Composite Nanofiltration Research Articles

Investigating the efficiency of a ceramic-based thin-film composite nanofiltration membrane for dyes removal

This study focuses on producing polyamide thin-film composite (TFC) ceramic membranes using interfacial polymerization, resulting in a polyamide layer on ceramic tubular substrates (Al2O3). These Al2O3 substrates possess robust mechanical and physical traits, featuring a porous surface structure. TFC membranes exhibit a thin, dense structure with root-like nanostructures on the ceramic base, with a thickness of around 260 nm. Atomic force microscopy confirms the smoother surface of TFC membranes with an average roughness value of 18 nm compared to ceramic tubular substrates. TFC membranes exhibit negative zeta potentials within a pH range of 4.7–10, while ceramic tubular substrates show more complex zeta potential behavior. Both substrate and TFC membranes are hydrophilic, with the TFC membrane having a slightly higher water contact angle (approximately 43 ± 1°). Zeta potential analysis reveals a negative potential of around −23 mV for the TFC membrane. In water permeability tests, the ceramic tubular substrate membrane demonstrates high permeability, whereas the TFC membrane displays slightly lower permeability (28 ± 0.8 L/m2 h bar) due to the presence of the polyamide selective layer. Importantly, the TFC membrane significantly enhances organic dye rejection compared to the ceramic tubular substrate, with rejection rates of 95% for CR, 92% for BTB, and 86% for MB. Rejection performance is mainly influenced by size exclusion and dye molecular charge. These novel TFC ceramic nanofiltration membranes offer improved water permeability while maintaining selectivity, holding promise for effectively removing organic pollutants in water treatment applications.

Laccase-triggered one-step fabrication of positively charged phenolic acid-amine networks for nanofiltration

Molecular deposition provides a flexible and versatile platform for preparing positively charged composite nanofiltration membranes. The widely studied building units for molecular deposition are polyphenols such as catechins and tannins, which usually cause the complexity of the ultimate selective layer due to their relatively high antioxidant activity and limited positive potential originated from the large number of hydroxyl groups. In this work, a laccase-triggered one-step process has been proposed to prepare composite nanofiltration membranes. Highly positively charged phenolic acid-amine networks, which are represented by ferulic acid (FA) and polyethyleneimine (PEI), are constructed as the dense selective layer with a thickness of about 49 nm. This process is conducted in aqueous solutions under mild conditions, driven by electrostatic adsorption, catalytic oxidation, and covalent crosslinking processes. The structure of the selective layer can be finely tuned by the molecular weights of PEI, the chemical composition, and the pH values of the solutions. The prepared composite nanofiltration membranes can effectively reject MgCl2 (94.5 %) and organic dyes such as alcian blue (AB) (>98.7 %) and methyl blue (MB) (>97.8 %). This work not only demonstrates a facile and versatile method for preparing positively charged composite nanofiltration membranes with great separation performance towards divalent cations, but also expands the membrane building blocks.

Preparation of high temperature resistant polyamide composite nanofiltration membranes by thermally assisted interfacial polymerization

The temperature of interfacial polymerization (IP) and feed temperature both have importance effects on the structure and properties of polyamide thin film composite nanofiltration (TFC NF) membranes. This experiment involved preparing TFC NF membranes using IP at 25, 60, 80, and 100 °C, and their performance was evaluated in the range of 25 to 90 °C. Results showed that the membrane prepared at an IP temperature of 100 °C maintained more than 99% retention of divalent salts. The high temperature allowed the reaction between piperazine (PIP) and 1,3,5-benzoyl chloride (TMC) to become more complete and the degree of crosslinking increased, resulting in a thicker and denser defect-free polyamide layer. With increasing the temperature of the feed solution, the increase of pores sizes caused by swelling made the permeance increase by 2 ∼ 3 times, but the rejection rate of salt (Na2SO4, MgSO4) by TFC NF membranes prepared at 80 and 100 °C remained unchanged (>99%). In addition, the TFC NF membrane obtained by high-temperature IP has excellent anti-fouling and long-term stability. By adopting high-temperature IP, the TFC NF membranes exhibited excellent anti-fouling and long-term stability, making them an economical and versatile method for treating water in high-temperature environments.

