Hygro-responsive membranes for effective oil–water separation

Abstract

There is a critical need for new energy-efficient solutions to separate oil-water mixtures, especially those stabilized by surfactants. Traditional membrane-based separation technologies are energy-intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil-water mixtures. Here we report membranes with hygro-responsive surfaces, which are both superhydrophilic and superoleophobic, in air and under water. our membranes can separate, for the first time, a range of different oil-water mixtures in a singleunit operation, with >99.9% separation efficiency, by using the difference in capillary forces acting on the two phases. our separation methodology is solely gravity-driven and consequently is expected to be highly energy-efficient. We anticipate that our separation methodology will have numerous applications, including the clean-up of oil spills, wastewater treatment, fuel purification and the separation of commercially relevant emulsions.

Ultrafast Oleophobic–Hydrophilic Switching Surfaces for Antifogging, Self-Cleaning, and Oil–Water Separation

“…3,4,5,6,7,8 Existing methods for the removal or collection of oils from an oil-water mixture utilise absorbent materials 9 such as zeolites, 10,11 organoclays, 12 non-woven polypropylene, 13,14 or natural fibres 15 (such as straw, 16 cellulose, 14 or wool 17 ).…”

Highly Polar Linkers (Urea, Carbamate, Thiocarbamate) for Superoleophobic/Superhydrophobic or Oleophobic/Hydrophilic Properties

“…[ 27 ] Kota et al reported also the preparation of superhydrophilic/superoleophobic coatings using fl uorinated polyhedral oligomeric silsesquioxane (POSS) and poly(ethylene glycol) crosslinkers. [ 28 ] Otherwise, hydrophilic/ oleophobic properties were also reported by copolymerization of polymers containing fl uorinated chains and pyridinium groups. [ 32 ] Here, this possibility can be explained by the presence of both oleophobic fl uorinated chains and the most hydrophilic urea linkers (NHCONH).…”

“…Surprisingly, it is also possible to have oil contact angles higher than water contact angles using urea linkers (NHCONH), which is rare in the literature. [27][28][29][30][31][32][33][34][35] In all the examples reported in the literature, there is the presence of both highly oleophobic parts such as fl uorinated materials and highly hydrophilic parts such as charged or highly polar species. For example, the group of Zhang reported the preparation of superhydrophilic/superoleophobic (in air) by mixing poly(diallyldimethylammonium chloride) (PDDA) with sodium perfl uorooctanoate (PFO).…”

“…Here, we show also that some of these monomers can lead to both hydrophilic and oleophobic properties. This unusual surface property is rare in the literature [27][28][29][30][31][32][33][34][35] but possible by combining hydrophilic and oleophobic materials, and can found other applications in oil/water separation, [36][37][38] for example.…”

Superlyophilic Interfaces and Their Applications

“…Kota et al reported hydro-responsive membranes with SHPL and superhydrophobic property both in air and under water, which can be applied for effective oil/water separation. [135] Jiang and co-workers reported a polyacrylamide-coated stainless steel mesh consisting of nanostructured papillae [32] Copyright 2016, Wiley-VCH. d) Schematic diagram illustrating the SLPL 3D interfaces consisting of 1D nanowires.…”