Dynamic Properties of Water Confined in Graphene-Based Membrane: A Classical Molecular Dynamics Simulation Study

Abstract

We performed molecular dynamics simulations of water molecules inside a hydrophobic membrane composed of stacked graphene sheets. By decreasing the density of water molecules inside the membrane, we observed that water molecules form a droplet through a hydrogen bond with each other in the hydrophobic environment that stacked graphene sheets create. We found that the water droplet translates as a whole body rather than a dissipate. The translational diffusion coefficient along the graphene surface increases as the number of water molecules in the droplet decreases, because the bigger water droplet has a stronger van der Waals interaction with the graphene surface that hampers the translational motion. We also observed a longer hydrogen bond lifetime as the density of water decreased, because the hydrophobic environment limits the libration motion of the water molecules. We also calculated the reorientational correlation time of the water molecules, and we found that the rotational motion of confined water inside the membrane is anisotropic and the reorientational correlation time of confined water is slower than that of bulk water. In addition, we employed steered molecular dynamics simulations for guiding the target molecule, and measured the free energy profile of water and ion penetration through the interstice between graphene sheets. The free energy profile of penetration revealed that the optimum interlayer distance for desalination is ~10 Å, where the minimum distance for water penetration is 7 Å. With a 7 Å interlayer distance between the graphene sheets, water molecules are stabilized inside the interlayer space because of the van der Waals interaction with the graphene sheets where sodium and chloride ions suffer from a 3–8 kcal/mol energy barrier for penetration. We believe that our simulation results would be a significant contribution for designing a new graphene-based membrane for desalination.

Terahertz-Light Induced Structural Transition and Superpermeation of Confined Monolayer Water

“…The structural and dynamic properties of water at interfaces and under nanoscale confinement have been proven to be considerably different from those of bulk water. − Under ambient conditions, a quasi-two-dimensional (2D) ice phase of confined monolayer water (2D confined water, labeled 2DCW) was observed between graphene-based membranes with an interlayer spacing of 6 Å ≤ d < 10 Å, , as well as in the vicinity of biological macromolecules − and natural solid substrates. , Surprisingly, the permeability of 2DCW across graphene-based membranes is a thousand times higher than that of water across existing commercial membranes . As a result, the fast permeation of 2DCW will save a considerable amount of energy if applied to seawater desalination and water purification .…”

“…As a result, the fast permeation of 2DCW will save a considerable amount of energy if applied to seawater desalination and water purification . More encouragingly, the van der Waals assembly of the membranes allows the creation of artificial capillaries with angstrom-scale accuracy, which is capable of excluding ions and amenable to industrial-scale production. ,− Therefore, the excellent performance of 2DCW combined with graphene-based membranes has aroused widespread interest in research − and shows promise for achieving the aspirational goal of replicating the aquaporin function for efficient desalination. − …”

“…14,15 Surprisingly, the permeability of 2DCW across graphene-based membranes is a thousand times higher than that of water across existing commercial membranes. 16 As a result, the fast permeation of 2DCW will save a considerable amount of energy if applied to seawater desalination and water purification. 17 More encouragingly, the van der Waals assembly of the membranes allows the creation of artificial capillaries with angstrom-scale accuracy, which is capable of excluding ions and amenable to industrial-scale production.…”

Heavy Metals Nanofiltration Using Nanotube and Electric Field by Molecular Dynamics

“…This block reduces the flow of matter and reduces the life of the membrane, requiring mechanical or chemical cleaning [75,76]. The separation process combined with the addition of an adjustable EF to the NF membrane was first investigated and denoted as electron filtration (EFT) [77] and brings together two driving forces: pressure and EF used mainly for the separation of charged molecules or particles electrically [78]. EFT works by trapping contaminants loaded in the membrane pores with the help of EF.…”

Density functional theory and molecular dynamics simulation of water molecules confined between parallel graphene oxide surfaces using new interaction potentials

“…We will consider the hydration level of 23.3% water and the interlayer spacing of 11 Å in this work. Lee [15] studied dynamics behavior of water and ions between GO surfaces using MD simulations. He used GO surfaces with different spacing and found that the self-diffusion coefficient of water decreases as the distance between the GO surfaces decreases.…”