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

TL;DR

This study uses molecular dynamics simulations to demonstrate that 2D nanoporous membranes like MoS2 and graphene can effectively reject multivalent ions such as Fe$^{3+}$ while maintaining high water permeability, with rejection rates depending on ion charge and membrane properties.

Contribution

It provides new insights into how ionic valence and membrane characteristics influence ion rejection and water permeability in 2D nanoporous membranes.

Findings

MoS2 membranes achieve 100% Fe$^{3+}$ rejection across pore sizes.

Ion rejection strongly depends on cation charge, especially for multivalent ions.

Water permeability is unaffected by ion valence, depending only on pore geometry and chemistry.

Abstract

Using molecular dynamic simulations we show that single-layers of molybdenum disulfide (MoS$_2$) and graphene can effectively reject ions and allow high water permeability. Solutions of water and three cations with different valence (Na$^+$, Zn$^{2+}$ and Fe$^{3+}$) 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, MoS$_2$ shows 100\% of Fe$^{3+}$ rejection for all pore sizes and applied pressures. On the other hand, the water permeation did not varies with the cation valence, having dependence only with the nanopore geometric and chemical characteristic. This study helps to understand the fluid transport through nanoporous membrane, essential for the development of new technologies for pollutants removal from water.