title: Anomalous hydration shell order of Na+ and K+ inside carbon nanotubes.
abstract: We performed molecular dynamics simulations of the hydration of Na+ and K+ in infinitely long single-walled armchair carbon nanotubes (CNTs) at 298 K. Simulation results indicate that the preferential orientation of water molecules in coordination shells of these two cations presents an anomalous change in the CNTs and causes a diameter-dependent variation for the interaction energy between the cation and water molecules in its coordination shell. In the five CNTs of this work, it is energetically favorable for confining a hydrated K+ inside the two narrow CNTs with diameters of 0.60 and 0.73 nm, whereas the situation is reverse inside the wide CNTs with diameters of 0.87, 1.0, and 1.28 nm. This finding is important for CNT applications in ionic systems that control the selectivity and the ionic flow.
authors.affiliation: State Key Laboratory of Materials-oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, People's Republic of China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Shao
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Linghong
authors.initials: L
authors.lastname: Lu
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Lu
authors.forename: Yudan
authors.initials: Y
authors.lastname: Zhu
authors.forename: Shaoyi
authors.initials: S
authors.lastname: Jiang
mesh_terms: D002244:Carbon; D002412:Cations; D003198:Computer Simulation; D007477:Ions; D036103:Nanotechnology / Q000379:methods; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D011188:Potassium / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D002412:Cations; D007477:Ions; D037742:Nanotubes, Carbon; D014867:Water; D002244:Carbon; D012964:Sodium; D011188:Potassium; D010100:Oxygen