Nanofiltration Performance Research Articles

Constructing nanofiltration membrane on hydrophobic PVDF and PTFE substrates via reverse interfacial polymerization

Polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE) porous membranes are ideal substrates for preparing thin-film composite (TFC) polyamide (PA) membranes with improved solvent resistance. However, it remains difficult to construct PA skin layers on PVDF and PTFE substrates via conventional interfacial polymerization (IP) due to the hydrophobic nature of these materials. To address this challenge, a reverse IP process was proposed to construct a defect-free PA skin layer on PVDF and PTFE substrates, in which the hydrophobic PVDF and PTFE substrates were soaked with the organic phase to ensure uniform coverage of reacted solution on the substrates. This novel strategy can effectively tackle the issue of uneven wetting of the aqueous phase on hydrophobic substrates in the conventional IP process. The resultant TFC membranes (i.e. Mrev-PVDF and Mrev-PTFE) exhibit excellent nanofiltration (NF) performance in both aqueous and organic solutions. Mrev-PVDF and Mrev-PTFE have MgCl2 rejections of 96.12% and 95.17%, alongside the water permeances of 12.8 LMH/bar and 11.2 LMH/bar, respectively (Mrev-PTFE was activated with DMF). It is further shown that Mrev-PVDF and Mrev-PTFE could also reject 99.4% and 98.5% of Congo red in methanol solution at solvent permeances of over 3.3 LMH/bar, while they also perform excellently in other polar protic solvents. Consequently, this work opens a new window for constructing high-performance TFC PA membranes on hydrophobic substrates and expands the application of the TFC PA NF membrane.

Adsorption efficiency of highly methylene blue dye concentrations with multilayer chitosan-modified clays for a precise nanofiltration performance of polluted water

The development of highly efficient non-conventional materials has been a potential solution in water treatment for both environmental and economic reasons. The present work is dedicated to montmorillonite (MMT) with surface modification by biopolymer chitosan at different pH for adsorption of methylene blue (MB) dye. Molecular dynamics (MD) simulations are performed to visualize the adsorption process and unveil the mechanisms at nanoscale. Results show that monolayer and multilayer adsorption of MB tends to occur on the pure MMT and chitosan-modified MMT (CMMT) surfaces, respectively. The mechanism behind the two adsorption modes is controlled by the attraction strength to MB: electrostatic attraction from MMT > intermolecular π–π interactions from dyes > H-bonding interaction from CMMT. Furthermore, to quantify the adsorption capacity and efficiency, an evaluation method for the identification of immobilized dyes based on individual molecular diffusion is proposed for the first time. The immobilization efficiency for MB on CMMT surfaces increases with pH and reaches a maximum value of 80 % (158.79 mg/g) at pH 9.5, assuming that effectively inhibited MB has D < 0.35– 0.95 × 10−9 m2/s. However, the stability of CMMT composites decreases with pH due to the detachment of some chitosan fragments when trapping dye molecules. This study suggests that the CMMT composite is more advantageous than MMT at high dye concentrations and alkaline conditions.

Phospho-modified polyamide nanofiltration membranes with high permeability by using alendronate sodium as additives

The conventional in-situ interfacial polymerization (IP) process, characterized by its rapid reaction rate, is known to be an uncontrollable process that can lead to defects in the performance of nanofiltration (NF) membranes. Herein, a novel NF membrane with a phosphorylated polyamide (PA) network was prepared through a controlled IP process with the addition of alendronate sodium (AS). The phosphoric acid groups of AS can restrain the diffusion of PIP, due to the synergistic interactions with piperazine (PIP) including electrostatic interaction and hydrogen bonding. Moreover, the amine groups of AS could react with trimesoyl chloride (TMC) in organic phase, which incorporated AS into the PA networks. Consequently, a more negatively-charged ionic PA layer with looser, rougher and more hydrophilic structure was obtained. The prepared membrane exhibited a water permeance of 25.0 L·m−2·h−1·bar−1 which was almost two-fold higher than that of NF membranes prepared without additives, while keeping an excellent salt rejection performance (Na2SO4 rejection >97 %), even in a high salt concentration (7.0 g/L). Furthermore, the membrane demonstrated high rejections for different dyes, long-term operation stability and comparable anti-fouling ability against typical contaminants. This work provided a facile and rational approach to preparing ionic NF membranes with high permeability.

