Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, CAS, Shanghai 201800, China.
Phys Chem Chem Phys. 2019 Apr 3;21(14):7623-7629. doi: 10.1039/c8cp07837h.
Recently, we have demonstrated that highly efficient ion rejection by graphene oxide membranes can be facilely achieved using hydrated cations to control the interlayer spacing in GO membranes. By using density functional theory calculations, we have shown that different hydrated cations can also precisely control the interlayer spacings between graphene sheets, which are smaller than graphene oxide sheets; this indicates ion sieving. The interlayer distances are 9.35, 8.96 and 8.82 Å for hydrated Li+, Na+ and K+, respectively. Since the radii of the hydrated Na+ and Li+ ions are larger than that of hydrated K+, graphene membranes controlled by the hydrated K+ ion can exclude K+ and the other two cations with larger hydrated volumes. Further analysis of charge transfer and orbit analysis showed that this type of control by the hydrated cations is attributed to the strong hydrated cation-π interactions; moreover, when soaked in a salt solution, graphene membranes adsorb hydrated Na+ and Li+ and form intercalation compounds. However, it is hard to find K-doped intercalation compounds in the inner part of graphene.
最近，我们已经证明，通过使用水合阳离子来控制 GO 膜的层间距，可以轻松实现氧化石墨烯膜的高效离子排斥。通过使用密度泛函理论计算，我们已经表明，不同的水合阳离子也可以精确控制石墨烯片之间的层间距，其小于氧化石墨烯片的层间距；这表明了离子筛分。水合 Li+、Na+ 和 K+的层间距离分别为 9.35、8.96 和 8.82 Å。由于水合 Na+ 和 Li+离子的半径大于水合 K+离子的半径，因此由水合 K+离子控制的石墨烯膜可以排除 K+和其他两种具有较大水合体积的阳离子。进一步的电荷转移和轨道分析表明，这种由水合阳离子控制的方式归因于强的水合阳离子-π 相互作用；此外，当浸泡在盐溶液中时，石墨烯膜吸附水合的 Na+和 Li+并形成插层化合物。然而，在石墨烯的内部很难找到 K 掺杂的插层化合物。
