The Ionic Composition and Chemistry of Nanopore-Confined Solutions

Abstract

There is increasing interest in understanding the properties of solutions confined within nanotubes and synthetic or biological nanopores. How the ionic content of a nanopore-confined solution differs from that of a contacting bulk salt solution is of particular importance, for example, to water desalinization, industrial electrolysis, and all living systems. This paper explores ionic content, ionic interactions, and ion-transport properties of solutions confined within the 10 nm diameter pores of a synthetic polymer membrane. The membrane has a fixed negative pore-wall and surface charge due to ionizable carbonate groups. As a result, under some conditions, the nanopore-confined solution contains only cations and no anions or salt present in a contacting solution, ideal cation permselectivity. This anion- and salt-rejecting ability varies greatly with the cation of the salt, a result that is in contradiction to the prevailing model for permselectivity in nanopores. The extant model fails because it does not account for specific chemical interactions between the cation and the carbonate groups. The nature of these ion-selective interactions is discussed here.

Thermodynamics of Charge Regulation during Ion Transport through Silica Nanochannels

“…However, we note that eq represents all ions as point charges, making C critical independent of specific ion identity when comparing 1:1 monovalent salts. This has recently been contradicted experimentally as C critical was found to vary over 10-fold when comparing the Nernstian behavior of 1:1 monovalent salts in negatively charged polycarbonate membranes …”

“…This has recently been contradicted experimentally as C critical was found to vary over 10-fold when comparing the Nernstian behavior of 1:1 monovalent salts in negatively charged polycarbonate membranes. 39 C critical presented in this study should therefore only be considered a rough approximation for the point of EDL overlap.…”

Nanoscale Pore–Pore Coupling Effect on Ion Transport through Ordered Porous Monolayers

“…The impact of the pore–pore coupling effect on the selectivity or electroneutrality recovery is still elusive and needs deep exploration when the screening length decreases sharply under high salinity concentration. On the other hand, Ma et al found an obvious ion mobility reduction at high electrolyte concentrations, because of the enhanced ion–ion and ion–water correlations within nanopores. , Moreover, the ion pairing between soluble ions with specific groups attached to the membrane surface should also be considered especially under high concentrations; i.e., a different ion-pairing strength for the monovalent cation, Cs + < K + < Na + < Li + , was observed in a carbonate group decorated porous polymer membrane with pore size of 10 nm …”

“…49,50 Moreover, the ion pairing between soluble ions with specific groups attached to the membrane surface should also be considered especially under high concentrations; i.e., a different ion-pairing strength for the monovalent cation, Cs + < K + < Na + < Li + , was observed in a carbonate group decorated porous polymer membrane with pore size of 10 nm. 51 Not only the ions but also the fluid transport behavior at the nanoscale confinement depart in many aspects from the continuum model, and most behaviors still lack proper explanation. For example, hydrodynamic interactions between adjacent pores at the micrometer scale have been observed to increase the flow rate of individual pore.…”

The Enhancing Ionic Current Rectification in Single Graphene Conical Nanochannel

“…Nanochannels fabricated by polymer materials have been identified as a promising candidate to simulate the ionic transport in biological systems, and various applications proposed. [1][2][3][4][5] Due to the strong ion selectivity and ionic current rectification (ICR), synthetic nanochannels have broad foreground and practical value in energy conversion, [6,7] DNA sequencing, [8,9] water desalination, [10] and ionic gates. [3,11] However, due to the characteristics and defects of polymer nanochannels, there are still some problems in the application of polymer nanochannels.…”