Loose Nanofiltration Membrane Research Articles

Fabrication of Loose Nanofiltration Membrane by Crosslinking TEMPO-Oxidized Cellulose Nanofibers for Effective Dye/Salt Separation

Dye/salt separation has gained increasing attention in recent years, prompting the quest to find cost-effective and environmentally friendly raw materials for synthesizing high performance nanofiltration (NF) membrane for effective dye/salt separation. Herein, a high-performance loose-structured NF membrane was fabricated via a simple vacuum filtration method using a green nanomaterial, 2,2,6,6-tetramethylpiperidine-1-oxide radical (TEMPO)-oxidized cellulose nanofiber (TOCNF), by sequentially filtrating larger-sized and finer-sized TOCNFs on a microporous substrate, followed by crosslinking with trimesoyl chloride. The resulting TCM membrane possessed a separating layer composed entirely of pure TOCNF, eliminating the need for other polymer or nanomaterial additives. TCM membranes exhibit high performance and effective dye/salt selectivity. Scanning Electron Microscope (SEM) analysis shows that the TCM membrane with the Fine-TOCNF layer has a tight layered structure. Further characterizations via Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed the presence of functional groups and chemical bonds of the crosslinked membrane. Notably, the optimized TCM-5 membrane exhibits a rejection rate of over 99% for various dyes (Congo red and orange yellow) and 14.2% for NaCl, showcasing a potential candidate for efficient dye wastewater treatment.

Bio-inspired co-deposition of dopamine and N-oxide zwitterionic polyethyleneimine to fabricate anti-fouling loose nanofiltration membranes for dye desalination

Developing anti-fouling loose nanofiltration membranes (LNMs) that can achieve dye desalination of saline textile wastewater through dye retention and salt permeation for resource utilization remains an urgent challenge that needs to be addressed. Inspired by the biomimetic adhesion of mussels and the excellent fouling resistance of saltwater fish surfaces, novel LNMs were prepared through co-deposition strategy using dopamine (DA) and N-oxide zwitterionic polyethyleneimine (ZPEI) as biomimetic functional materials. There are multiple interactions between them, including Schiff base reaction, Michael addition reaction, cation-π interaction and covalent polymerization. Compared with PEI-LNM prepared under the similar method, the optimized ZPEI-LNM displays more uniform surface, smaller average roughness (6 nm vs 22 nm), and denser pore size (0.69 nm vs 0.79 nm), indicating the zwitterionic N-oxide moieties in ZPEI regulate the deposition process and the cross-linking structure of the selective layer. ZPEI-LNM exhibits a high pure water flux of 203.0 L m−2h−1 under 0.6 MPa. Importantly, ZPEI-LNM shows high retention towards different dyes, including Congo red (CR, negative, 696.8 g/mol) of 100.0 %, Acid fuchsin (AF, negative, 585.5 g/mol) of 99.5 %, Crystalline violet (CV, positive, 408.0 g/mol) of 98.2 %, and Indigo carmine (negative, 466.4 g/mol) of 96.0 %, while the rejection of NaCl (8.7 %) and Na2SO4 (12.7 %) are both lower. As expected, for the mixture solution of AF/NaCl, the dyes are efficiently rejected, while salts can pass through, indicating that ZPEI-LNM displays an excellent dye desalination capability. Furthermore, multiple-cycle antifouling tests for bovine serum albumin (BSA) and sodium alginate (SA) reveal that the flux recovery ratios are higher than those of PEI-LNM (BSA: 90.4 % vs 81.9 %; SA: 86.6 % vs 80.5 %), indicating ZPEI-LNM exhibits better anti-fouling performance towards different model foulants owing to the outstanding hydration layer caused by zwitterionic N-oxide moieties and lower surface roughness. Consequently, the work offers a new viewpoint for the fabrication of anti-fouling LNMs via biomimetic strategy for dye desalination.

