Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (6): 1025-1034.doi: 10.3866/PKU.WHXB201504141


Molecular Dynamics Simulation of Reverse-Osmotic Salt Rejection and Water Transport through Double-Walled Carbon Nanotube

SHEN Zhuang-Lin, HE Gao-Hong, ZHANG Ning, HAO Ce   

  1. School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin 124221, Liaoning Province, P. R. China
  • Received:2014-12-11 Revised:2015-04-13 Published:2015-06-05
  • Contact: ZHANG Ning
  • Supported by:

    The project was supported by the National Natural Science Foundation for Distinguished Young Scholars of China (21125628), Fundamental Research Funds for the Central Universities, China (DUT14RC(3)077) and State Key Laboratory of Fine Chemicals (Panjin) Project, China (JH2014009).


Molecular dynamics simulation was used to study the effect of the outer-wall on water flux in the inner channel by varying the inter-layer spacing of unconventional double-walled carbon nanotube (DWCNT) under reverse-osmosis conditions. Salt rejection and the water transport behavior inside the DWCNT were also examined. In the simulation, 0.5 mol·L-1 NaCl aqueous solution was used to mimic seawater, and the chiral index of the inner-wall was fixed at (8, 8). A constant force on the salt solution produced pressure. Calculation of the number density profile of ions along the DWCNT axis showed that the water could be separated completely from the NaCl aqueous solution in some types of DWCNTs studied. Analyses of the hydrogen-bond lifetime, potential of mean force, and dipole moment distribution of the water molecules inside the DWCNT showed different permeabilities by water molecules and ions. An increase in the inter-layer spacing improved water flow in the DWCNT, which decreased the salt rejection performance. Finally, it was found that DWCNT with an inter-layer spacing of 0.815 nm gave the optimum balance between water flux and salt rejection. This study provides a molecular insight into the use of DWCNT in desalination, and will enable the design of improved reverse-osmosis membranes with high performance in terms of salt rejection and water permeability.

Key words: Double-walled carbon nanotube, Molecular dynamics simulation, Inter-layer spacing, Reverse osmosis, Desalination


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