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With the aggravation of the global water crisis, membrane distillation (MD) for seawater desalination and hypersaline wastewater treatment is highlighted due to its low operating temperature, low hydrostatic pressure, and theoretically 100% rejection. However, some issues still impede the large-scale applications of MD technology, such as membrane fouling, scaling and unsatisfactory wetting resistance. Bio-inspired super liquid-repellent membranes have progressed rapidly in the past decades and been considered as one of the most promising approaches to overcome the above problems. This review for the first time systematically summarizes and analyzes the mechanisms of different super liquid-repellent surfaces, their preparation and modification methods, and anti-wetting/fouling/scaling performances in the MD process. Firstly, the topology theories of in-air superhydrophobic, in-air omniphobic and underwater superoleophobic surfaces are illustrated using different models. Secondly, the fabrication methods of various super liquid-repellent membranes are classified. The merits and demerits of each method are illustrated. Thirdly, the anti-wetting/fouling/scaling mechanisms of super liquid-repellent membranes are summarized. Finally, the conclusions and perspectives of the bio-inspired super liquid-repellent membranes are elaborated. It is anticipated that the systematic review herein can provide readers with foundational knowledge and current progress of super liquid-repellent membranes, and inspire researchers to overcome the challenges up ahead. [Display omitted] • Concepts and mechanisms of bio-inspired super liquid-repellent surfaces were elaborated. • Methods to develop super liquid-repellent MD surfaces were summarized and discussed. • Their MD performance and mechanisms were summarized and analysed. • The perspectives of these super liquid-repellent membranes were illustrated. [ABSTRACT FROM AUTHOR]

Hydrophobic membranes suffer from wetting and scaling when treating hypersaline brine using membrane distillation (MD). Thus omniphobic membranes with re-entrant surfaces have been developed by diverse modifications to enhance anti-wetting/scaling properties. However, those post-modifications usually sacrifice membrane permeability in spite of improved stability. In this work, omniphobic membranes were fabricated by decorating polyvinylidene fluoride (PVDF) nanofibrous membranes with different silica nanoparticles (SiNPs) followed by fluorination. Compared to unmodified nanofibrous and commercial PVDF membranes, both smaller SiNPs coated membrane #P-Min and larger SiNPs coated membrane #P-Max can perfectly sustain liquids with low surface tensions on their surfaces without wetting. In contrast to #P-Max with an oil contact angle of 136 ± 1°, #P-Min exhibited better oleophobicity with an oil contact angle of 152 ± 1°. In addition, the rigidity of their omniphobic properties was confirmed by testing in harsh conditions. Moreover, #P-Min successfully overcame the trade-off relation between membrane permeability and rejection with an enhanced MD flux due to more effective water evaporation area on membrane surface and a higher membrane porosity. While #P-Max was wetted by a hypersaline feed solution composed of 25 wt% NaCl, #P-Min could maintain a stable flux of 15 L m−2h−1 in a continuous 7-h MD operation, which proved its excellent performance for brine treatment. Furthermore, #P-Min exhibited less scaling tendency when feed was a saturated gypsum solution. Compared to #P-Max , the better anti-scaling properties of #P-Min should be due to its higher surface energy barrier, better slippery property and less solid-liquid contact area, which effectively impede crystal nucleation and attachment. Image 1 • Effects of nano-scaled roughness on membrane omniphobicity were studied. • As-prepared omniphobic membranes were stable under harsh conditions. • Omniphobic membrane coated with smaller NPs exhibited better performance. • It should be due to high surface energy barrier, slippery property and less solid-liquid contact area. [ABSTRACT FROM AUTHOR]