Surface modification of thin film composite nanofiltration membrane with graphene oxide by varying amine linkers: Synthesis, characterization, and applications

We report surface modifications of thin film composite nanofiltration (TFC NF) membrane with amine and the characterization of the resulting membrane for anti-biofouling properties. Graphene oxide (GO) was grafted on the surface of the TFC NF membrane using three linkers, ethylene diamine, diethylene triamine and triethylene tetraamine. Grafting of GO on the surface was successfully validated through Raman Spectroscopy and XPS. Ring-like structures were observed on the surface of the dense polyamide layer of TFC NF membranes under SEM after modification with GO. A slight increase in the roughness, and hydrophilicity was noticed in the membranes modified with GO. GO-grafted membranes demonstrated enhanced chlorine stability, lower biofouling tendency, lower flux decline during filtration of seawater and improved hexavalent chromium rejection in the basic pH. The improved chlorine stability is attributed to intermolecular hydrogen bonding between GO and polyamide structure, while the enhanced biofouling resistance and lower flux decline is ascribed to hydrophilic GO. The membranes were further evaluated for rejection of heavy metal ions, in particular hexavalent chromium, which showed about 97% rejection in basic pH attributed to the rise in negative character of the membrane surface due to the grafting of GO. Na2SO4 rejection for control TFC was reduced by 9.6%, while a reduction between 1 and 5.5% was found in fGO grafted membranes after 1 h exposure to 1000 ppm NaOCl.

Nanomorphogenesis of template-induced crumpled polyamide nanofiltration membranes

Tailored thin-film composite (TFC) nanofiltration (NF) membranes can potentially achieve high permeance and effective salt separation during wastewater reclamation and water reuse. Recently, customized polyamide (PA) nanofilms with crumpled structures have received considerable attention owing to their outstanding separation performance; however, the underlying mechanism of the formation of crumpled features at the nanoscale remains poorly understood. Herein, we report the use of a particulate polydopamine (PDA) interlayer as a regulator for modulating chemical inhomogeneity (i.e., the diffusion and distribution of amine monomers) during the interfacial polymerization (IP) process, in which the characteristic spatial patterns of PA nanostructures are formed following a diffusion–reaction dynamics model in the Turing theory. Furthermore, the nanomorphologies and separation performance of PA membranes can be effectively controlled by tuning the physical inhomogeneity (i.e., the roughness of the organic–aqueous reaction interface) of the particulate interlayer. The interlayer-mediated TFC NF membrane exhibits crumpled nanosized stripes with three times higher permeance and four times higher Cl−/SO42− selectivity (up to 82.1) than those of pristine PA membranes. We have also identified an array of topographical parameters for both the PDA interlayer and PA nanostructures based on experimental observations and multiscale simulations (i.e., molecular dynamics and dissipative particle dynamics) to establish quantitative relationships between the interlayer morphology, PA morphology, and performance characteristics of NF membranes. Our work provides molecular insights into the nanomorphogenesis of crumpled PA nanofilms and interlayer effects on the IP reaction and final separation performance.

Fabrication of bamboo cellulose-based nanofiltration membrane for water purification by cross-linking sodium alginate and carboxymethyl cellulose and its dynamics simulation

