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According to the Freeman theory, increasing the backbone stiffness to some extent is an effective way to obtain the remarkable membrane with both high permeability and selectivity. In this work, a high performance nanofiltration (NF) membrane was prepared via tailoring the polyester/polyamide backbone stiffness. The flexible monomer-piperazine (PIP) and the rigid monomer-bisphenol F (BPF) were selected as the aqueous phase monomers, and they were interfacial reacted with trimesoyl chloride (TMC) on the polyethersulfone (PES) UF membrane to generate the polyester/polyamide layer. By mixing PIP with BPF, both of the polyester/polyamide backbone stiffness and microporosity degree enhanced. As a result, the PIP/BPF NF membrane possessed a 2.6-fold pure water flux (PWF) of the PIP NF membrane (the salt rejection remained at the same level), and 4.8-fold PWF of the BPF NF membrane. Our results revealed a novel and facile way to improve the NF membrane performance. [ABSTRACT FROM AUTHOR]

A novel polypiperazine-amide nanofiltration (NF) membrane with very high salt rejection was successfully developed in this work. The NF membrane chlorine-tolerant ability were improved greatly after mixing a small amount of α,ω-diamino poly(ethylene glycol) (NH 2 -PEG-NH 2 ) with piperazine (PIP) in the aqueous phase. The XPS result demonstrated that the polymerization degree of the NF membrane was notably enhanced with the addition of NH 2 -PEG-NH 2 . The solute rejections and chlorine tolerance were improved remarkably, while the permeate flux remained almost at the same level. When the NH 2 -PEG-NH 2 (2 kDa) content in the total amine was 1%w/w (0.01%w/v in the aqueous solution), NF membrane performance was optimal. This membrane exhibited a pure water flux (PWF) of 34.9 L m −2 h −1 along with Na 2 SO 4 , MgSO 4 , MgCl 2 and NaCl rejections of 99.5%, 99.2%, 90.9% and 58.3% (2000 ppm, 6 bar, 25 °C), respectively. Moreover, the NF membrane performance was maintained after being treated by 14,000 ppm NaClO for 1 h. Therefore, adding a small amount of NH 2 -PEG-NH 2 in the aqueous phase could be considered to be an effective way to improve the polypiperazine-amide NF membrane chlorine-tolerant ability. [ABSTRACT FROM AUTHOR]

In the practical application of nanofiltration (NF) membrane, regular chemical cleaning is necessary to eliminate the membrane fouling and ensure the normal operation of the system. Generally, the commercial NF membranes can be divided into MPD-TMC membranes and PIP-TMC membranes of which the permeability and pH resistance cannot be balanced. In this work, the ultra-low concentration monomers of MPD and TMC were used to fabricate the dense polyamide layer of NF membrane through a conventional interfacial polymerization reaction. The newly prepared membrane exhibited a smooth surface with very low roughness. Besides, the pore size distribution and desalination performance including water permeability and salt rejection of our membrane were comparable to the lab-made and commercial PIP-TMC membranes. The membrane was also confirmed to have an excellent separation efficiency to SO 4 2−/Cl− anions and good resistance to extreme pH conditions. Overall, this study presents a new insight for the preparation of high-performance NF membrane with good chemical stability. [Display omitted] • NF membrane fabricated by interfacial polymerization of low concentration MPD and TMC. • Separation degree changed from RO to NF with the decreasing monomer concentration. • MPD-based NF membrane presented high permeability and good selectivity to Cl−/SO 4 2-. • Higher acid and alkali resistance than a lab-made PIP-based NF membrane. [ABSTRACT FROM AUTHOR]

Novel high-flux thin film composite (TFC) nanofiltration (NF) membranes were fabricated by the sodium hypochlorite (NaClO) pre-oxidation of the mixed diamine monomers of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) in the aqueous phase solution, and via interfacial polymerization (IP) with trimesoyl chloride (TMC) on the polysulfone (PSF) ultrafiltration (UF) membrane. The chemical change of the pre-oxidation aqueous phase solution was characterized by LC-MS. By optimizing the NaClO and NaOH content in the aqueous phase solution, the pure water flux was improved greatly and the salt rejection kept on a high level (>90%). The properties of NF membranes were characterized by XPS, SEM, AFM and contact angle. Through the NaClO pre-oxidation of the mixed diamine monomers of PIP and BHTTM in the aqueous phase solution, the active layer of NF membrane became thinner and the pore size of NF membrane was enlarged. Besides, after oxidation treatment by 3000 ppm active chlorine solution for 1 h, the NF membrane exhibited pure water flux (PWF) with 161 (LMH) and Na 2 SO 4 rejection of 92.1% under 0.6 MPa. The molecular weight cut-off (MWCO) of the NF membrane was greater than 500, which was calculated from the carbohydrates rejection. The good performance and the satisfactory stability of the novel high-flux NF membrane demonstrated its good potential in the practical application. [ABSTRACT FROM AUTHOR]

