Performance Of Nanofiltration Membranes Research Articles

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.

Hydrophobic poly(vinylidene fluoride) / siloxene nanofiltration membranes

Hydrophobic, chemically resistant nanofiltration (NF) polymeric membranes could provide major improvements to a wide range of processes, from pharmaceutical manufacturing to hazardous waste treatment. Here, we report the fabrication of the first poly (vinylidene fluoride) (PVDF) NF membranes retaining their hydrophobicity and surface chemistry. This was achieved by incorporating in the polymer 2D siloxene, which induce a compaction of the PVDF chains, resulting in low free volume and a highly ordered microstructure. Siloxene nanosheets were obtained from deintercalation of Ca from CaSi2 using HCl, followed by exfoliation and size fractionation, with average lateral dimension of 1–2 μm and thickness of 3–4 nm. The resulting membranes, containing 0.075 wt% of siloxene, have a pure water permeance of 22 ± 2 L m-2 h-1 bar-1 and molecular weight cut-off (MWCO) of 530 Da. The same membrane also showed stable hexane permeance of 11 L m-2 h-1 bar-1 for 24 h with MWCO of around 535 Da. These results supersede the performance of commercial NF membranes, expanding the potential application of nanofiltration to processes requiring stable, chemically resistant and hydrophobic nanofiltration membranes.

Effect and regulation mechanism of oxidation degrees on the O–MoS2 structure and separation performance of nanofiltration membrane

Oxidized molybdenum disulfide (O–MoS2) as a two-dimensional (2D) functional nanosheets material, has been used to fabricate high separation performance nanofiltration (NF) membranes for water treatment. However, the effect and regulation mechanism of the degree of oxidation on structure and separation performance of O–MoS2 modified NF membrane has not yet been fully understood. In this work, O–MoS2 with different oxidation degrees was synthesized by adjusting the oxidation time and KMnO4 oxidant content via Hummers’ method. The results demonstrated that the O–MoS2 synthesized under with an oxidation time of 3 h and MoS2:KMnO4 ratio of 1:2 had excellent stability under acidic, neutral and alkaline conditions. The pure water flux increased 2.5 times and the Na2SO4 salt rejection increased to 97.6% with this O–MoS2 incorporation compared to the control membrane. The influence of different oxidation degrees on the performance of O–MoS2 is a breakthrough finding of this work to provide a theoretical basis for the application of O–MoS2 in the field of membrane separations.

Surface functionalization of nanofiltration membrane by catechol-amine codeposition for enhancing antifouling performance

Nanofiltration (NF) technology is promising for treatment of wastewater containing micropollutants (MPs) because it can retain both MPs and small organics while permeate inorganic salts. However, both MPs adsorption and organic fouling formation deteriorate NF membrane performance. In this work, a novel surface functionalization strategy is proposed to tackle both two issues. Based on catechol-amine chemistry, a commercially available NF membrane is modified by tannic acid-3-aminopropyltriethoxysilane (TA–APTES) coating and subsequent horseradish peroxidase (HRP) immobilization. Taking aflatoxin B1 (AFB1) as an example of MPs, its adsorption on the modified NF membrane is greatly inhibited by coating induced pore narrowing (enhancing size exclusion to MPs), surface barrier effect (alleviating the interaction between MPs and membrane) and enzymatic self-cleaning ability (degrading MPs adsorbed on the membrane), resulting in higher and more stable AFB1 rejection (~90%). The flux decline and irreversible fouling are also reduced by the amphiphilic property of the immobilized HRP on the membrane surface when treating corn soaking solution. Although the on-line self-cleaning operation in the presence of hydrogen peroxide can alleviate concentration polarization by interfacial catalytic reaction, the flux decline and irreversible fouling become severer possibly due to the pore blocking by the degraded products. The off-line self-cleaning after the filtration enables to remove loose fouling layer, but the dense fouling layer impedes the accessibility of hydrogen peroxide to the immobilized HRP, limiting its self-cleaning ability. Therefore, catalytic intensity, enzymatic products and substrate accessibility to enzyme should be considered when constructing a self-cleaning NF membrane to deal with combined fouling.

