Ion Selectivity of Graphene Nanopores
Figure 1: Experimental setup* [Reprinted with permission from AAAS]
As population growth continues to outpace development of water infrastructure in many countries, desalination (the removal of salts from seawater) at high energy efficiency will likely become a vital source of fresh water. Due to its atomic thinness combined with its mechanical strength, porous graphene may be particularly well-suited for electrodialysis desalination, in which ions are removed under an electric field via ion-selective pores.
Harvard Physics Associate Ryan Rollings, Aaron T. Kuan from SEAS, and Prof. Jene Golovchenko show in a new Nature Communications article* that single graphene nanopores preferentially permit the passage of K+ cations over Cl− anions with selectivity ratios of over 100, and conduct monovalent cations up to 5 times more rapidly than divalent cations. Surprisingly, the observed K+/Cl− selectivity persists in pores even as large as about 20 nm in diameter, suggesting that high throughput, highly selective graphene electrodialysis membranes can be fabricated without the need for subnanometer control over pore size.
*See: R.C. Rollings, A.T. Kuan & J.A. Golovchenko, "From Ion selectivity of graphene nanopores," Nature Communications 7: 11408 | doi:10.1038/ncomms11408