Using Polysulfone (PSF) ultrafiltration (UF) membrane as porous support, a chlorine-tolerant nanofiltration (NF) membrane was prepared by interfacial polymerization of piperazine (PIP) and 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4'-methylenedianiline (BHTTM) mixture with trimesoyl chloride (TMC). The XPS, SEM, AFM and contact angle methods were employed to characterize the physicochemical properties and morphology of the prepared NF membranes. The effects of preparation conditions such as reaction time, monomers mixing ratio and oxidation treatment on NF membrane performance were investigated. The salt rejection of the NF membrane met the order of Na 2 SO 4 >MgSO 4 >NaCl, indicating the membrane possessed a negative surface charge. The results showed the NF membrane prepared under the optimum conditions exhibited pure water flux (PWF) with 79.1 (L/m 2 h) and Na 2 SO 4 rejection of 99.5% under 0.6 MPa. The optimized post oxidation condition was treated by 3000 ppm NaClO solution for 1 h. The best NF membrane had a molecular weight cut-off (MWCO) less than 300 Da, corresponding to the pore size of 1 nm, which was calculated from the rejection of carbohydrates. The robustness of the NF membrane was proven by showing satisfactory stability in the long time running. [ABSTRACT FROM AUTHOR]

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]

Surface modification is an efficient post-treatment method to optimize the properties of nanofiltration (NF) membranes. Here, we report a facile surface modification strategy coupling with heat curing for grafting monoethanolamine (MEA), a monomer containing both a primary amine and a primary alcohol group, onto a nascent polyamide NF membrane. With grafting 0.5 wt% MEA at 50 °C, the pure water permeability of the polyamide NF membranes was improved from 7.9 to 19.5 L m−2 h−1 bar−1 due to their enhanced physicochemical property, such as superior hydrophilicity, rough surface morphology, and enlarged membrane pores. Meanwhile, the rejection of Na 2 SO 4 remained above 97.5%. More importantly, the optimal membrane modified with 0.5 wt% MEA exhibited a high Na 2 SO 4 rejection of 99.1% and a negative NaCl rejection of −20.1% when treating a mixed salt solution containing 2 g/L Na 2 SO 4 and 2 g/L NaCl. Our study provides a novel insight for the fabrication of high permselectivity NF membranes via surface modification. Image 1 • Surface grafting was creatively coupled with heat curing in water. • Monoethanolamine molecule was successfully grafted onto the nascent membrane, rendering a better hydrophilic nanofiltration membrane. • The modified membrane exhibited enhanced pure water permeability of 19.5 L m−2 h−1 bar−1. • The modified membrane owned superior Cl−/SO 4 2− selectivity. [ABSTRACT FROM AUTHOR]

By causing the water molecule vibration to generate heat, microwave has become a rapid and efficient heating method which is widely used in industrial production. Herein, microwave heating assistant interfacial polymerization (IP) process was innovatively applied to fabricate polypiperazine-amide nanofiltration (NF) membrane for the first time. With microwave heating, a uniform and faultless polyamide (PA) layer could be generated with low monomer concentration. The pure water flux (PWF) of the NF membrane fabricated with microwave heating was 157.1 L m-2 h-1 with the Na 2 SO 4 rejection of 97.7% under 0.6 MPa. Meanwhile, such NF membrane showed extraordinary selectivity to Cl- and SO 4 2− for a series of mixing solution with different concentrations. This new insight into microwave heating assistant IP provides a feasible method for the high-permselectivity NF membranes fabrication. Image 1 • The microwave heating was applied for the IP process to fabricate TFC NF membrane for the first time. • The uniform and faultless PA layer could be generated with low monomer concentration with microwave heating. • The NF membrane showed good permeability and rejection and high selectivity to Cl- and SO 4 2−. [ABSTRACT FROM AUTHOR]

Good mechanical strength, high water flux and salt rejection, and highly chlorine-tolerant property are essential for nanofiltration (NF) membrane. To achieve these properties, polyethersulfone (PES) NF thin-film composite (TFC) membrane was prepared via interfacial polymerization using piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) as aqueous monomers, trimesoyl chloride (TMC) as organic monomers, and PES three-channel capillary ultrafiltration (UF) membrane as substrate. The prepared NF membrane displays pure water flux of 36.1 L m −2 h −1 and Na 2 SO 4 rejection of 96.8% at 4 bar. NaClO solution was used to treat NF membranes for the evaluation of NF membrane chlorine-tolerant property. The effects of NaClO concentration, contact time and operating pressure on the chlorine-tolerant property of NF membrane have been thoroughly investigated. Particularly, the durability of NF membrane versus Cl was tested though long-term test. The pure water flux and Na 2 SO 4 rejection of NF membrane after 5000 ppm-h NaClO immersion was 43.4 L m −2 h −1 and 99.8% at 4 bar, respectively. The fabricated NF membrane could tolerant 13000 ppm-h Cl under 4 bar, and the water flux and Na 2 SO 4 rejection are maintain at 51.6 L m −2 h −1 and 99.6% during NF running process, respectively. Moreover, NF membrane exhibits 3.84×10 5 ppm-h chlorine-tolerant at 0 bar. These results indicated that the fabricated PES three-channel capillary NF membrane could be applied to practical process of desalination or water softening. [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]

