Membrane distillation holds promise for further recovery of reverse osmosis (RO)-concentrated seawater to realize zero-liquid discharge; however, severe scaling induced by high-concentration salts and fouling triggered by a naturally occurring substance would result in severe wetting of the hydrophobic distillation membrane. To retard membrane wetting during the concentration process, the membrane’s interfacial structure and the seawater’s ingredients were systematically investigated to improve the membrane’s durability. The results demonstrated that the dual-layer membrane with hierarchically rough beads-on-a-string structured fibers could enlarge the water evaporation area on the membrane surface to improve membrane water flux, and superhydrophobicity can reduce the contact area between the salt and membrane surface to prevent membrane scaling. Significantly, the membrane’s durability can be further improved by adjusting the seawater ingredients. This finding revealed that the scaling resulting from Ca2+ and Mg2+ when they exist alone is more severe than when they exist together. Therefore, eliminating the dominant Ca2+, Mg2+, and naturally occurring substance in seawater and maintaining it in a neutral state can stably concentrate the seawater with a high water recovery of ∼85%. The regulation of the membrane interface integrated with optimal seawater ingredients is essential for the application of membrane distillation in the treatment of RO-concentrated seawater.

Novel specially wettable membranes have been attracting significant attention for durable membrane distillation (MD). However, constructing a superhydrophobic interface often has to undergo complex modification procedures including roughness construction and hydrophobic modification. Herein, all-polymer and self-roughened superhydrophobic poly­(vinylidene fluoride) fibrous membranes (PVDF FMs) with robustly stable pores were successfully constructed via electrospinning of fluorinated polyhedral oligomeric silsesquioxanes/PVDF (F-POSS/PVDF) emulsion solution in combination with hot-pressing. The comparative experiment reveals that proper hot-pressing, including adequate temperature and pressure, can help improve membrane pore stability by welding the intersecting fibers and increase the membrane surface hydrophobicity by transferring the inner fluorine chains to the outer fiber surface, simultaneously advancing membrane scaling and fouling resistance. Nevertheless, excessive temperature or pressure will destroy the interconnected pores and surface wettability of the PVDF FM. Significantly, the hot-pressing-treated F-POSS/PVDF FM shows a high water recovery (∼90%) and robust stability after five rounds of the concentration process toward concentrating natural seawater as a target. Thus, the all-polymer and self-roughened superhydrophobic PVDF FMs constructed via electrospinning combined with the thermal treatment have potential applications in concentrating hypersaline brines, which make up for the other membrane technology, including reverse osmosis and nanofiltration technologies that failed to concentrate hypersaline solutions.