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Conventional interfacial polymerization (IP) requires excessive amounts of reactive monomers and solvents due to the dip-coating method. Herein, we report a rod-coating assisted IP process to prepare nanofiltration (NF) membranes. The results demonstrate that a perfect PA layer can be fabricated by using low monomer dosages of PIP (0.08 g/m2) and TMC (0.016 g/m2). This can significantly reduce the consumption of monomers and organic solvents, and effectively avoid the waste of hazardous and expensive chemicals. Thanks to the fewer monomer dosages, the prepared NF membranes were much thinner and looser, which significantly improved the membrane permeability. The highest permeance of the rod-coated membranes reached 204.0 L/(m2 h MPa), which was increased by ∼251% compared to the dip-coated NF membrane. More importantly, the rod-coated membranes possessed excellent Na 2 SO 4 rejections (>99.0%) and ultralow NaCl rejections (<14.4%). And the maximum NaCl/Na 2 SO 4 selective efficiency reached 125.7, which was about 7 folds to that of the dip-coated NF membrane. This study suggests that the rod-coating method is highly feasible for the preparation of polyamide NF membranes with high performance. It is reasonable to expect that this rod-coating assisted IP process offers a new approach to fabricating NF membranes. [Display omitted] • High performance PA-NF membranes fabricated by rod-coated assisted IP process. • The rod-coating method significantly reduce the consumption of the monomers. • The rod-coated membrane possesses an excellent permeate flux of 204.0 L/(m2 h MPa). [ABSTRACT FROM AUTHOR]

Highly porous polyvinylidene fluoride (PVDF) hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux of the process. For the first time in this paper, porous hydrophobic PVDF asymmetric hollow fiber membranes with a high outer surface porosity for use in vacuum membrane distillation (VMD) were successfully fabricated by applying a simultaneous co-extrusion spinning process through the non-solvent induced phase separation (NIPS) method. In this approach, five kinds of dual-layer composite membranes were prepared by employing different inner and outer polymer dopes. Single-layer membrane was also fabricated through the conventional dry-jet wet phase inversion method. Results revealed that the introduction of the simultaneous co-extrusion spinning process greatly increased the outer surface porosity of the dual-layer composite membranes. It was also observed that the VMD flux of the dual-layer membranes spun through the simultaneous co-extrusion spinning process was 54% higher than the single-layer membrane fabricated by the conventional dry-jet wet phase inversion method. A VMD flux as high as 61.8 kg/(m 2 h) at 70 °C was obtained for the novel dual-layer composite membranes. [ABSTRACT FROM AUTHOR]

In this study, a new simultaneous heat and mass transfer theoretical model of the membrane distillation process operating under direct contact membrane distillation (DCMD) mode has been developed for the hydrophobic/hydrophilic dual-layer composite membranes. Using the proposed model, a criterion parameter (β) was derived to determine whether the flux will be increased for the prepared hydrophobic/hydrophilic composite membranes. A flux ratio ( γ DL/SL M ) of dual-layer to single-layer membrane was also developed to predict the DCMD flux performance of the composite membranes. To validate the theoretical model, three sets of dual-layer hydrophobic/hydrophilic composite membranes and single-layer hydrophobic membranes with defined total thicknesses (240 μm, 260 μm, and 285 μm) and different thickness ratios (δ / δ o = 3.69, 2.48 and 2.19) were purposefully fabricated using electrospinning technique. Theoretical modelling results were compared with the experimental data in terms of DCMD flux ratio. The experimental data of flux ratios for the three sets of fabricated membranes at 60 °C, γ DL/SL E , are 2.75, 1.97 and 1.80, respectively, which fit well with the model prediction values ( γ DL/SL M = 2.96, 2.18, and 1.97) within high agreement level at a relative standard deviation of 9.6%. Furthermore, the flux ratio of DL2 to SL2 membranes (dual-layer and single-layer membranes with 260 μm total thicknesses and δ / δ o = 2.48 thickness ratio) at different feed inlet temperatures still maintain a high degree of consistency with model values. Overall, the results show the experimental data agree well with the theoretical model prediction for the flux ratio within relative standard deviation of 10.1%, thereby confirming the validity of the proposed model. Additionally, a critical value of the thickness ratio (χ) was calculated χ = 1 + 1 β , this value could provide useful guidance to design a highly efficient hydrophobic/hydrophilic dual-layer composite membrane for DCMD applications in the future work. Image 1 • Dual-layer nanofiber membranes were fabricated by electrospinning for DCMD. • The membrane was composed of PVDF-HFP nanofibers and Nylon 6,6 membrane substrate. • A mathematical model was developed to predict the flux of dual-layer membranes. • The theoretical model was tested and validated by the experimental results. • The experimental data resemble well with the theoretically calculated values. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes combining the processibility of polymers with the properties of porous nano-additives is an effective method to enhance the performance of membrane distillation (MD) process. In this work, a new type of hydrophobic hybrid PVDF hollow fiber membranes doped with aluminum fumarate metal-organic frameworks (AlFu MOF) was fabricated and their performance in direct contact membrane distillation were studied experimentally and theoretically. The results showed that the addition of MOF particles efficiently enlarged the effective porosity of membrane and increased the water flux as well as the thermal efficiency of MD process. At 1 wt% MOF loading, the effective porosity of membrane was enlarged by 52.4%, which induced 55.9% increment in overall mass transfer coefficient of the hybrid membrane, and the thermal conductivity of the membrane was decreased by 38.6%, which contributed to the reduction of sensible heat loss of MD. Correspondingly, the experimental water flux of the hybrid 1 wt% MOF/PVDF membrane was improved by 50.5% and the thermal efficiency increased by 46.2% (0.58 vs 0.31) at a feed temperature of 40 °C. Moreover, the MOF/PVDF membrane exhibited stable flux and retained high salt rejection (>99.9%) for 3.5 wt% NaCl solution over a 50 h desalination test period. Overall, this study provides an insight into the positive effects of AlFu MOF additives on the enhancement of membrane performance in distillation process. Image 1 • Aluminum fumarate MOF was blended with PVDF to fabricate hollow fiber membranes. • Effects of nanoparticle on membrane structure and performance were investigated. • Hybrid membranes showed 50.5% higher flux and 46.2% higher thermal efficiency. • The mechanism on the enhancement of heat and mass transfer performance were revealed. [ABSTRACT FROM AUTHOR]

