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Considerable efforts have been devoted to finding economic and simple preparation methods for polydimethylsiloxane (PDMS) superhydrophobic membrane in past decades. This study provides a simple method to electrospin PDMS membrane using poly (methyl methacrylate) (PMMA) as carrier polymer. Effects of PMMA concentration, PDMS/PMMA mass ratio and main parameters of electrospinning process (voltage and injection rate) were investigated to obtain superhydrophobic membrane with high water contact angle (WCA). A highest WCA of 163° could be obtained on the membrane surface fabricated by electrospinning solution containing PDMS: PMMA: tetrahydrofuran (THF): N , N -dimethylformamide (DMF) (mass ratio 1: 1: 8.88: 9.48) under applied voltage of 11 kV and injection rate of 0.1 mm/min. The superhydrophobic PDMS/PMMA membrane was further applied in membrane distillation process for desalination, and a high permeation flux of 39.61 L/m 2 h and an excellent salt rejection of 99.96% were achieved during long-term MD process (24 h). [ABSTRACT FROM AUTHOR]

• Hydrophilic-omniphobic-hydrophilic sandwich-like membrane was developed for MD. • Top PDA with hydration layer increased membrane energy barrier and oil resistance. • Bottom PDA layer maintained transmembrane temperature difference and driving force. • Water vapor transmembrane mass transfer was further promoted with shortened path. • Robust MD performance was obtained for surfactant-stabilized oil-in-water emulsion. Membrane distillation (MD) is attractive for water recovery from surfactant-stabilized oil-in-water emulsion due to its unique characteristics. To address the membrane fouling and wetting issues, a novel hydrophilic-omniphobic-hydrophilic sandwich-like membrane (PFZP) was firstly developed. Top PDA skin layer induced the hydration shell facing feed, which endowed membrane with high energy barriers (0.12 kT) to limit free hexadecane deposition. Omniphobic substrate (FZP) effectively avoided the deposition of free sodium dodecyl sulfate (SDS) and hexadecane-SDS aggregate. Bottom PDA skin layer was beneficial to maintain transmembrane temperature difference and driving force. Besides, both PDA layers (∼4.1 μm) partly intruded into FZP substrate to shorten water vapor transmembrane transfer path. Compared with pristine membrane, PFZP membrane displayed greatly improved anti-fouling, anti-wetting and water recovery performance with stable water flux (18.0 LMH) and high salt rejection (99.99%). Obtained findings further improved the understanding of robust MD membrane design, its anti-fouling, mass and heat transfer mechanism. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a promising hybrid thermal/membrane desalination process to treat high salinity industrial wastewater with near-complete rejection of nonvolatile solutes. However, MD membrane still suffers the membrane wetting, which largely affects the desalination performance. In this study, a facile method includes one-step in-situ growth of ZnO nanorods and dip coating of low surface energy 1H,1H,2H,2H -perfluorodecytriethoxysilane (PDTS) was applied to fabricate omniphobic membrane (FZnO-PVDF) with excellent anti-wetting performance. The anti-wetting performance of FZnO-PVDF membrane was systemically evaluated by treating pure water, feed with surfactant and sparingly soluble salts for the first time. Theoretical analysis such as numerical simulation, dynamic liquid entry pressure (LEP) changes and nucleation condition was carried out to explain its anti-wetting mechanism. Results showed that FZnO-PVDF membrane displayed high contact angles towards water droplets with (∼121.1°) or without alcohol (∼164.9°), and low sliding angle for water (10.6°). The resultant membrane not only exhibited excellent resistance for surfactant-induced membrane wetting towards 0.6 mM sodium dodecyl sulfate (SDS) due to its enhanced LEP value (225 kPa), but also remarkable resistance for scaling-induced membrane wetting because of the high energy barrier for CaSO 4 heterogeneous nucleation (34.2 mJ mol−1) and slip boundary condition of membrane. This study provides valuable insights for fabricating omniphobic membrane and comprehending its anti-wetting property in MD application. [Display omitted] • Omniphobic FZnO-PVDF membrane was prepared by facile ZnO growth and fluorination. • Numerical simulation indicated falling droplet rebounded from omniphobic surface. • Enhanced dynamic LEP led to great resistance for anti surfactant-induced wetting. • High ΔG heterogeneous and slip boundary endowed high anti scaling-induced wetting. [ABSTRACT FROM AUTHOR]