The cross-linking coating modification strategy was adopted to construct an environmentally sustainable bamboo cellulose-based composite nanofiltration membrane (CL-NF-BCM), with bamboo cellulose providing as the support material. Solid-state Nuclear Magnetic Resonance (13C NMR) results show that alginate (ALG) and carboxymethyl cellulose (CMC) were successfully cross-linked onto the cellulose membrane. Furthermore, the transfer of chemical elements was confirmed by X-ray Photoelectron Spectroscopy (XPS) measurements. The microscopic morphology illustrates that after cross-linking coating modification, the surface of the bamboo cellulose membrane turns from a uniform porous structure to a polymerized layer with interwoven network structure. In addition, the result of Brunauer-Emmett-Teller (BET) shows that the average pore size of the as-prepared CL-NF-BCM of about 1.1 nm. The performance testing results show that the CL-NF-BCM cellulose membrane had a rejection of 48% against 500 ppm NaCl solution and membrane flux of 17 L·m−2·h−1 under a nanofiltration condition of 0.5 MPa operating pressure. This work enriches a high value-added application of bamboo products, as well as provides a novel perspective for membrane surface modification.

The purification and concentration of amoxicillin by novel alkali-sensitive polypiperazine amide/polysulfate composite nanofiltration membranes

The recovery of amoxicillin from the mother liquor is crucial in reducing production costs and preventing environmental contamination. Amoxicillin separation was enhanced under an alkaline filtering environment. Therefore, the novel alkali-sensitive polypiperazine amide (PPA)/polysulfate (PSE) composite nanofiltration membranes were fabricated via interfacial polymerization for the concentration and purification of the amoxicillin crystalline mother liquor. The alkali sensitivity of the PPA/PSE composite nanofiltration membrane was investigated. The long-term stability of the membrane was also evaluated. Purification and concentration experiments of amoxicillin mother liquor were also carried out. The separation efficiency of amoxicillin was improved due to the pH sensitivity of amoxicillin and the pH sensitivity of the developed nanofiltration membrane. The results indicate 92.2% rejection of amoxicillin and 45.4 L⋅m−2⋅h−1 of flux at pH 10. In addition, PPA/PSE nanofiltration membranes exhibit good mechanical properties and long-term stability. This indicates its remarkable application potential and its use is expected to result in the large-scale recovery of amoxicillin from the crystalline mother liquor.

Preparation of a Solvent-Resistant Nanofiltration Membrane of Liquefied Walnut Shell Modified by Ethylenediamine.

N,N-dimethylformamide (DMF) has excellent chemical stability and is widely used as an aprotic polar solvent. In order to reduce production costs and reduce pollution to the surrounding environment, it is necessary to recycle and reuse DMF. Previous research has found that the thin film composite nanofiltration membrane prepared from liquefied walnut shells exhibited a high rejection rate in DMF, but relatively low permeance and mechanical strength. In order to increase permeance without compromising the separation performance, ethylenediamine (EDA) is used as a modifier to graft onto the structure of liquefied walnut shell through the Mannich reaction. Then, modified liquefied walnut shell as an aqueous monomer reacts with trimesoyl chloride (TMC) via the interfacial polymerization method on the EDA-crosslinked polyetherimide (PEI) membrane. The results show that the permeance of the prepared membrane is significantly improved by an order of magnitude, demonstrating a rejection rate of 98% for crystal violet (CV), and a permeance of 3.53 L m-2 h-1 bar-1 in DMF. In conclusion, this study reveals the potential of utilizing liquefied walnut shells as raw materials for preparing high-performance separation membranes and demonstrates that surface modification is a feasible approach to enhance permeance of membranes without sacrificing the rejection rate.

Fabrication of nano composite membrane filter from graphene oxide(GO) and banana rachis cellulose nano crystal(CNC) for industrial effluent treatment

