Resultant Nanofiltration Membranes Research Articles

Facile design of the nanofiltration membrane with Cu2+-incorporated aminated polyethylene substrate for highly selective magnesium/lithium separation

Efficient separation of magnesium and lithium ions (Mg2+/Li+) from high Mg2+/Li+ ratio salt-lake brines using nanofiltration (NF) technology is crucial for stabilizing lithium resources in light of the increasing demand for lithium-based products. Although positively charged NF membranes show promise in selectively separating Mg2+ and Li+ ions, the issues of inefficiency and undesirable trade-offs in perm-selectivity remain pressing. In this study, we presented a breakthrough in creating a highly permeable NF membrane tailored for selective Mg2+/Li+ separation using the cost-effective polyethylene (PE) as the substrate for the preparation of the NF supporting layer. Employing a facile and low-cost Cu2+-incorporated amination process, the hydrophilization of PE substrate was accomplished. This innovative Cu2+-incorporated amination technique not only facilitated rapid hydrophilization but also established a positively charged PE surface while simultaneously regulating the formation of a thinner and loose polyethyleneimine (PEI)-based polyamide (PA) skin layer (∼26 nm) through the coordination bonding between the Cu2+ and amine groups. Consequently, the resultant NF membrane achieved simultaneous enhancements in permeability (∼16 L m−2 h−1 bar−1) and selectivity for Li+/Mg2+ (33) during the nanofiltration of the simulated brine, effectively reducing high Mg2+/Li+ ratios in the feed close to 1 in the permeate, and making it suitable for the subsequent precipitation to produce Li2CO3. Furthermore, this membrane demonstrated remarkable long-term stability, with stable NF operation continuously for over 7 days, owing to its robust Cu2+-induced aminated PE supporting layer and PEI-based PA skin layer. Our work underscores the simplicity and cost-effectiveness of the Cu2+-incorporated amination process in achieving superior PE-based NF membranes, specifically targeting lithium extraction from salt-lake brines.

Fabrication of polyethersulfone/sulfonated polysulfone loose nanofiltration membranes for enhanced selectivity of pharmaceuticals and personal care products and minerals

Nanofiltration (NF) membranes have a high removal rate for pharmaceutical and personal care products (PPCPs) in drinking water, but they also reject critical minerals (e.g., calcium and magnesium) that are beneficial to health. Herein, polyethersulfone (PES)/sulfonated polysulfone (SPSf) loose NF membranes were fabricated using non-solvent induced phase separation (NIPS) to enable efficient rejection of PPCPs while preserving high mineral permeability. The resultant loose NF membrane showed increased negative charge owing to the -SO3- groups of SPSf. It also exhibited a high water permeance of ∼20.8 L m-2 h−1 bar−1 characterized by high PPCPs/minerals selectivity (i.e., rejection of PPCPs > 90 % and rejection of Mg2+ < 5 %). The filtration performance of resultant membrane indicated that the ionic PPCPs (e.g., Indomethacin, Diclofenac Sodium, Levofloxacin, Norfloxacin) were removed by the electrostatic repulsion and adsorption, while the removal of non-ionic PPCPs (e.g., Bisphenol A, Carbamazepine) was primarily dominated by the synergy of adsorption and size exclusion. Therefore, the superior removal rate of hydrophilic PPCPs was due to enhanced PPCP-membrane adsorptive interaction. This study provides a profound understanding of the selective separation mechanism of loose NF membranes for micropollutants and minerals.

