We report the molecular dynamics simulations of spontaneous and continuous permeation of water molecules through a single-layer graphyne-3 membrane. We found that the graphyne-3 membrane is more permeable to water molecules than (5, 5) carbon nanotube membranes of similar pore diameter. The remarkable hydraulic permeability of the single-layer graphyne-3 membrane is attributed to the hydrogen bond formation, which connects the water molecules on both sides of the monolayer graphyne-3 membrane and aids to overcome the resistance of the nanopores, and to the relatively lower energy barrier at the pore entrance. Consequently, the single-layer graphyne-3 membrane has a great potential for application as membranes for desalination of sea water, filtration of polluted water, etc.

We perform molecular dynamics simulations to demonstrate that when a nanodroplet is confined inside a carbon nanotube (CNT), unidirectional motion can be created by a nonzero surface energy gradient. It is found that the water nanodroplet moves along the direction of increasing surface energy. The transportation efficiency of the water nanodroplet is found to be dependent on the surface energy gradient; environmental temperature; and the flexibility, diameter, and defectiveness of the CNT. It is shown that higher surface energy gradient, the smaller diameter of the CNT, and fewer defects promote higher transportation efficiency. However, when the temperature is too high or too low, the water transport across the CNT is impeded. Except for the initial stage at the relatively low environmental temperature, higher flexibility of the CNT wall reduces the transportation efficiency. It is also found that the hydrogen bonds of water molecules play a role in the dynamic acceleration process with a wavelike feature. The present work provides insight for the development of CNT devices for applications such as drug delivery, nanopumps, chemical process control, and molecular medicine.

We propose a novel nanoscale design for unidirectional transport of water molecules through a single-walled carbon nanotube (SWCNT). This is achieved by using a vibration charge and a composite SWCNT with asymmetrical surface energy. With the proposed system, we demonstrated, using molecular dynamics simulations, that a continuous unidirectional water flow can be driven by a vibration charge without osmotic pressure or a drop in hydrostatic pressure. It is shown that the net flux of continuous unidirectional water flow can be controlled by adjusting the parameters of periodic vibration charge, temperature, and the degree of heterogeneity in surface energy. The remarkable net flux was the combined effect of the kinetic energy provided by the vibration charge, and the water density gradient resulted from the heterogeneous surface energy of the SWCNT. The present nanoscale design can efficiently convert the energy of vibration charges to the transport of water molecules. It may find applications in liquid circulation without a pressure gradient, lab-on-a-chip technology, desalination of sea water, filtration of polluted water, etc.