Tailored Graphene Oxide Membranes for the Separation of Ions and Molecules

Graphene oxide (GO) membranes, with 2D nanochannels and peculiar permeation performance, are promising nanobarriers for ion and molecule separations. However, practical applications have been challenged by dramatic deterioration in mechanical durability, structural stability, and sieving ability under aqueous solution. Thus, the enhancement of stability while maintaining species sieving under aqueous conditions is a key topic of GO-based membrane research. Herein, the functionalization of GO membranes was investigated by combining imidazolium complexation with electron beam irradiation to enhance membrane stability in aqueous solution, which included improvements in mechanical strength and suppression of interlayer spacing (d-spacing) of GO laminates in aqueous solution. Here, 1-allyl-3-vinylimidazolium chloride ([AVIM]Cl) was first used to complex with GO sheets and were subsequently covalently bonded onto adjacent GO sheets by electron beam irradiation. It was found that prepared GO-hybrid membranes could withstand 15.9 kPa of hydrostatic pressure and that d-spacing enlargement after water immersion was effectively suppressed, compared to original GO membranes. In addition, the properties of GO hybrid membranes were easily controlled via the mass ratio of [AVIM]Cl/GO in the mixed GO dispersions and the absorbed dose and dose rate of electron beam irradiation. Permeation results revealed that electrostatic repulsion between imidazolium cation and metal ions had a crucial influence on metal ion permeation through GO-hybrid membranes. The well-confined d-spacing in the wet state made the resultant membranes completely sieve out species with hydrated diameters >0.99 nm. This study confirmed that imidazolium-complexation coupling with electron beam irradiation was effective for tailoring GO membranes with enhanced mechanical durability and controlled d-spacing, which benefitted its applications for ion and molecule separations in aqueous solution.