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Membrane distillation (MD) has attracted increasing attention for seawater and brackish water desalination, wastewater treatment, and concentration of juices and pharmaceutical solutions due to its feasibility of using low-grade energy and achieving high solute rejection. However, the successful implementation of MD technology is still impeded by membrane wetting resulted from membrane scaling by inorganic crystals and membrane fouling by organic matters in the feed solutions, especially when dealing with challenging wastewaters. Herein, this study describes a novel strategy to develop a robust and superhydrophobic membrane via electrospinning followed by electrospray to enhance membrane anti-wetting properties caused by scaling and fouling. The robust superhydrophobic membrane PDMS-3 comprised a superhydrophobic surface layer fabricated by electrospraying a PVDF/PDMS/silica fume blended solution and an electrospun nanofibrous PVDF support. The newly developed membrane PDMS-3 not only exhibited an outstanding superhydrophobicity with a water contact angle of 170⁰ ± 1⁰, but also showed a unique anti-abrasive feature, which still possessed a slippery superhydrophobic property after 40 abrasion cycles. Moreover, the DCMD tests revealed that this rigid superhydrophobic surface rendered PDMS-3 with the best anti-scaling and anti-fouling properties compared to the nanofibrous and commercial PVDF membranes. It could achieve a superior MD flux of 28 kg m−2 h−1and a stable salt rejection above 99.99% during a continuous 160-h DCMD operation when the feed and permeation solutions were 3.5 wt% NaCl solution at 333K and distillate water at 293 K, respectively. These results underline the importance of anti-abrasive superhydrophobic membrane development to deal with wastewaters containing diverse inorganic and organic matters via MD. • The robust and superhydrophobic composite membranes were fabricated by electrospinning and electrospray. • The abrasive resistance of as-developed superhydrophobic membranes were examined. • PDMS-3 with the highest silica content exhibits the best anti-abrasive property. • Compared to nanofibrous PVDF membrane, PDMS-3 exhibits better anti-scaling and anti-fouling properties. • The surface property of PDMS-3 is significant in determining its long-term stability in MD. [ABSTRACT FROM AUTHOR]

Membrane fouling caused by natural organic matter (NOM) in water is a pressing problem. To address this, heated aluminum oxide particles (HAOPs) have been used as dynamic membranes pre-deposited onto the primary membrane to effectively remove NOM and thereby significantly diminish the fouling potential. An in-depth understanding of the mechanisms underlying the superior performance of HAOPs remains amiss, which motivated this study. Molecular dynamics (MD) simulations were conducted to systematically compare the performance of HAOPs, which have been reported to be particularly effective for high molecular weight (HMW) NOM, with the conventional powdered activated carbon (PAC) adsorbent. Six NOM constituents, three of which have HMW and three have low molecular weight (LMW), were studied. Results indicate that the mechanisms underlying the effective removal of HMW NOM by HAOPs include: (1) higher foulant-HAOPs interaction energy; (2) greater hydration of the HMW NOM, which thereby increases the affinity to the more hydrophilic HAOPs; (3) diminished mobility of the foulant once adsorbed, which deters desorption; and (4) higher peak intensities in the radial distribution functions for multiple functional groups on the HMW NOM foulants. These results are expected to be valuable towards the better design of such materials for mitigating membrane fouling. • Molecular-level insights on superior fouling-mitigation by HAOPs revealed. • Higher NOM-HAOPs interaction energy enhances adsorption. • Increased hydration of NOM increases the affinity to the more hydrophilic HAOPs. • Reduced mobility of NOM by HAOPs upon adsorption deters desorption. • High intensity of peaks in RDF for functional groups underlies improved NOM removal. [ABSTRACT FROM AUTHOR]

Polyamide thin film membranes have shown outstanding performance in organic solvent nanofiltration (OSN). However, it is still challenging to produce polyamide hollow fibres for OSN, mainly due to limited solvent resistance of hollow fibre substrates and the difficulty to synthesize polyamide thin film on the surface of hollow fibre substrates. In this study, polyamide-based hollow fibre composite members for low pressure OSN were successfully developed. Solvent resistant polyimide hollow fibre substrates were first prepared through a non-solvent induced phase separation process, followed by chemical cross-linking with hexamethylene diamine. A polyamide thin film layer was then synthesized via interfacial polymerization, by circulating the reactant monomers including polyethyleneimine (PEI), piperazine (PIP) and trimesoyl chloride (TMC) through the hollow fibre lumen. The polyamide thin film with a thickness of ~60 nm was formed on the inner surface of the hollow fibre substrates. The membranes exhibited excellent nanofiltration (NF) performance under 2 bar operating pressure. The permeability of water, acetone and isopropanol was 6.8, 11.6 and 4.5 l m−2 h−1 bar−1, respectively. The membranes also achieved 99.9% and 91.8% rejection to rose bengal (1017 Da) and acid fuchsin (585 Da), respectively, in acetone. Furthermore, a 72-h filtration test was conducted and the membrane showed steady performance throughout the testing period. This study demonstrates the possibility of fabricating polyamide hollow fibre membranes for organic solvent nanofiltration at low pressure, which is desirable for practical applications. • Solvent resistant polyimide hollow fibre membranes were fabricated through chemical cross-linking. • Polyamide-based (PEI/PIP) layer was formed onto polyimide substrate to obtain a relatively loose selective layer. • Membranes achieved 11.6 and 4.5 l m−2 h−1 bar−1 permeability in acetone and isopropanol at 2 bar respectively. • Membranes maintained more than 90% rejection for acid fuchsin in 72-h filtration test, showing stable OSN performance. [ABSTRACT FROM AUTHOR]

In this study, we presented a novel nanofiltration membrane fabrication strategy through rapid co-deposition of a versatile platform – metal phenolic networks (MPNs) and piperazine (PIP) on a porous substrate followed by trimesoyl chloride (TMC) crosslinking. Inspired by the catechol chemistry, tannic acid (TA) was functionalized to tether PIP monomers, and participated in the co-deposition via coordination bonds with Fe3+ ions on a substrate to form Fe3+/TA-PIP complex. A series of analyses (SEM, XPS, FT-IR, water contact angle and zeta potential) confirmed the successful synthesis Fe3+/TA-PIP deposition and polyamide (PA) layer. The resultant membrane exhibited water permeability of 13.73 LMH/bar and 89.52 % for MgSO 4 rejection. The fabrication was further improved by embedding modified graphene oxide (GO) nanosheets into the Fe3+/TA-PIP complex. The optimized nanocomposite membrane achieved a water permeability at 21.66 LMH/bar, along with a well maintained MgSO 4 rejection at 91.25 % and NaCl/MgSO 4 selectivity (α) at 10.02 under 2 bar operation pressure. The rapid co-deposition mediated by nanomaterials incorporation provides an effective approach to design high performance thin film composite (TFC) membrane. Image 1 • A novel fabrication strategy was designed for nanofiltration membrane. • Metal phenolic networks were rapidly co-deposited with piperazine followed by interfacial polymerization. • Graphene oxide was incorporated into the deposited layer without additional fabrication step. • The optimized thin film composite membrane exhibited high separation performance. [ABSTRACT FROM AUTHOR]