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Membrane wetting and fouling substantially limits application and deployment of membrane distillation process. Designing high-performance superhydrophobic membranes offers an effective solution to solve the challenge. In this work, a highly durable superhydrophobic surface (water contact angle of 170.8 ± 1.3°) was constructed via a facile and rapid spray-coating of extremely hydrophobic SiO 2 nanoparticles onto a porous polyvinylidene fluoride (PVDF) substrate for membrane distillation. The superhydrophobic membrane coated by fluorinated SiO 2 nanoparticles exhibited a superior physicochemical stability in a wide range of extreme environments (i.e., NaOH, HCl, hot water, rust water, humic acid solution, ultrasonication, and high-speed water scouring). During 8-h continuous membrane distillation desalination experiment, the coated superhydrophobic membrane experienced a consistently stable water vapor flux (ca. 19.1 kg·m−2·h−1) and desalination efficiency (99.99 %). Additionally, such a stable superhydrophobicity endowed the spray-coated PVDF membrane to overcome membrane wetting and fouling during membrane distillation of highly saline solutions containing foulants (i.e., humic acid and rust). Results reported in this study provides a useful concept and strategy in facile construction of robust superhydrophobic membranes via spray-coating for effective membrane distillation. [Display omitted] • Spray-coating of hydrophobic SiO 2 was used to fabricate superhydrophobic membranes. • Superhydrophobic membrane experienced strong physicochemical stability in harsh environment. • Superhydrophobic membrane had a superior desalination efficacy in membrane distillation. • Superhydrophobic membrane had excellent antifouling properties during membrane distillation. [ABSTRACT FROM AUTHOR]

• Superhydrophobic PVDF membrane was fabricated by spray-coating of fluorinated SiO 2 NPs. • Superhydrophobic PVDF membrane had a water contact angle of 171.8 ± 1.1° and sliding angle of 1.69 ± 0.13°. • The modified PVDF membrane maintained stable superhydrophobicity under harsh conditions. • The prepared membrane has consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions over 40 cycles. • Scale-up fabrication of superhydrophobic PVDF membrane was successfully performed. Hydrophobic anti-wetting membranes have many applications, such as oily wastewater treatment via oil/water separation, desalination via membrane distillation, and carbon capture via gas-liquid membrane contactors. Herein, we used a simple and scalable method to fabricate robust superhydrophobic polyvinylidene fluoride (PVDF) based membranes by one-step spray-coating of fluorinated SiO 2 nanoparticles. The prepared PVDF membrane was systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The modified PVDF membrane had excellent superhydrophobicity with an extremely high water contact angle up to 171.8 ± 1.1° and a low sliding angle of 1.69 ± 0.13°, due to the fluorinated close-packed hydrophobic SiO 2 nanoparticles on the surface. The modified PVDF membrane maintained its relatively stable superhydrophobicity under various harsh conditions, i.e., exposure in hot water, NaOH and HCl, ultrasonication and high-speed flushing, indicating the superior robustness and stability. The prepared membrane also exhibited consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions, and superior recyclability and durability over 40 cycles. In addition, spray-coating showed its great promise in engineering various superhydrophobic surfaces on different substrates and excellent scalability in fabricating large-size membranes. This study demonstrates a facilely scalable spray-coating method for engineering robust superhydrophobic surfaces and membranes that can be potentially used for various gas, vapor and water/oil separations. [ABSTRACT FROM AUTHOR]

