Electric‐Field‐Induced Ionic Sieving at Planar Graphene Oxide Heterojunctions for Miniaturized Water Desalination

Abstract Layered graphene oxide membranes (GOMs) offer a unique platform for precise sieving of small ions and molecules due to controlled sub‐nanometer‐wide interlayer distance and versatile surface chemistry. Pristine and chemically modified GOMs effectively block organic dyes and nanoparticles, but fail to exclude smaller ions with hydrated diameters less than 9 Å. Toward sieving of small inorganic salt ions, a number of strategies are proposed by reducing the interlayer spacing down to merely several angstroms. However, one critical challenge for such compressed GOMs is the extremely low water flux (<0.1 Lm −2 h −1 bar −1 ) that prevents these innovative nanomaterials from being used in real‐world applications. Here, a planar heterogeneous graphene oxide membrane (PHGOM) with both nearly perfect salt rejection and high water flux is reported. Horizontal ion transport through oppositely charged GO multilayer lateral heterojunction exhibits bi‐unipolar transport behavior, blocking the conduction of both cations and anions. Assisted by a forward electric field, salt concentration is depleted in the near‐neutral transition area of the PHGOM. In this situation, deionized water can be extracted from the depletion zone. Following this mechanism, a high rejection rate of 97.0% for NaCl and water flux of 1529 Lm −2 h −1 bar −1 at the outlet via an inverted T‐shaped water extraction mode are achieved.