Structure and mobility of water confined in AlPO4-54 nanotubes

Abstract

We performed molecular dynamics simulations of water confined within AlPO-54 nanotubes. AlPO-54 is an artificial material made of AlO and of PO in tetrahedra arranged in a periodic structure forming pores of approximately 1.3 nm in diameter. This makes AlPO-54 an excellent candidate for practical applications, such as for water filtration and desalination. In this work, the structural and dynamical properties of the confined water are analyzed for various temperatures and water loadings. We find that the water structure is controlled by the heterogeneity of the nanopore surface with the water molecules located preferentially next to the surface of oxygens of AlPO-54; consequently, at very low densities, water forms helicoidal structures in string-like arrangements.

Self-diffusion coefficient of bulk and confined water: a critical review of classical molecular simulation studies

“…Data are also available for theoretical confining media and some less frequently used materials, which are summarized in this section. Other confining materials with available selfdiffusion coefficient data are ionomers (Berrod et al, [260]), aluminum phosphate nanotubes (Gavazzoni et al, [261]), polyamide RO membranes (Ding et al, [262]), boron nitride nanotubes (Won and Aluru [263]), and surfactants such as Newton Black films (Di Napoli and Gamba, [264]).…”

Water Freezing in MoS2 Nanotubes

“…Experimental studies have demonstrated heterogeneous water dynamics inside aluminophosphate (AlPO 4 ) NTs, with the water structure controlled mainly by the pore’s surface heterogeneity . In a recent molecular dynamics (MD) study on the anomalous diffusion of water confined in AlPO 4 NTs, we have found that water molecules moved preferentially next to the oxygen sites at the nanotube surface; consequently, helicoidal structures were shown at very low densities with mobility increasing with density. Interestingly, Zang and colleagues have shown different diffusion of water through aluminosilicate (AlSi) NTs in comparison with other hydrogen-bonded liquids (methanol and ethanol), which highlights the peculiarities of water transport through heterogeneous nanopores.…”

Different Water Networks Confined in Unidirectional Hydrophilic Nanopores and Transitions with Temperature

“…Water confined in the nanopores of hydrophilic AlPO 4 -54· x H 2 O has been the subject of several recent studies involving variable pressure–temperature conditions. − AlPO 4 -54· x H 2 O (hexagonal VFI structure, space group P 6 3 , a = 18.9678(13) Å and c = 8.0997(4) Å, Al 18 P 18 O 72 · x H 2 O) exhibits highly hydrophilic one-dimensional (1D) pores along the c direction, with a diameter of 12.7 Å, which are among the largest pores known for zeolites and aluminophosphates. In the pores, H 2 O molecules form a disordered hydrogen-bonded network at ambient temperature and pressure.…”