The precise regulation of the graphene oxide film layer spacing is the key to its application in water treatment, ion/molecule separation, and battery/capacitor fields. However, it is a challenging task to accurately "bind" graphene oxide nanosheets into graphene oxide film and fix the interlayer spacing.

　　The precise control of the graphene oxide film layer spacing is the key to its application in water treatment, ion/molecule separation, and battery/capacitor fields. However, it is a challenging task to accurately "bind" graphene oxide nanosheets into graphene oxide film and fix the interlayer spacing. With funding from the National Natural Science Foundation of China (project numbers: 11290164, 41430644, 21490585, 11574339, 11404361, 21476107, 11722548), Fang Haiping, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Wu Minghong, Shanghai University, Jin Wanqin, Nanjing University of Technology, and Zhejiang Agriculture and Forestry University Scholars have cooperated in many ways to propose and realize the precise regulation of the interlayer spacing of the graphene oxide film by the hydrated ion itself. The membrane exhibits excellent ion screening and seawater desalination performance. Related work titled "IonSievinginGrapheneOxideMembranesviaCationicControlofInterlayerSpacing" (cationic control of graphene oxide membrane spacing for ion sieving) was published online on October 9 in Nature. Original link:

　　Fang Haiping’s team proposed that the ions in the solution themselves can effectively control the interlayer spacing of the graphene oxide film, and perform corresponding theoretical simulation calculations. They used Shanghai Light Source's small-angle X-ray scattering (BL16B1), fine absorption spectroscopy (BL14W1), and ultraviolet characterization methods to confirm the existence of hydrated ion-π interactions between the ions and the aromatic rings in the graphene sheet. This interaction supports the graphene oxide sheet layers like "bridge piers", and hydrated ions of different sizes are equivalent to "bridge piers" of different sizes, which can precisely control the layer spacing. Wu Minghong's team successfully realized through experiments and observed the specific interlayer spacing between the graphene oxide film and different ionic solutions. The spacing can be as small as about one nanometer, and the difference in the interlayer spacing after the interaction of different ions is on the order of angstroms. Jin Wanqin's team designed and prepared a series of graphene oxide composite membranes supported by porous ceramics controlled by hydrate ions to achieve precise screening of different ions. For potassium ions with the smallest hydration diameter, since the hydration layer of potassium ions is weak, the hydration layer deforms after entering the graphene oxide film, resulting in extremely small interlayer spacing. In this way, the graphene oxide membrane immersed in the potassium ion solution can effectively intercept all ions in the salt solution, including the potassium ions themselves, but can still effectively pass water molecules. This research not only provides theoretical and technical guidance for the design and preparation of graphene oxide membranes, but also opens up new ideas for the research of other two-dimensional materials in the field of separation membranes.