The textile industry consumes large quantities of freshwater and discharges large quantities of dye/salt wastewater, causing serious environmental problems. Nanofiltration (NF) has proven to be able to achieve efficient dye/salt separation. However, conventional polyamide (PA) NF membranes are often constrained by the trade-off between selectivity and permeability. Herein, we developed a highly dye/NaCl selective nanofiltration membrane with a rod-coated PVA interlayer. The rod-coating approach allows better control of PVA dosage to create a perfect PVA interlayer. The formation and effect of rod-coated PVA interlayer significantly improved the permeability. With an optimal PVA dosage of approximately 0.32 g/m2, the permeance of the iTFC membrane (>30.0 L/(m2 h bar)) was almost 3 times that of the control membrane. Moreover, the iTFC-PVA membrane had an outstanding Rhodamine B rejection (99.8 %), low sodium chloride (NaCl) rejection, and maximum NaCl/dye selectivity ratio as high as 428. It is anticipated that the iTFC membrane has great potential in the field of dyehouse wastewater treatment. Furthermore, our study proves that the Mayer rod-coating approach is suited to fabricating high-performance PA-NF membranes with PVA interlayers. It is anticipated that organic-containing wastewater can better be treated by the developed membrane to achieve a better water environment and resource recovery. [Display omitted] • Rod-coating approach works well to produce and regulate PVA interlayer. • Optimal PVA dosage for a perfect interlayer is about 0.32 g/m2. • iTFC-PVA membrane possesses an excellent NaCl/dye selectivity ratio of 428. [ABSTRACT FROM AUTHOR]

Membrane fouling research has become a focus, significant amount of work has been dedicated to membrane surface modification for improving anti-fouling performance. However, fouling still occurs, which means cleaning is inevitable. The present method is mainly inefficient offline chemical cleaning using specialized chemicals. So we put forward a new method of online chemical pulse cleaning accomplished by designing a kind of pH responsive molecular structure on the PVDF membrane surface, which was prepared through wet chemical strategy, under basic conditions, by using diethylenetriamine (DETA) as carrier of amino groups, and then these amino groups were activated with maleic anhydride (MAH) in order to introduce carboxyl groups. The modified membranes were characterized by attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), mechanical property, streaming potential and contact angle measurements. The results of water flux and swelling degree revealed the flexible chains had excellent pH-responsive. And the modified membranes showed outstanding anti-pollution capability and online chemical pulse cleaning effect when used to separate soybean oil-in-water emulsion and BSA solution. Meanwhile, the flux recovery rates after five times circulation could still reach 90.3% and 95.2%, respectively. This study provides a new way for building antifouling surface and improving cleaning efficiency. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a promising technology for treating saline industrial wastewater, but current hydrophobic MD membranes suffer significant wetting issues due to contaminants commonly present in wastewater. In this study, we report an effective method to fabricate a polyvinylidene fluoride- co -hexafluoropropylene (PVDF-HFP) electrospun nanofiber membrane with improved anti-wetting property against low-surface-tension substances. Without surface activation, the pristine electrospun nanofiber PVDF-HFP membrane with intrinsic re-entrant structure was directly fluorinated by 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS) employing vapor deposition (VD). The fluorinated membrane exhibited excellent surface omniphobicity with high water and ethanol contact angle of 154.1 ± 0.1° and 122.6 ± 1.7°, respectively. The fluorinated membrane showed highly stable omniphobicity and mechanical properties at harsh conditions such as ultrasonic, boiling water, acid and base treatment. More importantly, the resultant omniphobic membrane exhibited robust wetting resistance to the saline feed containing sodium dodecyl sulfate (SDS, 0.4 mM) in an 8-h dynamic direct contact MD (DCMD) test. This study provides an effective and benign approach to fabricate omniphobic nanofiber membranes which have great potential in treating saline wastewater containing low surface tension substances. • An omniphobic electrospun nanofiber membrane was fabricated by an effective method. • No need to activate the surface and creat secondary re-entrant structures before fluorination. • The fluorination was on the basis of physical interaction between PVDF-HFP and FDTS. • The obtained omniphobicity was very stable under harsh conditions. • The omniphobic membrane showed the robust anti-wetting property to surfactants in DCMD. [ABSTRACT FROM AUTHOR]