2D nanoporous membrane for cation removal from water: Effects of ionic valence, membrane hydrophobicity, and pore size.

Using molecular dynamic simulations, we show that single-layers of molybdenum disulfide (MoS2) and graphene can effectively reject ions and allow high water permeability. Solutions of water and three cations with different valencies (Na+, Zn2+, and Fe3+) were investigated in the presence of the two types of membranes, and the results indicate a high dependence of the ion rejection on the cation charge. The associative characteristic of ferric chloride leads to a high rate of ion rejection by both nanopores, while the monovalent sodium chloride induces lower rejection rates. Particularly, MoS2 shows 100% of Fe3+ rejection for all pore sizes and applied pressures. On the other hand, the water permeation does not vary with the cation valence, having dependence only with the nanopore geometric and chemical characteristics. This study helps us to understand the fluid transport through a nanoporous membrane, essential for the development of new technologies for the removal of pollutants from water.

Breakdown of the Stokes-Einstein water transport through narrow hydrophobic nanotubes.

In this paper the transport properties of water confined inside hydrophobic and hydrophilic nanotubes are compared for different nanotube radii and densities. While for wider nanotubes the nature of the wall plays no relevant role in the water mobility, for small nanotubes the hydrophobic confinement presents a peculiar behavior. As the density is increased the viscosity shows a huge increase associated with a small increase in the diffusion coefficient. This breakdown in the Stokes-Einstein relation for diffusion and viscosity was observed in the hydrophobic, but not in the hydrophilic nanotubes. The mechanism underlying this behavior is explained in terms of the structure of water under confinement. This result indicates that some of the features observed for water inside hydrophobic carbon nanotubes cannot be observed in other nanopores.

Stability, and optical and electronic properties of ultrathin h-BNC.

Spin polarized density functional theory has been used to study the stability, and electronic and optical properties when BN nanodomains are embedded in graphene and carbon patches are embedded in a single layer of h-BN forming h-BNC nanosystems. Our results show that graphene doped with BN nanodomains exhibits a non-zero gap, which depends on the nanodomain's shape and width. For h-BN with C domains we observe that we can tune the h-BN gap into the visible region, making the h-BNC a promising material for catalysis using solar energy. Furthermore, n-type and p-type semiconductors can be obtained by controlling the bond (C-N or C-B) in the border of the domain. These findings open the possibility to use h-BNC nanosheets for future applications in photocatalysis and optoelectronic devices.