Novel Nanofiltration Membrane Research Articles

A novel nanofiltration membrane with a dual-charged layer to simultaneously remove anions and cations from acid mine drainage

A novel nanofiltration (NF) membrane with a positively and negatively dual-charged layer was finely designed in this study. The membrane was prepared by co-deposition of 4-tert-butylpyrocatechol (TBC) and polyethyleneimine (PEI) and electrostatic interaction to assemble positively and negatively charged functional layers on a substrate which is polyamide (PA)-based NF membrane. The NF membrane achieved excellent retention capacity through the combined effects of Donnan repulsion and electrostatic field trapping. The prepared membrane had a dense but thin surface layer with an average pore size of 0.84 nm, enabling an improved membrane flux of 8.66 L/(m2·h·bar) and high rejection to divalent inorganic salt ions (93.56 % Mg2+, 99.56 % SO42-). The membrane was used to treat acid mine drainage (AMD) and achieved an excellent retention capacity for ions in AMD (93.25 % Mg2+, 91.58 % Ca2+, 94.22 % Mn2+, 95.96 % SO42-), meeting industrial wastewater discharge standards. In addition, the NF membrane demonstrated good anti-fouling performance during the AMD treatment and significant potential for environmental remediation applications.

Membranes with ZIF-8 regulated MXene nanosheet stacks for efficient molecular sieving

Thin film nanocomposite (TFN) membranes synthesized by introducing nanofillers into a polyamide layer have attracted increasing attentions. However, due to the aggregation of the nanofillers, the fabricated TFN membranes inevitably suffer from a reduced stability. In this work, a novel nanofiltration (NF) selective layer with in-situ formed ZIF-8 was fabricated by an integrated vacuum filtration and interfacial polymerization (IP) method. The d-spacing of MXene nanosheets could be well tailored by controlling the content of in-situ formed ZIF-8 nanoparticles, thus optimizing the surface morphology and chemical composition of the as-prepared NF membrane. The highly hydrophilic MXene nanosheets and controllable ZIF-8 size enabled the molecular sieving ability of the selective layer. Compared with the pristine thin film composite membrane, the optimal membrane exhibited an excellent pure water permeability up to 40.8 L m−2 h−1 bar−1 while maintaining high rejections (>99.0 %) for Congo red, reactive blue 19, xylene brilliant cyaninG250 and methyl blue, respectively. Furthermore, the membranes preserved low salt rejections for Na2SO4, NaCl, MgSO4 and MgCl2. This novel fabrication strategy provides new insights to augment the interlayer distance of 2D nanosheets and broadens the prospects to employ nanofillers inside a membrane matrix for efficient dye/salt separation.

High-performance nanofiltration membranes consisting of the new functionalized mesoporous for enhanced antifouling attributes and simultaneous removal of salts, dyes and heavy metals

For the first time, the tetrathioterephthalate functionalized KIT-6 (T-KIT-6) mesoporous was synthesized and then characterized using FTIR, XRD, zeta potential, and FESEM analysis. The synthesized T-KIT-6 mesoporous was used to prepare a novel nanofiltration (NF) membrane for the removal of dyes, salts, and heavy metal ions from contaminated waters. The effects of T-KIT-6 mesoporous loading on the membrane morphology, properties, and proficiency were studied by FTIR, EDS, TGA, FESEM, AFM, water contact angle and zeta potential measurements, etc. The performance of the prepared membranes was investigated by milk solution filtration experiments. The maximum pure water flux was 45.2 kg/m 2 h for the membrane containing 0.3 wt% T-KIT-6 mesoporous (TKM-0.3), which was much higher than that of the membrane without mesoporous. Moreover, the TKM-0.3 membrane featured effectual antifouling properties with a low irreversible fouling ratio of 4.8% and a high flux recovery ratio of 95.2%, accompanied by long-term stability. All membranes showed the highest rejection for Na 2 SO 4 and the lowest rejection for NaCl, which was in good accordance with the rejection sequence of the negatively charged NF membranes. The TKM-0.3 membrane also showed the highest dye rejections (˃ 98%) and superior removal of heavy metal ions (Mn 2 + = 98 . 21 % , Cu 2 + = 97 . 52 % , Ni 2 + = 95 . 00 % , Pb 2 + = 93 . 43 % ). Regarding the good performance in multipollutant removal and long-term stability for heavy metal removal, this study describes the fabrication of antifouling NF membrane as an economic and efficient technology for wastewater treatment. • A T-KIT-6 mixed matrix membrane was prepared for removal of salts, dyes and metals. • The effect of T-KIT-6 mesoporous enhanced the hydrophilicity and porosity. • The membrane exhibited superior antifouling properties and metal ions rejection.

