Nature-inspired construction of poly (vinylidene fluoride) membranes through the coordination coating of tannic acid with copper ions for oil-in-water emulsions separation

Construction of the separation membranes with underwater super-oleophobic property proposes a promising pathway in the field of oily wastewater treatment, but it is still plagued with the bottlenecks of the time-consuming preparation and the unsatisfied stability of resultant membranes. Herein, the alkali induced hy-droxylation and the nature-inspired construction through the coordination coating of copper ions with tannic acid (Cu2+/TA) were performed on the poly (vinylidene fluoride) (PVDF) membrane substrate prepared by the thermally induced phase separation (TIPS). The introduced hydroxyl groups resulted from the membrane hy-droxylation is beneficial for the subsequent construction of the Cu2+/TA coordination coating layer. The excellent hydrophilicity and the specifically hierarchical roughness of the immobilized coating layer endow the modified membranes with the hydrophilic/underwater super-oleophobic property. The optimized membrane correspondingly showed the improved flux of around 2000 L m - 2 center dot h- 1accompanied with the oil rejection of above 97.0% in treating two simulated oil-in-water emulsions (toluene and n-hexane). Besides, the flux recovery ratio increased from 72.4% of the pristine membrane to 93.3% of the modified membrane after the BSA fouling and regeneration test, which is also indicative of the improved antifouling behavior as a result of the hydrophilic coordination coating. The membrane stability was further demonstrated by the results of the sandpaper abrasion -resisting test and the long-term (up to 6 months) air-exposure treatment. This work might provide a straight-forward strategy for designing advanced membrane for the large-scale applications of oil/water separation.