Improving ion rejection of graphene oxide conductive membranes by applying electric field

Abstract

The influence of an electric field on graphene oxide (GO) membrane ion rejection rates was investigated. The variation in the rejection rate under unit voltage was used to evaluate the responsiveness of the GO membrane ion rejection rate in relation to an electric field. The results showed that the ratio of cations to anions in the nanochannel was a key factor that controlled the responsiveness to the electric field. The concentration of cations was higher than that of anions near GO flakes because the GO was negatively charged. The responsiveness was 0.62%/V for GO membranes without any membrane reduction, indicating that the rejection of Na2SO4 was enhanced by only 0.62% under a voltage of 1 V. When the GO membrane was partially reduced, the responsiveness increased to 21.83%/V due to the increased wrinkles (roughness), which increased specific capacitance of the membrane. With further reduction, the specific capacitance of the membrane was reduced due to the decreased charge density, leading to an enhanced Donnan effect under electric field. Therefore, the responsiveness decreased to 15.45%/V. These findings provide an effective method to promote ion rejection by regulating the responsiveness of membrane ion rejection to an electric field.