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Issue 85, 2017, Issue in Progress
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Desalination by dragging water using a low-energy nano-mechanical device of porous graphene

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Abstract

We propose a nano-structured suction system based on graphene sheets for water desalination processes. The desalination system modeled in this work is an alternative process to the commonly employed but energy intensive reverse osmosis process. The nano-structured system generates drag forces, which pull water molecules from the saline solution into a chamber. Our molecular simulations consist of two rigid walls of graphene: one wall with 5 Å pores permeable to water molecules forms the membrane, while the other wall acts as a plunger to induce and control the transfer of desalinated water molecules, which accumulate in a chamber between the two walls. Prior to the desalination process, the chamber is saturated with one monolayer of water molecules. The desalination occurs when the plunger moves to create unsaturated space inside the chamber. At plunger speeds up to 10 cm s−1, the system desalinates saltwater films in the open part of the membrane. At higher plunger speeds, the desalination chamber expands faster than molecules can fill the chamber, resulting in cavitation and poor desalination. At plunger speeds of 0.5 cm s−1, the desalination occurs via a quasi-equilibrium process, which minimizes the energy necessary to drive desalination. Our findings suggest that the desalination process requires less energy than reverse osmosis methods at plunger speeds up to 0.15 cm s−1 (for the chosen pore density). The filling profile of desalinated water molecules inside the chamber occurs via three distinct regimes: the first two regimes correspond to the formation of one and then two monolayers adsorbed to the chamber's walls. The third regime corresponds to the filling of molecules between the adsorbed layers, which approaches a density close to the density of bulk liquid water. Including flexibility in the graphene sheets does not affect the energy consumption for desalination processes occurring after the formation of the second monolayer, but flexible membranes require a slightly larger pore diameter (7 Å) than rigid membranes.

Graphical abstract: Desalination by dragging water using a low-energy nano-mechanical device of porous graphene

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Publication details

The article was received on 04 Sep 2017, accepted on 14 Nov 2017 and first published on 22 Nov 2017


Article type: Paper
DOI: 10.1039/C7RA09847B
Citation: RSC Adv., 2017,7, 53729-53739
  • Open access: Creative Commons BY license
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    Desalination by dragging water using a low-energy nano-mechanical device of porous graphene

    J. L. Rivera, F. Villanueva-Mejia, P. Navarro-Santos and F. W. Starr, RSC Adv., 2017, 7, 53729
    DOI: 10.1039/C7RA09847B

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