Modulating the Asymmetry of the Active Layer in Pursuit of Nanofiltration Selectivity via Differentiating Interfacial Reactions of Piperazine

Self Cite

Thin film composite polyamide (TFC) nanofiltration (NF) membranes represent extensive applications at the water-energy-environment nexus, which motivates unremitting efforts to explore membranes with higher performance. Intrusion of polyamide into substrate pores greatly restricts the overall membrane permeance because of the excessive hydraulic resistance, while the effective inhibition of intrusion remains technically challenging. Herein, we propose a synergetic regulation strategy of pore size and surface chemical composition of the substrate to optimize selective layer structure, achieving the inhibition of polyamide intrusion effective for the membrane separation performance enhancement. Although reducing the pore size of the substrate prevented polyamide intrusion at the intrapore, the membrane permeance was adversely affected due to the exacerbated “funnel effect”. Optimizing the polyamide structure via surface chemical modification of the substrate, where reactive amino sites were in situ introduced by the ammonolysis of polyethersulfone substrate, allowed for maximum membrane permeance without reducing the substrate pore size. The optimal membrane exhibited excellent water permeance, ion selectivity, and emerging contaminants removal capability. The accurate optimization of selective layer is anticipated to provide a new avenue for the state-of-the-art membrane fabrication, which opens opportunities for promoting more efficient membrane-based water treatment applications.

Section: Implicationmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Implicationmentioning

confidence: 99%

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Inhibiting Polyamide Intrusion of Thin Film Composite Membranes: Strategies and Environmental Implications

Qian

et al. 2023

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“…For all membranes, the rejection of SO 4 2– was much higher than that of Cl – , which is a characteristic of negatively charged membranes, relatively regardless of the negative charge density. The higher rejections of Mg 2+ and Ca 2+ than Na + even when the membrane surface negative charge density was enhanced, different from the rejection behavior for single salt solutions, was due to the fact that Mg 2+ and Ca 2+ have stronger steric hindrance and dielectric effects compared with Na + and higher hydration energy so that they are not easy to dehydrate to enter membrane pores, especially when the membrane pore sizes are relatively small. ,− …”

Section: Resultsmentioning

confidence: 99%

Molecular Design of the Polyamide Layer Structure of Nanofiltration Membranes by Sacrificing Hydrolyzable Groups toward Enhanced Separation Performance

Wang

et al. 2022

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Nanofiltration (NF) is an effective technology for removing trace organic contaminants (TrOCs), while the inherent trade-off effect between water permeance and solute rejections hinders its widespread application in water treatment. Herein, we propose a novel scheme of "monomers with sacrificial groups" to regulate the microstructure of the polyamide active layer via introducing a hydrolyzable ester group onto piperazine to control the diffusion and interfacial polymerization process. The achieved benefits include narrowing the pore size, improving the interpore connectivity, enhancing the microporosity, and reducing the active layer thickness, which collectively realized the simultaneous improvement of water permeance and enhancement of TrOCs rejection performance. The resulting membranes were superior to both the control and commercial membranes, especially in water-TrOCs selectivity. The effects of using the new monomers on the membrane physicochemical properties were systematically studied, and underlying mechanisms for the enhanced separation performance were further revealed by simulating the polymerization process through density functional theory calculation and measuring the trans-interface diffusion rate of monomers. This study demonstrates a novel promising NF membrane synthesis strategy by designing the structure of reaction monomers for achieving excellent rejection of TrOCs with a low energy input in water treatment.

“…The probable swelling and deformation of polyelectrolyte layers induced by high salinity and pressure conditions are obstacles which need to be solved for the practical applications of PEM membranes. , Large-scale fabrication of these membranes also remains a challenge. Besides the commonly used modification methods and polymer-based novel chemistry of selective layers elaborated in detail in this review, other delicate strategies (e.g., capillary-assisted IP and amine modification , ) to regulate the formation of PA membranes and exploitation of two-dimensional nanomaterials (e.g., graphene oxide, molybdenum disulfide, MXene, , etc.) as building blocks of selective layers have attracted growing research interests in recent years.…”

Section: Concluding Remarks and Research Outlookmentioning

confidence: 99%

Boosting the Performance of Nanofiltration Membranes in Removing Organic Micropollutants: Trade-Off Effect, Strategy Evaluation, and Prospective Development

Liu

Wang

Zhou

et al. 2022

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In view of the high risks brought about by organic micropollutants (OMPs), nanofiltration (NF) processes have been playing a vital role in advanced water and wastewater treatment, owing to the high membrane performance in rejection of OMPs, permeation of water, and passage of mineral salts. Though numerous studies have been devoted to evaluating and technically enhancing membrane performance in removing various OMPs, the trade-off effect between water permeance and water/OMP selectivity for state-of-the-art membranes remains far from being understood. Knowledge of this effect is significant for comparing and guiding membrane development works toward cost-efficient OMP removal. In this work, we comprehensively assessed the performance of 88 NF membranes, commercialized or newly developed, based on their water permeance and OMP rejection data published in the literature. The effectiveness and underlying mechanisms of various modification methods in tailoring properties and in turn performance of the mainstream polyamide (PA) thin-film composite (TFC) membranes were quantitatively analyzed. The trade-off effect was demonstrated by the abundant data from both experimental measurements and machine learning-based prediction. On this basis, the advancement of novel membranes was benchmarked by the performance upper-bound revealed by commercial membranes and lab-made PA membranes. We also assessed the potentials of current NF membranes in selectively separating OMPs from inorganic salts and identified the future research perspectives to achieve further enhancement in OMP removal and salt/OMP selectivity of NF membranes.