Efficient Nanofiltration Research Articles

Collaborative intercalation and reduction of graphene oxide for highly stable and efficient nanofiltration membranes

Two-dimensional (2D) materials, known for their atomically thin profiles and micrometer transverse dimensions, have garnered considerable attentions in membrane technology. Despite their potential, 2D membranes comprising stacked nanosheets often suffer from low permeability and poor stability. Addressing these challenges, we applied collaborative intercalation and reduction strategies to enhance permeability and stability of graphene oxide (GO)-based membranes. We intercalated 2-hydroxypropyl-β-cyclodextrin (2β-CD) into the GO nanosheet dispersion under heat treatment and employed vacuum assisted self-assembly to fabricate the 2β-CD intercalated reduced GO (CD-rGO) membrane. During this process, GO nanosheets underwent reduction, facilitating the formation of hydrogen bonds between 2β-CD and GO. The resulting CD-rGO membrane exhibited markedly improved water permeance at 96.9 L m−2 h−1 bar−1 and an impressive rejection rate at 99.5 % towards Congo red, alongside enhanced stability under a 20 min ultrasonic test at 180 W, and pressure and long-term stability under the cross-flow filtrate tests. The introduction of 2β-CD during heat treatment not only increased the interlayer distance but also utilized the intrinsic pores of 2β-CD and enhanced surface hydrophilicity, contributing to superior separation performance These collaborative strategies offer a facile and promising approach towards high-performance 2D laminated GO-based membranes.

Construction of low-resistance nano-transport channels with UiO-66-(NH2)2 “transmembrane” in polyamide layer structure for efficient nanofiltration

Metal-organic frameworks (MOFs) is always a research hotspot as the modifier for fabrication of thin-film nanocomposite (TFN) membrane due to their excellent chemical tunability and suitable pore size. However, the traditional strategy for the involvement of MOFs into interfacial polymerization (IP) process has its limitations, as the addition of MOFs only serve to modulate the structure of the polyamide (PA) layer and to optimize the transport path of water molecules, rather than play an important role in selectively sieving solutes. To solve the problem that MOF embedded under the PA layer cannot directly participate in solute sieving, this study designed a “transmembrane” structure of MOF in the PA layer. Here, the feasibility of 1,3,5-Benzenetricarbonyl chloride modified UiO-66-(NH2)2 was verified based on Gibbs free energy calculations. By adding chlorinated UiO-66-(NH2)2 nanomaterials in the dual IP process, a high-throughput nanofiltration membrane was innovatively constructed. In contrast to conventional thin-film composite membrane prepared by only one IP process, the sieving mechanism no longer relied solely on the free volume of the PA chain segments. Instead, it was determined by the combination of the pore channels of UiO-66-(NH2)2 and the matrix gaps. Based on density functional theory (DFT), the calculated diffusion energy barriers of H2O and Na2SO4 in UiO-66-(NH2)2 and PA matrices reveal the reasons for the improvement of water flux and changes in retention rate of TFN membranes. In addition, the gap size between PA-MOFs was determined by comparing the solvation and de-solvation structures of dye molecules. This work provides a new theoretical basis for explaining the changes in the separation performance of TFN membranes, and offers new ideas for the development of novel TFN membrane structures.

Dehydration-modulated pomelo peel cellulose nanofiber interlayer customized polyamide membrane with highly uniform pores for efficient nanofiltration

The development of high-performance polyamide nanofiltration (PA NF) membranes by introducing interlayers holds promise for efficient desalination. In this study, a novel PA NF membrane was prepared by incorporating the special biomass interlayer, which consisted of dehydration-modulated pomelo peel cellulose nanofiber (PCNF). Due to the removal of water, the proportion of exposed oxygen-containing functional groups within the PCNF interlayer increased significantly, and thus the diffusion of piperazine (PIP) could be slowed down effectively. Consequently, the diffusion-restricted PIP was enriched and anchored by PCNF and formed a PA layer with a unique layered structure in the interfacial polymerization (IP) reaction. The surface PA layer with lower a cross-linking degree could optimize water transport pathways and improve membrane permeability (28.67 LMH/bar). Meanwhile, the bottom PA layer, which was closely interspersed with PCNF, reduced pore size of the membrane and enhanced the rejection of Na2SO4 (98.63%). This study reveals a low-cost and eco-friendly strategy for preparing effective biomass interlayers, which provides a feasible approach for designing high-performance NF membranes.

