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Efficient lithium/magnesium (Li+/Mg2+) separation attainment is fundamental to the extraction of lithium from brine by nanofiltration membrane separation process, which is essential for resource recovery and a circular water economy. However, for poly(piperazine‐amide) nanofilm composite membranes, the higher electronegativity affects the Mg2+ rejection and consequently Li+/Mg2+ separation performance. Manipulating the positive charge density and pore size regulation of the nanofiltration membranes are determinative of the Li+/Mg2+ separation performance improvement. Here, a new monomer 1,1′‐(hexane‐1,6‐diyl)bis(1‐methylpiperazin‐1‐ium) bromide containing bis‐quaternary ammonium cations is employed as a molecular building block to fabricate polyamide nanofilms via interfacial polymerization. The dual quaternary ammoniums and the rod‐shaped conformation of the monomer confer enhanced electropositivity, steric hindrance, loosely packed microporous network structure (pore diameter∼0.8–1.35 nm), and high free volume. The resultant membrane exhibits high water permeance of 28.34 L m−2 h−1 bar−1 with good Li+/Mg2+ selectivity of up to 76.9. In addition, the membrane also exhibits chlorine stability performance owing to the lack of the chlorine sensitive −NH groups in the formed tertiary amide structures. Computational insights on the structural properties, nanofilm formation, and transmembrane water and ion transport behaviors are provided. This study offers insightful theoretical and technological concepts to design and construct membrane materials for energy‐efficient separations. [ABSTRACT FROM AUTHOR]

Efficient magnesium-lithium separation is key to extracting lithium resources from salt lake brines. However, efficient magnesium-lithium separation is constrained by the high magnesium-to-lithium ratios on the nanofiltration separation performance due to the weakened Donnan effect and inherent permeability-selectivity trade-off behaviour. To address this challenge, a dual methylpiperidinium ionic liquid was designed in this work and incorporated into polyamide networks to manipulate the structural properties of polyamide membrane for improved magnesium/lithium separation. We demonstrate that the piperidinium modification of polyamide networks not only modulated and enhanced the morphology, hydrophilicity, free volume and electropositivity, but also synergized the steric hindrance differentiation inside the membrane nanochannels. These structural advantages enabled the modified membrane to achieve high-separation performance with enhanced water permeance of 37.3 L m−2 h−1 bar−1 and Mg2+/Li+ selectivity of 30.6 (for Mg/Li mass ratio of 31.2). Molecular dynamics simulations further confirmed that the fast water transport and the difference in the ion separation behaviour are strongly correlated to the enhanced structural properties of membranes. We expect this work to provide insightful guidance for engineering high-performance membranes and make contributions in the application of nanofiltration in lithium mining from high Mg/Li ratio brines. Synopsis: A new dual methylpiperidinium ionic liquid was integrated into polyamide nanofilm to develop nanofiltration membrane with high free volume and steric hindrance differentiation for magnesium/lithium separation. The resultant membrane achieved enhanced permeance combined with improved Li+/Mg2+ selectivity, which was corroborated by molecular dynamics simulations studies. [Display omitted] • Novel dual methylpiperidinium based ionic liquid was designed and synthesized. • Polyamide nanofilm composite membrane with tuned network structures and properties fabricated. • Piperidinium-modification endowed high free volume, enhanced electropositivity and specific surface area properties. • Membrane exhibited enhanced water permeance of ∼37.3 Lm−2 h−1 bar−1 and improved Mg2+/Li+ selectivity of 30.6 • Molecular fundamental insights were provided on membrane structure and water and ion trans-membrane transport. [ABSTRACT FROM AUTHOR]

Phosphorous recovery from wastewater by nanofiltration (NF) is a feasible and sustainable approach, but challenges still exist in the development of highly efficient membranes for the selective permeation of phosphorus. Herein an interpenetrating network (IPN) of crosslinked polyvinyl alcohol (PVA) is integrated with Zn2+ moieties through coordination with the amino groups of crosslinked polyethyleneimine (PEI) and deposited on borate crosslinked polydopamine‐grafted carbon nanotubes (B‐PDA‐CNT) intermediate layer incorporated into the microfiltration substrate to form the composite membrane. The positively charged membrane in acidic conditions affords good rejection (>85%) of heavy metals ions including Cd2+, Cu2+, Zn2+, Pb2+, and Ni2+. Meanwhile, a low phosphorus rejection of <15% is realized with the application of a relatively low transmembrane pressure. This presupposes that the developed approach achieves selective removal of heavy metals from a phosphate solution and is attractive for low pressure recovery of phosphorus. © 2018 American Institute of Chemical Engineers AIChE J, 65: 755–765, 2019 [ABSTRACT FROM AUTHOR]