Ultra-permeable polyamide nanofiltration membrane modified by hydrophilic-hydrophobic alternated lignocellulosic nanofibrils for efficient water reuse

Polyamide nanofiltration (NF) membranes are instrumental in water reuse due to their capability to efficiently remove trace organic contaminants (TrOCs), which pose potential health risks. However, while the current NF membranes offer acceptable TrOC rejection, their water permeance, which is highly related to the process energy consumption in water reuse, is relatively low. To address this limitation, we introduced a novel NF membrane by incorporating a lignocellulosic nanofibril interlayer—specifically, nanowires with alternating hydrophilic-hydrophobic regions (denoted as HONW). The resultant NF membrane achieved remarkable water permeance (52.4 L m−2 h−1 bar−1) while still ensuring high TrOC retention (including endocrine-disrupting compounds, pharmaceuticals, and antibiotics). A detailed mechanistic investigation revealed that the eliminated funnel effect or introduced gutter effect induced by the HONW interlayer, improved polyamide layer structure characterized by lower cross-linking degree and higher surface wettability, and reduced interlayer resistance (due to a unique water transport pattern: hydrophilic regions absorbed water molecules while hydrophobic regions strengthened water penetration) were significantly responsible for the enhanced membrane permeance. Moreover, the membrane also demonstrated low specific energy consumption as well as outstanding stability. This investigation unveils an appealing approach for constructing the ultra-permeable NF membrane for efficient water reuse.

Deciphering the role of polyketone substrates in tuning the structure and properties of polyamide nanofiltration membranes

Recent studies have emphasized the importance of porous substrates in the formation of a polyamide layer during the interfacial polymerization process. However, few studies have focused on the underlying effect of the porous support substrate on the structure and properties of the prepared polyamide nanofiltration (NF) membrane. In this study, various polyketone (PK) porous substrate supported NF membranes were successfully fabricated and optimized by tuning the pore structure and surface roughness of the PK substrate layer. Structural optimization was achieved by changing only the PK casting solution concentration during nonsolvent-induced phase separation without additional modification steps. The results demonstrated that the prepared hydrophilic fibrous PK membrane was conducive for the rapid and even diffusion of amine monomers and was an ideal substrate for NF membranes. Compared to the PK-16-supported NF membrane, a polyamide film with a more ridge-shaped nanostrip structure was easily formed on the PK-8 substrate with a large pore size and rougher surface, which greatly improved the permeance of the resultant NF membrane with a slight loss in salt rejection. Each PK substrate-supported NF membrane showed competitive separation performance compared to that of several reported membranes. This study highlights the superiority of PK porous membranes and provides a simple strategy for NF membrane production and water treatment applications.

Simultaneous regulation of pore size and surface charge of nanofiltration membrane using carbon quantum dots for improved selective separation

Designing nanofiltration (NF) membranes with tunable pore sizes and surface charges is highly desirable to meet the growing demand for precise separation. In this study, carbon quantum dots generated through lysine pyrolysis (l-CQDs) were utilized as monomers to fabricate NF membranes via interfacial polymerization (IP). Intriguingly, the surface charge (from negative to positive) and effective pore size (from loose to dense structure) of the resultant NF membranes could be simultaneously modulated by simply adjusting the diffusion of l-CQDs during the IP process, which endowed the obtained l-CQD-based NF membrane with a tunable separation performance. The negative and loose NF membranes (l-CQD; 0.1 wt%) achieved excellent dye/salt fractionation performance even at high NaCl concentrations (20 g/L). The recovered NaCl from the highly saline dyeing effluent could be directly reused in cotton fabric dyeing, indicating potential application prospects in the treatment of saline textile effluents. A dense and positive NF membrane was obtained when l-CQD concentration increased to 1.0 wt%; this membrane showed exceptional desalination performance with high rejection of MgCl2, CuCl2, and CaCl2 (98.77 %, 99.06 %, and 99.0 %, respectively), demonstrating the ability to remove metal ions from water. This work provides an approach for preparing NF membranes with tailorable pore size and surface charge and highlights the potential of l-CQD-based NF membranes for the practical separation toward various charged components.