Agricultural bio-waste based cellulosic materials are highly biodegradable and naturally occurring with high adsorption and capable of outstanding physico-chemical properties. This study elicits neoteric upliftment and impending significance of graphene oxide(GO) – cellulose nanocrystal(CNC) nano-filter composite membrane (NFCM) for high removal of Cr3+, Co2+, Ni2+, Pb2+, Cd2+ and Methylene blue molecules from industrial wastewater. We tried to direct comparison between conventional filter and NFCM composites filter and their physical and chemical properties, production costs, use and disposal in order to show the potential of Nano structural cellulose materials as a sustainable replacement for NFCM filter for removal of heavy metals and dyes from industrial wastewater treatment technologies. The prepared GO, CNC, and NFCM were characterized by using X-ray Diffraction(XRD), Fourier Transform Infrared (FTIR), Field Emission Scanning Electron Microscopy(FESEM), Thermogravimetric Analysis(TGA) etc. The efficiency of wastewater purification of fabricated NFCM were determined by Ultra Violet(UV)-vis spectrophotometer and Inductively Couple Plasma Optical Emission Spectroscopy(ICP-OES). Whereas the fabricated NFCM were highly crystalline, thermally stable, have good surface activity, exhibit remarkable removal efficiency against the toxic heavy metals and soluble dye. The maximum R% was found for Cd2+ and Pb2+, around 99%. Beside this all dye molecules were removed from the wastewater simultaneously and successfully.

EMT-NH2 zeolite interlayer induces the formation of high-performance polyamide membrane

Conventional nanofiltration (NF) thin-film composite (TFC) membranes are strongly restricted by the trade-off between their water permeance and selectivity as well as the poor structural stability for desalination and wastewater treatment. Herein, we report an interlayer-based thin-film composite (i-TFC) NF membrane with high performance using amino-functionalized EMT zeolite (EMT-NH2) nanocrystals as the interlayer. By adjusting the distribution density of EMT-NH2 on the substrate, a thin and dense polyamide (PA) layer with heterogeneity multi-level morphology (nanosized nodules and nanoscale stripes) can be formed and regulated. The EMT-NH2 zeolite nanocrystals with numerous hydrophilic groups (hydroxy and amino groups) and internal cavities can provide an additional priority water channel, increase the amine monomer storage on the substrate, and slow down the diffusion of amine monomer, thereby leading to the construction of a dense PA layer with high performance. As a result, the i-TFC-15 membrane depicted a water permeability of 13.82 ± 0.47 L m-2h−1⋅bar−1 (2.5 times that of the controlled one), while maintaining an excellent retention ability for divalent salts (98.55% for Na2SO4, 98.42% for MgSO4 and 97.40% for MgCl2). Additionally, the rigid hydrophilic interlayer containing zeolite nanocrystals endowed the i-TFC-15 membrane with excellent pressure resistance (up to 2.4 MPa), long-term operating stability, and antifouling propensity (flux-recovery ratio, 90.1%). This work provides an approach for fabricating a novel high-performance NF membrane and deepens our understanding of the role of porous interlayer affecting the formation of the PA layer.

Self-cleaning photoelectrocatalytic filtration based on Ca(OH)2/Ti3C2Tx composite nanofiltration membranes for synergistically enhanced separation and degradation of phenolic compounds

Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membranes has emerged as an attractive technology for removing organic pollutants in wastewater treatment, however, the separation and degradation performance are still challenging. Herein, novel composite NF membranes were constructed by cross-linking a Ca(OH)2/Ti3C2Tx (CT) catalyst to a polyamide membrane using tannic acid (TA). In these CT@TA (CTTP) membranes, Ti3C2Tx reduces the charge-transfer resistance and recombination rate of CT, leading to enhanced PEC activity. The optimal CTTP membrane had a high water flux (27.9 L·m−2·h−1·bar−1) and excellent rejection rates for phenolic compounds (phenol: 85.1 %, 4-nitrophenol: 91.1 %, and bisphenol A (BPA): 94.6 %). Under visible-light irradiation with electrical assistance (3 V), the BPA degradation rate (92.2 %) was 13.7 % higher than that under light irradiation alone, and a higher flux recovery rate was achieved (94.1 %). Superoxide (O2−) and hydroxyl (OH) radicals were critical active species in catalytic BPA degradation, and the observed intermediates suggested that the degradation pathway involves oxidation, hydroxylation, and aromatic ring cracking. The developed NF membranes, which exhibit synergistic separation and degradation effects and self-cleaning properties, provide an innovative solution for the treatment of organic pollutants in wastewater.

