Search

Various salt additives were widely used to enhance the permeability of thin-film composite (TFC) membranes. Researchers attributed the improvement in TFC membranes to the change in the polyamide (PA) layer. However, the contribution degree of PA layer to TFC membrane permeability enhancement and the effect of salt additives on the substrate are ambiguous. In this study, the effect of salt additives on the permeation resistance of FTC membranes was analyzed. The results showed that the salt additives could reduce both the permeation resistance of the PA layer and substrate, but the effect on the substrate was more pronounced. For example, after adding NaCl, the permeation resistance of the substrate in the heat curing membrane reduced from 0.1764 to 0.0201 bar h m−1, which was much more than that in the PA layer. This study revealed a new mechanism of salt additives improving the permeability of TFC membranes and deepened the understanding of the action mechanism of salt additives. [Display omitted] • A series of TFC membranes with salt additives are fabricated. • TFC membranes with salt additives show a looser and thinner PA layer. • Salt additives greatly reduce the increase of substrate resistance during heat curing. • A new mechanism of salt additives to enhance membrane's permeability is revealed. [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]

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]

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]

In recent years, the incorporation of nanoparticles in nanofiltration membranes has received extensive attention as a practical approach to improve membrane performance. However, previous studies attributed the enhancement of TFN membrane performance primarily to the advanced properties of nanoparticles and the structural impact on the polyamide layer, while ignoring the influence and contribution of the substrate. This study provides compelling evidence that the effect on the substrate of blending nanoparticles contributes to the enhancement of membrane permeability. We quantified the changes in permeation resistance composition of the TFC and TFN membranes before and after heat treatment by a resistance-in-series model, combined with the addition of polyvinylpyrrolidone. After incorporation of ZIF-8, the permeation resistance of substrate decreased from 0.177 h bar m−1 to 0.0313 h bar m−1 after heat curing, while that of PA layer decreased from 0.1375 h bar m−1 to 0.0972 h bar m−1. In addition, we removed the PA layer of TFC and TFN membranes by acid hydrolysis. The results indicated that the PWP of TFN membrane were continuously greater than that of the TFC membrane, which supports our conclusion that nanoparticles impacted the shrinkage of substrate during heat curing. The current study provides a novel mechanistic understanding of the improvement of TFN membrane performance by nanoparticles. [Display omitted] • Mechanism of permeability enhancement for thin-film nanocomposite nanofiltration membrane is investigated. • The water permeation resistance of PES support and polyamide layer of the TFC and TFN membranes are quantitatively revealed. • The polyvinylpyrrolidone molecule was employed to alleviate the shrinkage of substrate structure caused by heat curing. [ABSTRACT FROM AUTHOR]