Unveiling the role of post-treatment in thin-film composite nanofiltration membranes: Performance and mechanism

The deep role and mechanism of post-treatment in the morphology and performance of thin-film composite (TFC) nanofiltration (NF) membranes have rarely been revealed. In this work, four solutions of pure water, hexane, Na2CO3, and glycerol were selected for the post-treatment of TFC-NF membranes, and the performances of the resultant NF membranes were systematically investigated. The results showed that the hexane could effectively remove the residual acyl chloride groups and prevent the subsequent second growth of polyamide (PA) layers, thus leading to the formation of smoother and thinner PA membranes with higher water permeance and excellent salt rejections. Hydrolysis and swelling of unstable PA fragments in solutions (water, Na2CO3, and glycerin) contributed to greater negative charge, higher hydrophilicity, and enlarged pore size. The resultant NF membranes exhibited significantly enhanced water permeance and comparable separation behaviors to the control NF membrane. In addition, the well-constructed NF membranes possessed superior monovalent/multivalent ion selectivity, excellent antifouling, and stability. The mechanisms of the post-treatment on the performance enhancement of NF membranes were proposed from the perspective of interfacial interactions. The facile post-treatment strategy provides new insights into tailoring high-performance NF membranes for water treatment applications.

Multi-carboxyl based zwitterionic nanofiltration membrane with ion selectivity and anti-scaling performance

Membrane scaling is one of the drawbacks of nanofiltration (NF) impeding its wide application in treatment of salt-containing water. Especially, the high concentration of Ca2+ and SO42− easily lead to a CaSO4 scale layer on the membrane surface, limiting the separation process. Herein, a zwitterionic NF membrane with anti-scaling performance was fabricated through multi-carboxyl carboxylate (sodium citrate) incorporated by interfacial polymerization. Due to the synergistic effect of sodium citrate, the resulting NF membrane had a more negatively charged surface and a larger pore size than the pristine membrane. In desalination, this zwitterionic NF membrane exhibited a high selectivity (15.9) between SO42− (73.1 ± 2.4% rejection) and Ca2+ (4.6 ± 1.4% rejection) with a flux of 39.6 LMH, much higher than that of the commercial NF membrane (NF-270, a selectivity of 1.5). Based on the high SO42− and Ca2+ selectivity, it is difficult to form a CaSO4 scale layer on the membrane surface, which yields an excellent anti-scaling performance of the resulting membrane. Furthermore, the zwitterionic monomer endowed the membrane with an anti-fouling effect due to zwitterions materials have strong hydration to resist nonspecific protein adsorption. This design strategy of ion selectivity zwitterionic membranes through the incorporation of carboxylate provides guidance for the design of highly ion selective anti-scaling NF membranes, which has potential applications in water treatment for salt-containing solutions.

Preparation of high-performance nanofiltration membranes with quaternized cross-linked microgels as intermediate layer

The high-performance nanofiltration (NF) membranes were fabricated by using hydrolyzed polyacrylonitrile (HPAN) ultrafiltration (UF) membranes with negatively surface charges as the substrate membranes, quaternized crosslinked microgels (PNI6) with positive charges as the intermediate layer, piperazine (PIP) and trimesoyl chloride (TMC) as the monomers for the formation of polyamide selective layer via interfacial polymerization (IP). The introduction of positively charged PNI6 microgels as the intermediate layer improved the hydrophilicity of resultant NF membranes and rendered the NF membranes with surface positive charges. The obtained NF membranes (MG-NF) with PNI6 microgel interlayer simultaneously achieved excellent water flux and the rejection of salts including Na2SO4, MgSO4, MgCl2, and CaCl2. Increasing the deposition time of PNI6 microgels on the HPAN UF substrate membranes increased the water flux and rejection of MgCl2 of the resultant MG-NF series NF membranes. The nanofiltration performance of obtained MG-NF series NF membranes exhibited thermo-sensitivity and long-term stability. For MG-NF-6 NF membrane, the water flux and rejection of MgCl2 reached 10.1 L·m−2·h−1·bar−1 and 93.4 % at 25 °C, respectively. With increase of temperature, the water flux of MG-NF-6 membrane was significantly enhanced to be 13.4 L·m−2·h−1·bar−1 at 45 °C, while the rejection of MgCl2 slightly decreased to be 90 %.