Development and investigation of high‐flux antifouling NF PES membranes decorated by aniline oligomers and application for wastewater treatment

AbstractIn this research, first branched aniline oligomers functionalized polyethersulfone (BAO‐PES) were prepared by diazonium‐induced grafting, and then the embedded membranes were fabricated at five different compositions using the conventional phase inversion process. The influence of BAO‐PES as a modifier on membrane preparation was investigated in terms of membrane topography, membrane morphology, hydrophilicity, permeability, antifouling performance, and chemical stability. The function of blended membranes was evaluated by computational analysis, Fourier transform infrared (FTIR) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle (WCA) measurement. Our computational analysis has substantiated that BAO‐PES (25 wt. %)/PES, characterized by a lower Flory–Huggins parameter (0.65), emerges as a promising contender for the blending of BAO‐PES with PES. The maximum water flux of 67.6 kg/m2 h was observed for the M1 membrane with the optimum dosage of BAO‐PES (25 wt. %) at a low pressure of 3 bar. To assess the nanofiltration performance of the mixed matrix BAO‐PES/PES membranes, the removal efficiency was studied for Direct Red 16 and tannic acid dye. From the results, it was found that the loose BAO‐PES/PES membranes had great dye rejection ability (more than 97%) compared to the bare membrane (88%–89%). The fouling resistance property of the loosely prepared membranes was tested by protein rejection, and the results revealed that the best antifouling property was observed at optimum dosage of the BAO‐PES modifier (25%, FRR = 98.37%). The embedded BAO‐PES/PES membranes, after exposure to harsh environments, exhibited such long‐term chemical stability that it is an important specification for real management in industry.

Modulation of charge properties inside thin-film composite polyamide membranes towards enhanced nanofiltration performance

Nanofiltration (NF) is receiving increasing attention worldwide as a high-efficiency technology for water purification. One viable approach to enhance the performance of NF membranes involves the meticulous optimization of their physicochemical and structural attributes through the introduction of additives. Nonetheless, the predominant NF membrane additives currently accessible primarily exert their influence at the membrane's surface. In this context, we introduce a novel strategy for fabricating polyamide (PA) NF membranes endowed with augmented negative charge density, capable of permeating the innermost stratum of the separation layer. This innovation hinges on the straightforward inclusion of 2-Methylimidazole (Hmim) into the aqueous phase. The ramifications of Hmim's incorporation of the structural configuration, morphological composition, physicochemical characteristics, and overall performance of the thin-film composite (TFC) membrane were meticulously scrutinized through an array of comprehensive characterizations. The integration of Hmim affords PA nanofiltration membranes the remarkable capability to achieve a rejection rate as formidable as 99.5% for Na2SO4 and 42.8% for NaCl, all the while maintaining an unswerving flux. As a result, a high SO42-/Cl- separation factor of up to 116.1 was achieved. Our work provides insights and directions for the development of additives in the preparation of NF membranes.

Swift fabrication of thin-film composite membranes with azine-linked covalent organic framework for high-temperature organic solvent nanofiltration

