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Membrane distillation (MD) is a promising desalination technology as it is less sensitive to feed's salinity and can handle high-salinity water. However, the industrial application of MD is restricted by the limited availability of cost-effective hydrophobic membranes. This study developed a simple method to fabricate hydrophobic MD membranes through the coating of a fluoroethylene vinyl ether polymer called LUMIFLON™ LF-200. The fluoropolymer was effectively coated on porous nitrocellulose (NC) and nylon membrane through dip-coating followed by a thermal crosslinking. The coating layer was thin and uniform, covering the surface of the whole membrane matrix, while the high porosity and the microstructure of the membranes were still mostly preserved. After modification, the originally hydrophilic NC and nylon membranes were transformed into hydrophobic, with water contact angles of ∼130°. The 12LF-NC membrane showed a high flux of 10.1 kg m−2 h−1 with salt rejection >99.99% over 120 h in the direct contact MD fed with 10 wt% NaCl solution, which outperformed the commercial PVDF membrane. This coating method has the potential to modify various substrates to produce MD membranes with good performance, which broadens the availability of appropriate membranes for MD application. [Display omitted] • Fluorinated copolymer, LUMIFLON LF-200 is used to prepare hydrophobic MD membranes. • LF-200 was simply dip-coated on hydrophilic substrates and crosslinked under mild heating. • The WCAs of modified nitrocellulose and nylon membranes increased to ∼130° from 0°. • The 12LF-NC membrane had excellent flux >10 kg m−2 h−1 treating 10 wt% salt water. • This method has high efficiency, wide versatility and the potential to scale up. [ABSTRACT FROM AUTHOR]

Solvent resistant membrane distillation (SR-MD) is a novel technology to effectively separate water from waste streams containing solvents with high boiling points, avoiding the high chemical costs and release of harmful gas in conventional treatments. Ceramic membranes are promising for this process as they are highly stable chemically but they require modification to tune the hydrophilicity to hydrophobicity. However, the widely used silanization for hydrophobic modification often involves expensive chemicals and may produce toxic substances. Here, we present a new hydrophobic modification method with the use of fatty acid chloride (FAC), as a greener and cheaper alternative to silanes. In the grafting reaction, the acyl chloride groups react with the –OH groups on the ceramic membranes to form strong ester bonds. We successfully grafted stearoyl chloride (SC) and palmitoyl chloride (PC) on the ceramic tubular membranes. With long carbon chains grafted, the modified membranes exhibited high hydrophobicity with a water contact angle >141° and a liquid entry pressure >3 bar. When tested in SR-MD with a feed solution containing 50 wt% dimethyl sulfoxide, the PC-modified membrane demonstrated a flux of 3.2 kg m−2 h−1, with rejection >98% and separation factor >110 at 60 °C, and a high flux of 4.5 kg m−2 h−1 with rejection >96% at 70 °C. The FAC-modified membranes allow a cost-effective treatment of challenging wastewater containing organic solvents through SR-MD. [Display omitted] • Hydrophobic ceramic membranes for solvent resistant MD were synthesized through fatty acid chloride grafting. • The acyl chloride groups formed strong ester bonds on ceramic surface and the modified membranes had high hydrophobicity. • Flux of 3.2 kg m−2 h−1, rejection >98% and separation factor >110 can be achieved when treating 50 wt% DMSO in SR-MD. • The hydrophobicity and separation performance are comparable to ceramic membrane grafted with silanes. • This study presents a greener and cheaper surface modification chemistry to synthesize hydrophobic ceramic membranes. [ABSTRACT FROM AUTHOR]

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]