Fabrication of highly positively charged nanofiltration membranes by novel interfacial polymerization: Accelerating Mg2+ removal and Li+ enrichment

Li+, a vital green energy source, is mainly extracted from salt lakes, which also contain high concentration of Mg2+. Therefore, there is an imminent need for separation of Li+ and Mg2+. Recent innovations highlight the great potential of positively charged nanofiltration (NF) membranes for separating Mg2+ and Li+. Typically, positively charged NF membranes are prepared by the interfacial polymerization approach, where the most commonly applied aqueous phase monomer is polyethyleneimine (PEI). In this work, a new class of polyallylamine (PAA)-based NF membrane with a high density of positive charge, was developed to achieve high perm-selectivity for separating Mg2+ and Li+. The results indicated that the abundant primary amine (-NH2) groups on the PAA molecular chain endowed the NF membrane with a highly hydrophilic and positively charged polyamide layer. The resulting NF membrane exhibited superior Mg2+/Li+ separation ability with a high separation factor SMg2+/Li+ of 82.8 and a water permeance of 7.39 L/(m2hbar). It is also noteworthy that the SMg2+/Li+ value is more than 4 times higher than that of the previously reported PEI-based membrane. Moreover, our work also provides a new potential candidate for the future development of positive charged NF membranes.

Triethanolamine-modulated interfacial polymerization toward microcrumpled nanofiltration membranes: Performances and mechanisms

Highly permeable thin-film composite (TFC) nanofiltration (NF) membranes featuring high separation efficiencies are of great importance for purifying surface water and ground water. Increasing the filtration area of NF membranes via accurate control of the interfacial polymerization (IP) is proposed to be an efficient way to achieve this goal. In this work, a triethanolamine (TEOA)-modulated IP was utilized to tailor the IP reaction rate and thus regulate the separation performance of NF membranes. The resultant NF membranes were characterized in terms of chemical structures, morphologies, and separation behaviors in detail. The reaction dynamic of the TEOA-doped IP was evaluated by stopped-flow spectroscopy and molecular dynamics. The results showed that the incorporation of TEOA could efficiently regulate the IP reaction rate through hydrogen bonds, increased viscosity, and acid-neutralization effects. As result, a high-performance NF membrane possessing a microcrumpled structure and excellent separation efficiency for ground water was achieved. Hence, the TEOA-modulated IP method is expected to be a maneuverable approach for tailoring excellent NF membranes for ground water treatments.

High‐Performance PA Nanofiltration Membrane with Coral‐Reef‐Like Morphology atop Polydopamine Decorated EVOH Nanofiber Scaffold

AbstractThe pursuit of highly permeable thin‐film nanocomposite (TFNC) nanofiltration (NF) membranes with desirable selectivity is an eternal topic for desalination and wastewater treatment. Herein, a facile route to engineer polyamide (PA) NF membranes is reported with a coral‐reef‐like thin PA active layer atop a polydopamine pre‐decorated ethylene vinyl alcohol copolymer (EVOH) nanofiber scaffold (EVOH‐PDA) via interfacial polymerization (IP). EVOH‐PDA possesses a submicron pore size and super‐hydrophilic surface, which provides abundant thin water layers covering nanofibers in the IP process resulting in the PA layer with a morphology of coral‐reef‐like highland surrounded by flat low‐lying regions. The resultant NF membrane presents high permeance of 32.19 L m−2h−1bar−1 and high rejection of 96.52% to 1000 ppm Na2SO4 feed solution with a stable performance against operation time and high salt concentration. This work provides a new approach to fabricating PA TFNC membranes with outstanding NF performance in liquid separation applications.

