Water confinement in nanoporous silica materials

Abstract

The influence of the surface polarity of cylindrical silica nanopores and the presence of Na(+) ions as compensating charges on the structure and dynamics of confined water has been investigated by molecular dynamics simulations. A comparison between three different matrixes has been included: a protonated nanopore (PP, with SiOH groups), a deprotonated material (DP, with negatively charged surface groups), and a compensated-charge framework (CC, with sodium cations compensating the negative surface charge). The structure of water inside the different pores shows significant differences in terms of layer organization and hydrogen bonding network. Inside the CC pore the innermost layer is lost to be replaced by a quasi bulk phase. The electrostatic field generated by the DP pore is felt from the surface to the centre of pore leading to a strong orientation of water molecules even in the central part of the pore. Water dynamics inside both the PP and DP pores shows significant differences with respect to the CC pore in which the sub-diffusive regime of water is lost for a superdiffusive regime.

On the structure and rejection of ions by a polyamide membrane in pressure-driven molecular dynamics simulations

“…Indeed, it offers unique opportunities to connect some macroscopic properties to a microscopic description of the physical phenomena involved in the separation. Although MD has been already applied to investigate both water and ion transports through nanopores with well-defined geometries [12][13][14][15][16][17][18], the limited information about the three-dimensional molecular structure of RO polyamide membranes makes the use of this computational method much more challenging. As a result, the identification and the understanding at a microscopic level of the underlying mechanisms governing water and ion transport through RO membranes are proceeding very slowly and only few studies reported on the attempt of building full atomistic models of RO polyamide membranes [19][20][21][22][23][24][25].…”

Hydrogen bond analysis of confined water in mesoporous silica using the reactive force field

“…35 g OH (r)r 2 dr . (9) g OH (r) in Eq. 9 is calculated for oxygen atoms in each layer with a width of 1.0 A.…”

“…The behavior of confined water has been widely studied by both theoretical [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and experimental [26][27][28][29][30][31] techniques in the past few decades. These works have indicated that the properties of confined water may strongly differ from that of bulk water depending on surface properties and size of confinement space.…”

The behaviour of water and sodium chloride solution confined into asbestos nanotube

“…However, just a few publications give some results on orientational behaviour of confined water [17,21,22].…”

“…However, in this case, mostly silica pores were considered (see e.g. [15][16][17]), although some other confining substances were investigated too (e.g. in [18], water confined in porous AlPO 4 was studied).…”