk liquid [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Surfactant systems self assemble into a variety of structures which present particular organizations of the membranes and provide model system to host small or significant amounts of water for mimic confinement in biological objects [1,[19][20][21][22].…”

Insights into Structure Direction of Microporous Aluminophosphates: Competition between Organic Molecules and Water

“…The sorption and structure of water molecules in calcined microporous aluminophosphates have been widely studied; [14][15][16] it was found that water molecules adopt interesting helicoidal structures with double (in AlPO-5 [17] ) or triple (in VPI-5 [18,19] ) water helices, stabilised by H-bond networks. However, these structural studies usually considered adsorption of water in the structures in post-synthetic steps (after calcination of the SDA molecules used to obtain the microporous material).…”

Adsorption Property of Water Vapor on AlPO₄-5 Synthesized from Aluminum Dross

“…12,14) It is considered that H 2 O molecules are adsorbed in the pore of AlPO 4 -5 and the water vapor adsorption increases sharply at the P/P 0 = 0.25 because of the strong interaction between H 2 O molecules in the AlPO 4 -5 pore due to the hydrogen bond. 8) Adsorption isotherms of water vapor in the aluminum dross-derived AlPO 4 -5 are shown in Figs. 8, 9 and 10.…”