Scalable graphene oxide membranes with tunable water channels and stability for ion rejection

Abstract

Graphene oxide (GO) membranes (GOMs) are robust and demonstrate excellent rejection of ions and are promising for use in water treatment. However, maintaining the stability of GOMs during processing and scale-up is difficult in practice and is somewhat counterintuitive. Herein, we report the synthesis of GOM by the blade casting technique, followed by cation (K⁺, Na⁺, Li⁺, Mg²⁺, Ca²⁺, and Ba²⁺) intercalation, leading to membranes that possess different thicknesses and interlayer spacings. The thickness and interlayer spacing as controlled by different cations were crosschecked after immersion in water and the changes were examined by SEM and XRD. The thickness and interlayer spacing was ultimately dependent on the hydrated radius of the cations and only K⁺, Mg²⁺, Ca²⁺, and Ba²⁺ were able to effectively stabilize GOM. Moreover, GOM with Ca²⁺ (GOM-Ca²⁺), and after reduction (GOM-Ca²⁺-R), was further examined in water, acidic and alkaline solutions to check the stability. The water flux of GOM-K⁺, GOM-Ba²⁺, GOM-Ca²⁺ and GOM-Mg²⁺ was decreased relative to membrane thickness, whereas the rejection % of different ions (Na⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Mg²⁺) was based on the interlayer spacing. Based on these findings, we demonstrate a simple and scalable method to obtain graphene-based membranes with good stability, adjustable thickness and tunable interlayer spacing, thereby eliminating the problems caused by aggregation and functional moieties.