Preparation of polyaniline conductive membranes through immersion of dopant solution for dye/salt separation

The preparation of conductive loose nanofiltration (NF) membranes for effective separation of dye/salt wastewater mixtures remains a great challenge. In the current study, a novel method of immersing the polyaniline (PANI) membrane in some organic salt solutions to dope PANI membrane was employed to prepare conductive PANI loose NF membranes. Three dopants with different molecular weight, poly (sodium 4-styrene sulfonate) (PSS), sodium dodecyl sulfate (SDS), and sodium dodecylbenzene sulfonate (SDBS), were chosen to prepare the doping solutions under neutral and acidic (pH = 0.5 in HCl) conditions. The neutrally doped PANI membranes all had lower pore size distribution, lower Zeta potential, and higher conductivity compared with the undoped PANI membrane; and these properties were further enhanced for the membranes doped under acidic condition. The PANI membrane doped by acidic PSS solution (PANI-PSS-HCl membrane) had a pore size of 1.7 nm and a pure water flux of 44.7 L·m−2·h−1, and exhibited a rejection of over 99.9 % for eriochrome black T, acid fuchsin, congo red, and sunset yellow in the dye solutions, whereas less than 5 % for NaCl solution, which was suitable for dye/salt separation due to the large molecular size of PSS. When PANI-PSS-HCl membrane was used as the cathode, the membrane exhibited excellent anti-fouling performance with increased external voltage due to enhancement of electrostatic repulsion force between the anionic dyes and the surface of the conductive membrane. This work provides a simple and reliable method to prepare conductive loose NF membranes for effective separation of dye/salt wastewater with excellent anti-fouling performance under external voltage.

Pressure-driven membranes for advanced treatment of textile wastewater: Dye/salt fractionation, concentration, and cleaning strategies

Textile wastewater commonly contains various organic compounds and salt mixtures, potentially raising serious environmental and health concerns. Traditional treatment approaches are hindered by high salinity; consequently, membrane separation technologies have attracted increasing attention over the past few decades. Herein, four commercial pressure-driven membranes with molecular weight cut-off (MWCO) gradients were employed for the advanced treatment of different types of textile wastewater. Specifically, these membranes were initially subjected to a fractionation test toward the dye/salt mixtures, followed by deep concentration of the dye molecules. Using Congo red (CR), methyl blue (MB), NaCl, and Na2SO4 as representative dyes and salts, the results indicated that all membranes could effectively separate dye/salt mixtures and further conduct a deep concentration process toward the separated dye solutions. However, their efficiency and effectiveness largely depend on the membrane pore size and solution characteristics. For instance, membranes with lower MWCOs experience less fouling and shorter operation durations when treating CR-related solutions. All membranes showed improved fractionation efficiency toward MB/salt mixtures, requiring only approximately 10.2–42.9 % of the operation duration compared to CR-related solutions. The loose nanofiltration membrane proved superior to tight ultrafiltration membranes in both fractionation and concentration processes. Further research on cleaning methodologies demonstrated that both alkali and ethanol cleaning were influential in restoring the membrane performance. An appropriate ethanol/water concentration can effectively regenerate severely fouled membranes, achieving a high flux recovery ratio of ∼95 %. This study evaluated state-of-the-art pressure-driven membranes for textile wastewater treatment and guided cleaning strategies for optimal performance recovery.

Effects of mixed amines on the microstructure and performance of PVDF LNF membranes by Co-deposition via IP

Selective recovery of recyclables is a major challenge when treating textile wastewater. For this reason, there is an urgent need to develop nanofiltration membranes with high permeability and selective filtration. In response, a novel composite PVDF loose nanofiltration membrane was developed by combining two different mixed amines system/dopamine (DA) followed by interfacial polymerization with benzoyl chloride (TMC). The two different amines systems were a mixture of GAZ and PEI and a mixture of PIP and PEI, respectively. The effects of GAZ/PEI and PIP/PEI on the microstructure was characterized by SEM, AFM, FTIR and XPS and performance of the membrane was also investigated. The effects of GAZ/PEI and PIP/PEI on the microstructure and the selective layer of membranes were different. The results stated that with the increase of GAZ/PEI the thickness of the selective layer, surface roughness decreased, while the fluxes of pure water and dye wastewater increased. However, with increasing PIP/PEI, surface nodules and roughness both increased. Contrarily, the thickness of the selective layer and PEG800 rejection first decreased and then increased, while the flux of pure water and the dye wastewater first increased and then decreased. The optimal GAZ/PEI and PIP/PEI were 9/91 and 50/50, respectively. When the GAZ/PEI was 9/91, the pure water flux and the RB5 wastewater flux were 20.7 L∙(m2∙h)−1 and 11.5 L∙(m2∙h)−1. The dye (RB5) retention rate was 94.3% and salt retention rate was 2.1%. However, when the PIP/PEI was 50/50, the pure water flux and RB5 wastewater flux were 26.6 L∙(m2∙h)−1 and 17.1 L∙(m2∙h)−1 increased by 87.3% and 134.2% respectively. The retention rates of RB5 and NaCl were 96.3% and 1.7%. The above results indicate that the composite PVDF LNF membranes prepared with mixed amine monomers instead of single amine monomers have good selective filtration performance.

