Construction of two dimensional anion exchange membranes to boost acid recovery performances

Currently, the development of two dimensional (2D) lamellar membranes for acid recovery via the diffusion dialysis process is still in its infancy. In this work, we proposed the concept of 2D anion exchange membranes (AEMs) to synergistically improve the H+ dialysis coefficient and separation factor. The 2D AEMs were fabricated by layer by layer stacking the graphene oxide nanosheets decorated by imidazolium cations (Im-GO). Benefitting from the attachment of imidazolium cations, the Im-GO membrane exhibits higher hydrophilicity and wider interlayer channels compared with the original GO membrane, favorable of quicker H+ migration. Additionally, imidazolium cations serving as typical anion exchange sites help with rapid H+ transfer and better distinguishing H+ and Fe2+ via the electrostatic exclusion mechanism. The diffusion dialysis results show that the acid dialysis coefficients gained by Im-GO (5.9 × 10−3- 8.2 × 10−3 m h−1) are an order of magnitude higher than GO (0.7× 10−3 m h−1). Ideally, Im-GO also gives rise to higher separation factors (24–37) toward H+ and Fe2+ than GO (15). Moreover, after 10 times continuing acid recovery testing, Im-GO demonstrates no declines of dialysis coefficients and separation factors. We believe the engineering strategy reported here could act as a versatile method for modifying 2D membranes, to further extend their usage scope.