Highly permeable acid-resistant nanofiltration membrane based on a novel sulfonamide aqueous monomer for efficient acidic wastewater treatment

Thin-film composite (TFC) membrane with high permeability and selectivity is appealing in the field of industrial wastewater treatment. However, polyamide (PA) TFC membranes, the premier choice for water treatment, undergo structure deterioration when continually exposed to acidic environment. Here, we apply surface activation assisted multi-step interfacial polymerization (IP) of 3-aminobenzenesulfonamide (ABSA) and trimesoyl chloride (TMC) to prepare a poly(amide-sulfonamide) (PASA) nanofiltration (NF) membrane with strong acid resistance. Thereinto, stable sulfonamide structure of ABSA effectively prevents the direct attack of acid to the PASA layer. Importantly, the nascent PASA layer acting as a hydrophilic interlayer can promote the subsequent IP reactions to form a less defective separation layer. When the surface activation (water soaking) is carried out during the multi-step IP process, the surface smoothness and hydrophilicity as well as the water permeability of the membrane are improved. Compared to the control, the resultant NF membrane exhibits ~200% increase in water permeability (12.4 Lm−2h−1bar−1) and >95.0% Na2SO4 rejection. Benefiting from the strong steric exclusion, it also has high color removal when treating model acidic dye solutions (>99.3%) or real resin elution wastewater, showing great potential in the acid reuse for decolorization resin regeneration. Moreover, such membrane owns impressive long-term stability after exposure to strong acid (20 wt% of H2SO4 for 30 days), and its hydrophilic surface contributes to excellent anti-fouling performance. This acid-resistant NF membrane with high permeability and stability provides a new perspective in acidic wastewater treatment.

Enhanced removal efficiency of heavy metal ions by assembling phytic acid on polyamide nanofiltration membrane

The water pollution caused by heavy metals is bringing serious damage to public health and environment, and significant efforts have been devoted to explore advanced materials and technologies for eliminating toxic metal ions more efficiently. Herein, a phytic acid (PA)-incorporated polyamide thin-film composite nanofiltration (NF) membrane is constructed though traditional interfacial polymerization and electrostatic assembly of PA with polyethyleneimine. Owing to the high negative charges of PA, the resultant NF membrane exhibits ultrahigh binding affinity for heavy metals cations, and is highly capable of removing heavy metal ions from aqueous solution. As a result, the PA-functionalized NF membrane can reduce Cd2+ and Pb2+ concentrations from 500 ppm to the ultralow level of ~0 and 5 ppb, and achieve record-breaking remove rates of 100.000% for Cd2+ and 99.999% for Pb2+. Additionally, the as-prepared NF membrane also delivers excellent long-term stability in continuous 120-h operation, and can be easily regenerated and reused without remarkable fading of the initial Cd2+ removal rate even after six filtration cycles. This work demonstrates the potential usage of the PA-functionalized NF membrane for serving as a promising platform to eliminate heavy metal ions in waste water.

Crumple-textured polyamide membranes via MXene nanosheet-regulated interfacial polymerization for enhanced nanofiltration performance

Nanofiltration (NF) membranes based on polyamide (PA) chemistry have been broadly utilized in saline water desalination and advanced treatment of drinking water. The creation of a nanomaterial interlayer between the support and PA film is known as a promising strategy to improve the filtration performance of traditional PA NF membranes. However, an ultrahigh selective PA NF film featuring ultrathin and crumple-like morphology is still in great challenge. Herein, a highly efficient NF membrane with both enhanced water permeance and salt rejections was prepared via a brush-painting MXene-assisted interfacial polymerization (MA-IP) process. An ultrathin and crumple-textured PA film with ~15 nm thickness was constructed on the MXene-painted polyethersulfone support. The effects of MXene painting cycles on the performance of the support and subsequent PA layer were systematically characterized. The presence of the MXene layer increased the hydrophilicity and PIP adsorption of the pristine support, leading to an accelerated IP reaction rate. The resultant NF membranes exhibited rougher surface, greater hydrophilicity, higher electronegativity and denser skin layer. Excellent water permeability of 27.8 ± 2.1 L m−2 h−1 bar−1 together with satisfactory α(NaCl/Na2SO4) of ~480 was obtained for the MXene-interlayered NF membrane, overcoming the trade-off effects between water permeance and salt selectivity. The MA-IP strategy of this work is expected to provide a new approach for fabricating low-pressure NF membranes for brackish water desalination.

