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Heavy metals pollution is an urgent problem that seriously hazards human health and ecosystems. Herein, dually charged nanofiltration (NF) membranes were prepared via a facile modification with diethylenetriamine (DETA) after interfacial polymerization. More amine groups were imported after grafting and a polyamide layer with opposite charges was constructed. The as-prepared membranes had a pure water permeability of 17.0 L m−2 h−1 bar−1 and maintained ideal rejection for both Na 2 SO 4 (98.2%) and MgCl 2 (94.1%), illustrating dually charged property. In addition, the dually charged NF membranes had high rejection to a series of heavy metals, showing good application potential in heavy metals removal. [Display omitted] • The dually charged NF membranes were fabricated by microwave-assisted grafting of diethylenetriamine after interfacial polymerization. • The as-prepared membrane showed a PWP of 17.0 L m−2 h−1 bar−1 and high rejection to both Na 2 SO 4 (98.2%) and MgCl 2 (94.1%)。 • The dually charged NF membranes had high rejection to a series of heavy metals, showing good application potential in heavy metals removal. [ABSTRACT FROM AUTHOR]

Separation performance of nanofiltration (NF) membranes is constrained by the trade-off between permeability and selectivity. Herein, a facile and environmental friendly water activation before microwave heating was performed to improve the performance of NF membranes and overcome this trade-off. The water activation before microwave heating facilitated the hydrolysis of acyl chloride, resulting in a loose polyamide layer with enhanced hydrophilicity and surface charge. The activated NF membrane showed a permeance of 29.9 L m-2 h-1 bar-1, which is almost 2 times higher than the control. The membrane possesses a Na 2 SO 4 rejection of 96.8% and high selectivity to antibiotics and NaCl. At the meantime, the fouling resistance to model foulants including bovine serum albumin and sodium alginate was significantly enhanced. The water activation before microwave heating is proved to be an adequate strategy for fabricating NF membranes. [Display omitted] • A facile water activation before microwave heating was performed to prepare PA NF membranes. • The activated NF membrane showed a 95.9% increment in permeance compared to the control. • The activated NF membrane had good performance in separating antibiotics and NaCl. • The activated NF membrane showed enhanced fouling resistance to BSA and SA. [ABSTRACT FROM AUTHOR]

The TFC RO/NF membranes are the predominant membranes applied in desalination, and heat curing is an essential step in its industrial production, which increases the polyamide cross-linking degree and facilitate packing but leads permeability decrease. Nevertheless, the mechanism of heat curing on TFC membranes permeation resistance changes is still ambiguous. Figuring it out will aid in crafting a more effective optimization strategy in high flux membrane preparation. Herein, we prepared a range of TFC RO/NF membranes with various monomer concentrations on different substrates and quantified the permeation resistance changes by a resistance-in-series model. For nascent TFC RO/NF membranes, the PA layer provided almost all permeation resistance. After heat curing, the substrate exhibited a marked increase in permeation resistance. The change in the permeation resistance composition was further exacerbated by the decrease in monomer concentration. For TFC NF membranes with heat curing, the proportion of substrate permeation resistance increased significantly, rising from 31.62 % to 75.05 %. This study made a comprehensive analysis of the impact of the permeation resistance in TFC RO/NF membranes caused by heat curing, enriched the insight into the impact of heat curing on TFC membranes, and helped to prepare TFC membranes with better desalination performance. [Display omitted] • The resistance proportions of RO/NF membranes are quantitatively revealed. • The substrate resistance increases significantly due to heat curing. • Low monomer concentration results in high substrate resistance. [ABSTRACT FROM AUTHOR]