Nanofiltration Membranes via Layer-by-layer Assembly and Cross-linking of Polyethyleneimine/Sodium Lignosulfonate for Heavy Metal Removal

Layer-by-layer (LbL) assembly technology is a facile method for constructing thin film composite membrane. Herein, a novel nanofiltration (NF) membrane was prepared by LbL assembly of polyethyleneimine (PEI) and sodium lignosulfonate (LS) followed by cross-linking. The surface composition, morphology, and property of PEI/LS bilayer were detailedly investigated by FTIR/ATR, XPS, SEM, AFM, and water contact angle test. The PEI/LS bilayer full of amino and hydroxyl groups presents increased roughness and improved hydrophilicity. Moreover, the NF performance of PEI/LS LbL assembly membranes can be modulated by bilayer number, polyelectrolyte concentration, and salt content. The water flux reduced while the salt rejection greatly improved as increasing the bilayer numbers, PEI concentration, or NaCI content. More than 95% MgSO4 and MgCI2, as well as 80% NaCI can be rejected by a NF membrane prepared by 6 PEI/LS bilayers, 1 wt% PEI, 0.5 wt% LS, and 1 mol/L NaCI. Furthermore, this NF membrane can be used to remove more than 95% heavy metal ions (Cd2+, Zn2+, Mn2+, Cr2+, Cu2+, and Ni2+). This work proposed a promising NF membrane by using PEI/LS as low cost polyelectrolytes and facile LbL assembly method, which should receive much attention in water purification.

“Bridge” graphene oxide modified positive charged nanofiltration thin membrane with high efficiency for Mg2+/Li+ separation

To improve the efficiency during the process of Mg2+/Li+ separation, a novel nanofiltration (NF) membrane was optimized by doping graphene oxide (GO) additives into the ultrafiltration (UF) base membrane. The effects of GO doping content on the morphology, structure and surface properties of UF membrane and the final NF membrane were studied comprehensively. The hydrophilic GO acted as a “bridge” between UF membrane and polyamide layer due to the “anchor effect”, which significantly enhanced the interaction between base membrane and polyamide layer. The results revealed that with ultra-low GO doping content of 0.05 wt%, the final NF005 membrane exhibited a high selective separation capacity for Mg2+ and Li+ (SMg,Li≈0.062), and the flux increased by about 119% compared with the pure NF0 membrane. Additionally, due to the high stability of membrane, the excellent separation capacity of NF005 membrane only changed slightly after 7-day cycle filtration test. Importantly, a small amount of GO doping greatly improved the permeability of both UF and NF membranes, which correspondingly improved the separation efficiency and accelerated the filtration rate. This work provides a new direction for designing membrane with high efficiency for Mg2+/Li+ separation, which is potential in the field of lithium extraction.