Room temperature aqueous synthesis of defect-engineered MOF-801 membrane towards efficient nanofiltration

Room temperature (RT) aqueous preparation of MOF membranes is of significant interest in meeting the demands of sustainability. Nevertheless, there remains no report on RT aqueous synthesis of water-stable high-valence MOF membranes to date. In this study, we developed a one-step RT protocol for fabricating defect-engineered MOF-801 membrane in aqueous media. Owing to enhanced structural hydrophilicity and enlarged micropore size, water was enabled to diffuse through the membrane with higher permeation flux. Obtained membrane exhibited exceptional dye rejection rate (CR:99.75 %, MB:99.69 % and MG:99.41 %) and unprecedented water flux (CR:77.33 L m−2 h−1·bar−1, MB:71.43 L m−2 h−1·bar−1 and MG:81.28 L m−2 h−1·bar−1), which were superior to state-of-the-art 3D pure MOF membranes. Our protocol paves a promising way towards sustainable production of water-stable MOF membranes under mild conditions.

Enhancing ion separation efficiency: Janus charged nanofiltration membrane fabricated via polyethyleneimine-manipulated interfacial polymerization

This research introduces highly efficient nanofiltration (NF) membranes designed for the effective rejection of both divalent cations and anions, a critical feature for advanced water treatment technologies. We have devised a simple yet adaptable approach for fabricating Janus polyamide (PA) thin-films characterized by dual charges, which exhibit pronounced selectivity towards both mono-/divalent anions and cations. Leveraging a straightforward interfacial polymerization (IP) process, we integrated high molecular weight polyethyleneimine (PEI) within the PA matrix. This strategy ensured the preferential formation of a dense, negatively charged upper layer dominated by piperazine (PIP), while cationic macromolecular PEI facilitated the emergence of a loose and positively charged lower layer, thus giving rise to a distinctively charged and structurally heterogeneous PA thin-film. Furthermore, the strategic inclusion of PEI inhibits the diffusion of the PIP, thereby promoting the development of nano-wrinkled structures. This structural innovation not only enhances pure water permeance (16.0 L m−2 h−1 bar−1) but also optimizes ion selectivity through the coordination of steric hindrance and Donnan effects. Consequently, the Janus charged NF membranes we developed exhibit exceptional selectivity for mono-/divalent ions, particularly demonstrating remarkable ion selectivity for Cl−/SO42− and Li+/Mg2+ of 102 and 24, respectively. Our findings introduce a pioneering avenue for fabricating NF membranes that proficiently separate mono-/divalent ions, promising significant advancements in water treatment and purification endeavors.

A synergistic polyelectrolytes-Zr-MOF hydrated construction graphene oxide nanofiltration with enhanced dye wastewater remediation

In recent years, developing an efficient nanofiltration membrane had been a thorny challenge for dye/salt wastewater purification. In this study, a novel graphene oxide-based nanofiltration membrane (GO/UiO@S-GO-8) was constructed by intercalating the synergistic polyelectrolytes-Zr-MOF hydrated construction (UiO@S-GO) into GO nanosheets. Here, combining the hydrophilic high-density anionic sulfonic groups (SO3-) with cationic amino groups (-NH2), GO-based nanofiltration membrane demonstrated outstanding separation ability, anti-pollution performance and structure stability. Compared to pure GO membrane, benefiting by effective expansion of graphene layer spacing from intercalation effect of UiO@S-GO, the water permeance of GO/UiO@S-GO-8 membrane increased to 8 times (about 66.3 ± 1.5 L m−2 h−1 bar−1). Importantly, the permeances of various dyes wastewater also reached up to 65.1 ± 1.8 L m−2 h−1 bar−1 at the high removal rate (exceeding 99.4%). Furthermore, strong hydratability of polyelectrolytes and hard porous crystal constructed the robust anti-fouling micro/nano rough structures onto the membrane surface, which made flux recovery rate (FRR) of GO/UiO@S-GO-8 enhanced to 96.7 ± 1.3%. Remarkably, the salt-resistant behavior of the polyelectrolytes and porous MOF could maintain the stability of the membrane filtration channels, the GO/UiO@S-GO-8 membrane could realize efficient removal rate of dyes (over 98%) faced the complex dye wastewater with different salt concentrations. Meanwhile, the GO/UiO@S-GO-8 membrane also could maintain the high permeance (46.7 ± 1.5 L m−2 h−1 bar−1) as well as excellent removal rate (97.2 ± 1.4%) after 10 cycle experiments. Hence, the GO/UiO@S-GO-8 nanofiltration membrane with Polyelectrolytes-Zr-MOF hydrated construction possessed a broad application inspiration in the purification of high-salt/dye wastewater.