Effect of solution ions on the charge and performance of nanofiltration membranes

Considering growing efforts to understand and improve the solute-specific selectivity of nanofiltration (NF) membranes, we explored the ion-specific effects that govern the charge and performance of a loose polyamide NF membrane that is commonly used for solute-solute separations. Specifically, we systematically evaluated the zeta potential of the membrane under different conditions of pH, salinity, and ionic composition, and correlated the obtained data with membrane performance tested under similar conditions. Our results identify the pKa of both carboxylic and amine groups bonded to the membrane surface and suggest that the highly polarizable chloride anions in the solution adsorb to the polyamide, increasing its negative charge. We also show that monovalent cations of different “stickiness” can neutralize the negative membrane charge to different extents due to their varying tendency to sorb to the polymer matrix or screen the fixed carboxyl groups on the membrane surface. Notably, our correlation between zeta potential measurements and permeability experiments indicates the substantial contribution of solution ions to Donnan exclusion in NF membranes.

Manufacturing supported loose-nanofiltration polymeric membranes with eco-friendly solvents on an R2R System

In this study, loose nanofiltration membranes made of polysulfone dissolved in co-solvents PolarClean and gamma-Valerolactone were prepared via slot die coating (SDC) on a roll-to-roll (R2R) system by directly coating them onto a support layer or free standing. A solution flow rate of 20 mL/min, substrate speed of 17.1 mm/s, and coating gap of 0.1 mm resulted in the formation of membranes without structural defects. Pre-wetting the support layer with dope solution minimized shrinkage of membrane layer thickness and improved interfacial adhesion. Membrane samples produced using SDC exhibited properties and performance consistent with bench-scale doctor blade extruded samples; pre-wetted and uncompressed samples (SDC-3) exhibited the highest rejection of bovine serum albumin (99.20% ± 1.31%) and along with adequate mean permeability during filtration (70.5 ± 8.33 LMH/bar). This study shows that combining sustainable materials development with SDC provides a holistic approach to membrane separations to bridge materials discovery and membrane formation.

A novel salt-swelling nanofiltration membranes for drinking water purification: High mineral ions passage and efficient organic removal

BackgroundMunicipal drinking water treatment demands nanofiltration (NF) membranes with high removal efficiency for organics, high passage for mineral ions, and low operating pressure. The development of innovative and loose NF membranes is imperative. MethodsA loose-network-structured NF membrane (L-NF) was synthesized through interfacial polymerization (IP) on a PES substrate by utilizing lysine (with a flexible aliphatic chain) as standalone aqueous phase monomers. The separation performance for typical organics and mineral ions in water, as well as the permeability of the membrane were investigated. Significant findingsThe lysine-based NF membranes exhibit a reversible and appropriate salt-induced swelling effect. The increased salt concentration leads to a significant enhancement of both permeate flux and salt passage, while maintaining unaffected removal efficiency for organics. The optimized membrane (L-NF3), synthesized with a 1 % (w/v) concentration of lysine, demonstrated remarkable retention (>98 %) for organics (humic acid and sodium alginate), while concurrently displaying low retention (5.22 %-16.40 %) for mineral ions (Mg2+ / Ca2+). Furthermore, the salts in the feed led to a substantial improvement in permeate flux (239.61 %-385.70 %) compared to salt-free feed. The Lys-TFC membrane showcased outstanding performance of separation, permeability, and operational stability, underscoring its significant potential in municipal drinking water purification.

