Hydrogel network of polyvinyl alcohol (PVA), pyrogallol (PG) and Fe(III) for building superhydrophilic PVDF membrane

High hydrophobicity of polyvinylidene fluoride (PVDF) membrane surface results in adsorption of oil droplets and membrane fouling. A hydrogel coating with crosslinking network of polyvinyl alcohol (PVA), pyrogallol (PG) and Fe(III) based on PVDF membrane was proposed. Hydrogen bonds between PVA and PG in water were regulated by ethanol to form a uniform hydrophilic hydrogel coating on PVDF membrane. Chelation between PG and Fe3+ significantly enhanced hydrogel adhesion. The surface energy of the developed PVDF-PVA/PG-Fe3+ membrane was 39.96 mJ·m-2, 2.71 times that of the pristine PVDF membrane, while its adhesion to oil is close to 0 μN. The permeate flux reached 1341 L·m−2· h−1 at 0.1 bar for separating isooctane-in-water emulsions with good separation efficiency (>99%) and cycling stability. The developed membrane could also effectively separate petroleum ether-in-water and dodecane-in-water emulsions.