A special underoil superhydrophilic (UOSHL) membrane: Growing of copper phosphate (Cu3(PO4)2) nanosheet to achieve self-cleaning and efficient oil-water separation

Due to the high surface tension of water, underoil superhydrophilic surfaces are usually difficult to obtain. But some sarcocarps such as apple and pear are found to possess the special underwater superhydrophilic property. Some previous studies have demonstrated that hydrophilic groups may contribute to durable superhydrophilicity. Among the hydrophilic head group in the sarcocarp’s cell membrane, we believe that the strong hydrophilicity of phosphate may play an important role in this property. Inspired by this special property of some sarcocarp like apple and pear, the phosphate was used as a key factor in constructing the underoil superhydrophilic surfaces. Herein, with a substrate of stainless steel mesh (SSM), we reported a simple electrochemical method to construct mesh membrane made of cupric phosphate (Cu3(PO4)2) nanosheets (denoted as SSM-Cu3(PO4)2). The similar wetting of the sarcocarp and membranes was systematically studied. Then the ability of the membrane to separate oil-in-water emulsions and water-in-oil emulsions is determined by COD and Karl Fischer, respectively. Finally, the self-cleaning, anti-oil-fouling and recyclability of the membrane is explored. The membrane exhibits an outstanding underoil superhydrophilic(UOSHL) and underwater superoleophobic(UWOHB) property similar to the sarcocarps. And the membrane exhibits an excellent anti-oil-fouling and self-cleaning property due to the UWOHB property. Simultaneously, the SSM-Cu3(PO4)2 membrane with adaptable wettability can realize the on-demand separation of water-in-oil emulsion and oil-in-water emulsion with the separation efficiency higher than 99%. The superior anti-oil-fouling property, self-cleaning property, environmentally friendly and easily scaled-up preparation process of the membrane exhibits great potentials in separating water-oil emulsion. And the adding of phosphate could be extended to other surface need to achieve UOSHL property. The phosphate may provide an excellent method on combination of underoil superhydrophilic and underwater superoleophobic property and promote the preparation of oil-water separation materials with self-cleaning and anti-oil-fouling properties.