Bio-inspired surface engineering of hydrophobic membranes with nano-structured hydrogel toward viscous oil-in-water emulsion separation

•The process for constructing nanostructured hydrogel is simple and time-saving (<10 min)•The method is green and mild, without cumbersome surface activation process.•Nanostructure is generated by in-situ growth, without adding extra nanomaterials.•The strategy can transform various hydrophobic membranes into superhydrophilic ones.•The resultant membrane exhibits excellent anti-crude oil-adhesion property.