A loose polyethersulfone hybrid nanofiltration membrane incorporated with polyethyleneimine-decorated silica nanoparticles for highly-efficient dye/salt separation

Loose nanofiltration (LNF) is a newly-developing technology for desalting dye-containing saline effluents, but suffers from membrane materials with low permeance and poor dye/salt separation selectivity. Herein, a hybrid polyethersulfone (PES) LNF membrane for dye/salt separation was prepared via a nonsolvent-induced phase inversion method, which was carried out using polyethyleneimine (PEI)-modified silica nanoparticles as a dopant. This design not only featured a hybrid PES LNF membrane with high porosity and small mean pore size, but also partially neutralized its charge and enhanced its hydrophilicity. Hybrid PES LNF membrane from a 21-wt% PES solution with 3-wt% PEI-decorated silica nanoparticles addition was demonstrated to achieve high water permeance (92.0 L m−2 h−1 bar−1) and dyes retention ratio (98.4 % for Congo Red, 98.8 % for Nile Blue A, and 95.1 % for Methyl Blue) accompanied with fully-pass for various salts (Na2SO4, NaCl, MgCl2 and CaCl2). In addition, the hybrid membrane exerted excellent resistances to strong acidic, oxidative and hot water (90 °C) environments and exhibited a pH-sensitive permeability. Multicycle test revealed that the hybrid membrane had high permeance recovery ratio (>92.8 %) and maintained its high dye retention and complete salt permeation even after 10 cycles, manifesting its outstanding fouling resistance and recyclability. Besides, the hybrid membrane repelled 92.6 % of dyes from a simulated wastewater consisting of multiple industry-applied direct dyes and salts after 12 h consecutive test, but allow 100 % of mixed salts passing through the membrane, proving its practical applicability to industrial dyeing wastewater. This study provided a simple and economically feasible route to high-performance LNF membrane production for dye/salt separation, thus popularizing LNF process in dyeing wastewater treatment, organic products purification, and resource recovery.

Application and environmental impact of loose nanofiltration in surface water treatment

Loose nanofiltration (LNF) membranes with a molecular weight cutoff (MWCO) of about 1000 Da have great potential for high selectivity between natural organic matter (NOM) and mineral salts. Therefore, they are interesting for treatment plants for purifying oligotrophic lake waters with an elevated NOM concentration. This study was conducted to determine the design and operational expenses as well as the environmental impact of an LNF-based drinking water treatment process that removes NOM from Finnish surface water. Two LNF membranes with similar MWCOs were selected, and the results were compared to ultrafiltration, nanofiltration, and conventional treatment. One LNF membrane demonstrated a rejection rate of NOM higher than 95 % and a low rejection rate of hardness at about 40 %, while the other LNF membrane performed similarly to an ultrafiltration membrane. The LNF-based treatment process would increase operational expenses by 53—69 % but at the same time decrease the environmental impact by >18 %. Improved removal of aromaticity and low molecular weight compounds could lower the disinfection byproduct formation potential and microbial growth in the network, thus reducing the required chlorine dosage in the network and possibly bringing further cost savings.

Surface Bioengineering of Mo2Ga2C MAX Phase to Develop Blended Loose Nanofiltration Membranes for Textile Wastewater Treatment.

The potential of blended loose nanofiltration membranes (LNMs) to fractionate dyes and inorganic salts in textile wastewater has become a focus of attention in recent years. In this research work, we fabricated LNMs based on polysulfone (PSf) membranes blended with l-histidine amino acid-functionalized Mo2Ga2C MAX phase (His-MAX). Scanning electron microscopy (SEM), atomic force microscopy (AFM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), contact angle, ζ-potential, porosity, and pore size analyses were employed to characterize the LNMs. Blending 0.75 wt % of His-MAX additive with the PSf tailored the LNM's features by making it more water-friendly, increasing its porosity, enlarging its pores, and making its surface smoother. The pure water flux of 127.6 L/m2 h was achieved by LNM containing 0.75 wt % His-MAX, which was 2.5 times greater than the bare one. The mentioned LNM displayed a flux recovery ratio (FRR) of 68.27 and 98.57, 98.31, and 99.7% rejections for Direct red 23, Acid brown 75, and Reactive blue 21 solutions (100 mg/L), respectively. The 0.75 wt % His-MAX LNM could reject 99.1% of dye and 11.5% of salt while maintaining an FRR of 91.19% after four cycles of filtering a binary mixture solution containing Reactive blue 21 and Na2SO4. These findings highlight the potential of the fabricated LNM for desalinating dye solutions.

