Abstract

Abstract Due to highly adhesive property, crude oil is easier to adhere on foul filtration membranes. Separation of crude oil‐in‐water emulsion is a continuing tough work. Hydrogels with low‐adhesive superoleophobicity are ideal materials for modifying filtration membranes to achieve efficient and antifouling separation of crude oil‐in‐water emulsion. A key challenge in fabricating the hydrogel modified filtration membranes is to design an ultrathin hydrogel layer with sufficient anti‐crude‐oil‐fouling ability and with controllable thickness, thus not blocking the micro‐ and nanosized membrane pores. Inspired by the novel harsh‐environment‐tolerant superoleophobicity of alginate‐rich seaweed, the construction of an ultrathin Cu 2+ /alginate hydrogel multilayer with controllable thickness at the nanometer scale on a polymer filtration membrane via a layer‐by‐layer self‐assembly method is achieved. Both the nanosized pores and the high flux of original membrane are well‐maintained. The Cu 2+ /alginate multilayer modified ultrafiltration membrane behaves a biomimetic superhydrophilicity, underwater superoleophobicity, and antifouling ability for crude oil. It is capable of efficiently separating crude oil‐in‐water emulsion with a high water flux of 1230 L m −2 h −1 bar −1 , an ultrahigh efficiency of 99.8%, and an outstanding antifouling and cyclic ability. What's more, the membrane exhibits good salt‐tolerance, antibacterial ability, and long‐term stability.