Covalent organic frameworks (COFs) belong to a class of crystalline and porous solids that are generated by the self-assembly of reactive monomers via covalent linkage. Most existing methods for fabricating COF membranes are tedious, and they focus on quality control challenges associated with thickness uniformity, pore size, and mechanical properties. In this study, TraHz and TpaHz COF-based thin-film composite (TFC) membranes were prepared via the swift interfacial polymerization (IP) of hydrazine and aldehyde monomers on a polyacrylonitrile (PAN) support. Hydrazine played a dual role in one-pot synthesis, where PAN was crosslinked and IP was initiated. Varying the polymerization time allowed for fine-tuning the membrane thickness and performance. The membranes displayed robust high-temperature separation performance in polar aprotic solvents at temperatures of up to 80 °C. The toluene permeance of the membranes was remarkable. The permeance was highly dependent on both the applied pressure and temperature; however, the rejection performance was less dependent on these parameters. Based on the results of the nanofiltration performance evaluated using different molecular-weight dyes, a molecular-weight cut-off value of ∼650 g mol−1 and a rejection higher than 98 % for the Congo red and Chicago blue dyes in water, THF, and ethanol were observed. The dye rejection in toluene was higher than 98 % for Rhodanile blue, while maintaining high toluene permeances of 47 and 33 L m−2 h−1 bar−1 using TraHz-30 and TpaHz-30, respectively. In addition, both membranes exhibited stable separation performance. Our TFC membranes demonstrate a new approach for designing robust and high-flux nanofiltration membranes for precise molecular sieving even at high temperatures.

Quantification of overcompensated cations in layer-by-layer membrane by Orange yellow II

The charge density of the nanofiltration (NF) membrane separation layer is critical for ion separation because the charge-based Donnan exclusion plays a critical role. To quantified the charge density has been an important but difficult task. We recently discovered the excellent performance of poly(styrene sulfonate) (PSS)/ poly (allylamine hydrochloride) (PAH) layer-by-layer (LBL) NF membranes for Mg2+/Li+ separation. The overcompensated amine groups (R-NH3+) in PAH were assumed to be the main contribution, but lacked a quantification of the charge density for further proof. Here, a simple quantitative experimental method by Orange yellow II staining was reported for the first time to measure the overcompensated amine groups in the separation layer. The sulfonic acid group (R-SO3-) in Orange yellow II stoichiometrically adsorbed to the excessive R-NH3+ at pH = 3 by electrostatic interaction, and desorbed at pH = 12. Thermodynamics and kinetics analysis of the sorption process demonstrated a Langmuir monolayer sorption and the sorption was controlled by sorption reaction not diffusion. The pore size distribution and rejection measurement confirmed that Orange yellow II sorption did not disrupt the original PSS/PAH layer. A linear relationship was observed between the charge density and the coating bi-layers or PAH layers. The accurate, easy assessment of charge density of LBL NF membrane provides future possibility for understanding overcompensation during LBL assembly and a bottom-up understanding of the charges to the NF performance in separation.

Polyamide nanofiltration membranes by vacuum-assisted interfacial polymerization: Broad universality of Substrate, wide window of monomer concentration and high reproducibility of performance

Vacuum assistance is used for filtering solid substances onto porous substrates to create composite membranes typically. However, the potential of this approach has rarely been assessed in facilitating the distribution of liquids within those porous substrates to fabricate composite membranes in typical interfacial polymerization. In this work, we demonstrate the advantages of vacuum-assisted interfacial polymerization (VAIP) in terms of substrate universality, monomer concentration range, and performance reproducibility in the fabrication of polyimide nanofiltration membranes. Aqueous solutions of PIP can be homogeneously distributed by vacuum filtration on diverse microfiltration substrates of polyether sulfone (PES), Nylon-66, polyvinylidene fluoride (PVDF), cellulose acetate (CA), and mixed cellulose esters (MCE), respectively. Interfacial polymerization is then performed on these substrates using different concentrations of piperazine (PIP, 0.0075–0.1000 wt%) and trimoyl chloride (TMC, 0.0112–0.1500 wt%). Remarkably, a uniform and ultra-thin polyamide layer with a thickness of 15 nm can be achieved at an exceptionally low PIP concentration of 0.0250 wt%, exhibits a rejection rate of over 98.8 % for Na2SO4 and a water permeance of 25.8 L·m−2·h−1·bar−1. The membranes with a diameter of 30 cm demonstrate reproducibility in nanofiltration performance and satisfactory long-term stability. This method offers a simple yet effective strategy for regulating the liquid distribution and optimizing interfacial polymerization in fabricating polyamide composite membranes.

