Modulation of cation trans-membrane transport in GO-MoS2 membranes through simultaneous control of interlayer spacing and ion-nanochannel interactions.

ABSTRACT

The interlayer spacing and ion-nanochannel interactions of graphene oxide membranes (GOMs) were simultaneously modulated by thermal reduction and mixing with MoS2 flakes for realizing selective ion separation, which was evaluated by the ratio of ion trans-membrane penetration rates (IPR). The results showed that the ratio of IPRCu2+ to IPRNa+ increased to 1.90 in GOM after thermal reduction for 5 h, which was ∼9.56 times higher than that without thermal reduction, indicating the increase of selectivity of Cu2+ over Na+. This was because the reduction of oxygen-containing groups narrowed the interlayer spacing and moderated the coordination between Cu2+ and sp3 clusters in GO, leading to an enhancement of the size-sieving effect but a decrease in the Cu (II)-nanochannel interaction. Meanwhile, the value of IPRCu2+/IPR Na+ was 0.374 after intercalating MoS2 into GO laminates (GO-MoS2 membrane, GMM), which was ∼1.87 times higher in comparison with that in GOM. This might be because the intercalation of MoS2 narrowed the interlayer spacing, enhanced the size-sieving effect, and strengthened the Na+ ion-nanochannel interactions (cation-π and ion-MoS2 chemical interactions) according to density functional theory calculations. Furthermore, IPRCu2+/IPR Na+ was ∼5.09 in GMM under thermal reduction for 5 h, which was ∼25.5 times higher in comparison with that in GOM without thermal reduction, exhibiting a great enhancement in selectivity for Cu2+. This indicated that thermal reduction and MoS2 intercalation could work in concert to control the size-sieving effect and ion-nanochannel interactions to achieve fine separation of heavy metal ions from main group metal ions.