Preparation of PMIA loose nanofiltration membrane with electrostatic layer-by-layer self-assembled for dye/salt filtration

Poly (m-phenylene isophthalamide)-based loose nanofiltration membranes were fabricated by electrospinning and subsequential electrostatic layer by-layer self-assembly methods, and the polyelectrolyte multilayers (PEMs) generated by polyacrylic acid (PAA) and polyethyleneimine (PEI) were adopted to contribute the surface functional layer of nanofiber membranes. The incidences of spraying parameter and nano-SiO2 content on the morphology, chemical constitution and dyes separation performance of PEMs functional layer was investigated, respectively. The results showed that the construction of the PEMs functional layer could obviously enhance the Congo red (CR) filtration efficiency by increasing the rejection from 4.9% to 99.8% and improve the surface hydrophilicity by reducing the water contact angle (WCA) from 90.1° to 51.8°. Nano-SiO2 is introduced as a filler to regulate the assembly density of PEMs functional layers, the prepared PEMs/PMIA/SiO2 membrane achieved a relatively stable permeation flux (22.9 L·m−2·h−1), and maintained high separation efficiency of CR/NaCl solution, revealing the excellent dye desalination performance, which exhibited a potential for the dye/salt wastewater treatment. In particular, we offered a new method to prepare loose nanofiltration (LNF) membranes by electrospinning and electrostatic self-assembly technique with accurate separation of inorganic salts and dye molecules.

Structural and separation evaluation of polysulfone-based loose NF membrane modified with itaconic acid-choline chloride deep eutectic solvent as additive

In this research, a type of deep eutectic solvent (DES) based on itaconic acid-choline chloride (IA-CC) was used as an efficient additive to modify the structure of the polysulfone-based membrane. Structural investigation of the as-obtained loose nanofiltration (LNF) membrane was performed through various analyses. The results showed that the use of a very low amount of IA-CC DES in the structure of the polysulfone (PSF) membrane caused the formation of finger-like pores in the structure and increased the porosity. Consequently, a significant increase in the water flux was obtained compared to the membrane synthesized with polyvinylpyrrolidone (PVP) as a common pore former (from 18.22 to 257.14 LMH). The rejection for anionic and cationic dyes as well as the binary mixtures of dyes was evaluated. The rejection of divalent Mg and Ca ions was 16.5% and 15.0%, respectively, while that of monovalent sodium ions was less than 3%. Based on the best of our knowledge, the highest water flux at low pressure (2 bar) despite the high rejection for dyes among all the NF membranes has been reported in this work. Moreover, the antifouling properties of DES-modified membrane against bovine serum albumin (BSA) showed a slight increase in the antifouling index.

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

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

Branched polymer grafted loose nanofiltration membrane with high surface potential for dye desalination

Herein, a thin and high-potential loose nanofiltration (LNF) membrane was fabricated by one-step cross-linking with branched polyethyleneimine (PEI) using the reactive sites on the styrene maleic anhydride/chlorinated polyvinyl chloride membrane surface to for alkylation and nucleophilic addition reactions, respectively. As the molecular weight of branched PEI increased, the thickness of LNF membranes decreased and their pore sizes and surface potential increased (i. e., potential value of LNF membrane above 59 mV at pH = 7). Density functional theory calculations were used to understand the separation mechanism of LNF membranes. The rejection mechanisms of these membranes for Brilliant Blue R250, Methyl blue, Congo red, and Acid fuchsin were based on size-sieving, with rejection for all >95 %. However, the rejection mechanisms of Bromocresol green and Bromothymol blue were affected by the size-electrostatic synergy. Pleasingly, the NaCl rejection was <10 %. Furthermore, the 22 k-PEI-modified LNF membrane could not only effectively separate dye/NaCl under high pressure and high salinity but also maintain long-term stable desalination performance. Notably, the assessment of dye rejection in LNF membranes revealed that it is not solely based on the molecular weight of dye but is also related to the geometric shape of the organic substance.