Carbon nanotubes regulated polyamide membrane by intercalation to improve the organic solvent nanofiltration performance

Carbon nanotubes (CNT) are considered as promising materials for enhancing thin-film composite (TFC) membranes by introducing an intermediate layer. However, the specific function of the CNT intermediate layer in the formation of the selective polyamide (PA) layer using interfacial polymerization (IP) remains unclear. Consequently, in this study, a network of CNT was applied as a coating on a polyketone (PK) substrate to control its surface characteristics and act as an intermediate layer for PA formation. By adjusting the amount of CNT, the PK surface became less hydrophilic and had smaller surface pores. The CNT intermediate layer facilitated PA formation by expediting the release of IP monomers, reducing the interaction between PK and the monomers. Nevertheless, excessive CNT loading could lead to the retreat of large leaf-like structures, which are essential for achieving high performance in organic solvent nanofiltration (OSN). OSN tests revealed that the optimal TFC-0.5 membrane displayed a methanol permeance of 5.34 L m−2 h−1/bar with an extremely low molecular weight cut-off (MWCO) of 170–180 g/mol. This result was attributed to the reduced PA intrusion, enlarged PA filtration area, and the gutter layer effect brought about by the CNT intermediate layer.

Simultaneous Regulation of Surface Properties and Microstructure of Graphene Oxide Membranes for Enhanced Nanofiltration Performance.

The surface properties and microstructure of graphene oxide (GO)-based membranes are both crucial for enhanced nanofiltration performance. Herein, a GO nanofiltration membrane is fabricated with regulatable surface properties and microstructure via a facile two-step impregnation in KOH and following HCl aqueous solutions. The type and number of oxygen-containing groups in GO membranes change with fewer C-O-C/C-OH and C═O but more COOH groups, and they are readily regulated by alkaline treatment time, which enables enhanced surface hydrophilicity and larger surface ζ potentials. Meanwhile, a few tiny defects are present in the GO sheets, which could increase the number of pores and decrease the length of water nanochannels. Such surface properties and microstructure together determine the excellent nanofiltration performance of the GO membranes with fast and selective water permeation, e.g., ∼99.5% rejection toward CBB G250 and flux of 56.9 ± 1.0 L m-2 h-1. This work provides insights into the design of high-performance two-dimensional laminar membranes.

The metal organic framework of UiO-66-NH2 reinforced nanofiltration membrane for highly efficient ion sieving

Metal organic framework (MOF) with fine pore structures, ultra-high porosity and large specific surface area can provide more water transport channels while achieving precise sieving of different sizes of ions, which is a promising material for high efficiency desalination. However, particle agglomeration, interface incompatibilities and interface defects severely restrict the performance of MOF-based membranes. It is still a challenge to construct MOF-based desalination membranes with both high water permeability and high ion sieving. Herein, the UiO-66-NH2 based nanofiltration membrane was fabricated by in-situ growth of UiO-66-NH2 on Nylon membrane and composed with polyamide (PA) layer by interfacial polymerization (IP). With 12 h solvothermal reaction, the UiO-66-NH2 nanoparticles are found uniformly loaded on the Nylon substrate. Therefore, the water molecule transport channels provided by UiO-66-NH2 nanoparticles reduce the transport resistance, which can improve the water permeability. More importantly, UiO-66-NH2 nanoparticles are found to be involved in the IP process, which can reduce the interfacial defects and thus enhance the bonding force between the PA layer and base film. The synergistic effect of the UiO-66-NH2 and PA layer improves the nanofiltration performance of the membrane with rejection rate of 92.97% for Na2SO4 and the pure water permeance (PWP) of 11.55 L m−2 h−1 bar−1. The N-UN12 @PA membrane also has excellent antifouling performance (flux recovery ratio (FRR) of 95.86%, reversible fouling ratio (Rr) of 33.93%, irreversible fouling ratio (Rir) of 4.14%). Unlike the mixed-matrix membrane (MMM) and polycrystalline MOF membrane, this strategy provides a promising method to prepare high-performance nanofiltration membrane for desalination.

