Graphene oxide embedded “three-phase” membrane to beat “trade-off” in acid recovery

The development of polymeric anion exchange membranes (AEMs) for recycling acid is facing a serious difficulty, the desired acid passage and undesired salt leakage dilemma. Ionic domains are the only channels to conduct H+ ions and metallic ions, and thus viable modifications on ionic domains render the permeation of two ions simultaneously enhanced or limited, leading to “trade-off” effect. Herein, we propose an origin strategy of “three-phase” AEMs to beat this “rade-off” effect. Apart from typical hydrophobic polymer backbone and hydrophilic cation phase domains, the auxiliary phase domains built by graphene oxide (GO) sheets were added. Due to the abundant oxygen containing groups distributing on GO, the auxiliary phase domains not only aid to transport H+ ions, but also capture metallic ions. With only 0.5 wt% GO loadings, the “three-phase” AEM increased acid recovery efficiency and separation factor by 40% and 51% for the FeCl2/HCl system respectively, compared with the “two-phase” AEM. To explain these results, density functional theory (DFT) simulation was applied to study the interactions between GO and Fe2+ ions.