Lignin/mesoporous hollow silica nanosphere thin film nanocomposite loose nanofiltration membrane for dye/salt separation

It has been still expected to explore a green and low-cost raw material for fabricating high performance loose nanofiltration (LNF) membrane with high permeance and dye/salt selectivity. In this report, aminated mesoporous hollow silica (AHS) nanospheres are first synthesized. Then, a lignin-based LNF membrane is fabricated employing aminated lignin as raw material, trimesoyl chloride as a crosslinker, and AHS nanospheres as nano additives by interfacial polymerization. It shows excellent pure water permeance, high dye rejection, and salt permeation. After being modified with L-arginine, the PWP (49.9 LMH bar−1) and salt permeation are further improved. Simultaneously, the dye rejections are kept at a high level. The AHS nanospheres provided abundant water/salt diffusion channels for the lignin-based separation layer. The hollow structure of the nanospheres decreases the diffusion resistance of the water and salt. Moreover, the membrane shows satisfactory structural and separation performance stability during immersion in acid and/or alkaline solutions. After being treated with 5500 ppm h chlorination strength, it still exhibits excellent BBR/NaCl selectivity accompanied by a small permeance increase. Furthermore, the membrane shows excellent fouling resistances, satisfactory bactericidal (92.5 %) and bacterial anti-adhesion properties. The membrane shows excellent performance stability in a long-term (80 h) dye/salt separation process.

Hydrolysis co-deposition of bio-inspired hybrid hydrophilic network antifouling loose nanofiltration membrane for effective dye/salt separation

Nowadays, loose nanofiltration (LNF) membranes with effective filtration performance toward textile wastewater have drawn intensive attention. In this work, a high-performance LNF membrane was prepared via fast co-deposition of bio-inspired TA-based hydrophilic coating with in-situ hydrolysis of tetra butyl titanate (TBT) on polyethersulfone (PES) substrate. Various additives containing amino acid (l(+)-Arginine) and silane coupling agent (KH792) were mixed in the coating solution and researched their synergistic effects during membrane preparation. In-situ growth of TiO2 and co-deposition of TA-based coating endowed the LNF membrane with a uniformly rough hydrophilic surface. Therefore, the optimal LNF membrane showed a significantly high pure water permeability (92.9 L m−2 h−1·bar−1) with high rejection (>99.0 %) in treating negatively charged dyes including Eriochrome Black T, Congo Red, Chlorazol Black T, and Coomassie Brilliant Blue G. Meanwhile, low rejections for inorganic salts (Na2SO4: 7.9 %, NaCl: 2.5 %, MgCl2: 2.8 %, MgSO4: 7.3 %) were reached, and it kept distinguished separation performance in dealing with highly saline dye wastewater (containing 50 g L−1 NaCl and Na2SO4, respectively). Beyond that, the membrane had excellent antifouling properties with low flux decline of multiple model pollutants and stability during separation dye/salt mixture, which revealed the LNF membrane prepared promising potential in actual textile wastewater treatment.

Review of MOFs and their applications in the preparation of loose nanofiltration membranes for dye and salt fractionation