Robust KOH-thiourea-graphene oxide cross-linked membranes for desalination

Due to the well-defined two-dimensional nanochannel nanostructures, graphene oxide (GO) membranes hold huge possibilities for sustainable brackish water desalination and wastewater purification. However, achieving effective nanofiltration performance and sufficient structural stability of GO membranes in aqueous environments remains a major obstacle. Herein, the TU-GO-KOH membrane - the GO membrane cross-linked by thiourea (TU) after KOH treatment, was prepared for achieving relatively high water permeance (∼14.2 Lm−2 h−1) and high rejection (∼86.3 %) for NaCl rejection. These performances exceeded the nanofiltration performances of most GO–based membranes and commercial membranes reported in the literature. More importantly, the TU-GO-KOH membrane exhibited excellent separation stability over long-term (for 168 h) and under high pressures (up to 9 bar). Furthermore, even under ultra-sonication treatment and after long-term immersion in solutions with harsh pH values, the TU-GO-KOH membrane still maintained its own stability, which holds considerable promise for sustainable water treatment under harsh conditions. Additionally, the TU-GO-KOH membrane also showed enhanced mechanical properties. Overall, the superior desalination performance and notable stability of the TU-GO-KOH membrane make it a highly promising candidate for practical desalination and wastewater treatment.

Microfiltration, ultrafiltration and nanofiltration as a post-treatment of biological treatment process with references to oil field produced water of Moran oilfield of Assam

The selection of an apt technology for the treatment of Oilfield Produced Water (OFPW) depends mainly on the quality of OFPW and methods of pre-and post-treatment processes. The most challenging part of the OFPW treatment process is the removal of Suspended Solid (SS), Oil & Grease (O&G) and dissolved organics. SS and O&G pose an acute problem to the membrane filtration system by fouling the membrane surface which increases operation & maintenance costs and decreases the life of the membrane. Fouling of the membrane surface is mainly attributed to the presence of low molecular weight aromatic compounds and naphthenic acids in the suspended and dissolved organic compounds. Thus, the removal of these suspended and dissolved organic compounds before membrane filtration proffers a challenge to the researchers. In this research, bioremediation process has been applied to remove the organic compounds and the performance and fouling behaviour of hollow fibre Microfiltration (MF), Ultrafiltration (UF) and Nanofiltration (NF) membranes after the bioremediation process has been analyzed in detail. The level of toxicity was determined by comparing the pollutants with the safe discharge limit for disposal into the environment set by Central Pollution Control Board (CPCB), India. The research presents its novelty by using a hydrocarbon-degrading bacteria, Pseudomonas aeruginosa for the Reduction of Organic Loads (ROL) from OFPW of Moran oil field of Upper Assam as a pre-treatment to membrane filtration. The Total Sum Corrected Area (TSCA) method through chromatographic analyses was used for this. The organic loads removal from OFPW by the TSCA method was found to be 67–100%, 100% and 100% after 7, 14 and 21 days of bioremediation respectively. The major parameters in feed OFPW of Moran oil field were found to be pH (7.5–9.3), Total Dissolved Solid (TDS) (1.79–4.75) ppt, O&G (1.78–2.8) ppt, Salinity (2.94–6.98) ppt, Chloride (Cl−) (1.6–3.86) ppt, Bicarbonate (HCO3−) (2.89–4.03) ppt. It was observed that the ranges of pollutants removal by NF was highest such as TDS (26–86%), salinity (81–86%), turbidity (78–94%), hardness (67–75%), O&G (96–99%), Cl− (80–89%) and HCO3− (95–97%).

