Design of a Janus F-TiO₂@PPS Porous Membrane with Asymmetric Wettability for Switchable Oil/Water Separation

Abstract

Extremely asymmetric wettability, high wetting selectivity, instantaneous superwetting behaviors (low transmembrane resistance), and superior resistance to chemicals and solvents are needed for Janus membranes for switchable oil/water separation. However, it is still challenging to obtain Janus membranes with such properties. In this study, a surface with metastable hydrophobicity is constructed on one side of the chemically stable superhydrophilic TiO 2 @PPS membrane by adjusting the hydrophobization depth and the morphology of the hydrophobic layer via a water−oil interfacial grafting. The prepared Janus membrane exhibits a high water contact angle difference of ∼150°between its two surfaces with maintaining the superior penetrability of the original membrane, which makes it capable to separate both oil-in-water and waterin-oil emulsions with high fluxes and accuracy. The separation efficiency is higher than 98% for the separation of the two kinds of emulsions. The fluxes of the surfactant-free toluene-in-water and water-in-toluene emulsions are up to 6.4 × 10 2 and 9.5 × 10 2 L m −2 h −1 , respectively. Furthermore, the Janus membrane exhibits desirable antifouling performance and reusability during usage.

Alkyl Chain Grafted-Reduced Graphene Oxide Membrane for Effective Separation of Water/Alcohol Miscible Mixtures

“…However, complicated processes are required in the pervaporation, such as vacuum equipment and heating and cooling devices. Previously, membrane-based separation for oil/water mixtures via direct filtration has been extensively reported by Jiang (Qu et al, 2019), Seeger (Chu et al, 2015), Tuteja (Tuteja et al, 2007;Kota et al, 2012), and others (Cao et al, 2019;Wang et al, 2019;Yang et al, 2019). Our group has also demonstrated a pH responsive coating and self-healing electrospun membrane for the separation of oil and water mixtures (Dang et al, 2016;Fang et al, 2016).…”

Asymmetric Surface Engineering for Janus Membranes

“…In this way, the modification depth could be controlled to some extent via the deposition time. [ 49 ] The modifiers used for the single‐side interface‐confined modification include dopamine, [ 49–59 ] hydroxyapatite, [ 60 ] catechol, [ 61 ] starch paste, [ 62 ] KOH solution, [ 63,64 ] 1H,1H,2H,2H‐perfluorodecyltriethoxysilane, [ 65 ] octadecylamine, [ 66 ] fluoropolymer emulsion foam, [ 67 ] paraffin, [ 68 ] polydimethylsiloxane, [ 69 ] and TiO 2 nanoparticle slurry. [ 70 ] Note that the prerequisite of this method is that the membrane surface should be nonwettable to the modifier solution for ensuring a nonuniform modification.…”

“…[ 70 ] Note that the prerequisite of this method is that the membrane surface should be nonwettable to the modifier solution for ensuring a nonuniform modification. [ 49–70 ] It is thus not suitable for the wettable system because the modification solution would easily penetrate through membrane pores due to capillary effect, leading to an indiscriminate decoration on both sides. This substrate‐dependent issue could be addressed to some extent through the single‐side spraying technique.…”

“…As the liquid gradually diffuses along the membrane pores, it has been found that the modification thickness is increased over time. [ 49,50,52,65,66,103,104 ] However, the reproducibility of the thickness control is relatively low and the exact relationship between the modification depth and time is still unclear. For the energy irradiation induced postmodification, the energy gradient along the membrane thickness would be easily disturbed by intrinsic properties of membrane such as transparency, refractive index, pore morphology, and porosity, reducing the controllability on the modification depth.…”

“…Accordingly, the combination of thick lyophilic layer and thin lyophobic layer is able to achieve a rapid one‐way delivery of liquid. Such particular gating property has endowed Janus membranes with competitive advantages in the applications of liquid manipulation, including oil collection, [ 29,40,49,53,106,107 ] oil−water separation, [ 34,37–39,44,46,54,59,65,69,100,108 ] fog harvesting, [ 16,20,32,78,82,85,88 ] and biofluid management. [ 22,23,25,35,36,60 ]…”