Gradient Adhesive Hydrogel Decorated Superhydrophilic Membranes for Ultra‐Stable Oil/Water Separation

Abstract Hydrogels are excellent for protecting membranes from oil fouling for oil/water separation. However, conventional hydrogels including adhesive hydrogels have a contradictory between high adhesion on membranes and anti‐oil‐fouling ability. Herein, the design of an adhesive hydrogel on membranes is proposed by ingeniously integrating high adhesion on membranes, outstanding anti‐oil‐fouling ability, ultrathin thickness suitable for membrane decoration and satisfactory durability, where an inside‐out gradient distribution of adhesive protocatechuic acid (PCA) and hydrated calcium alginate (CaAlg) on membranes is constructed. The innermost PCA enables the adhesive hydrogel to tightly adhere to the membranes. The outermost CaAlg defends membranes from oil fouling. The gradient distribution and uniform integration of PCA/CaAlg guarantee an excellent stability. Membranes decorated with the adhesive hydrogel demonstrate superhydrophilicity, anti‐fouling to various oils, and anti‐abrasion to external damaging. The membranes achieve ultra‐stable and efficient separation of surfactant‐stabilized oil‐in‐water emulsions and crude oil/water mixture with the most advanced cycling ability of ≈100% flux recovery and nearly zero irreversible oil fouling. This study provides a new strategy for designing anti‐oil‐fouling membranes toward practical oil/water separation applications.