Membrane filtration, activated sludge and solar photocatalytic technologies for the effective treatment of table olive processing wastewater

The table olive industry produces a high quantity of wastewater (TOPW) whose management represents a challenge due to its environmental risk. TOPW samples from an industrial site were characterized and different individual and integrated treatment methods were applied and their efficiency compared. Aerobic biodegradation (i.e., activated sludge) and TiO2 solar photocatalysis were not able to effectively treat raw TOPW mainly due to slow organic matter removal and excessive electrical conductivity (EC) of the resulting effluents (c.a. 10 mS·cm−1). Reverse osmosis (RO) and nanofiltration (NF) treatments of TOPW, however, showed good results in terms of removals of chemical oxygen demand (COD, 82–93%), total phenols (TP, 81–100%) and EC (60–98%). The effects of several pre-treatments of TOPW (i.e., microfiltration, coagulation-flocculation, biodegradation and solar photocatalysis) on the performance of NF and RO membranes were studied. MF pre-treatment increased the permeate flux recovery in NF and allowed the membrane to be satisfactorily reused. The NF effluent could be successfully subjected to either aerobic biodegradation or solar TiO2 photocatalytic post-treatment in order to fulfill requirements for discharge into the municipal sewage system.

Influence of compatibility between sol and intermediate layer on the performance of yttria-stabilized zirconia nanofiltration membrane

This paper reports the synergistic effect of the sol and intermediate layer on the performance of yttria-stabilized zirconia (YSZ) nanofiltration (NF) membranes. We have focused on the characterization of the microstructure, pure water permeance, and molecular weight cut-off (MWCO) of the NF membranes derived from zirconia sols of different precursor concentrations on two types of supported ZrO2 ultrafiltration (UF) membranes. We found that the performance of YSZ membranes strongly depends on the sol concentration and the pore size of the intermediate layer. In addition, YSZ gel membrane formation was found to follow the filtration process. Therefore, it is essential to maintain the compatibility between the sol and intermediate layer to fabricate high-performance NF membranes. A crack-free thin YSZ layer with an MWCO of 816 Da (pore size: 1.4 nm) and a water permeance of 25 L m-2 h-1 bar-1 was fabricated using a precursor concentration of 0.03 mol/L, on ZrO2 UF membrane with a pore size of 5.5 nm. The YSZ NF membrane exhibited a relatively high retention rate towards MgCl2 (71%), whereas a lower retention rate was observed for NaCl (35%).

Fabrication of halloysite nanotubes embedded thin film nanocomposite membranes for dye removal

AbstractEnvironmental friendly Halloysite nanotubes (HNTs) are used to fabricate novel nanofiltration membranes by in situ interfacial polymerization of piperazine and trimesoyl chloride. The removal of excess amine solution from the porous support membrane surface is a critical step to obtain defect free active layer. Hereby, two main removal tools for the excess aqueous amine solution; a rubber roll or air knife are compared to fabricate a defect free thin film nanocomposite (TFN) nanofiltration (NF) membrane. Removal by the rubber roll is eventuated more favorable than air knife in terms of the reproducibility of NF membranes by comparing salt rejections. By determining the removal step of excess amines, various HNTs concentrations are used to fabricate NF membranes and, these membranes are tested with salt and dye solutions at various pH and temperature ranges. R2 membrane (containing 0.02% [w/v] HNTs) performs the best flux results beside higher rejections of MgSO4 (93.0%) and dye (99.5%). To evaluate the extreme conditionals, further performance tests such as pH and temperature resistance are also performed for R2 membrane. Considering the performances of R2 membrane, HNTs can be demonstrated for tailoring the balance between flux and separation performance of NF membranes.

Bio-inspired construction of ion conductive pathway in covalent organic framework membranes for efficient lithium extraction

Summary As the most sophisticated separation system, biological membranes have served as natural prototypes for the design of artificial membranes because they provide high permeability and solute selectivity, owing to the presence of specialized ion channels. However, developing stable and selective artificial ion channels remains a formidable challenge. Herein, we demonstrate the construction of lithium nanochannels in two-dimensional covalent organic frameworks (COFs) to create biomimetic membranes. Implanted lithiophilic oligoethers conferred specificity and facilitated Li+ diffusion along the pore pathway of the COF. The ion channel characteristics were indicated by reversal potential measurements, showing that the relative permeability decreased in the order Li+ > K+ > Na+ > Ca2+ > Mg2+. The Li+ transfer was enhanced, while other ions were obstructed, allowing for high selectivity and permeability. A Li+/Mg2+ separation factor of 64 was achieved, confirming high lithium affinity. This study may serve as a design principle to develop selective artificial membranes for effective ion separation.