Role of molybdenum disulfide (MoS2) nanosheets doping position on the thin-film nanocomposite (TFN) membrane during brackish water treatment

Brackish water desalination based on nanofiltration (NF) has been regarded asa feasible solution to address the scarcity of freshwater. However, the trade-off effect and membrane fouling are challenges for the thin-film composite NF membranes, restricting their further application in desalination. Herein, modified thin-film nanocomposite (TFN) membranes were constructed with molybdenum disulfide (MoS2) nanosheets incorporated either into the polyamide layer (P-TFN) or as an interlayer (I-TFN). The surface morphology, chemical element, electronegativity, pore size, hydrophilicity, separation performance and antifouling property of the membranes were systematically evaluated and compared. The P-TFN membrane exhibited superior salt rejection of Na2SO4 up to 98.4% and preeminent flux recovery ratios (FRRs) of 95.4% and 92.2% for humic acid (HA) and bovine serum albumin (BSA) filtration, respectively, which possessed high electronegativity and small effective pore size. While, without compromising its salt retention and foulant resistance, the I-TFN membrane exhibited 51% better permeability than the control TFC membrane, due to its unique crumpled structure of the PA layer and the “dragging effect” of the interlayer on water molecules. Furthermore, we elaborated on the mechanism underlying the differences in surface properties, and verified the effectiveness of the modified membranes in authentic brackish water desalination. Significantly, the comparison provides novel insight for the customization and regulation of the PA layer.

High-performance thin film composite nanofiltration membranes with MoS2 nanosheet interlayer

High-performance polyamide thin film composite (TFC) nanofiltration membranes have received great attention in recent years. Herein, we report the preparation of TFC nanofiltration membranes by interfacial polymerization using MoS2 nanosheets as the nanomaterial interlayer. The aqueous monomer and MoS2 nanosheets are distributed on the surface of microporous membrane substrates by a one-step method. The MoS2 interlayer improves the uniformity and smoothness of the microporous substrates, helping to form polyamide nanofilms at ultralow monomer concentration. Moreover, the hydrophilic and negatively-charged MoS2 nanosheets enhance the water permeability and negative charges of the nanofiltration membranes. The composite membranes show both high water permeance of 33.5 L m−2 h−1 bar−1 and Na2SO4 rejection of 97.5%, as well as significantly improved mono-/divalent anions selectivity and antifouling property. It is proved that the interfacial polymerization strategy assisted by the MoS2 interlayer is effective for preparing high-performance nanofiltration membranes.

Development of micropollutants removal process using thin-film nanocomposite membranes prepared by green new vapour-phase interfacial polymerization method

The presence of emerging micropollutants in water bodies and potable water, has become a topic of great concern globally. In this study, a newly modified vapour-phase interfacial polymerization (VP-IP) method has been used to fabricate thin-film composite (TFC) and thin-film nanocomposite (TFN) nanofiltration (NF) membranes to study the removal of micropollutants, diclofenac (DIC) and triclosan (TRI) from water. The method used is an economically and environmentally greener method as the reaction takes place between the aqueous monomer solution and vapours of the organic phase, thereby avoiding the utilization of organic solvent hence named as vapour-phase interfacial polymerization (VP-IP) method. Polydopamine (PDA) coated polyethersulfone (PES) membranes were used to support the TFC and TFN membranes. The TFN membranes were incorporated with different concentrations of amine-functionalized cloisite Na+ 2D clay nanosheets (NH2-CMMT) to enhance the physicochemical properties of the TFN membranes. The performance study of the prepared TFN membranes based on different hours and pressures demonstrated an excellent rejection percentage of ∼99 ± 0.5% for both DIC and TRI compared to the TFC membrane. The membranes showed improved water permeate fluxes of ∼109 ± 5 Lm-2h-1 for DIC and ∼150 ± 5 Lm-2h−1 for TRI. The prepared TFN membranes demonstrated positive results for the antifouling test as well as exhibited antibacterial activity tested against Escherichia coli (E. coli) bacteria. The findings of this study show that our prepared TFN membranes combined with NH2-CMMT 2D clay nanosheets exhibit enhanced hydrophilicity, improved flux rate, excellent removal efficiency, antibacterial activity, and improved antifouling properties, indicating the potential to be used for removing emerging micropollutants from water.