This study investigated the chemical stability differences between dry and wet nanofiltration membranes when immersed in strong acid and base environments. Systematic experimental studies were conducted on both types of nanofiltration (NF) membranes, supplemented by Molecular Dynamics (MD) simulations and Density Functional Theory (DFT) calculations. The results indicate that wet NF membranes, soaked in deionized water for a week, exhibit higher chemical stability compared to dry membranes treated only with air. Traditional air heating causes membrane pore contraction and excessive crosslinking. However, after a week of immersion in water, the polyamide (PA) layer gradually becomes a loose and well-extendable PA layer. MD simulations revealed that H+ and OH− ions possess lower diffusion coefficients and extended residence times in dry NF membranes, making them more prone to damage. Additionally, DFT calculations disclosed that the Gibbs free energy (ΔG) for amide bond hydrolysis in wet NF membranes, in the presence of water molecules, is elevated, significantly delaying their hydrolysis rate under extreme conditions. This study highlights the pivotal role of membrane wetness in the chemical durability of NF membranes and offers a novel perspective for improving membrane lifespan and efficiency. [Display omitted] • Wet NF membranes show markedly higher chemical stability in acidic and basic environments. • MD simulations indicate lower ion diffusion and longer residence times in dry NF membranes. • DFT calculations reveal slower amide bond hydrolysis in wet membranes, enhancing durability. • Study offers new insights for extending NF membrane lifespan and improving filtration efficiency. [ABSTRACT FROM AUTHOR]

Given the critical requirements of environmental preservation and resource reutilization, the recovery of lithium from spent lithium-ion (LIBs) batteries holds immense significance. This study investigates the viability of nanofiltration (NF) membranes for selectively separating lithium from spent LIBs leaching solution. A membrane-based approach uniquely sidesteps the significant metal losses often encountered in traditional methods that necessitate initial pH adjustments. The NF270 and DK membranes were characterized and evaluated. DK demonstrated superior rejection capabilities for high-valence metal ions with over 99.0 % rejection, while allowing a notable 40.1 % lithium passage rate. Furthermore, DK showcased enhanced acid resistance compared to NF270. The findings underscore the characteristics essential for NF membranes in this application, and the study affirms the feasibility of membrane-based lithium recovery, marking a stride in battery recycling research. [Display omitted] • Proposed a novel membrane-based process for spent lithium battery recycling • The battery-grade lithium carbonate can be obtained through two-stage nanofiltration. • DK membrane exhibits excellent acid resistance and high-valence metal ion rejection to the leaching solution. [ABSTRACT FROM AUTHOR]

Recent research has focused on the acid resistance of polyamide nanofiltration (NF) membranes, a critical aspect for their stability during practical applications. However, the impact of different acids, particularly the role of various anions, on NF membrane acid resistance remains unexplored. Our research systematically evaluates NF membrane performance and property alterations under various acids at identical pH levels, supplemented by density functional theory (DFT) simulations. Results reveal that membranes treated with H₃PO₄ retain desirable NF performance, in stark contrast to those treated with H₂SO₄ and HCl, which undergo significant degradation. Specifically, H₃PO₄-treated membranes showed only a 4.2 % decline in Na₂SO₄ rejection, compared to a dramatic 83.3 % decline for HCl-treated membranes under identical pH. This degradation is linked to the acids infiltrating the polyamide structure. The membrane's enhanced resistance to H₃PO₄ is primarily due to the strong negative charge of phosphate ions, influenced by the Donnan effect, which prevents deep penetration into the membrane. This is further supported by DFT simulations, which reveal that the interaction energy between the membrane surface and phosphate ions is over twice as high as with chlorine ions, highlighting the importance of ion-specific interactions. This research highlights the crucial role of anions in acidic environments for the maintenance and operation of NF membranes in industrial applications. It provides key insights for enhancing membrane efficiency and longevity under acidic conditions. [Display omitted] • Filled the research gap in polyamide membranes resistance to different acids. • Revealed the variance in acid resistance for anionic charge-induced Donnan effect. • Provides insights for optimizing acid utilization in industrial processes. [ABSTRACT FROM AUTHOR]