• Electrostatic spraying was firstly used in COF-LZU1 formation on membrane substrate. • Membrane fouling behavior in DCMD for different ECs was systematically investigated. • COF-based membrane performance in temperature changing DCMD process was studied. Emerging contaminants (ECs) in aqueous ecosystem are becoming a global threat to human beings, which are mainly discharged from industrial wastewater. Direct contact membrane distillation (DCMD) can utilize waste heat to treat industrial wastewater containing ECs, achieving a better balance between removal efficiency and operation cost than other technologies. However, membrane fouling is the major obstacle that impedes DCMD application. Therefore, anti-fouling covalent organic framework COF-LZU1/PVDF composite membranes were prepared via electrostatic spraying and used in DCMD for the first time. Four typical EC compounds (ibuprofen, acesulfame, sulfamethoxazole, and N,N-diethyl-3-methylbenzamide) were selected as targets to investigate the effect of water affinity and charge on membrane fouling. Results showed that COF-1.0 membrane with relatively hydrophilic COF-LZU1 structure exhibited higher permeate flux and salt rejection than commercial PVDF substrate when treating sulfamethoxazole and ibuprofen within pH range of 4–7 and temperature of 40–70 °C. This could be attributed to the weaker hydrophobicity and closer-to-neutral zeta potential of COF-1.0, which weakened the electrostatic and hydrophobic-hydrophobic interactions between membrane and ECs. In addition, the membrane performance comparison in temperature changing DCMD process further showed that COF-1.0 performed better in terms of permeate flux, especially in the gradually decreased temperature condition. Overall, these findings would advance the fundamental understanding and practical application of COF-based membranes in DCMD for ECs treatment. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is an emerging water treatment technology suitable for hypersaline wastewater. However, membrane wetting is a primary obstacle to restrict its widespread industrial use. In this study, a superhydrophobic nanofibrous membrane (labeled as FZP) with high water contact angle of 162.3° and sliding angle of 9.8° was fabricated through fluorinating of zinc oxide (ZnO) blended electrospun polyvinylidene fluoride (PVDF) membrane. In comparison with neat and ZnO blended PVDF (ZP) nanofibrous membranes, FZP membrane has much better anti-wetting property due to its superhydrophobicity and higher liquid entry pressure (LEP) value when desalinating both pure NaCl solution and NaCl solutions with low-surface-tension sodium dodecyl sulfate (SDS) and sparingly soluble salt CaSO 4. LEP values of membranes for SDS and CaSO 4 contained feed solutions were calculated to be smaller than that for pure NaCl solution, accelerating the occurrence of membrane wetting. Temperature gradient across the membrane and Gibbs free energies of CaSO 4 heterogeneous nucleation were further calculated to elucidate the wetting mechanism. Our results provide valuable insights for better developing superhydrophobic membrane and understanding its anti-wetting property in MD process. Image 1 • Superhydrophobic FZP membrane was facilely obtained by ZnO blending and fluorination. • The highest LEP and lowest transmembrane ΔT led to best anti-wetting performance. • The highest ΔG heterogeneous of CaSO 4 is least prone to membrane hydrophilization. [ABSTRACT FROM AUTHOR]

