Molecular grafting and zwitterionization based antifouling and underwater superoleophobic PVDF membranes for oil/water separation

Effective surface modification strategies are at the core of developing efficient and antifouling membranes for a range of separation, purification, and wastewater treatment applications. The inherently hydrophobic nature of most polymeric membranes is one of the primary factors for their high fouling susceptibility. In this work, we have designed a simple and straightforward membrane modification methodology utilizing the reactive nature of polydopamine to molecularly graft short chain amino alkanes followed by zwitterionization using 1,3-propanesultone. The prepared membranes demonstrated superhydrophilicity accompanied with underwater superoleophobicity originating from the hydrophilic nature of polydopamine, aminoalkanes, and strong hydration due to zwitterionic functionality. The surface chemistry, nanostructuring, and surface roughness play an essential role in delivering required properties in the membranes. The prepared membranes showed ultrahigh BSA protein resistance and low oil droplets adhesion. The functionalized membranes showed a manifold boost in permeability for pure water and BSA solution, and separation of oil-water emulsion at high permeation rates. The antifouling nature of the membranes helped in maintaining the permeation behavior for multiple cycles with >96% flux recovery after ten consecutive cycles and excellent rejection in oil-water emulsion separation (>98%). The superwetting properties, along with high permeation, rejection, and antifouling properties, make these membranes a potential candidate for oily water separation and demonstrate the effectiveness of simple molecular level grafting and functionalization as a straightforward method for membrane modifications. [Display omitted] •A simple and straightforward surface modification to effectively control fouling and wetting properties.•Molecular grafting and zwitterionization of aminoalkanes on the polydopamine layer.•The functionalized membranes showed superhydrophilic and underwater superoleophobic properties.•Zwitterionized membranes exhibited strong resistance towards BSA adsorption and oil droplets adhesion.•The zwitterionic membranes showed >96% flux recovery after ten consecutive cycles with >98% oil rejection.