Although covalent organic frameworks (COFs) membranes have promising applications in water treatment due to their ordered structure and adjustable pore size, most of them are imine-linked ones, which severely limits their application in harsh environments. Herein, we offer a stable novel COFs membrane which is composed of hydrazone bonds and β-ketoenamine structures. Such β-ketoenamine based COFs composite membrane was fabricated via interfacial catalytic polymerization on a nylon substrate, which was generated at the water (P-Toluenesulfonic acid)/n-hexane (2,5-dimethoxyterephthalhydrazide, 1,3,5-triformylphoroglucinol) interface. The resultant COFs membrane demonstrates excellent chemical stability in strong acidic (2 mol/L)/alkaline (9 mol/L)/organic solvents (dioxane, acetone, methanol, and ethanol) media. The optimized COFs membrane achieved 109.73 L m−2 h−1 bar−1 permeance in Congo Red aqueous solution and 99.56 % CR rejection. This study exploits a novel approach to produce robust COFs membranes under extreme conditions. [Display omitted] • TpDMTH COFs membranes were fabricated via interfacial catalytic polymerization. • The combination of hydrazone bonds and β-ketoenamine structures makes membranes show stable chemical structure. • Such COFs membranes maintained excellent separation performance in 9 M NaOH solution. • Such COFs membranes showed excellent dye/salt separation performance. [ABSTRACT FROM AUTHOR]

Monomers are elementary units that constitute the polyamide layer, which determines the properties of nanofiltration membranes. The design of nanofiltration membranes with both high separation performance and outstanding chemical stability remains a challenge. In this study, two typical monomers, heterocyclic monomer molecule-piperazine (PIP) and carbon ring molecule-1,4-cyclohexane diamine (CHDA), were applied as aqueous monomers for interfacial polymerization to generate polyamide nanofiltration membranes. The physicochemical properties of the two nanofiltration membranes were comprehensively investigated. The results demonstrated that the nanofiltration membrane fabricated via CHDA exhibited more chemical stability than that fabricated via PIP. The mechanisms influencing the chemical stability difference were elucidated via multiscale simulation. The CHDA polyamide has higher levels of HOMO-LUMO energy and Gibbs-free energy, which make it more stable under harsh chemical environments. Overall, this work presents the effect of the diamine structure on the chemical stability of polyamide NF membranes, which can inspire highly chemically stable nanofiltration membrane fabrication. [Display omitted] • Effect of diamine structure for NF membrane chemical stability was investigated. • Carbon ring molecule had better chemical stability than heterocyclic molecule. • Experimental study showed a high correlation with simulation calculations. [ABSTRACT FROM AUTHOR]

Currently, most nanofiltration membranes exhibit satisfactory separation performance on the anions or cations, and few membranes could concurrently separate anion and cation. Therefore, preparing nanofiltration membranes with excellent separation performance for both anionic and cationic ions remains a challenge. Herein, we have developed a series of nanofiltration membranes using conventional interfacial polymerization with different ratios of trimesoyl chloride (TMC) and piperazine (PIP) concentrations. In the interface polymerization process, the amine groups carried by PIP imparted a positive charge, while the hydrolysis of acyl chloride groups resulted in the generation of carboxylic acid groups that introduced a negative charge. The mix-charged nanofiltration membrane could be fabricated by varying PIP/TMC concentration ratios. The optimized membrane exhibited high rejection rates for bivalent ions (Na 2 SO 4 rejection of 96.6 %, MgCl 2 rejection of 93.0 %), and its selectivity for Mg2+/Li+ mixed solution was improved significantly. This work provides a novel approach for the development of nanofiltration membranes capable of effectively separating mono-/divalent ions. [Display omitted] • Fabrication of mixed-charged polyamide membranes via regulating the PIP/TMC ratio directly. • High PIP/TMC ratio leads more unreacted amine groups in the polyamide which was beneficial to MgCl 2 rejection. • Such NF membrane showed excellent separation efficiency to Mg2+/Li+ and SO 4 2−/Cl−. [ABSTRACT FROM AUTHOR]