Graphene has potential applications in many fields. In particular, two-dimensional graphene nanochannels assembled from graphene sheets can be used for filtration and separation. In this work, molecular dynamics simulations were performed to investigate the microscopic structural and dynamical properties of water molecules confined in pristine and hydroxyl-modified graphene slit pores with widths of 0.6-1.5 nm. The simulation results indicate that water molecules have layered structure distributions within the graphene nanoscale channels. The special ordered ring structure can be formed for water confined in the subnanometer pores (0.6-0.8 nm). Graphene surfaces are able to induce distinctive molecular interfacial orientations of water molecules. In the graphene slits, the diffusion of water molecules was slower than that in bulk water, and the hydroxyl-modified graphene pores could lead to more reduced water diffusion ability. For the hydroxyl-modified graphene pores, water molecules spontaneously permeated into the 0.6 nm slit pore. According to the simulation results, the dynamic behavior of confined water is associated with the ordered water structures confined within the graphene-based nanochannels. These simulation results will be helpful in understanding the penetration mechanism of water molecules through graphene nanochannels, and will provide a guide for designing graphene-based membrane structures.
Received: 26 November 2014
Published: 01 June 2015
Fig 1 Configuration of the simulation system (a) the pristine graphene slits; (b) the hydroxyl modified graphene slits; (c) the hydroxyl arrangement on the graphene surface; H: slit pore width
εii/(J · mol-1)
Cg: carbon atom in the pristine graphene, Ch: carbon atom connected with hydroxyl group in modified graphene, Oh: oxygen atom in hydroxyl group, Hh: hydrogen atom in hydroxyl group, Ow: oxygen atom in water, Hw: hydrogen atom in water
Table 1Force field parameters used in the simulation
Fig 2 Changes of number of water molecules over time inside slit pores (a) the pristine graphene slit pores; (b) the hydroxyl modified graphene slit pores
Fig 3 Density profiles along the z-axis and the configurations inside the slit pores for confined water molecules (a) the density profile for the pristine graphene slit pores; (b) the density profile for the hydroxyl modified graphene slit pores; (c) the configuration of confined water inside the pristine graphene slit pores with width of 0.7 nm; (d-f) the configurations of confined water inside the hydroxyl modified graphene slit pores with widths of 0.6, 0.7, 0.8 nm, respectively.
Fig 4 Lateral radial distribution function (gO-O(r)) for the water molecules adjacent to the graphene wall in different slit pores (a) the pristine graphene slit pores; (b) the hydroxyl modified graphene slit pores
Fig 5 Orientation angle (φ, ψ) distributions of confined water molecules (a, b) the pristine graphene slit pores; (c, d) the hydroxyl modified graphene slit pores
Fig 6 (a, b) Mean square displacement of xy plane (MSDxy ) for several typical water molecules in different confinement environments and bulk phase; (c, d) trajectories of the confined water molecules along the z-axis (a, c) the pristine graphene slit pores; (b, d) the hydroxyl modified graphene slit pores
Fig 7 (a, b) Average number of hydrogen bond profiles along the z axis for water inside slit pores; (c, d) the intermittent time correlation function (CHB(t)) for the H2O-H2O hydrogen bond numbers inside the nanochannnel as well as bulk water (a, c) the pristine graphene slit pores; (b, d) the hydroxyl modified graphene slit pores
Pan Y. S. ; Birkedal H. ; Pattison P. ; Brown D. ; Chapuis G. J. Phys. Chem. B 2004, 108 (20), 6458.
Newsome D. A. ; Sholl D. S. J. Phys. Chem. B 2005, 109 (15), 7239.
Milischuk A. A. ; Ladanyi B. M. J. Chem. Phys 2011, 135 (17), 174709.
Qiao, Y.; Xu, X.; Li, H. Appl. Phys. Lett. 2013, 103 (23), 233106. doi: 10.1063/1.4839255
Han S. ; Choi M. Y. ; Kumar P. ; Stanley H. E. Nat. Phys 2010, 6 (9), 685.
Du F. ; Qu L. T. ; Xia Z. H. ; Feng L. F. ; Dai L. M. Langmuir 2011, 27 (13), 8437.
Strauss I. ; Chan H. ; Král P. J. Am. Chem. Soc 2014, 136 (4), 1170.
Cicero, G.; Grossman, J. C.; Schwegler, E.; Gygi, F.; Galli, G. J. Am. Chem. Soc. 2008, 130 (6), 1871. doi: 10.1021/ja074418+
Thomas J. A. ; McGaughey A. J. H. Nano Lett 2008, 8 (9), 2788.
Mashl R. J. ; Joseph S. ; Aluru N. R. ; Jakobsson E. Nano Lett 2003, 3 (5), 589.
Liu Y. C. ; Wang Q. ; Lü L. H. ; Zhang L. Z. Acta Phys. -Chim. Sin 2005, 21 (1), 63.
刘迎春; 王琦; 吕玲红; 章连众. 物理化学学报, 2005, 21 (1), 63.
Iiyama T. ; Nishikawa K. ; Otowa T. ; Kaneko K. J. Phys. Chem 1995, 99 (25), 10075.
Koga K. ; Gao G. T. ; Tanaka H. ; Zeng X. C. Nature 2001, 412 (6849), 802.
Stoller M. D. ; Park S. ; Zhu Y. W. ; An J. H. ; Ruoff R. S. Nano Lett 2008, 8 (10), 3498.
Chandra V. ; Park J. ; Chun Y. ; Lee J. W. ; Hwang I. C. ; Kim K. S. ACS Nano 2010, 4 (7), 3979.
Zhang H. ; Lv X. J. ; Li Y. M. ; Wang Y. ; Li J. H. ACS Nano 2010, 4 (1), 380.
Cohen-Tanugi D. ; Grossman J. C. Nano Lett 2012, 12 (7), 3602.