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]

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]

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]

This work describes a novel nanofiltration membrane fabrication strategy in which the octadecylamine-grafted GO with the organophilic property is incorporated in organic phase during interfacial polymerization (IP) in order to protect the polyamide backbone from the attack of free chlorine. Meanwhile, the aqueous phase containing mixed amines of piperazine (PIP) and the fluorine-containing monomer (2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline, BHTTM) enables further improvement in chlorine resistance of the thin film nanocomposite (TFN) membrane. The modified GO was systematically characterized by TEM, FT-IR, TGA and XRD. And the membrane properties were investigated by XPS, TEM, AFM and dynamic contact angle. The octadecylamine-grafted GO TFN membrane (TFNMA-GO-ODA) exhibits measurably smoother and less hydrophilic surface compared to TFC membrane with mixed amines as well as the similarly fabricated GO TFN membrane. The TFNMA-GO-ODA demonstrated a pure water flux of 49.6 L m −2 h −1 (0.6 MPa), which was nearly 2.5 times than that of pristine PIP TFC membrane and 1.6 times than that of mixed-amine TFC membrane, while keeping high Na 2 SO 4 rejection of 98.4%. More importantly, the TFNMA-GO-ODA presented excellent chlorine resistance, benefiting from the existence of fluorine-containing groups in BHTTM and the protective effect of stable graphene nanosheets. The results indicate great potential of such membrane in water desalination and purification in industrial scale. [ABSTRACT FROM AUTHOR]

In this study, we utilized the NaOH solution as a heat-treating medium to replace the conventional oven-heating process after interfacial polymerization for the RO membrane fabrication. XPS result confirmed that the nascent RO membrane possessed a gradient cross-linking density along the polyamide layer depth, which is relatively loose on top and dense facing the substrate. The top loose polyamide could be exfoliated under NaOH treatment. The TFC membrane treated in a 1.5 mol L-1 NaOH solution exhibited a pure water flux nearly 3 times higher than that heat-treated in a water bath and also maintained a high NaCl rejection. In consideration of the practical operation process, membrane stability was evaluated, and the results showed that the membrane heat-treated by 1.5 mol L-1 NaOH solution possessed good long-term and pH stability. Thus, the facile heat-treating strategy provides a new path for fabricating high flux TFC-RO membranes. • Novel heat-treating medium of NaOH solution was utilized to fabricate the novel RO membrane. • The top loose layer of the nascent polyamide membrane could be exfoliated under NaOH treatment. • The modified heat-treating strategy showed great superiority over traditional oven-heating process. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membranes with both high permeability and salt rejection are in dire need for water treatment. Generally, heat treatment is an essential step for fabricating polyamide NF membranes. Conventional heat treatment in an oven causes membrane pore shrinkage and over cross-linking, which often leads to a severe loss of permeation performance. Herein, we report a single-step method by heat-treating membranes in non-neutral solutions to avoid pore shrinkage and generate graded hydrolysis in membrane selective layer. As confirmed by the XPS result, the polyamide NF membrane fabricated via controlled hydrolysis possesses a gradient cross-linking degree vertically along the membrane surface. This optimal polyamide NF membrane had a superior pure water permeability (PWP) of 27.5 L m−2 h−1 bar−1 and high Na 2 SO 4 rejection of 98.5%. Such controlled hydrolysis approach provides novel strategy for fabricating high performance polyamide membranes. • Heat treatment in water was employed to avoid pore shrink and over cross-linking of the polyamide active layer. • The performance of NF membrane with gradient cross-linked structure can be easily tuned by adjusting the pH value of water. • The optimal membrane owns a superior pure water permeability of 27.5 L m−2 h−1 bar−1 and a high Na 2 SO 4 rejection of 98.5%. [ABSTRACT FROM AUTHOR]

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na 2 SO 4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane. • Interfacial polymerization is terminated by liquid nitrogen to preserve the instantaneous polyamide layer morphology. • Polyamide layer roughness increases first and then decreases as a function of the heat curing time. • The nascent membrane exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and Na 2 SO 4 rejection of 97.4%. [ABSTRACT FROM AUTHOR]