Employing Visible Light To Construct Photoinitiated Polymerized Nanofiltration Membranes for High Permeation and Environmental Micropollutant Removal.

Improving the nanofiltration (NF) performance of membrane-based treatment is conducive to promoting environmental water recycling and addressing water resource depletion. Combinations of light, electricity, and heat with traditional techniques of preparing membranes should optimize membrane performance. Interfacial polymerization and photopolymerization were integrated to construct a photopolymerized thin-film composite NF membrane with a ridged surface morphology. Under visible light initiation, 2-acrylamido-2-methyl-1-propanesulfonic acid was crosslinked with the polyamide network. The control effects of light on the membrane surface and physicochemical properties were revealed via infrared thermal images and response surface methodology. To present the diffusion motion of piperazine molecules, molecular dynamics simulations were implemented. Through density functional theory simulations, the crosslinking mechanism of the photoinduced NF network was identified and verified. The surface physicochemical characteristics and perm-selectivity performance were systematically illustrated. The photopolymerized membrane outperformed the pristine in permeability and selective separation competence; without degradation of solute repulsion, the water permeation was enhanced to 33.5 L m-2 h-1 bar-1, 6.6 times that of the initial membrane. In addition, the removal of organic contaminants and antifouling capacities were improved. This work represents a novel lead for applying sustainable resources in constructing high-performance membranes for environmental challenges.

Preparation and performance of “three-layer sandwich” composite loose nanofiltration membrane based on mussel bionic technology

Abstract In this study, a novel “three-layer sandwich” composite loose nanofiltration (NF) membrane structure by mussel bionic technology was constructed on a porous polyvinylidene fluoride (PVDF) substrate membrane, with a mussel bionic coating as the middle layer and the complex network of polyphenols and metal ions as the top layer. The new composite NF membrane had comprehensive properties such as excellent separation performance, good hydrophilicity and strong antifouling ability. The experimental results showed that the combination of tannic acid (TA) and iron ion (Fe3+) could significantly improve the comprehensive performance of the composite NF membrane, with water flux of more than 3000 L/(m2∙h), and the retention rate of dyes and bovine serum protein (BSA) exceeded 90 %, and contact angle was up to 30°. The combination of TA and copper ion (Cu2+) can greatly enhance the antifouling performance and interception ability of methylene blue. The complexation activity of metal ions and polyphenols was related to the oxidation of metal ions. The PVDF/DA-PEI/TA-M+ composite structure scheme of “three-layer sandwich” NF membrane provides a new idea and future development direction for the development of novel NF membranes with excellent comprehensive performance.

Low fouling/scaling double network thin film composite nanofiltration membranes with improved desalination performance

Conventional poly(piperazineamide) [poly(PIP)] thin film composite (TFC) nanofiltration (NF) membranes undergo severe fouling/scaling and -show low barrier towards heavy metal ions and organic solutes. Herein, we report the preparation of double network (DN) TFC NF membranes to address these issues. In situ interfacial polymerization between PIP + poly(2-dimethyl aminoethyl)methacrylate (PDMA) and trimesoyl chloride+activated dihalide provides DN-TFC NF membranes. Formation of DN leads to the lowering of negative charge and narrowing down the pore size distribution of the membranes. PEGylated DN-TFC membranes have been prepared using copolymers of PEG and PDMA to demonstrate the adaptability of this chemistry and to increase the antifouling property. The DN-TFC membranes show water permeance of 7.9–8 L m−2 h−1 bar−1 and higher rejection of MgCl2 (90–94 %), Co2+ (96–98 %) and bisphenol A (91–94 %) as compared to that of the pristine (74 %, 70 % and 80 %) and the reported negatively charged (9–83 %, 60 % and 48–97.6 %) NF membranes. DN-TFC membranes show Na2SO4 rejection of ∼98 %, close to the reported membranes (98–99 %). The fouling and scaling resistant behaviors of the DN-TFC membranes (Flux recovery ratio = 90–94 % and 93–95 %) are greatly enhanced as compared to that of the pristine membrane (∼82 % and 76 %). DN-TFC membranes show great promises for the purification of water.