The improper disposal of unused dyes by various industries is a significant contributor to water pollution. Thus, it is very important to remove the dyes from water. For the treatment of dyes, a number of technologies have been developed, including coagulation/flocculation, adsorption, and chemical oxidation. The main drawbacks of such techniques are their ineffective secondary pollution control and low treatment efficiency. Nanofiltration technology, in comparison, has a high removal rate and is simple to use. Due to its superior selective separation performance, loose nanofiltration (NF) is a potential technique for the fractionation of dyes and salts. Thus, the loose nanofiltration membranes need to be researched and developed more. However, the MOFs are often used in the preparation of loose nanofiltration membranes till now. So, it is necessary to get to know the chemical structure, prospect and challenges in the applications of loose nanofiltration membranes. Metal-organic frameworks, often known as MOFs, are completely novel family of hybrid materials used as adsorbents that are comprised of organic linkers and metal ions or clusters. MOFs and their derivatives have shown unprecedented potential in membrane applications due to their distinct porosity architectures and unique characteristics. They have the benefits of Highly porous, a huge area, flexible pore size, and strong stability due to their unique structural composition. This review provides an overview of MOF membrane fabrication techniques and kinds of MOFs like; UiO-66, MILs, HKUST-1, ZIFs. The review discusses MOF-based membranes for dye/saltwater separation, highlighting challenges and applications. It also discusses modified MOF membranes and their prospects for implementation. While challenges remain, ongoing research and advancements in membrane fabrication techniques hold the key to unlocking the promise of membranes based on MOF for various environmental and industrial applications.

CoFe2O4 modified bentonite-based mixed matrix loose nanofiltration membranes for effective wastewater treatment

Mixed-matrix membranes (MMMs) with an ideal polymer/hydrophilic flux enhancer interface considerably recuperates the separation and purification performance of membrane. In this direction, a novel CoFe2O4 functionalized natural clay-bentonite (CoFe2O4@BT) material as a compatible flux enhancer was synthesized for preparation of mixed matrix based in polyethersulfone (PES) matrix. Here, the influences of CoFe2O4@BT on the morphology and performance of the MMMs membranes were systematically investigated using various analytical techniques. Meanwhile, the water flux and sepration eficiency of the CoFe2O4@BT-PES membranes significantly enhanced due to the incorporation of CoFe2O4@BT that altered hydrophilicity, pore and surface characteristic features. The water flux as well as separation efficiency range up to 95%, 94.69%, 94.16% of Congo red (CR), Crystal violet (CV), and humic acid (HA) respectively. Meanwhile, the fouling parameters demonstrated that the CoFe2O4@BT-PES membranes exhibited better antifouling property in the long term experiment comparing with commercial polyamide membrane. CoFe2O4@BT material incorporated membranes showed less decline ratio and a better recovery ratio. The high rejection of dyes with a high permeation flux of the newly designed membranes indicated an amazing possibility for dye purification. In this study, a potential dye mechanism for composite membranes impacted by synthetic CoFe2O4@BT was also put forth. Within the context of application considerations for environmental protection, new materials stock in membranes show good potential for the separation of different organic contaminants.

Removal of a cyanotoxins mixture by loose nanofiltration membranes applied in drinking water production

Cyanobacterial toxins may threaten human health if their levels in drinking water exceed certain thresholds. Therefore, it is important for water works that use raw water sources prone to cyanobacterial blooms to have efficient barriers against such toxins. Nanofiltration (NF) is one potential barrier. The efficacy and mechanism of removing four cyanotoxins, namely microcystins (MCs), cylindrospermopsin (CYN), saxitoxins (STXs), and anatoxin (ATX), were studied at bench-scale using NF membranes commonly applied in Norwegian drinking water facilities. The average removal of the different cyanotoxins under the tested operating conditions ranged from 15 % to 96 %. The membrane with the lowest molecular weight cut-off (MWCO) of 0.3 kDa made of polyamide (PA) was deemed the most suitable for the removal of all studied cyanotoxins. A gradual improvement of rejection observed with the 2 kDa cellulose acetate (CA) membrane was linked to the formation of fouling on the membrane surface. Sulfonated polyethersulfone (SPES) membranes with MWCO of 1 and 3 kDa could not efficiently and consistently remove cyanotoxins, except for MCs. The rejection of MCs over time was over 80 % by the SPES membranes during two days of filtration. The influence of pressure and pH as relevant operating parameters was evaluated. However, the analysis of the cyanotoxin concentrations in the permeate indicated that the investigated NF membranes alone would generally not be able to meet the WHO guidelines for drinking water during a severe cyanobacterial bloom. Thus, incorporating other water treatment technologies should be considered to effectively remove cyanotoxins.