Preparation and wetting properties of graphene-based

In recent years, Janus membrane, whose one side is hydrophilic and the other is hydrophobic, has attracted much attention due to its special properties. Janus membrane is generally composited by hydrophobic material and hydrophilic material, while it has the defects of low interfacial bonding strength and irreversible conversion. In this study, a graphene-based Janus membrane with different wettability properties on both sides was prepared, whose hydrophobic surface could be reversibly transformed into super-hydrophilic surface. First, the graphene oxide (GO)/diphenyl ether system was treated with high-speed shear to prepare stabilized Pickering emulsion, and the emulsion was lyophilized and reduced with hydrogen iodide (HI) to fabricate graphene-based hydrophobic material with bowl-shaped and thin-walled spherical shell structure. Then, oxygen functional groups, such as COOH, C=O and C-O, were attached to one side of the membrane by means of plasma treatment, so the hydrophobic graphene-based membrane was transformed into the super-wettable Janus membrane with different wettability properties on both sides, and the super-hydrophilic surface could be restored to hydrophobic surface by electric Joule heat treatment. Finally, the stability of the hydrophilic-hydrophobic conversion was tested by static contact angle, and the dynamic spreading process of water droplet on the graphene-based Janus membrane was recorded via a high-speed video camera. Results show that it cost 10 s to change the hydrophobic graphene-based membrane into the super-hydrophilic under plasma treatment, and the hydrophilic-hydrophobic conversion was completed in 8 s under DC voltage (20 V). After 10 cycles of hydrophilic-hydrophobic conversion, the hydrophilicity contact angle remained 0° and the hydrophobicity contact angle was 152°. It only took 20 ms for the water droplet to complete the spreading process on the hydrophilic surface of the graphene-based membrane. The chemical functional groups of the material were analyzed by XPS, and the microstructure was characterized by SEM and TEM. The structure of bowl-shaped spherical micro shell connected by the holes in the wall was the key to fulfill the hydrophilic-hydrophobic conversion of the material under plasma treatment and electric Joule heat treatment, and the pure graphene component was the base of the two treatments. Copyright ©2022 Journal of Harbin Institute of Technology.All rights reserved.