The relatively large pore size of electrospun membranes might limit their application for direct contact membrane distillation (DCMD). Incorporation of ionic liquid is a potential approach to decrease the pore size of electrospun membranes, which was attributed to the increased conductivity of electrospinning solution. In this study, a novel nanofibrous membrane based on the blends of poly(vinylidene fluoride) (PVDF), polytetrafluoroethylene (PTFE) and ionic liquid (BMIMPF6) was fabricated and applied for the DCMD. The effects of the BMIMPF6 on the morphology, pore size and DCMD performance of the PVDF‐PTFE nanofibrous membrane were investigated. Compared with neat (PVDF‐PTFE) membranes (average pore size: 0.93 μm), the incorporation of BMIMPF6 resulted in a smaller mean pore diameter (0.58 μm). The liquid entry pressure value of the modified composite membrane also increased from 62.75 kPa (neat) to 83 kPa, due to the decreased pore size. The composite membrane exhibited a longer lifespan (about 26 h) than neat membrane during long‐term DCMD process, which makes this composite membrane a promising candidate for DCMD application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48467. [ABSTRACT FROM AUTHOR]

• Triple layer hydrophobic-hydrophilic composite membrane was firstly fabricated. • The driving force of the composite membrane was theoretically calculated. • Hydrophilic layer could increase the driving force of water vapor across membrane. Electrospinning is a notable technique to prepare nanofibrous membranes with remarkable features required for membrane distillation (MD). However, hydrophobic membrane fabricated by electrospinning alone could hardly ensure a high flux. In this study, triple layer membrane that is composed of a PVDF-PTFE hydrophobic layer, a PET support layer, and a chitosan-polyethylene oxide (CS-PEO) hydrophilic layer, was fabricated by electrospinning. Firstly, the PVDF-PTFE and CS-PEO layers were optimized, whose contact angles and thicknesses were 144.3°, 55 μm and 20°, 75 μm, respectively. Then, the triple layer membrane (TL-M), dual layer membrane without hydrophilic layer (DL-M) were fabricated and tested in a DCMD process using 3.5 wt% NaCl as the feed to illustrate the effect of hydrophilic layer. The triple layer composite membrane (average flux: 19 kg/m−2 h−1, rejection rate: 99.92%) showed better performance in comparison to the dual-layer membrane (average flux: 15 kg/m−2 h−1, rejection rate: 99.88%). In addition, the driving forces of TL-M (from 14.34 to 14.16 kPa) and DL-M (from 13.26 to 12.88 kPa) were calculated. Results suggested the incorporation of hydrophilic layer could increase the driving force, and largely enhance the membrane flux which could ensure the triple layer membrane possesses a good potential for DCMD application. [ABSTRACT FROM AUTHOR]

• Patterned PA-based dense Janus membrane with high performance was fabricated by a facile R-IP. • PA/PVDF Janus-2.0 showed anti-fouling/-wetting/-scaling properties without compromising flux. • Size-sieving effect, rather than breakthrough pressure, was probably the critical anti-wetting mechanism. • Superhydrophilic and dense enough surface layer was the key to scaling-resistant Janus membrane. Membrane fouling, wetting and scaling are three prominent challenges that severely hinder the practical applications of membrane distillation (MD). Herein, polyamide/polyvinylidene fluoride (PA/PVDF) Janus membrane comprising a hydrophobic PVDF substrate and a patterned dense PA layer by reverse interfacial polymerization (R-IP) was developed. Direct contact MD experiments demonstrated that PA/PVDF Janus membrane could exhibit simultaneously superior resistance towards surfactant-induced wetting, oil-induced fouling and gypsum-induced scaling without compromising flux. Importantly, the size-sieving effect, rather than the breakthrough pressure of the membrane, was revealed as the critical factor that probably endowed its resistance to wetting. Furthermore, a unique possible anti-scaling mechanism was unveiled. The superhydrophilic patterned dense PA layer with strong salt rejection capability not only prevented scale-precursor ions from intruding the substrate but also resulted in the high surface interfacial energy that inhibited the adhesion and growth of gypsum on the membrane surface, while its relatively low surface -COOH density benefited from R-IP process further ensured the membrane with a low scaling propensity. This study shall provide new insights and novel strategies in designing high-performance MD membranes and enable robust applications of MD facing the challenges of membrane fouling, wetting and scaling. [Display omitted] [ABSTRACT FROM AUTHOR]