Molecularly grafted PVDF membranes with in-air superamphiphilicity and underwater superoleophobicity for oil/water separation

Microporous polyvinylidene fluoride (PVDF) based membranes are widely used in separation and purification applications, including oil/water separation. However, due to hydrophobic nature, these membranes are prone to high fouling and wetting by low surface tension liquids and substances, thereby limiting its full potential in many important applications such as oil/water separation. Herein, we present a simple and straight forward method to modify and produce in-air superamphiphilic and under-water superoleophobic PVDF membranes by molecular grafting using three different amino silanes. The molecular grafting imparted novel properties due to the combined effect of chemistry, nanostructuring, and roughness. After grafting, the membranes exhibited in-air superamphiphilicity in both dry and wet conditions. In water, the membrane does not allow the attachment of oil droplets, making it superoleophobic. However, when placed under oil, the membrane showed superhydrophobicity but still allowed the adhesion of water droplets. After thorough characterization for structure, modification, and physicochemical properties, the membranes were tested for oil/water mixture separation. The functionalized membranes showed > 99% oil rejection and flux recovery. These results showed great promise for molecular grafting of membranes for separation and purification applications.