Tannic acid-based complex coating modified membranes with photo-Fenton self-cleaning property for sustainable oil-in-water emulsion separation

The separation of oil-in-water emulsions containing surfactants has been a challenge in the field of water purification. The main reason limiting the use of membrane separation technology for emulsions is the reduction in flux due to membrane fouling. Introducing photo-Fenton self-cleaning reaction into membrane filtration to reduce the adverse effects of membrane fouling represents a promising direction in membrane fields. In this study, a two-step immersion method was used to prepare tannic acid (TA)-Fe(III) as a composite coating on a pristine polyvinylidene fluoride (PVDF) membrane, and then HPO42- was added to the coating, which greatly improved the hydrophilicity and compactness of the coating. The resulting membrane had separation fluxes of more than 1500 L m-2 h−1 for various oil-in-water emulsions at a transmembrane pressure of 0.1 bar, and the carbon content of all filtrates was less than 50 ppm. The prepared membranes exhibit satisfactory antifouling ability. After 50 min of continuous high-efficiency separation, the membrane undergoes a photo-Fenton reaction under ultraviolet light to restore the original wettability and flux. After 5 self-cleaning cycles, it can still recover to 96.96% of the original flux. The high permeation and excellent self-cleaning property of the PVDF/TA-Fe(III)-HPO4 membrane manifest its attractive potential application in water purification.