Superoleophilic, Mechanically Strong Electrospun Membranes for Fast and Efficient Gravity-Driven Oil/Water Separation

Abstract

Separating oil–water mixtures is a common obstacle in many processes from wastewater treatment to biofuel manufacture to cleanup of oil spills. There is an urgent need for new, fast, and simple technologies for such separations. In this work, we describe a simple and practical route for creating superoleophilic electrospun membranes that are capable of selectively passing oil and organic compounds at very high rates in a gravity-driven system while retaining water. To prepare these membranes, we blended a new, highly fluorinated random copolymer (FCP), poly­(methyl methacrylate-random-perfluorodecyl methacrylate), P­(MMA-r-FDMA), with the commodity polymer poly­(vinylidene fluoride) (PVDF) and prepared electrospun membranes from their mixture. Membranes composed of nonwoven fibers with uniform and bead-free morphology were obtained upon electrospinning of PVDF blended with this FCP. The PMMA segments provided anchors to the PVDF matrix, resulting in significant enhancement in the mechanical properties with up to 7 times higher Young’s modulus for the blend membranes. Moreover, the self-organization of the long, pendant FDMA side groups within the PVDF matrix resulted in fluorine-rich, highly hydrophobic and superoleophilic surface. As a result, the FCP-containing membranes exhibited up to 17 times faster permeation of oil and organic solvent, compared with pure PVDF membrane in gravity-driven filtration experiments. Their performance was highly stable during a 70 min continuous gravity-driven filtration experiment for oil/water separation, reflecting their excellent fouling resistant properties. This easy-to-implement and cost-effective approach, combined with the high porosity and re-entrant structure created by the electrospinning, can create membranes with excellent mechanical properties and fouling resistance.

Thermal properties and structure of electrospun blends of PVDF with a fluorinated copolymer

“…This surface effect may be the reason for the observed contact angle decrease, despite the high level of fluorination. As presented in our recent complementary publication on the oil–water separation and fouling resistant performance of these membranes, contact angle tests performed with oil droplets show that the membranes modified with FCP exhibit superoleophilicity with oil contact angles <1°.…”

“…Contact angle testing shows that the addition of FCP increases the water contact angle of the fibers, indicating greater hydrophobicity. In a complementary publication, the performance of these electrospun fiber membranes in oil–water separation applications has been reported to be excellent . These two publications report the complete first findings on the synthesis, structure and physical properties, and excellent performance of this novel, highly FCP and its blends with PVDF.…”

“…The copolymer composition was characterized using proton nuclear magnetic resonance ( 1 H‐NMR) spectroscopy using a Bruker Avance III 500 spectrometer (Bruker Optics Inc., Billerica, MA). The copolymer composition was found to be 68/32 w/w MMA/FDMA, which was quite close to the nominal composition.…”

“…Our team has recently reported the copolymer synthesis, performance, and fouling resistance of these membranes . However, detailed structure and thermal properties of PVDF/P(MMA‐ r ‐PFDMA) blends have not been reported.…”

Free-Standing Sodium Titanate Ultralong Nanotube Membrane with Oil-Water Separation, Self-Cleaning, and Photocatalysis Properties

“…But when the aging time is 14 h, the contact angle decreases. Because with the increase of aging time, MTMS gel with poor fluidity forms, which leads to the uneven surface of the F-60 membrane (Additional file 1: Figure S3) and the decrease of contact angle [37]. The aging times range between 10 and 12 h are suitable for obtaining a hydrophobic membrane.…”