Strengthening cationic repulsion on graphene oxide membrane to boost water desalination

Background

As a hydrophilic two-dimensional material with oxygen-containing groups on its basal planes, graphene oxide (GO) has been used for the fabrication of GO-based membranes to purify/desalinate water. However, promoting salt rejection of GO-based membranes is challenging while maintaining high water permeability.

Methods

First, the mercaptoethylamine-modified Ag NWs (Ag-MA) were prepared by mixing Ag NWs and MA to form Ag—S bonds. Then, Ag-MA was deposited on the GO membrane under externally assisted filtration to achieve the GO/Ag-MA membrane, which ensures the well-stacking of GO sheets and the even coating of GO membrane. Therefore, the delicately fabricated membrane possesses great electropositive cations and high swelling-tolerance in water solution.

Significant findings

We found that a high electrostatic repulsive interaction between the amino group and metal cations in GO/Ag-MA membrane aided the promotion of rejection rates, which was up to 75 % for both K⁺ and Mg²⁺, surpassing that of the previously reported values. This work highlights a new approach for enhancing the electrostatic repulsion with metal cations near the surface/interface of GO-based membranes and their application in the development of water desalination and purification.