Performance of mixed matrix nanofiltration membranes in wastewater treatment: A review

Water covered close to 70% of the Earth’s surface; however, it is a struggle to access 3% of it as freshwater, suitable for human intake. The shortage of water has become a global issue due to climate change, pollution and the demand of growing freshwater. The fabrication of high performance and antifouling nanofiltration membranes are of utmost importance as a result of their capability of treating contaminated water and to also regulate the quality of freshwater. However, there is need for improvement in the fabrication of membrane using different nanofillers to produce mixed matrix membranes (MMMs). Mixed matrix nanofiltration membranes with nanofillers were reviewed for different applications.

Enhancing nanofiltration performance for antibiotics/NaCl separation via water activation before microwave heating

Separation performance of nanofiltration (NF) membranes is constrained by the trade-off between permeability and selectivity. Herein, a facile and environmental friendly water activation before microwave heating was performed to improve the performance of NF membranes and overcome this trade-off. The water activation before microwave heating facilitated the hydrolysis of acyl chloride, resulting in a loose polyamide layer with enhanced hydrophilicity and surface charge. The activated NF membrane showed a permeance of 29.9 L m-2 h-1 bar-1, which is almost 2 times higher than the control. The membrane possesses a Na2SO4 rejection of 96.8% and high selectivity to antibiotics and NaCl. At the meantime, the fouling resistance to model foulants including bovine serum albumin and sodium alginate was significantly enhanced. The water activation before microwave heating is proved to be an adequate strategy for fabricating NF membranes.

Synthesis of Novel Hybrid NF/FO Nanocomposite Membrane by Incorporating Black TiO2 Nanoparticles for Highly Efficient Heavy Metals Removal

In this study, a hybrid of nanofiltration (NF) and forward osmosis (FO) has been used with the aim of improving the efficiency of heavy metal removal. Here, black TiO2 nanoparticles (BNPs) were synthesized first and embedded in the polyamide (PA) active layer of TFC NF membrane to rectify the performance of membranes. The resulting TFN NF membranes were then tested in hybrid NF/FO system properly. The presence of BNPs was confirmed with XPS and FTIR, while the morphological alterations in the synthetized membranes were characterized using FESEM and AFM. Nanofiltration membrane performance was examined using multivalent ions such as of MgSO4, Na2SO4, CaCl2, and NaCl monovalent ion. We demonstrated that the addition of BNPs led to a significant decrease in surface roughness and hydrophilicity, showing a further reduction with increased concentrations of BNPs. In addition, TFC membrane showed a water flux of 25 L/m2h compared to 39, 41, and 66 L/m2h for TFN0.01, TFN0.05, and TFN0.1 membranes, respectively. We also showed that under the FO process, TFN membrane demonstrated the best performance with regards to heavy metal rejection and the highest Cr (III) and Pb (II) rejection was shown in TFN0.05 under the FO process. The ideal heavy metal rejections and acceptable water flux indicate the potential of these developed membranes under FO process for the removal of heavy metals from wastewater.

Influence of monomers involved in the fabrication of a novel PES based nanofiltration thin-film composite membrane and its performance in the treatment of common effluent (CETP) textile industrial wastewater

In this article, monomers (tannic acid (TA) and m- phenylenediamine (MPD)) were used in the fabrication of a novel PES based thin-film composite nanofiltration (TFC-NF) membrane for the treatment of a common effluent treatment plant (CETP) of textile industrial wastewater. PES support sheets and TFC layers were fabricated via non-solvent induced phase inversion and in-situ interfacial polymerization (IP) process. The ultra-thin active layer was synthesized via the IP process with monomers such as tannic acid (TA) and m- phenylenediamine (MPD). T and M series membranes correspond to (PES/x wt% TA, x = 2, 4, 6) as T1, T2, T3 -TA and (PES/x wt% MPD, x = 2, 4, 6) as M1, M2, M3-MPD respectively. M0 corresponds to PES which is the virgin membrane. The chemical structure, surface morphology, surface roughness and surface properties were explored using fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and contact angle, respectively. The filtration performance of the thin-film composite nanofiltration (TFC-NF) membranes was investigated by various properties like pure water flux, salt rejection, porosity, mean pore radius and antifouling analysis. T1-TA membrane showed better water permeability, high salt rejection and better industrial effluent rejection with 94.4% of TDS that are suitable for industrial reuse and agricultural irrigation. Moreover, for T1-TA membrane, the water flux, porosity, mean pore radius, salt rejection, surface roughness and contact angle of 43.5lm- 2 h - 1, 47.1%, 16.7nm, 72.7%, 11.7nm and 41.48°was achieved respectively that was found to be higher than that of all the other fabricated membranes. Further, the rejection efficiency rate of textile effluent characteristics such as pH, turbidity, TDS, alkalinity, total hardness, BOD and COD were also achieved with maximum deduction in the T1-TA TFC-NF membrane compared to the M0-Virgin PES membrane. From the results, it can be confirmed that the T1-TA membrane significantly reduced the alkalinity, total hardness, BOD and COD rejections of 78%, 77.3%, 58.5% and 67.5% respectively, present in the effluent. Water flux recovery ratio (FRR) was improved from 74.6% for M0-Virgin PES membrane to 94.8% for T1-TA membrane. The modified TFC-NF membranes especially T1-TA, had better anti-fouling property and excellent hydrophilicity than the unmodified M0-Virgin PES membrane. The online version contains supplementary material available at 10.1007/s40201-021-00624-x.

