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Thin film nanocomposite membranes have become a feasible technology for heavy metal wastewater treatment. However, how to enhance the dispersibility and compatibility of nanomaterials in the selective layer is an important issue to improve the membrane performance of heavy metal removal. In this study, silica-poly(ionic liquid) nanoparticles were incorporated in the selective layer of TFN membranes. 1-Allyl-3-methyl imidazolium hexafluorophosphate ([AMIm]PF6) was selected to modify silica (SiO2) particles. The formed poly([AMIm]+) brushes provided charge properties to enhance dispersibility and organic part to improve compatibility in the polyamide layer of NF membranes. The resultant TFN membranes incorporated with SiO2-[AMIm]PF6 particles exhibited an increment of 34% water permeation and 41.6% MgCl2 rejection. Moreover, with an average rejection improvement of around 15% for heavy metal ions at pH = 5–6, the SiO2-[AMIm]PF6/PA membrane showed its superiority beyond the PA membrane. The electropositivity and microporous structure of the SiO2-[AMIm]PF6 particles enhanced their dispersibility and compatibility in the polyamide layer. Meanwhile, the proper pore size and structure of the SiO2-[AMIm]PF6 particles contributed to the channels for water transport and the sieving effect for most heavy metal ions. This work may facilitate the applications of TFN membranes in heavy metal wastewater treatment to alleviate the “trade-off” phenomenon.

Electrically conductive membranes have been regarded as a new alternative to overcome the crucial drawbacks of membranes, including permeability-selectivity trade-off and fouling. It is still challenging to prepare conductive membranes with good mechanical strength, high conductivity and stable separation performance by reliable materials and methods. This work developed a facile method of simultaneous phase inversion to prepare electrically conductive polyethersulfone (PES) membranes with carboxylic multiwalled carbon nanotubes (MWCNT) and graphene (Gr). The resultant MWCNT/Gr/PES nanocomposite membranes are composed of the upper MWCNT/Gr layer with good conductivity and the base PES layer providing mechanical support. MWCNT as nanofillers effectively turns the insulting PES layers to be electrically conductive. With the dispersing and bridging functions of Gr, the MWCNT/Gr layer shows an enhanced electric conductivity of 0.10 S/cm. This MWCNT/Gr/PES membrane in an electro-filtration cell achieves excellent retention of Cu(II) ions up to 98 % and a high flux of 94.5 L m−2∙h−1∙bar−1 under a low driven-pressure of 0.1 MPa. The conductive membrane also shows improved anti-fouling capability during protein filtration, due mainly to the electrostatic repulsion and hydrogen evolution reaction on the electrode. This facile strategy has excellent potential in electro-assistant membrane filtration for fouling control and effective separation.

Aminosilane materials, with their low cost and ease of modification, have exhibited great potential for the adsorption of perfluorinated compounds (PFCs) from water. However, this kind of material may be facing two drawbacks during its application: low resistance to hydrolysis and difficulties in separation from the water matrix. This work proposed a strategy of grafting N-(2-aminoethyl) aminopropyltrimethoxysilane (AE-APTMS) on the surface of magnetic γ-Fe2O3 nanoparticles by full utilization of the sorption sites provided by the aminosilane and the magnetism by γ-Fe2O3. The FTIR and XRD results verified the formation of the magnetic AE-APTMS nanocomposite. The core-shell nanocomposite showed a superparamagnetic property and an isoelectric point at pH = 8.2. Particularly, compared to the aminopropyltriethoxysilane (APTES) nanocomposite, the AE-APTMS nanocomposite exhibited improved hydrolytic stability with 60% less loss of the amine groups during the 48 h adsorption process, as the longer alkyl chain hindered the aminosilane detachment. The AE-APTMS nanocomposite exhibited a rapid adsorption with the removal efficiency of 78% for perfluorooctane sulfonate (PFOS) and 65% for perfluorooctanoate (PFOA) due to the electrostatic interaction and hydrophobic interaction. The regeneration and reuse of the magnetic AE-APTMS nanocomposite were conveniently realized with the removal efficiency higher than 70% for both PFOS and PFOA even after 15 adsorption-desorption cycles. The stable magnetic aminosilane nanocomposite with the ease of separation may provide a new strategy to achieve the economical and effective removal of typical PFCs from water.

Electric membrane bioreactor (E-MBR) for wastewater treatment and water purification has attracted significant interest due to its remarkable performance in fouling mitigation. The performance is much relevant to the electric and physicochemical properties of the conductive membranes in E-MBR. This study proposed a facile method to prepare a conductive membrane with low electrical resistance and enhanced hydrophilicity. Oxidative polymerization of pyrrole doping with ionic liquids was conducted on the surface of polyvinylidene fluoride (PVDF) membranes. Among the studied ionic liquids, 1-butyl-3-vinylimidazolium tetrafluoroborate (BVIMBF4) was the most suitable in this work. The electrical resistance of the PVDF membrane modified by pyrrole and BVIMBF4 (PPy-BVIMBF4/PVDF membrane) was as low as 9.76 Ω/sq, and its water contact angle reduced from 81° to 45°. In the fast-filtration tests, these conductive microfiltration membranes exhibited high rejections of Cu2+ ions (~85%) and Ni+ ions (~65%) and enhanced antifouling performance during the bovine serum albumin filtration with the application of an electric field. A long-term E-MBR operation demonstrated that the transmembrane pressure (TMP) rise and the flux decline of the PPy-BVIMBF4/PVDF membrane were significantly alleviated due to its improved conductivity and hydrophilicity. Its total membrane resistance for water transport was only 27% of the base PVDF membranes under a minute electric field of 0.8 V/m. Overall, the incorporation of ionic liquids in the oxidative polymerization of pyrrole offers a novel and effective strategy in conductive membrane fabrication and serves as an excellent method in fouling mitigation in MBR.

In this study, we aimed to design PBI (poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole) blend membranes with a higher water flux by using a less amount of the expensive PBI material and by employing environmentally friendly ionic liquids as the solvent. Five commercially available polyimides and polyimide–amides were screened and P84 (BTDA-TDI/MDI, co-polyimide of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 80% methylphenylenediamine +20% methylenediamine) was chosen to blend with PBI because it formed miscible blends with PBI and interacted closely with the ionic liquid of 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc). An interesting interconnected network of the PBI/P84/[EMIM]OAc solution was evolved based on the highly charge-ordered characteristics of [EMIM]OAc. The blend solution displayed unusual rheological behavior: an initial shear thinning behavior under low shear rates followed by a Newtonian plateau. The incorporation of P84 in the blend system not only lowered the overall viscosity for easier membrane fabrication but also retarded the phase inversion process favorably to form a macrovoid-free morphology. PBI/P84 blend membranes were therefore fabricated for ultrafiltation via non-solvent induced phase inversion method. The effects of PBI/P84 composition and casting temperature on membrane morphology and separation performance were studied according to their phase inversion mechanisms. Compared to plain PBI ultrafiltration membranes, the newly developed PBI/P84 blend membranes exhibit an open cell structure and a reduced thickness which leads to a 50% higher pure water permeability and a larger pore diameter.