Influence of contaminants in glycerol/water mixtures during post-treatment on physicochemical properties and separation performance of air-dried membranes

Lithium chloride (LiCl)-modified polyethersulfone (PES) substrate surface pore architectures on thin poly(dimethylsiloxane) (PDMS) dense layer formation and the composite membrane's performance in gas separation

The use of pore forming agents has been notable for improving the water flux in a water-based separation membrane but are rarely being studied as a methodology to influence the substrate's surface architectures for composite membrane fabrication in gas separation. In this study, the influence of lithium chloride (LiCl) on the surface pore architectures and hence, the gas permeance, has been studied in both bare and composite forms with poly(dimethylsiloxane) (PDMS). 1-4 wt% of LiCl was mixed with the dope solution of PES/NMP in the ratio 0.19 and was casted via the dry-wet phase inversion method. Bare substrates were noted to possess increasingly larger surface pore sizes but at a diminishing surface pore density with maximum surface porosity at 2 wt% LiCl. The permeances were, however, significantly reduced with the increase in the LiCl content from 105 300 to 4300 GPU for N₂ gas, presumably due to the thicker skin layer. Nevertheless, the porous surface morphology was confirmed and exhibited Knudsen selectivity with a CO₂/N₂ selectivity of about 0.8, signifying minimal gas flow resistance by the substrates. Upon coating with a similar amount of thin PDMS layer, the composite permeances retain the same trend with values from 361.9 GPU for 0 wt% LiCl substrates to 68.8 GPU for 4 wt% LiCl substrates for CO₂ gas at a consistent selectivity of about 14. As the PDMS layer of the same volumes were used and no significant difference in the coating thickness was noted, the mixed influence of pore intrusion and lateral diffusion is hypothesised at the substrate-coating interface owing to the different surface pore architectures of the substrates.

Low pressure modified polyamide 6 membrane for effective fractionation of dyes and NaCl

A co-polymer (SPAA6) of 5-sulfoanthranilic acid (5SAA) and ε-caprolactam was used to prepare membrane through nonsolvent induced phase separation (NIPS) method. The micro-structure of membrane was adjusted by small molecules to improve mechanic strength and performance, involving 7 commercial ionic surfactant and a self-synthesized one, S20. S20 showed the best compatibility with SPAA6, which converted spherical phase into network of strip-like units in micro-structure of membrane. Meanwhile, average pore size of the membrane was narrowed from 4.271 nm to 3.391 nm, tested by BET method. Tensile strength of membrane was improved from 2.5 MPa to 2.9 MPa. Therefore, anionic dyes rejection and membrane stability were both improved. It actually demonstrated that molecular weight distribution of SPAA6 was crucial for micro-structure construction of membrane since S20 was the SPAA6 of low molecular weight. In blend solution filtration test, membrane MS2 (1:2 for S20:SPAA6) displayed 98.22% rejection to Congo Red (CR) acid and 96.18% NaCl permeation under 1 bar. It showed 80.18% rejection to chrome blue K (ABK) and 96.28% NaCl permeation. Both water permeance were higher than 3.5 L·m^-2·h^-1·bar. Membrane MS2 showed the potential of fractionation of dye and NaCl, which was promising in textile waste water treatment.

Multifunctional Core-Shell Zwitterionic Nanoparticles To Build Robust, Stable Antifouling Membranes via Magnetic-Controlled Surface Segregation

Novel multifunctional core-shell nanoparticles (Fe₃O₄@PSBMA NPs) with magnetic and zwitterionic properties were first synthesized and efficiently incorporated into the poly(vinylidene fluoride) (PVDF) membranes via magnetically controlled surface segregation toward the better water-energy-food nexus. The combination of zwitterionic polymers poly(sulfobetaine methacrylate) (PSBMA) and Fe₃O₄ particles can improve the compatibility of additives with the PVDF matrix and significantly improve the migration of Fe₃O₄@PSBMA NPs onto membrane surfaces under magnetic fields during nonsolvent-induced phase separations. The modified membrane with surface-enriched multifunctional zwitterionic NPs had an enhanced water flux (168%, ∼630.5 L m^-2 h^-1), excellent fouling resistance (∼93.8%), and increased rejection to bovine serum albumin (94.1%). Most importantly, the PVDF/M-Fe₃O₄@PSBMA membrane had excellent stability under the long-term filtration test for practical water-treatment applications.