Diffusion dialysis employing anion exchange membranes (AEMs) as an energy-efficient and environmentally-friendly technology is highly desirable for acid recovery from acidic wastewater. Herein, porous AEMs with high acid permeability were tailored via a simple one-step route, in which porous chloromethyl polyethersulfone (CMPES) membrane substrate was modified by 1,4-dimethylpiperazine (DMP) to achieve simultaneous crosslinking and quaternization. The prepared piperazine-functionalized AEMs were characterized by morphology, ion exchange capacity, water uptake, water contact angle, stabilities and diffusion dialysis performance. Specifically, the optimal AEM (i.e., DPES-3h) applied in acid recovery from the simulated HCl (1.0 mol L−1)/FeCl 2 (0.2 mol L−1) mixed solution at 25 °C possessed a proton dialysis coefficient (U H + ) of 43.2 × 10−3 m h−1 and an acid/salt separation factor (S) of 29.6, remarkably outperforming the previously reported state-of-the-art AEMs. Furthermore, the DPES-3h AEM showed excellent thermal stability and acid resistance, suggesting considerable durability for long-term application. These results indicated that our piperazine-functionalized porous AEMs appear to be promising for acid recovery from the acidic waste streams via diffusion dialysis. [Display omitted] • Piperazine-functionalized porous anion exchange membranes are prepared via a one-step method. • The obtained membranes present high proton dialysis coefficient due to high free space volume. • Our porous membranes show great potential for large-scale commercial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Superhydrophilic g-C 3 N 4 /SiO 2 composite membrane is prepared by vacuum filtration. • The g-C 3 N 4 /SiO 2 composite membrane has effective oil/water separation performance. • Incorporation of g-C 3 N 4 endows the composite membrane with photocatalytic self-cleaning property. • g-C 3 N 4 /SiO 2 composite membrane effectively retains and inactivates the bacteria. Conventional membrane processes, e.g., microfiltration and ultrafiltration, suffer from severe permeation flux decline and fouling during the oily wastewater treatment. The superhydrophilic surface decoration provides an important and effective strategy to address this challenge. Herein, a surperhydrophilic/underwater superoleophobic nanocomposite surface with the photocatalytic properties was constructed via one-step facile vacuum-assisted filtration of a g-C 3 N 4 nanosheet/SiO 2 nanoparticle dispersion onto a microfiltration membrane substrate. Specifically, with the intercalation of 20 mg∙L−1 SiO 2 nanoparticles into the g-C 3 N 4 nanosheets, the g-C 3 N 4 /SiO 2 composite membrane showed the superhydrophilic/underwater superoleophobic properties with an underwater oil contact angle of 170.0 ± 0.3°. Such a g-C 3 N 4 /SiO 2 composite membrane yielded a permeation flux of >1290 LMH·bar−1 with an oil rejection of >99.91% during the vacuum filtration of oil-in-water emulsions. The g-C 3 N 4 /SiO 2 composite membrane significantly outperformed the pristine microfiltration substrate that had severe fouling caused by oil blockage. Additionally, the g-C 3 N 4 /SiO 2 composite membrane not only effectively retained the E. coli bacteria through size exclusion effect, but also promoted the inactivation of bacteria via visible-light photocatalysis. Therefore, our membrane has a great promise in practical oily wastewater treatment due to its excellent separation performance and biofouling resistance. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has gained considerable interest as an attractive membrane-based desalination technology due to its reversible fouling and potentially low costs. Thin-film composite (TFC) membranes, composed of a microporous substrate and a selective polyamide layer, have been widely used for FO. Compared with the substrate in pressure-driven TFC membranes (e.g., reverse osmosis and nanofiltration membranes), the substrate in TFC FO membranes has a more significant impact on membrane performance due to its extra effect on the membrane structural parameter that determines internal concentration polarization (ICP). Many researchers have not differentiated the substrate surface properties from the substrate bulk properties, resulting in misleading conclusions. This review clarifies the individual roles of the substrate surface and the substrate bulk in TFC FO membrane performance. We analyze how the substrate surface properties, such as the surface hydrophilicity, porosity, pore size, pore size distribution and pore number density, impact the PA layer formation during IP, thereby influencing the PA layer permeability/selectivity and thus FO performance. We also evaluate how the substrate bulk properties, such as the bulk porosity, tortuosity and pore structure, affect the membrane structural parameter, thereby influencing ICP and thus FO membrane performance. A desirable substrate surface should have reasonably high hydrophilicity (e.g., water contact angles of 40°–60°), high porosity, small pore size, narrow pore size distribution and high pore number density. A desirable substrate bulk should have high porosity, low tortuosity and interconnected pore structures, thereby minimizing the membrane structural parameter and thus ICP. This review highlights the significant roles of the substrate surface and bulk properties in FO membrane performance. It provides significant insights into developing all kinds of high-performance TFC membranes (e.g., FO, reverse osmosis and nanofiltration) by tailoring the substrate properties. [Display omitted] • Substrate in TFC FO membranes has a more significant impact on membrane performance. • Roles of the substrate surface and bulk in FO membrane performance are clarified. • Desirable properties for the substrate surface and bulk in FO membrane performance are proposed. • The mechanisms on how substrate affects FO membrane performance are analyzed. • This work provides significant insights into developing high-performance TFC membranes. [ABSTRACT FROM AUTHOR]

Designing a stable and uniform hydrophilic material for separation of oil and water is strongly desired for sustainable management of oily wastewater. Herein, a stable and uniform bio-inspired coating onto the non-woven fabric substrate with superhydrophilicity and underwater superoleophobicity via rapid co-deposition of dopamine and polyethylenimine was demonstrated. Ammonium persulfate outperformed other oxidants (e.g., Cu2+-H 2 O 2 and NaIO 4) to rapidly trigger the co-deposition of dopamine and polyethylenimine for homogeneous superhydrophilic and underwater superoleophobic surface engineering. Furthermore, the co-deposition conditions, i.e., concentration of ammonium persulfate and exposure duration, have a positive dependence on the hydrophilicity and underwater oleophobicity of the coated fabric membranes. Specifically, the superhydrophilicity and underwater superoleophobicity (underwater oil contact angle of 165.4 ± 1.1°, sliding angle of 2.5 ± 0.5°) can be obtained for the coated fabric membranes at the optimal co-deposition condition (i.e., 28.5 mmol L−1 persulfate and coating duration of 7 h), showing a great potential in gravitational oil-water separation (permeation flux >115,000 L m−2 h−1; oil rejection >99.2%). Integrating with a superhydrophobic copper mesh, the oil-water mixed solution can be continuously and sufficiently separated, realizing simultaneous recovery of pure oil and water from oily wastewater. In addition, the bio-inspired coating displays a strong long-term chemical robustness and stability in extreme environments (i.e., acidic/alkaline solutions and oils). The study provides a facile, cost-effective and practical strategy in constructing superhydrophilic and underwater superoleophobic interfaces for sustainable treatment of oily wastewater. Image 1 • Mussel-inspired coating endows non-woven fabric membranes with robust superhydrophilic interface. • Persulfate have an impressive efficacy to rapidly trigger the mussel-inspired coating. • The mussel-inspired coating yields an underwater oil contact angle of 165.4 ± 1.1°. • The superhydrophilic fabric membrane has a permeation flux of >115000 L m−2 h−1 with >99.2% oil rejection. • Integrating bio-inspired fabric membrane with superhydrophobic copper mesh can continuously recover oil and water. [ABSTRACT FROM AUTHOR]