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.
Separation of emulsified water/oil mixtures is a worldwide concern. However, poor chemical and solvent resistance of general polymeric membranes limit these membranes for application in the separation process. In this study, a poly(phenylene sulfide) (PPS) porous membrane with a rough concave topographic feature was fabricated, which exhibited excellent superoleophilicity and under-oil superhydrophobicity. The membrane is capable of separating both surfactant-free and surfactant-stabilized emulsions with a high flux. All of the water contents of the treated oils were below 300 ppm. The excellent water resistance property and cycling performance support the PPS membrane displaying an excellent reusability. Additionally, this PPS membrane was also certified to be used in strong solvents for a long time. In conclusion, the successful application of the thermally induced phase separation (TIPS) method may provide a new approach to fabricate the PPS membrane and improve its properties, and the application of the PPS membrane to separate water-in-oil emulsions is promising in practical applications.
Covalent organic frameworks (COFs) have been widely used in catalysis, energy storage, environmental protection, and separation. However, they require a long assembly period (∼3 days) and complex synthesis conditions; differences in water resistance have restricted their overall versatility. In this paper, the preparation of COF-DhaTab was optimized, and this process can be easily performed in air. Thus, it is feasible for the scale-up of COF-DhaTab in the near future. The superhydrophobic properties of COF-DhaTab (water contact angle, >150°) can be created by regulating the wettability of COF-DhaTab by grafting fluoride. When the grafting degree of fluoride increased to 4.32%, the water contact angle of COFs increased from 0°to more than 150°. The grafted COFs are termed COF-DhaTab fluoride (COF-DTF). The chemically modified COF-DhaTab maintains its original porosity and crystallinity. The superhydrophobic COF-DTF can be applied to various substrates, for example, foam, fabric, and glass. These all exhibit outstanding water repellency, self-healing, and excellent self-cleaning. Importantly, the coating maintains its original superhydrophobicity even under extremely acidic/basic conditions (pH = 1−14) and toward boiling water (100 °C). Furthermore, COF-DTF displays long-term stability and is easily scaled. It is a promising and practical candidate for hydrophobic modifications to various substrates.
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