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Owing to its 100% theoretical salt rejection capability, membrane distillation (MD) has emerged as a promising seawater desalination approach to address freshwater scarcity. Ideal MD requires high vapor permeate flux established by cross-membrane temperature gradient (∆T) and excellent membrane durability. However, it’s difficult to maintain constant ∆T owing to inherent heat loss at feedwater side resulting from continuous water-to-vapor transition and prevent wetting transition-induced membrane fouling and scaling. Here, we develop a Ti3C2Tx MXene-engineered membrane that imparts efficient localized photothermal effect and strong water-repellency, achieving significant boost in freshwater production rate and stability. In addition to photothermal effect that circumvents heat loss, high electrically conductive Ti3C2Tx MXene also allows for self-assembly of uniform hierarchical polymeric nanospheres on its surface via electrostatic spraying, transforming intrinsic hydrophilicity into superhydrophobicity. This interfacial engineering renders energy-efficient and hypersaline-stable photothermal membrane distillation with a high water production rate under one sun irradiation.

The electrospinning technique as a method for fabricating hydrophobic membranes for membrane distillation (MD) has received much attention in recent times. In this study, TiO 2 functionalized with 1H,1H,2H,2H-perfluorooctyltriethoxysilane was added directly to the dope solution for electrospinning in order to increase the hydrophobicity of the resulting MD membranes. Three concentrations (10%, 15% and 20%) of polyvinylidene fluoride-cohexafluoropropylene (PH) dope solution were used for electrospinning with various amounts of TiO 2 (1%, 5% and 10%) to generate nanofibers. The electrospun nanofiber membrane (ENM) of 20% PH with 10% TiO 2 exhibited the highest surface hydrophobicity (contact angle = 149°) resulting from good dispersion of the TiO 2 particles, while the highest liquid entry pressure of 194.5 kPa was observed for the ENM comprising 10% PH with 10% TiO 2 due to its reduced pore sizes. Furthermore, the ENMs containing 10% TiO 2 exhibited better flux and stable salt rejection than commercial and ENMs without TiO 2. Notably, there was no severe wetting in the 20% PH ENM with 10% TiO 2 over seven days of operation, despite the high salt concentration (7.0 wt% NaCl) of the feed water.

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a b s t r a c tIn the present study, a magnetic nanofibrous composite mat composed of polystyrene (PS)/polyvinylidene fluoride (PVDF) nanofibers with selective incorporation of iron oxide (Fe 3 O 4 ) nanoparticles (NPs) on/in PS was successfully prepared via a facile two-nozzle electrospinning process for oil-in-water separation. Field emission scanning electron microscopy and infrared spectroscopy showed the mats to be highly-porous in structure and confirmed the presence of the Fe 3 O 4 NPs on/in the nanofibers. Both PS and PVDF nanofibers exhibited oleophilic and hydrophobic properties. The results showed improved mechanical properties when PVDF was added to the composite mat compared to the pristine PS mat. In addition, the incorporation of magnetic Fe 3 O 4 NPs in the composite mat helps in the easy recovery of the mats after the oil-in-water sorption process. The composite mats showed good oil sorption capacity (35 e46 g/g) and improved mechanical property. The present electrospun magnetic PVDF/Fe 3 O 4 @PS nanofibers could be potentially useful for the efficient removal of oil in water and recovery of sorbent material.

To consolidate the position of membrane distillation (MD) as an emerging membrane technology that meets global water challenges, it is crucial to develop membranes with ideal material properties. This study reports a facile approach for a polyvinylidene fluoride (PVDF) membrane surface modification that is achieved through the coating of the surface with poly(dimethylsiloxane) (PDMS) polymeric microspheres to lower the membrane surface energy. The hierarchical surface of the microspheres was built without any assistance of a nano/microcomposite by combining the rapid evaporation of tetrahydrofuran (THF) and the phase separation from condensed water vapor. The fabricated membrane exhibited superhydrophobicity-a high contact angle of 156.9° and a low contact-angle hysteresis of 11.3°-and a high wetting resistance to seawater containing sodium dodecyl sulfate (SDS). Compared with the control PVDF-hexafluoropropylene (HFP) single-layer nanofiber membrane, the proposed fabricated membrane with the polymeric microsphere layer showed a smaller pore size and higher liquid entry pressure (LEP). When it was tested for the direct-contact MD (DCMD) in terms of the desalination of seawater (3.5% of NaCl) containing SDS of a progressively increased concentration, the fabricated membrane showed stable desalination and partial wetting for the 0.1 and 0.2 mM SDS, respectively.

Electrospun nanofiber membranes (ENMs) have garnered increasing interest due to their controllable nanofiber structure and high void volume fraction properties in membrane distillation (MD). However, MD technology still faces limitations mainly due to low permeate flux and membrane wetting for feeds containing low surface tension compounds. Perfluorinated superhydrophobic membranes could be an alternative, but it has negative environmental impacts. Therefore, other low surface energy materials such as silica aerogel and polydimethylsiloxane (PDMS) have great relevancy in ENMs fabrication. Herein, we have reported the high flux and nonwettability of ENMs fabricated by electrospraying aerogel/polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) over electrospinning polyvinylidene fluoride-co-hexafluoropropylene (PVDF–HFP) membrane (E-PH). Among various concentrations of aerogel, the 30% aerogel (E-M3-A30) dual layer membrane achieved highest superhydrophobicity (∼170° water contact angle), liquid entry pressure (LEP) of 129.5 ± 3.4 kPa, short water droplet bouncing performance (11.6 ms), low surface energy (4.18 ± 0.27 mN m–1) and high surface roughness (R a: 5.04 μm) with re-entrant structure. It also demonstrated nonwetting MD performance over a continuous 7 days operation of saline water (3.5% of NaCl), high antiwetting with harsh saline water containing 0.5 mM sodium dodecyl sulfate (SDS, 28.9 mN m–1), synthetic algal organic matter (AOM).

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