(385g) Solvation and Solubility of Ions in Nanopore

Molecular dynamics simulations have been used to investigate the effect of confinement on solvation (hydration shell) and solubility of electrolyte solutions (NaCl) confined in nanopores. The co-ordination number and solubility of NaCl in water confined in graphitic slit nanopores ranging from 8-20 Angstroms(Å) in width is investigated. A similar study is also conducted in a 27 Angstrom(Å) diameter single wall carbon nanotube (SWCNT). The solubility limit is defined at the concentration when a discontinuous decrease in the hydration number and ion-water radial distribution functions is observed due to ion pairing. Results show a significant effect of confinement on the solubility of NaCl ; dropping by almost a factor of 2 in the 8 Angstrom(Å) slit pore and the 27 Angstrom(Å) SWCNT. A sharp increase in solubility is observed in the slit nanopore, as the pore width is increased. These changes in solubility are rationalized with the structuring and layering of water in the nanopore. With advances in technology, this study is relevant to our understanding of ions in biological systems and transport of electrolytes in nano-devices.