Exploiting sulfonated covalent organic frameworks to fabricate long-lasting stability and chlorine-resistant thin-film nanocomposite nanofiltration membrane

Incorporating hydrophilic and charged porous nanofillers to prepare high-performance thin film nanocomposite (TFN) nanofiltration (NF) membranes is an effective method to achieve efficient water treatment. In this study, we synthesize the sulfonated covalent organic framework nanosheets (S-CONs) with higher hydrophilicity and electronegativity by immobilizing sulfonic acid groups (–SO3H) on TpPa-1 nanosheets. The S-CONs are incorporated in the PA layer by interfacial polymerization (IP) reaction. The results indicated that the S-CONs could modulate the hydrophilicity, thickness, and electronegativity of TFN-NF membranes. At the optimal addition of S-CONs (0.006 g), the pure water permeance increases to 8.84 L⋅m−2⋅h−1⋅bar−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm{L}}\\cdot{\\rm{m}}^{-2}\\cdot{\\rm{h}}^{-1}\\cdot{\\rm{bar}}^{-1}$$\\end{document}, which is about 1.75 times than the TFC membrane, with a high Na2SO4 rejection reaching 98.97%. The improvement of the separation performance mainly results from the reduction of PA layer thickness (from ~178.00–198.00 to ~100.00–128.00 nm) and the increase of surface electronegativity (from −20.37 to −44.41 mV at pH = 7.00). More interestingly, the amide bond formed between the S-CONs and TMC improved the chlorine resistance of the membranes. This study reveals the potential of using functionalized 2D CONs as nanofillers to modify TFC membranes for efficient nanofiltration.

Preparation of highly efficient nanofiltration membranes resistant to organic solvents by adjusting zinc oxide nanoparticle-loaded attapulgite

Zinc oxide nanoparticle-loaded attapulgite was successfully added to the polyamide layer for the preparation of high-efficiency organic solvent nanofiltration membranes. The addition of zinc oxide nanoparticle-loaded attapulgite to the aqueous monomer regulates the diffusion rate of interfacial polymerization, generating a thin and loosely packed polyamide layer. In addition, the abundant hydrophilicity of the nanoparticles lays the foundation for increased polar solvent permeation. The organic solvent nanofiltration membrane with the best performance exhibited an optimum methanol permeability of 13.19 L m−2h−1 bar−1, which was 1.54 times higher than that of the unadded membrane. Meanwhile, the optimum membrane consistently rejected more than 99.40 % of Evans blue dye, and the rejection rates of different dyes were consistent with the size-sieving effect. Furthermore, the permeation capacities of the membranes were evaluated using organic solvents with different polarities, viscosities, and molecular diameters, and the permeability of acetonitrile reached 16.98 L m−2h−1 bar−1. In addition, the optimum membranes retained excellent rejection capacity after soaking in the strongly polar solvent N, N-dimethylformamide (DMF) for 10 days at room temperature.

Desalination Performance in Janus Graphene Oxide Channels: Geometric Asymmetry vs Charge Polarity.