Polymeric membranes are the most practical separation technology for extracting target ionic species necessary for water purification and clean energy, but are limited by the multi-scale heterogeneity, and transient and dynamic free volume pores. Modulated interfacial polymerization techniques are emergent concepts for preparing polyamide composite membranes with reduced thickness and homogeneous pore structures to satisfy the requirements for efficient ion separation applications. Herein, N–Cyclic cation-assisted kinetically regulated interfacial polymerization strategy to generate polyamide nanofilm composite membranes with tuned pore network and asymmetric structures for water purification is reported. Experimental characterization techniques and molecular dynamic simulations revealed that the N-Cyclic cations control the kinetic diffusion behaviour of the amine monomers to the aqueous/organic interface conducing to the formation of nanofilm membranes with fine-tuned polyamide network structures. Meanwhile, the N–Cyclic cation–regulated IP process not only affords to decrease the thickness of the formed polyamide nanofilm selective layers but also effectively narrows the effective pore size of the membranes. These membranes with thinner, homogeneous and asymmetric polyamide network structures exhibit enhanced water permeance of 55.7–60.42 L m−2 h−1 bar−1, and showed Na 2 SO 4 rejection of 99.59–99.66% and MgCl 2 rejection of 98.94–98.96% in nanofiltration separations, thereby outperforming the permeance–selectivity performance of the state-of-the-art polyamide-based membranes. The membranes also exhibit improved forward osmosis performances. We envision that this research will provide insightful foundations for the molecular tuning and construction of the next-generation structurally modulated polyamide nanofilms for various applications in molecular separation and water purification. Novel Ionic bulky N–Cyclic piperidine-based cations are used to molecularly tune the nanoscale homogeneity and microstructure of polyamide-based thin-film composite membranes via N–Cyclic cation-assisted kinetically regulated interfacial polymerization strategy. The resultant membranes with reduced thickness, homogenous pore network and asymmetric structure exhibits enhanced performances, thereby improving the permeance–selectivity trade-off of the structural polyamide membranes in nanofiltration and forward osmosis separations. [Display omitted] • Novel Ionic bulky N–Cyclic piperidine-based cations are designed and synthesized. • Polyamide-based membranes are fabricated via interfacial polymerization in the presence of N–Cyclic cations. • Steric hindrance of the N-Cyclic cations regulates the spatial distribution of amine monomers. • N-Cyclic cation-assisted regulation leads to reduced thickness, homogenous pore network and asymmetric structure. • Modified membrane exhibit enhanced performances for efficient nanofiltration and forward osmosis separations. [ABSTRACT FROM AUTHOR]

Wastewater containing volatile organic compounds (VOCs) is generated in various industrial processes and is seriously harmful to the natural environment and human health. Its treatment has become extremely important due to increasing environment concerns. Here, a high permeable membrane for fast and high-efficient VOCs removal from aqueous solutions by pervaporation is reported. The as-prepared PIM-1 membrane allows ultrafast permeation of VOCs and exhibits excellent VOCs selectivity, particularly for ethyl acetate, dimethyl ether, and acetonitrile. Typically, the PIM-1 membrane exhibits an ultrahigh flux and separation factor of 39.5 kg μm m−2 h−1 and 189, respectively, in the pervaporation of 1.0 mol% aqueous ethyl acetate solution. Furthermore, the solubility-diffusion mechanism is revealed in the pervaporation of 10 kinds of 1.0 mol% VOCs solutions. It is found that the pervaporation performance is affected directly by physicochemical properties of VOCs. Moreover, effects of feed composition and temperature on the pervaporation are studied in details. © 2015 American Institute of Chemical Engineers AIChE J, 62: 842-851, 2016 [ABSTRACT FROM AUTHOR]

There are increasing requirements for highly efficient and solvent-resistant nanoporous membranes in various separation processes. Traditional membranes usually have a poor solvent resistance and a thick skin layer leading to a low permeation flux. Currently, the major challenge lies in fabrication of ultrathin few-nanometers-pore membranes for fast organic filtration. Herein, a facile approach is presented to prepare ultrafine cellulose nanofibers for fabrication of ultrathin nanoporous membranes. The obtained nanofibers have a uniform diameter of 7.5 ± 2.5 nm and are homogeneously dispersed in aqueous solutions that are favorable to the fabrication of ultrathin nanoporous membranes. The resulting cellulose nanoporous membranes have an adjustable thickness down to 23 nm and pore sizes ranging from 2.5 to 12 nm. They allow fast permeation of water and organics during pressure-driven filtration. Typically, the 30 nm thick membrane has high fluxes of 1.14 and 3.96 × 104 L h−1 m−2 bar−1 for pure water and acetone respectively. Furthermore, the as-prepared cellulose nanofibers are easily employed to produce a novel syringe filter with sub-10 nm pores that have a wide application in fast separation and purification of nanoparticles on few-nanometers scale. [ABSTRACT FROM AUTHOR]