Fabrication of a superhydrophilic PVDF membrane with excellent chemical and mechanical stability for highly efficient emulsion separation

The separation and recovery of oil from oily wastewater was still challenging due to the limitations of conventional separation techniques in its limited application fields, high operation cost and low separation efficiency. Membrane separation was a novel candidate to satisfy various separation tasks. Seeking for an efficient and facile strategy to manipulate the membrane performance was urgently needed. Chinese ink was a promising material to functionalize the membrane by virtue of the self-adhesion and intrinsic hydrophilicity. Herein, a composite polyvinylidene fluoride (PVDF) microfiltration membrane was fabricated via a facile rub-coating strategy. The micro/nano structures derived from the nanoparticles in Chinese ink readily facilitated the membrane with the superhydrophilicity and underwater superoleophobicity (underwater various oils contact angle above 150°, underwater dichloromethane roll off angle ~ 3°). The composite membrane exhibited a high permeation flux, a considerable separation efficiency for separating various oil-in-water emulsions and a superior recyclability for separating gasoline-in-water emulsion in ten cycles. Moreover, the membrane maintained a desirable underwater dichloromethane contact angle (above 145°) after respectively being immersed in pH = 1 HCl, pH = 13 NaOH and 3.5 wt% NaCl solutions for one week, and a sandpaper abrasion test, demonstrating an excellent chemical stability and a robust mechanical durability.