Improving the desalination performance of membranes is always in the spotlight of scientific research; however, Janus channels with polarized surface charge as nanofiltration membranes are still unexplored. In this work, using molecular dynamics simulations, we demonstrate that Janus graphene oxide (GO) channels with appropriate geometry and surface charge can serve as highly efficient nanofiltration membranes. We observe that the water permeability of symmetric Janus GO channels is significantly superior to that of asymmetric channels without sacrificing much ion rejection, owing to weakened ion blockage and electrostatic effects. Furthermore, in symmetric Janus GO channels, the transport of water and ions is sensitive to the charge polarity of the channel inner surface, which is realized by tuning the ratio of cationic and anionic functionalization. Specifically, with the increase in cationic functionalization, the water flux decreases monotonously, while ion rejection displays an interesting maximum behavior that indicates desalination optimization. Moreover, the trade-off between water permeability and ion rejection suggests that the Janus GO channels have an excellent desalination potential and are highly tunable according to the specific water treatment requirements. Our work sheds light on the key role of channel geometry and charge polarity in the desalination performance of Janus GO channels, which paves the way for the design of novel desalination devices.

Fabrication of highly efficient nanofiltration membranes decorated with praseodymium based triamino-functionalized MCM-41 for desalination and micropollutants removal

The nanofiltration membranes with a stable decoration of inorganic fillers such as zeolites are desperately required for enhancing the desalination performance of the membranes and hence three nanofiltration membranes were fabricated by decorating the membranes with praseodymium-based triamino-functionalized MCM-41 (Pr-(NH)2NH2-MCM-41). The membranes were applied for the removal of emerging pharmaceutically active micropollutants from water. The Pr-(NH)2NH2-MCM-41 was synthesized by using an in-situ approach where praseodymium oxide was chemically decorated in the framework of MCM-41 followed by simultaneous amine functionalization using N1-(3-Trimethoxysilylpropyl)diethylenetriamine (TMSPTA). A thorough characterization of the synthesized Pr-(NH)2NH2-MCM-41 was carried out by using HR-TEM, SEM, WCA, XRD, FTIR, BET, elemental and mapping analysis. Three different concentrations of synthesized Pr-(NH)2NH2-MCM-41 were decorated in the membrane active layer through interfacial polymerization in the presence of an aqueous tetra-amine solution and using terephthaloyl chloride as an organic crosslinker. Subsequently, the fabricated membranes were used for desalinating saline feed containing divalent (CaCl2, MgCl2, Na2SO4, MgSO4) and monovalent (NaCl) ions. The rejection of salts by PA/0.05-Pr-MCM@PSU/PET membrane was found to be the highest among all the fabricated membranes which were found to be 98 %, 96 %, 95 %, 87 %, and 82 % for CaCl2, MgCl2, MgSO4, Na2SO4 and NaCl, respectively. The permeate flux was found to be dependent on the applied feed pressure which was found to be 56 L m-2 h-1 (LMH) at 25 bar for PA/0.050-Pr-MCM@PSU/PET membrane. The rejection performance of the membranes was also evaluated by using different well-known pharmaceuticals (Caffeine, Sulfamethoxazole, Amitriptyline, and Loperamide) as micropollutants in the feed. All the pharmaceutical drugs were found to be highly rejected > 96 % by PA/0.5-Pr-MCM-41@PSU/PET membrane followed by PA/0.025-Pr-MCM-41@PSU/PET membrane. Therefore, the current approach of synthesizing functionalized zeolites is quite effective and efficient for the stable decoration of inorganic fillers in the membrane active layer and should be extended to other zeolites such as zeolites with antimicrobial potential.

Facile and sustainable fabrication of carbon membranes through mechanical rubbing for efficient nanofiltration

Although having shown great promise in gas separation, reverse osmosis, and nanofiltration, preparation of carbon membranes, which commonly involves elaborate high-temperature pyrolysis or exfoliation-reassembly, still suffers from complicated fabrication procedure and/or high production cost. In this study, we pioneered the preparation of continuous asymmetric carbon membrane through facile mechanical rubbing of a pencil graphite. Among them, 2B-type pencil with 64 wt% graphite exhibited superior nanofiltration performance (Congo Red rejection rate of 99.4% and water flux of 21.91 L·m−2·h−1·bar−1). Long-time operation confirmed its excellent stability. Of particular note, the spent membrane could be facilely recovered by erasing, resulting in not only zero pollutant discharge but also full recovery and reutilization of the substrate. The above protocol is anticipated to pave an avenue for facile and sustainable production of versatile carbon membranes with superior separation performances.

