Superhydrophilic Electrospun Polyamide-Imide Membranes for Efficient Oil/Water Separation under Gravity

The efficient separation of oil/water mixtures by membrane technology is highly dependent on the performance of membrane materials. The emergence of electrospinning has opened up opportunities for designing super porous structures with excellent oil/water separation efficiency. Herein, we prepared electrospun nanofibrous membranes using a highly hydrophilic and thermomechanically stable polyamide-imide (PAI) polymers. The fabricated membranes by a set of optimized electrospinning processes were examined in the gravity-driven separation of various oil/water emulsions. The effect of polymer concentration on fiber diameter and porosity of membranes was evaluated. It was observed that increasing the PAI concentration in the electrospinning dope resulted in the fabrication of membranes with larger fibers and a larger pore size. The fiber diameter and thus, the porosity and pore size of the membrane influenced the flux and separation efficiency during filtration. The membrane with a 12% PAI concentration (EM1) showed a lower flux, whereas the 21% PAI membrane (EM4) offered a higher flux but lower separation efficiency. The membranes exhibited excellent underwater antioil adhesion behavior by completely repelling n-hexane, mineral oil, n-hexadecane, and gasoline droplets from their prewetted surfaces. Compared to other membranes, the 15% PAI membrane (EM2) was found to strike a balance between water flux and oil rejection while also exhibiting strong resistance to oil fouling, as evidenced by its relatively lower flux decline (FD) and higher flux recovery ratio (FRR) when filtering various emulsions. The EM2 membrane demonstrated an excellent pure water flux of 800 to 900 L/m2 h (LMH) and an emulsion flux of 380 to 410 LMH. The FRR and oil rejection of the membrane were 91–97 and >99%, respectively. Moreover, the prepared membrane was stable at pH 3 to 9 with a consistent separation performance. The EM2 membrane was also utilized for n-hexane/water emulsion separation in cyclic tests and provided stable oil rejection and FRR after 10 cycles, demonstrating the high potential of this membrane in real oil/water emulsion separation processes.