A self-assembled FeNPs/metal polyphenol structured superhydrophilic PVDF membrane with capability to activate PMS for efficient oil-water separation

Despite the membrane technology as an efficient method for treating emulsified oily wastewater, the issue of membrane fouling remains an enormous challenge during extended operation. Hence, a unique self-assembled method was proposed to clean membrane fouling for oil/water (O/W) separation, where the tannic acid/iron (TA/Fe) coating layer improved hydrophilicity and doped with iron nanoparticles to activate peroxymonosulfate (PMS) for removing of the irreversible oil fouling. The TA/Fe coating, which contained phenolic hydroxyl groups, rendered the modified membrane superhydrophilic and underwater oleophobic properties to resist membrane surface oil droplets. The iron nanoparticles/TA/polyvinylidene fluoride (FeNPs/TA/PVDF) achieved notable permeation flux of 1571.13 L m-2 h-1 and 1490 L m-2 h-1 in O/W mixture and oil-in-water emulsion (liquid paraffin as oil phase), respectively. Meanwhile, the membrane exhibited a distinguished oil removal rate, surpassing 98% for various emulsions (e.g. N-hexane, isooctane, soybean oil). Notably, in the pollution and cyclic experiments, the regeneration water flux of FeNPs/TA/PVDF increased from 71.7% of pristine PVDF to 91.5% after final modification, which proved the enhancement of the membrane anti-oil-fouling capability through the deposition of the hydrophilic coating. Moreover, after catalytic cleaning, the water permeation flux of FeNPs/TA/PVDF could reach approximately 90% of its original value. Obviously, we observed that FeNPs/TA/PVDF exhibited a high regenerative capacity during the PMS-assisted catalytic cleaning process, where the radical and nonradical pathways coexisted. Generally, the research offered a simple approach to creating functional membranes suitable for efficient O/W separation.