Role of alkane-[formula omitted],[formula omitted]-diamine in the nanostructure of carboxylic functionalized multiwalled carbon nanotubes grafted on amino-enriched nylon fabric toward metal ion absorption

Through a direct two-step functionalization reaction with alkane-α,ω-diamine (H2N(CH2)nNH2, n = 2, 4, 6, 8) and carboxylic functionalized multi-walled carbon nanotubes (MWCNT-COOH), the membrane labeled as C@(A[n]-nylon), is made up of nylon 6 fabric and intermediate amino-enriched nylon (A[n]-nylon) fabric. FTIR and Raman spectra confirm the efficient formation of amide bonds between the two amino heads of the alkane-α,ω-diamine, both with hydrolyzed nylon 6 and MWCNT-COOH. As a result, MWNCT-COOH were grafted to the nylon fiber side wall without causing damage to the nylon backbone. The SEM images confirm the plexus of MWCNT covering the amino-enriched nylon fibers. The long carbon chain of alkane-α,ω-diamine as an arm help amino groups reach beyond the surface of polyamide fiber, making it easier for -COOH groups of MWCNT-COOH to form amide bonds instead of being ejected when approaching CO groups on the polyamide surface. As-prepared C@(A8-nylon) membranes have metal ion rejection of more than 10% in vacuum filtration test with solution of M(CH3COO)2 (M = Ca, Co, Pb). Such membrane is long lasting for about 20 cycles, showing potential of turning polyamide fabrics with large pore sizes into highly efficient nanofiltration of reverse osmosis (RO) membranes. This unique structure opens up new possibilities for nanocomposite membranes and mass production by the proposed simple method.

Silicification-interlayered nanofiber substrates regulated crumpled ultrathin polyamide nanofilms for highly enhanced nanofiltration

Thin-film nanofiber composite (TFNC) membranes have shown great potentials for highly efficient nanofiltration. However, it remains a challenge to construct defect-free ultrathin polyamide nanofilms with designed crumpled structures on polymeric nanofiber substrates via traditional interfacial polymerization (IP) to realize high permeability and selectivity synchronously. Herein, a novel strategy is reported to regulate the polyamide nanofilm by a silicification-interlayered nanofiber substrate with hydrophilic and rugged surface. The silica interlayer could enrich piperazine (PIP) monomers in aqueous solutions and control the releasing towards the interfacial reaction zone, enabling the homogeneous IP reaction and the reduced thickness of PA nanofilms. The silicified nanofiber substrate can also serve as a templating support to crumple the PA nanofilms and thus increase their effective infiltrating area. Furthermore, deep insight has been taken into the intermolecular interactions in the IP system and the fundamental mechanism of the silicification-interlayered nanofiber substrate regulating the IP process via density function theory (DFT) and dissipative particle dynamics (DPD) simulations. The membrane morphologies were observed by SEM and AFM, and chemical structures of membrane surfaces were characterized by FTIR/ATR, XPS and XRD in detail. The hydrophilicity and charged properties of different membrane surfaces were analyzed by water contact angle and Zeta potential tests, respectively. As a result, an ultrathin crumpled PA nanofilm is generated on top of the nanofiber substrate as selective layer, enabling the composite membrane with enhanced water permeability of 19.6 L m−2 h−1 bar−1 (approximately two folds higher than that of the pristine PA membranes) and high Na2SO4 rejection of 96.5%. Meanwhile, the prepared membranes reveal good structural stability not only under different operation pressures but also during long-term filtration processes. This work is believed to provide a facile approach to engineer advanced TFNC membranes with high-efficiency nanofiltration performance.

Recent Advances in Stimuli‐Responsive Smart Membranes for Nanofiltration

AbstractNanofiltration membrane plays an increasingly important role in many industrial applications, such as water treatment and resource recovery. The performance of the smart nanofiltration membrane is largely controlled by pore size, the Donnan effect, and surface wettability, which are determined by the function of stimuli‐responsive components. Smart membranes, which contain stimuli‐responsive components, are capable of changing their physical and chemical properties in response to changes in the environment so that the microstructure of the membrane will have more efficient performances and broader application prospects than the current traditional nanofiltration membranes. Herein, the preparation methods of stimuli‐responsive membranes are described and they are systematically classified accordingly to their mechanisms. Moreover, the latest progress of stimuli‐responsive membranes in nanofiltration and the main mechanism of each stimuli‐response type through relevant examples are discussed and summarized. Finally, this review provides new insights into the remaining challenges and future directions of stimuli‐responsive membranes. Fueled by advances in chemistry and materials science, it is expected to build a smart and efficient nanofiltration membrane platform for the benefit of mankind.

