Polyphenol mediated α-FeOOH/g-C3N4 heterojunction membrane for fast purification of surfactant-stabilized O/W emulsions with super-wetting and Photo-Fenton self-cleaning functions

In the practical purification of oily wastewater, the application of polymer-based membrane is greatly restricted due to the oil adhesion and complicated fouling problems. Herein, to conquer the aforementioned challenges, we prepared the polyphenol mediated Photo-Fenton self-cleaning and superhydrophilic/underwater superoleophobic alpha-FeOOH/g-C3N4@PVDF composite membrane via simple vacuum-assisted self-assembly technology. The g-C3N4 nanosheets modified by tannic acid were introduced into the surface of PVDF ultrafiltration membrane, in which the intercalation structure was regulated by the random interpenetration of alpha-FeOOH nanorods. The abundant hydroxyl and amino groups and the rough micro-nano structure formed by intercalation structure were favorable for the superhydrophilic feature (WCA = 0 degrees, UOCA>150 degrees), thus resulting in ultra-low oil adhesion. Specially, the intercalation structure improved the water permeation channel, further promoting the water/oil separation flux. Therefore, the composite membrane exhibited superior separation flux (452.35-650.21 L m(-2) h(-1)) and separation efficiency (>99.06 %) for various surfactant-stabilized emulsions. Moreover, thanks to the Photo-Fenton reaction, the composite membrane showed excellent degradation efficiency on simulated pollutants (various dyes) within 60 min (MeB: 95.55 %, CR: 90.83 %, MO: 98.90 %, CV: 95.11 %), showing satisfactory photocatalytic self-cleaning performance. This work provides a strategy for the potential application of polymer-based membranes in the treatment of complex surfactant-stabilized emulsion wastewater from petrochemical industry.