Potential Dependent Ionic Sieving Through Functionalized Laminar MoS2 Membranes

TL;DR

This study investigates how chemical functionalization affects ion transport in MoS2 membranes, revealing significant permeability reduction and potential for enhanced ion sieving in water treatment applications.

Contribution

It demonstrates that functionalizing MoS2 membranes with a dye drastically reduces ionic permeability and explores the effects of pH, concentration, and ionic properties on selectivity.

Findings

Ionic permeability decreased by over a factor of 10 after functionalization.

Potential-dependent ion transport enables charge selectivity.

Functionalized MoS2 membranes show promise for electro-dialysis and ion exchange.

Abstract

Laminar MoS2 membranes show outstanding potential for practical applications in energy conversion/storage, sensing, and as nanofluidic devices. For water purification technologies, MoS2 membranes can form abundant nanocapillaries from layered stacks of exfoliated MoS2 nanosheets. These MoS2 membranes have previously demonstrated excellent ionic rejection with high water permeation rates, as well as long-term stability with no significant swelling when exposed to aqueous or organic solvents. Chemical modification of these MoS2 membranes has been shown to improve their ionic rejection properties, however the mechanism behind this improvement is not well understood. To elucidate this mechanism we report the potential dependant ion transport through functionalized MoS2 membranes. The ionic permeability of the MoS2 membrane was transformed by chemical functionalization with a simple naphthalene sulfonate dye (sunset yellow) and found to decrease by over a factor of ~10 compared to the pristine MoS2 membranes and those reported for graphene oxide and Ti3C2Tx (MXene) membranes. The effect of pH, solute concentration, and ionic size/charge on the ionic selectivity of the functionalized MoS2 membranes is also reported. The potential dependant study of these dye functionalized MoS2 membranes for ionic sieving with charge selectivity should enable future applications in electro-dialysis and ion exchange for water treatment technologies.