Covalent organic framework-immobilized wood membrane for efficient, durable, and high-flux nanofiltration

Covalent organic frameworks (COFs) are promising for the construction of nanofiltration membranes owing to their uniform, ordered channel structures and high chemical stability. However, developing a low-cost strategy for fabricating COF-based nanofiltration membranes and increasing the long-term stability of the membranes are challenging. Here, we developed a TpPa-wood membrane through the in-situ formation of massive imine COFs on the top surface of a wood block for the rapid and efficient nanofiltration-based separation of organic pollutants. The numerous hydroxyl groups of cellulose in wood provided nucleation sites for the growth of dense, defect-free COFs with a diameter of 1.8 nm. The nano porous COFs enabled efficient separation, while the long and low-tortuosity channels of wood with a diameter of 10–30 μm facilitated rapid water transport and augmented the mechanical robustness of the membrane. Therefore, the prepared TpPa-wood membrane showed an outstanding separation efficiency of ∼97.0% toward organic pollutants such as dyes and pharmaceutical molecules at a flux rate of 600 L m−2 h−1. In addition, the TpPa-wood membrane exhibited excellent stability at a wide pH range (3–11) and over continuous filtration for 48 h. The TpPa-wood membrane opens up a new avenue for rapid and efficient nanofiltration by combining the merits of nano porous COFs and biomass with numerous micro-channels and high hydrophilicity.

Nanofiltration Membranes Formed through Interfacial Polymerization Involving Cycloalkane Amine Monomer and Trimesoyl Chloride Showing Some Tolerance to Chlorine during Dye Desalination.

Wastewater effluents containing high concentrations of dyes are highly toxic to the environment and aquatic organisms. Recycle and reuse of both water and dye in textile industries can save energy and costs. Thus, new materials are being explored to fabricate highly efficient nanofiltration membranes for fulfilling industrial needs. In this work, three diamines, 1,4-cyclohexanediamine (CHD), ethylenediamine (EDA), and p-phenylenediamine (PPD), are reacted with TMC separately to fabricate a thin film composite polyamide membrane for dye desalination. Their chemical structures are different, with the difference located in the middle of two terminal amines. The surface morphology, roughness, and thickness of the polyamide layer are dependent on the reactivity of the diamines with TMC. EDA has a short linear alkane chain, which can easily react with TMC, forming a very dense selective layer. CHD has a cyclohexane ring, making it more sterically hindered than EDA. As such, CHD’s reaction with TMC is slower than EDA’s, leading to a thinner polyamide layer. PPD has a benzene ring, which should make it the most sterically hindered structure; however, its benzene ring has a pi-pi interaction with TMC that can facilitate a faster reaction between PPD and TMC, leading to a thicker polyamide layer. Among the TFC membranes, TFCCHD exhibited the highest separation efficiency (pure water flux = 192.13 ± 7.11 L∙m−2∙h−1, dye rejection = 99.92 ± 0.10%, and NaCl rejection = 15.46 ± 1.68% at 6 bar and 1000 ppm salt or 50 ppm of dye solution). After exposure at 12,000 ppm∙h of active chlorine, the flux of TFCCHD was enhanced with maintained high dye rejection. Therefore, the TFCCHD membrane has a potential application for dye desalination process.

Anionic covalent organic framework engineered high-performance polyamide membrane for divalent anions removal

Porous framework materials hold great promise in tuning the chemical and physical structure of polyamide membranes for efficient nanofiltration. In this work, anionic covalent organic framework (aCOF) with abundant sulfonic acid groups was embedded into polyamide matrix via interfacial polymerization to modulate both membrane charge property and thickness for the removal of divalent ions. Benefiting from the high negative charged density, aCOF not only enhanced the membrane electronegativity from −25.6 mV to −71.5 mV but also slowed down the diffusion rate of piperazine by electrostatic interaction to decrease the membrane thickness from 93 nm to 18 nm. The enhanced electronegativity can intensify the charge exclusion to divalent anions (Na2SO4 rejection above 97%), while the ultrathin structure endows membrane with high water permeance of up to 39 L m−2 h−1 bar−1, about 2.4 times higher than that of pristine PA membrane. Our membranes provide a new path to rational design and controllable construction of high-performance nanofiltration membranes.