Deep learning models for assisted decision-making in performance optimization of thin film nanocomposite membranes

The performance of thin film nanocomposite nanofiltration membranes (TFNNMs) is frequently constrained by the trade-off between the permeability and rejection/selectivity of the membrane. In this study, to provide assisted decision-making in performance optimization of TFNNMs, we utilized a dataset comprising four categories of impact parameters, including membrane manufacturing conditions, membrane performance, nanoparticle material performance, and organic solvent nanofiltration conditions, and trained a dual output neural network (D-ANN) to simulate the relative permeability (RP) and relative rejection/selectivity (RR) of TFNNMs. The D-ANN model outperformed conventional machine learning models and single-output neural networks in predicting both RP and RR, indicating its potential in uncovering correlations between output variables. The Shapley additive explanation method was employed to elucidate the contribution and marginal effects of each influencing parameter on RP and RR, among them, NP size, NP loading, water contact angle, and chloride concentration were influential parameters that are important for both RP and RR. Based on the D-ANN model, we extrapolated two sets of unknown data and achieved good predictive performance (RP-error <15%, RS-error <7% for most sample points). Furthermore, we observed that the predicted performance of the data points rarely exceeded the actual performance, indicating a low probability of overestimation. Based on these premises, the influential parameters can be optimized using the D-ANN model, which ultimately led to exceptional performance for a total of 22 datasets in four pairs of organic solvent and solute purifications guided by the D-ANN model. This study demonstrates that the D-ANN model can provide decisions for the performance optimization of TFNNMs while highlighting the enhancement of nanofiltration performance by thin film nanocomposites, significantly facilitating the design of high-performance TFNNMs.

Theoretical rejection of fifty-four antineoplastic drugs by different nanofiltration membranes

The rise of nanofiltration technologies holds great promise for creating more effective and affordable techniques aiming to remove undesirable pollutants from wastewaters. Despite nanofiltration’s promising potential in removing antineoplastic drugs from liquid matrices, the limited information on this topic makes it important to estimate the rejection rates for a larger number of compounds, particularly the emerging ones, in order to preview the nanofiltration performance. Aiming to have preliminary estimations of the rejection rates of antineoplastic drugs by nanofiltration, 54 antineoplastic drugs were studied in 5 nanofiltration membranes (Desal 5DK, Desal HL, Trisep TS-80, NF270, and NF50), using a quantitative structure-activity relationship (QSAR) model. While this methodology provides useful and reliable predictions of the rejections of compounds by nanofiltration, particularly for hydrophilic and neutral compounds, it is important to note that QSAR results should always be corroborated by experimental assays, as predictions were confirmed to have their limitations (especially for hydrophobic and charged compounds). Out of the 54 studied antineoplastic drugs, 29 were predicted to have a rejection that could go up to 100%, independent of the membrane used. Nonetheless, there were 2 antineoplastic drugs, fluorouracil and thiotepa, for which negligible removals were obtained (<21%). This study’s findings may contribute (i) to the selection of the most appropriate nanofiltration membranes for removing antineoplastic drugs from wastewaters and (ii) to assist in the design of effective treatment approaches for their removal.

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.

Pyrrole/MXene membranes with simultaneously high structural stability and permeability for nanofiltration: Implication for water transport

Laminar MXene membranes hold great promise for aqueous separation applications. However, their susceptibility to oxidation in water cause chemical degradation and functional loss, impeding their separation efficiency and durability. In this study, an enhanced MXene nanofiltration membrane was fabricated by simply incorporating pyrrole with Ti3C2Tx, resulting in significantly improved oxidation resistance and permeability. Compared with pure MXene membrane, the pyrrole/MXene membrane exhibited a 3.52-fold increase in water permeance (465.9 L m−2 h−1 bar−1) and achieved excellent rejection performance for various dye molecules. The molecular dynamics simulations revealed that the pyrrole/MXene system presented a higher diffusion coefficient due to the weaker interaction energy at the interface between water molecule and pyrrole/MXene membrane. Normally, a larger transmembrane energy barrier meant a higher transport resistance that prevented the molecule from passing through the membrane. In this way, the determination of activation energy showed that the introduction of pyrrole facilitated a reduction in the requisite activation energy of water transfer from 9.37 to 4.86 kJ mol−1. More importantly, we explored the fact that the stabilization of MXene membranes had a significant impact on their separation performance during a long-term operation. Compared with pristine MXene membrane, the pyrrole/MXene membrane maintained initial two-dimensional structure and stable nanofiltration performance after prolonged operation. The radial distribution function calculations demonstrated that the chemical interactions between Ti3C2Tx and pyrrole were strong and involved the formation of Ti–C bonding and intermolecular interaction. This research provides a facile and effective method to prepare a high-performance and stable MXene nanofiltration membrane.