Comparative analysis of salt cleaning and osmotic backwash on calcium-bridged organic fouling in nanofiltration process

The cleaning efficiency of salt cleaning and osmotic backwash in a nanofiltration (NF) process is evaluated using model organic foulants in the presence of calcium ions (Ca2+). In particular, the organic fouling behavior—which depends on Ca2+ concentration—and cleaning mechanism in both salt cleaning and osmotic backwash are studied. The results show that Ca2+ aggravates organic fouling, and the fouling formation rate is affected by the Ca2+/foulant ratio. Salt cleaning and osmotic backwash effectively clean Ca2+-bridging fouling, and the important cleaning mechanism in both methods is ion-exchange between the monovalent and divalent cations, resulting in the breakup of Ca2+–foulant binding and Ca2+-induced intermolecular bridging. The cleaning efficiency of osmotic backwash is 26% higher than that of salt cleaning, primarily owing to that the backwash flux creates synergy effect with ion-exchange to removes the weakened fouling structure on the membrane surface. In addition, the cleaning efficiency for irreversible fouling is of the order of osmotic backwash > chemical cleaning > salt cleaning, and osmotic backwash exhibited a 7.3% and 20.8% higher cleaning efficiency than chemical cleaning and salt cleaning, respectively. Therefore, osmotic backwash can stably maintain NF membrane performance for organic fouling and potentially replace the traditional chemical cleaning.

An engineering model for solute transport in semi-aromatic polymeric nanofiltration membranes: Extension of Solution-Electro-Diffusion model to complex mixtures

Pressure-driven membrane processes, such as reverse osmosis (RO) and nanofiltration (NF), are preferred solutions for salinity reduction in ground, surface and sea waters as well as in mining and urban wastewaters. Interest in NF is increasing because it enables a more cost-efficient operation than RO. However, predictive projection tools for NF applications are still lacking. Whereas in RO the solute rejections are usually above 95% and approximately independent of feed composition, the performance of NF membranes is highly influenced by the feed-solution composition. Moreover, in both processes, concentration polarisation (CP) affects the transport of species and membrane scaling. This study presents an extended Solution-Electro-Diffusion model for the description of the transport of solutes through NF membranes in complex multi electrolytes (strong and weak) taking into account CP, namely “Solution-Electro-Diffusion-Film coupled with Reactive Transport” (SEDFRT) model. The model is first validated by using a semi-aromatic polymeric membrane (NF270) and electrolyte mixtures containing two dominant (MgSO4 and MgCl2) and two minor salts (NH4Cl and NaBr). The membrane permeances to all the species are determined as key parameters to be used in design projections. Finally, the model is applied for the description of the performance of NF270 membrane with model brackish surface water, influenced by urban, industrial and agriculture discharges.

Performance of NF90 and NF270 commercial nanofiltration membranes in the defluoridation of Algerian brackish water

Performance of NF90 and NF270 commercial nanofiltration membranes in the defluoridation of Algerian brackish water

Mechanism of Permselectivity Enhancement in Polyelectrolyte-Dense Nanofiltration Membranes via Surfactant-Assembly Intercalation.

