Effectively\nSieving Alkali Metal Ions Using Functionalized\nGraphene Oxide Membranes by Exploiting Water-Repellent Interactions

Sieving membranes capable of discerning different alkali\nmetal\nions are important for many technologies, such as energy, environment,\nand life science. Recently, two-dimensional (2D) materials have been\nextensively explored for the creation of sieving membranes with angstrom-scale\nchannels. However, because of the same charge and similar hydrated\nsizes, mostly laminated membranes typically show low selectivity (<10).\nHerein, we report a facile and scalable method for functionalizing\ngraphene oxide (GO) laminates by dually grafting cations and water-repellent\ndimethylsiloxane (DMDMS) molecules to achieve high selectivities of\n∼50 and ∼20 toward the transport of Cs<sup>+</sup>/Li<sup>+</sup> and K<sup>+</sup>/Li<sup>+</sup> ion pairs, surpassing many\nof the state-of-the-art laminated membranes. The enhanced selectivity\nfor alkali metal ions can be credited to a dual impact: (i) strong\nhydrophobic interactions between the incident cations’ hydration\nshells and the water-repellent DMDMS; (ii) the efficient screening\nof electrostatic interactions that hamper selectivity.