Cationic hyperbranched poly(amido-amine) engineered nanofiltration membrane for molecular separation

High-efficient separation of molecules is of great significance in food, biotechnology, pharmaceutical and dairy industries. To this end, cationic hyperbranched poly (amido-amine)s (HBPs) with different numbers of quaternary ammonium groups were employed as a new kind of 3D spherical macromonomers to fabricate nanofiltration (NF) membranes, through interfacial polymerization (IP) between cationic HBPs and trimesoyl chloride (TMC) on a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane surface. Apart from the inner voids inside cationic HBP molecules for fast transport of water molecules, sizes and charge properties of the outer voids between cationic HBP molecules can be modulated by changing the numbers of quaternary ammonium groups on cationic HBP molecule surfaces for enhancing both high permeability and selectivity (water permeance and MgCl2 rejection rate of the resultant NF membrane are up to 310.5 L m−2 h−1 MPa−1 and 92.0% respectively). Based on the separation mechanism of combined steric and Donnan effects, the resultant NF membrane exhibits ultrahigh retentions to molecules with high molecular weights (MWs) or positive charges, thus molecular-level selectivity to VB12/VB2 (neutral molecules with distinct MWs) or VB1/VB2 (cationic/neutral molecules with similar MWs) can be achieved.

Construction of a gelatin scaffold with water channels for preparing a high performance nanofiltration membrane

In order to realize energy saving and resource recovery in desalination and waste-water treatment, it is urgent to develop nanofiltration (NF) membranes with high permeability and selectivity. Therefore, many researchers devote to designing different hydrophilic polymer-interlayers for the thin-film composite (TFC) membranes, targeting to prepare NF membranes with outstanding separation performance. However, the thin polymer-interlayer (<10 nm) can only slow down the diffusion rate of aqueous monomer and affect the interfacial polymerization (IP) process, forming a thin and defect-free polyamide (PA) layer. Herein, we constructed a hydrophilic and homogeneous gelatin (GT) scaffold with a thickness of over 100 nm on polysulfone (PSF) substrate and prepared a PA separation layer by IP process to obtain a high-performance TFC based NF membrane. The scaffold can not only affect the diffusion rate of piperazing (PIP) in IP process to form a thin PA layer, but also provide additional channels for water diffusion, which would significantly improve the permeability of NF membranes. Moreover, the fabricated PA layer has a high cross-linking degree and a negative surface potential, endowing the NF membrane with a high salts rejection rate, especially for divalent anions. Hence the permeability of the resulting NF membrane (up to 16.95 ± 1.18 L m−2 h−1 bar−1) is about 2.5 times as compared with the controlled membrane, while achieving a high Na2SO4 rejection of 99.3% ± 0.2%. In addition, the coefficient of selectivity for NF membrane are 97.73 for αNaCl/Na2SO4 and 45.66 for αNaCl/MgSO4 respectively, which are several times higher than those of the controlled NF membrane. This work provides a low-cost and facile method to prepare a TFC based NF membrane with a high permeability and selectivity.

Electrospun transition layer that enhances the structure and performance of thin-film nanofibrous composite membranes

Electrospun nanofibers with completely interconnected pore structures are increasingly considered as substrates for fabricating thin-film nanofibrous composite (TFNC) nanofiltration (NF) membranes. The poor adhesion between the large-pore substrate and dense selective layer has been considered as the bottleneck for wide application. This work presents the role of a transition layer on membrane structure as well as performance enhancement. Specifically, both polyethyleneimine (PEI)/polyacrylonitrile (PAN) transition layer and PAN substrate layer are formed by electrospinning. Interfacial polymerization (IP) is subsequently performed with trimesoyl chloride and piperazine. The introduction of the PEI modified transition layer improves the hydrophilicity, provides additional reaction sites for IP, and avoids the polymerization in the pores of nanofibers. The resultant composite NF membranes exhibit a compact and defect-free selective layer. Such an optimal structure leads to an excellent separation performance of 95.6% for orange ΙΙ dye (MW = 350.32 g/mol) rejection and 38.5 L m−2h−1 bar-1 for the pure water permeability. It exhibits stable long-term performance during low pressure (0.2 MPa) nanofiltration, which will afford significant directions for the actual application of the TFNC membranes in water purification and other fields.