Influence of structurally and morphologically different nanofillers on the performance of polysulfone membranes modified by the assembled PDDA/PAMPS-based hybrid multilayer thin film

A highly efficient nanofiltration membrane should exhibit high separation performance in removing divalent salts and organic solutes, as well as high permeation to meet practical separation and purification applications in aqueous media. Here, we designed a series of hybrid multilayer thin film membranes filled with the structurally and morphologically different nanofillers such as hexagonal boron nitride (HBN) nanosheets and metal-organic framework (MOF) nanoparticles, consisting of 3 and 6 layer pairs of polyelectrolyte through the layer-by-layer self-assembly technique (LBL) and characterized them in terms of dye and salt separation, as well as permeation. The rejection performance and permeability of the designed membranes manifested that HBN nanosheets were more effective than MOF nanoparticles in achieving a high-performance membrane. As compared to the bare multilayer thin film membrane, the addition of HBN nanosheets within the negatively-charged layers of the multilayer thin film membrane consisting of 6 bilayers resulted in good retention of up to 93% and 92% for acid blue (ACB) and bromophenol blue (BPB) dye molecules, respectively. Besides, this membrane exhibited 60% and 45% improvement in the water flux for ACB and BPB solutions, respectively, while the rejection of the sulfate ions maintained an acceptable value around 78%. Furthermore, it was found that this HBN-embedded hybrid multilayer membrane had superior potential for the removal of coherent foulant compared to all samples.

An efficient nanofiltration system containing mixture of rice husk ash and Fe/CeO2–SiO2 nanocomposite for the removal of azo dye and pesticide

Abstract Fe/CeO2–SiO2 nanocomposite was synthesized by using zwitterionic surfactant 3-(N,N-dimethyloctadecylammonio) propane sulfonate (SB3-18) by sol–gel and hydrothermal methods. The nanocomposite was well characterized before its use. X-ray diffraction (XRD) results confirmed the synthesis of the Fe/CeO2–SiO2 nanocomposite. Crystallite size calculated by using Scherrer equation was 5.33 nm while it was found 5.26 nm by Williamson–Hall equation. Bandgap of Fe/CeO2–SiO2 nanocomposite shows redshift after the doping of Fe. Degradation studies of methylene blue (MB) and chlorpyrifos (CP) were investigated by nanofiltration (NF) column under visible light irradiation. Degradation and adsorption of MB was investigated by three different types of columns under visible light irradiation. It was observed to achieve 100 % removal of MB and 91 % of CP through column in which rice husk ash (RHA) slurry was mixed with the nanocomposite.

Thin-film composite membranes with mineralized nanofiber supports for highly efficient nanofiltration

Nanofiltration has exhibited broad application prospects in the field of precise separation attributed to its unique sieving performance for ions and small molecules, high permeation flux and low energy consumption. However, it remains a great challenge for current nanofiltration membranes (NFMs) to improve the permeability while maintaining the high rejection for divalent (or multivalent) ions. In this work, we design and fabricate a novel thin-film composite (TFC) nanofiltration membrane, for which an electrospun polyacrylonitrile nanofiber membrane is adopted as the support after modified by a zirconia mineral layer via surface biomimetic mineralization method, and then an ultrathin selective layer of polyamide (PA) with wrinkled structure is constructed on it via interfacial polymerization. The hydrophilic mineralized nanofiber surface can help to decrease the thickness of the PA layer significantly. Meanwhile, the abundant zirconia particles acting as templates will generate a wrinkled structure for PA layer, providing an improved effective filtration area. Therefore, the resultant NFMs exhibit a high water flux of 38.2 L m−2 h−1 (under 4 bar) accompanied with excellent rejection rate for divalent anions (e.g. 97.6% for SO42−) and cations (e.g. 92.4% for Mg2+). This study could pave an avenue to develop highly efficient NFMs for comprehensive separation applications.