Shanghai Applied Radiation Institute, Shanghai University, Shanghai 200444, China.
Division of Interfacial Water, Key Laboratory of Interfacial Physics and Technology and Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
Nature. 2017 Oct 19;550(7676):380-383. doi: 10.1038/nature24044. Epub 2017 Oct 9.
Graphene oxide membranes-partially oxidized, stacked sheets of graphene-can provide ultrathin, high-flux and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution. These materials have shown potential in a variety of applications, including water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike the pores of carbon nanotube membranes, which have fixed sizes, the pores of graphene oxide membranes-that is, the interlayer spacing between graphene oxide sheets (a sheet is a single flake inside the membrane)-are of variable size. Furthermore, it is difficult to reduce the interlayer spacing sufficiently to exclude small ions and to maintain this spacing against the tendency of graphene oxide membranes to swell when immersed in aqueous solution. These challenges hinder the potential ion filtration applications of graphene oxide membranes. Here we demonstrate cationic control of the interlayer spacing of graphene oxide membranes with ångström precision using K, Na, Ca, Li or Mg ions. Moreover, membrane spacings controlled by one type of cation can efficiently and selectively exclude other cations that have larger hydrated volumes. First-principles calculations and ultraviolet absorption spectroscopy reveal that the location of the most stable cation adsorption is where oxide groups and aromatic rings coexist. Previous density functional theory computations show that other cations (Fe, Co, Cu, Cd, Cr and Pb) should have a much stronger cation-π interaction with the graphene sheet than Na has, suggesting that other ions could be used to produce a wider range of interlayer spacings.
氧化石墨烯膜——部分氧化的堆叠石墨烯片——可以为水溶液中的精确离子和分子筛分提供超薄、高通量和节能的膜。这些材料在各种应用中显示出了潜力，包括海水淡化和净化、气体和离子分离、生物传感器、质子导体、基于锂的电池和超级电容器。与具有固定尺寸的碳纳米管膜的孔不同，氧化石墨烯膜的孔——即氧化石墨烯片之间的层间距（膜中的一个片是单个薄片）——的尺寸是可变的。此外，很难将层间距充分减小到足以排斥小离子，并在氧化石墨烯膜浸入水溶液时保持这种间距，因为氧化石墨烯膜有膨胀的趋势。这些挑战阻碍了氧化石墨烯膜在潜在的离子过滤应用中的发展。在这里，我们使用 K、Na、Ca、Li 或 Mg 离子，以 Ångström 的精度展示了对氧化石墨烯膜的层间距的阳离子控制。此外，由一种类型的阳离子控制的膜间距可以有效地和选择性地排斥具有较大水合体积的其他阳离子。第一性原理计算和紫外吸收光谱揭示了最稳定的阳离子吸附位置是氧化物基团和芳环共存的位置。以前的密度泛函理论计算表明，其他阳离子（Fe、Co、Cu、Cd、Cr 和 Pb）与石墨烯片之间的阳离子-π 相互作用应该比 Na 强得多，这表明其他离子可以用来产生更广泛的层间距。