Regulating the morphology of nanofiltration membrane by thermally induced inorganic salt crystals for efficient water purification

Nanofiltration (NF) membrane typically prepared by interfacial polymerization (IP) technology is facing the problems of low permeance and flux-selectivity trade-off effect, which will seriously affect the efficiency of water purification. Here, novel NF membranes with a thin and crumpled polyamide (PA) layer were obtained by introducing low concentration of soluble inorganic salts (≤2 wt%) in the IP process and thermally induced crystallization of inorganic salts in the heat treatment process. The forces generated by the growth of inorganic salt crystals inevitably stretched the nascent and flexible PA layer, and further the inorganic salt crystals can sacrifice themselves in water, contributing to the formation of a thin and rough PA layer with crumpled nanostructure. Using NaCl as an example, the resulting NF membrane exhibited the permeation flux as high as 84 L/m2 h at 4 bar while maintaining a high rejection of 96.2% for Na2SO4. Meanwhile, it is universal for other soluble inorganic salts such as KCl, Na2SO4, KNO3 and CaCl2 to improve the filtration performance of NF membrane. This study is the first to combine the growth of inorganic salt crystals with the morphology regulation of PA active layer in the heat treatment process, which will further expand the research method of NF membrane with efficient water purification.

Three-channel capillary nanofiltration membrane with quaternary ammonium incorporated for efficient heavy metals removal

High-performance nanofiltration (NF) membranes have profound implications for water purification. Here, we reported a novelty polyamide NF membrane through introducing bis (2-hydroxyethyl) dimethyl-ammonium chloride (BHDA) in interfacial polymerization (IP) process on three-channel substrate membrane. This new monomer bearing abundant quaternary ammonium (N+) and hydroxyl could participate in the reaction between piperazine (PIP) and trimesoyl chloride (TMC). Then, not only was positive charge introduced into the NF membrane, but the hydrophilic of the resultant NF membrane was also significantly improved. Thus, the as-prepared PIP/BHDA-TMC (MPQ) membrane exhibited enhanced pure water flux (12.9 L·m−2·h−1·bar−1) which is 2.4 times as high as that of the PIP-TMC (MP) membrane, coupled with the salt rejection sequence as MgSO4 (93.46%) > Na2SO4 (91.61%) > MgCl2 (88.15%) > NaCl (22.03%). Meanwhile, MPQ exhibited a promising separation performance to various heavy metal salts (96.43% CuSO4, 96.16% ZnSO4, 91.69% Cu(NO3)2, 89.69% ZnCl2, 88.37% Pb(NO3)2). The stability of MPQ was tested with simulated wastewater, and the results illustrated that it has a potential applicability for heavy metals removal.

A loose polyamide nanofiltration membrane prepared by polyether amine interfacial polymerization for dye desalination

It is crucial for fractionating dye/salt mixture in dyeing wastewater treatment. Herein, a polyamide nanofiltration (NF) membrane (PEA-TMC) for high efficient dye desalination was prepared through polyether amine (PEA) and trimesoyl chloride interfacial polymerization. Due to the large molecular size and hydrophilicity of PEA, the resulting NF membrane possessed a relatively loose membrane structure and good hydrophilicity, which improved membrane water flux and dye desalination performance. The influences of PEA concentration and reaction time on the NF performance were systematically investigated. Under the optimal conditions, the membrane exhibited a high water flux of 66.4 L m-2h−1 at low operating pressure (0.4 MPa), and showed a high methyl blue rejection (95.4%) and low NaCl rejection (16.4%) when nanofiltrated methyl blue/ NaCl mixture solution. Moreover, PEA-TMC membrane exhibited good stability in continuous operation and antifouling performance. These results disclosed the promising applications of PEA-TMC membrane in dye/salt separation process.