Enhancing the water permeance while maintaining the solute rejection of a nanofiltration (NF) membrane can potentially result in significant cost-reduction for NF-a membrane process that excels in several unique environmental applications of growing interests. In this work, we demonstrate for the first time that intercalation of surfactant self-assemblies in the polyelectrolyte multilayer (PEM) can lead to significant performance enhancement of salt-rejecting dense NF membranes fabricated using layer-by-layer assembly of polyelectrolytes. Specifically, the intercalation of sodium dodecyl sulfate (SDS) bilayers in a PEM comprising poly(diallyldimethylammonium chloride) (PDADMAC) and poly (sodium 4-styrenesulfonate) (PSS) resulted in a decrease in PEM thickness, increase in pore size, and a smoother and more hydrophilic surface. The water permeance of the resulting PEM NF membrane increased by 100% without compromising the rejection of Na2SO4. Experiments with a quartz crystal microbalance also provide direct evidence that the intercalation of the surfactants substantially reduces the subsequent adsorption of the polyelectrolytes of a similar charge. Based on its mechanism of performance enhancement, surfactant intercalation may become a universally applicable and highly cost-effective approach for dramatically enhancing the performance of PEM NF membranes.

High-flux robust PSf-b-PEG nanofiltration membrane for the precise separation of dyes and salts

We report a novel high-flux nanofiltration (NF) membrane for the precise separation of dyes and salts, which was fabricated using polysulfone-block-polyethylene glycol (PSf-b-PEG) block copolymer through the non-solvent induced phase separation (NIPS) method. The PSf-b-PEG membrane exhibited a very dense sponge-like porous structure with rich interconnected pores, contributing to its superior mechanical strength of 22.4 ± 0.9 MPa. The pore size of PSf-b-PEG membrane was mostly distributed around 1.3 nm in diameter with the mean effective pore size of 3.8 nm in diameter, while the membrane molecular weight cut off (MWCO) towards dyes was about 655 Da. The PSf-b-PEG membrane exhibited a very high water permeance of 49.3 ± 0.9 L m−2 h−1 bar−1 and a precise separation of salts and dyes with high above 98% Congo Red dye rejection and nearly 100% Na2SO4 passage, succeeding the separation performances of current NF membranes used for the separation of dyes and salts. Long-term NF tests prove the highly stable and outstanding separation performances of PSf-b-PEG membrane with the top dense skin layer as the effective selective layer. Our work suggests that the PSf-b-PEG membrane has a great potential to be further optimized and used for practical applications.

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.

Development of polyethersulfone (PES)/reduced graphene oxide nanocomposite nanofiltration membrane

Polyethersulfone (PES) is a polymeric material that is commonly used due to its chemical resistance, high mechanical strength, and thermal stability. The improvement of PES hydrophilicity and anti-fouling properties can be facilitated by mixing additives into the polymer casting solution. This study involved the preparation and characterization of PES/pluronic F108/chitosan/reduced graphene oxide (rGO) nanocomposite nanofiltration membrane. The modified PES membrane was developed by employing the phase inversion method via immersion precipitation. The effect of varying concentration of rGO nanocomposite ranging from 0.05 to 0.20 wt% in the fabricated membrane was evaluated in terms of membrane pure water permeation (PWP), salt rejection, morphology, and hydrophilicity. Images obtained from scanning electron microscopy (SEM) showed increasing rGO nanocomposite concentration in the casting solution, resulted in the increase in membrane sub layer thickness, hydrophilicity, salt rejection, and improvement in the membrane pore structure. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of the hydrophilic functional group and chemical compound in the prepared membrane. PES with 0.20 wt% of rGO nanocomposite obtained the highest PWP at 28.64 (L/m2h) at 5 bar pressure, whereas the highest rejections of monovalent and multivalent salt were obtained by PES with 0.15 wt% rGO nanocomposite with 75% and 89% rejections, respectively at 5 bar pressure. This study shows that the utilization of rGO nanocomposite as an additive in the PES casting solution can enhance nanofiltration membrane performance and morphological structure.

Sharpening Nanofiltration: Strategies for Enhanced Membrane Selectivity.

Nanofiltration plays an increasingly large role in many industrial applications, such as water treatment (e.g., desalination, water softening, and fluoride removal) and resource recovery (e.g., alkaline earth metals). Energy consumption and benefits of nanofiltration processes are directly determined by the selectivity of the nanofiltration membranes, which is largely governed by pore-size distribution and Donnan effects. During operation, the separation performance of unmodified nanofiltration membranes will also be impacted (deleteriously) upon unavoidable membrane fouling. Many efforts, therefore, have been directed toward enhancing the selectivity of nanofiltration membranes, which can be classified into membrane fabrication method improvement and process intensification. This review summarizes recent developments in the field and provides guidance for potential future approaches to improve the selectivity of nanofiltration membranes.