In situ construction of chemically heterogeneous hydrogel surfaces toward near-zero-flux-decline membranes for oil-water separation

Construction of zero-flux-decline membrane surfaces with superior antifouling properties is in great demand for the treatment of oil-water mixture. Inspired by nature, simultaneously incorporating hydrophilic and low-surface-energy groups to form a chemically heterogeneous hydrogel surface holds great promise. In this study, membranes with heterogeneous hydrogel surfaces were fabricated through a one-step reaction enhanced surface segregation method. In details, we synthesized a fluorine-containing copolymer as the modifier in casting solution, and designed tannic acid (TA) aqueous solution as the coagulation bath. During non-solvent induced phase separation, TA can in situ crosslink the modifier at the water-polymer interface through hydrogen bonds, forming a heterogeneous hydrogel layer over the membrane surface. Meanwhile, the hydrophilicity of TA rendered the hydrogel underwater superoleophobic properties. The thickness and chemical composition of the hydrogel layer were facilely manipulated by varying the TA concentration. To our surprise, the unique physicochemical characteristics of heterogeneous hydrogel layer greatly fortified the antifouling mechanisms on membrane surfaces, rendering the membrane zero-flux-decline feature with a flux of 330 L m−2 h−1 at 0.05 MPa during a 60-h cross-flow filtration of five different oil-in-water emulsions.