Unveiling the importance of surface ionization on desalination and ion-sieving performance of graphene oxide membranes

Abstract

The experimental results have confirmed the negative surface charge of graphene oxide (GO) membranes. However, little work considered the influences of surface ionization on the performance of GO-based desalination or ion-sieving membranes. In this work, the surface charge of GO was included to explore its effects on the desalination performance adopting molecular dynamics (MD) simulation methods. The MD results indicated the enhanced interactions between GO nanochannel and water as well as ions with the increase in surface charge density. Consequently, the water flux enhanced but the ion rejection rate decreased with the increase in surface charge density. We further explored the influences of intercalated cations on the comprehensive desalination performance of GO membranes. The simulation results turned out that the performance of GO nanochannel was optimized at an appropriate interlayer distance. Among all the investigated cases, GO nanochannel intercalated with Mg2+ possesses the best desalination performance. It was found that surface charge density exerted little effect on optimizing the Li+/Mg2+ separation performance. However, Li+/Mg2+ separation performance could be optimized by narrowing the interlayer distance of GO nanochannel. The revealed mechanisms in this work might provide useful suggestions for designing strategies for nanosheet-based membranes to achieve better desalination and ion-sieving performance.