Abstract
Graphene oxide (GO) membranes have exhibited excellent molecular sieving properties in several areas, such as water treatment and gas separation, but unsatisfactory permeability and/or selectivity for ionic separation. Meanwhile, the instability of pure GO membranes in acidic solution has significantly impeded the ionic sieving applications. In this study, a kind of GO composite membranes (GO-Cu-TAa) with exceptional aqueous stability and superior ionic sieving properties are successfully prepared by employing a unique natural deposition strategy to introduce copper ions and tannic acid (TA). Based on the synergistic effect of the two cross-linking agents of copper ion and TA, the structural stability and ionic sieving performance of GO-Cu-TAa membranes are obviously enhanced. The resultant membrane with 20% TA loading displays excellent ionic sieving performance in a mixed solution containing K+, Mg2+ and Cr3+ three metal cations, and the selectivities of K+/Mg2+ and K+/Cr3+ are 46.43 and 185.32, respectively. Especially, the permeation rate of K+ ion reaches up to 0.75 mol m-2 h-1. Meanwhile, the ionic sieving property of such GO membranes possesses outstanding reusability and long-term stability. Such a membrane can also effectively separate mono-/multivalent metal cations from the mixed solution contained of the nine metal cations. The selectivities of monovalent/divalent metal cations (such as K+/Pb2+, K+/Ca2+, K+/Mg2+) are as high as 7.69–51.49, and those of monovalent/trivalent metal cations (such as K+/Fe3+, K+/Cr3+, K+/Al3+) are as high as 247.62–346.67. These results indicate that the GO-Cu-TAa membranes fabricated by the method of natural deposition strategy are expected to be used in the practical applications of lithium extraction from Salt Lake and wastewater purification, etc.
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