Nanofiltration membrane with asymmetric polyamide dual-layer through interfacial polymerization for enhanced separation performance

Thickness reduction of polyamide separation layer played an important role in permeability enhancement of thin film composite (TFC) nanofiltration membrane. However, the practical application of TFC nanofiltration membrane with ultrathin polyamide layer is still a great challenge. Herein, we proposed a strategy for preparing nanofiltration membrane with asymmetric polyamide dual-layer through interfacial polymerization. The top polyamide layer is thin, smooth and dense. The bottom polyamide layer is relatively thick, rough and porous. The thin and dense top polyamide layer enabled membrane with relatively high water permeability (18.5 ± 1 L m−2 h−1 bar−1) and Na2SO4 rejection (97.2 ± 0.8 %) performance. The thick and porous bottom polyamide layer guaranteed membrane stability. This study offers a promising strategy for polyamide composite membrane fabrication with enhanced separation performance.

In-Situ Modification of Nanofiltration Membranes Using Carbon Nanotubes for Water Treatment.

Modification of thin-film composite (TFC) nanofiltration (NF) membranes to increase permeability and improve separation performance remains a significant challenge for water scarcity. This study aimed to enhance the permeability and selectivity of two commercial polyamide (PA) NF membranes, NF90 and NF270, by modifying them with carbon nanotubes (CNTs) using microwave (MW)-assisted in-situ growth. The conducting polymer, polypyrrole (Ppy), and a ferrocene catalyst were used to facilitate the growth process. Chemical and morphological analyses confirmed that the surface of both membranes was modified. The NF270-Ppy-CNT membrane was selected for ion rejection testing due to its superior permeability compared to the NF90-Ppy-CNT. The modified NF270 membrane showed a 14% increase in ion rejection while maintaining constant water permeability. The results demonstrated that it is feasible to attach CNTs to a polymeric surface without compromising its functional properties. The Spliegler-Kedem model was employed to model the rejection and permeate flux of NF270-Ppy-CNT and NF270 membranes, which indicated that diffusive transport contributes to the modification to increase NaCl rejection. The present study provides a promising approach for modifying membranes by in-situ CNT growth to improve their performance in water treatment applications, such as desalination.

Polyethyleneimine modified polyamide composite nanofiltration membrane for separation of lithium and magnesium

The application of nanofiltration (NF) membrane with positive charge on the surface in the separation of lithium‑magnesium is a convenient, energy-saving and sustainable strategy. In this work, polyethyleneimine (PEI) was introduced into the composite NF membrane through two methods to investigate and make a comparation in surface morphology and properties, application in the separation of membrane to Li+ and Mg2+, respectively. Both PEI and PIP were involved in the preparation of membranes as aqueous monomers, which can reduce the cross-linking degree of active layer but reduce the electronegativity of membrane surface. The rejection of Mg2+ reached 98.1 % and the purity of Li+, which is the mass fraction of Li+ in cations of permeate, reached 62 %, respectively, the separation factor SLi,Mg reached 32.6. By contrast, PEI with different molecular weight and concentration was grafted on the PA layer which improved the density of membrane but reduced the electronegativity of the membrane surface. The rejection of Mg2+ reached 97.2 % and the purity of Li+ reached 63 %, respectively, the SLi,Mg reached 33.6 with an acceptable flux. Both of two modification methods had a preferable performance on separation of lithium‑magnesium with a higher SLi,Mg. Therefore, it is an efficient strategy to add PEI through different methods into the preparation of NF membrane to separate lithium‑magnesium and extract the Li+ from salt lake brine with high Mg/Li mass ratio.