Fabrication of antifouling UiO-66 nanofiltration membranes via surface fluorination engineering

Membrane fouling is a primary hindrance in the efficient utilization of nanofiltration technology in wastewater treatment, which increases energy requirements and reduces membrane life. In this work, a highly antifouling UiO-66 nanofiltration (NF) membrane was fabricated via a facile surface engineering for dye rejection, where fluoromonomer with a long fluoroalkyl chain was fast UV-polymerized on the surface of UiO-66. Fluoroalkyl chains have low surface energy and provide the surface with non-stick and fouling-release properties, and fluoroalkyl is highly incompatible with dyes. Meanwhile, the bridged rigid fluoroalkyl produces an effective barrier to repel the foulants because of the narrowed pore structure and smooth surface. Results showed that the resulting membrane shows an excellent NF performance including high rejection of Methyl Blue, Cango Red and Chrome Black T (all over 99.7 %) with a high water permeance of 249.6 L m2 h−1 bar−1, and salt permeation of MgSO4 (89.26 %) and NaCl (99.02 %). The long-term stability testing exhibits basically stable performance for separating the CT/NaCl mixture. The outcome of the work offers an effective strategy to solve the membrane fouling and maintain the outstanding separation performance by fluorination modification. This newly UiO-66-based NF membrane showed excellent application potential in the dye wastewater treatment.

PH-responsive BNNS/PAA nanofiltration membrane for tunable water permeance and efficient dye separation

Two-dimensional lamellar nanofiltration membranes have great application potential for water purification. Here, in order to achieve tunable water permeance and efficient dye separation, we reported a pH-responsive boron nitride nanosheets (BNNS)-based nanofiltration membrane by introducing polyacrylic acid (PAA). The strong hydrophilicity and electronegativity of PAA endow BNNS/PAA membrane with a fast water flux of 228 L·m−2·h−1 and a high methylene blue (MLB) rejection of 98%, increased by 235% and 4% compared to the neat BNNS membrane, respectively. Owing to the size sieving effect, the BNNS/PAA membrane possesses the better selectivity for the different types of dyes and dye/salt mixture from the potential pollutants in the water. Meanwhile, it exhibits diverse and tunable nanofiltration performances at different pH, implying excellent pH-responsive ability of BNNS/PAA membrane. In addition, the BNNS/PAA membranes also display the exceptional separation and long-term stability at different environments. This work provides a novel and simple strategy for designing the BNNS-based nanofiltration membrane with the pH-responsive ability, the tunable water permeance and selectively.

Nitrate rejection of sulfonic acid group incorporated polyethersulfone‐type nanofiltration membrane and reutilization of the concentrated solution

AbstractThe nanofiltration (NF) membrane technology has attracted considerable attention for the rejection removal of various salts. However, the practical application of this membrane separation process has been severely retarded due to the ineffective rejection of monovalent ions (such as nitrate and chloride), undesirable filtration flux, and insufficient disposal of the concentrated solution. In this work, three polyethersulfone‐type NF membranes were fabricated and their morphologies, functional groups, chemical components, wettabilities, chargeabilities, and rejection molecular weights were characterized. Among them, the membrane of NF_M3 bearing sulfonic acid group (SO3H) shows the desirable rejection efficiency of nitrate (90.32%), acceptable solution filtration flux (10.15 L m−2 h−1 at 0.6 MPa), and the decent pure water permeation flux (50.8 L m−2 h−1 at 0.6 MPa). The introduction of SO3H can significantly enhance the performances of NF_M3 membrane in hydrophilicity, chargeability, anti‐fouling, and the oxidation resistance. Promisingly, the concentrated nitrate was ingeniously recycled for the electrochemical intercalation of flake graphite to prepare expandable graphite, and the obtained expanded graphite has an acceptable expanded volume (243 mL g−1 via the microwave expansion process), thereby achieving the resource utilization of NF concentrated solution.