Thin-film composite nanofiltration membranes with high flux and dye rejection fabricated from disulfonated diamine monomer

Novel nanofiltration (NF) membranes with improved flux, dye rejection, high pH and temperature resistance were developed using a disulfonated diamine co-monomer, disodium-3-3′-disulfone-4-4′-dichlorodiphenylsulfone (S-DADPS). Thin film composite (TFC) NF membranes were fabricated on a porous polysulfone-based ultrafiltration support layer via the interfacial polymerization between trimesoyl chloride (TMC) in the organic phase and S-DADPS/piperazine (PIP) mixture in the aqueous phase. The effect of S-DADPS content was investigated on the structure and properties of fabricated TFC-NF membranes by varying the ratio between S-DADPS and PIP from 0/100 to 100/0 (w/w). The chemical structure, surface properties and the morphology of TFC-NF membranes were characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), optical profilometry, contact angle, and zeta potential measurements. Salt and dye rejection behaviors of fabricated TFC-NF membranes were evaluated using 2000 ppm MgSO4 and NaCl solutions and 100 ppm Setazol Red and Reactive Orange 16 dyes, respectively. Dyes were filtrated in acidic, neutral and alkaline conditions for pH resistance tests. The temperature resistance of membranes was evaluated using pure water and dye solutions at 15 °C, 25 °C, and 40 °C. Among all TFC-NF membranes fabricated by varying the S-DADPS/PIP ratio, the membrane with an 80/20 ratio of S-DADPS/PIP resulted in superior properties such as increased water flux without considerable salt and dye rejection loss compared to the neat TFC-NF membrane without S-DADPS. In addition, the variation of S-DADPS/PIP ratio was demonstrated as a powerful tool to tune the balance of flux, separation and rejection performance of NF membranes for custom purification purposes.

Carbon quantum dots (CQDs) nanofiltration membranes towards efficient biogas slurry valorization

In this article, novel nanofiltration (NF) membranes with highly selective surface and fast water and ion transport channels were fabricated for the valorization of biogas slurry. Unlike conventional thin film composite (TFC) membranes, the novel NF membranes compose hydrophilic carbon quantum dots (CQDs) as the interlayer. The carboxyl groups from CQDs react with the polyethyleneimine (PEI), leading to the lower cross-linking degree in the interfacial polymerization layer of NF membranes. Besides, the presence of the hydrophilic CQDs can create fast water and ion transport channels in the NF membranes. The water permeability of membranes is therefore enhanced significantly from 3.6 to 9.7 LMH·bar−1. The NF membranes were used to concentrate the amino acids from biogas slurry; it achieved rejection rates above 90% towards model amino acids such as lysine, glutamic acid and leucine, due to its highly positive electrical properties, while allowing most of the unwanted salt ions to permeate through. The excellent selectivity between amino acids and salt ions demonstrates the great potential application of the NF membranes in biogas slurry valorization.

Preparation of Layer-by-Layer Nanofiltration Membranes by Dynamic Deposition and Crosslinking.

In recent decades, the advancements in layer-by-layer (LBL) assembly technology have provoked increasing interest in the preparation of multilayer polyelectrolyte membranes with excellent performance. In the current study, a novel nanofiltration (NF) membrane was prepared by pressure-driven layer-by-layer (LBL) assembly of polyethylenimine (PEI) and polyacrylicacid (PAA) on a porous substrate with chemical crosslinking. The effect of deposition pressure on separation performance of the prepared membranes was studied. The surface morphology, hydrophilicity and the charge property of the dynamically-deposited membranes were compared with those prepared by static adsorption. The characterization results showed that dynamic deposition process resulted in a smoother membrane surface with improved hydrophilicity. The mechanism of water-path formation was proposed to interpret the effect of pressure on the membrane performance. Glutaraldehyde (GA) was used as a crosslinker to reduce the number of polyelectrolyte bilayers for obtaining good separation performance. The rejections of different inorganic salts of the dynamically-deposited NF membrane were also investigated.

Recovery of iron after Fenton-like secondary treatment of olive mill wastewater by nano-filtration and low-pressure reverse osmosis membranes

In this work, the performances of novel nano-filtration (NF) and low-pressure reverse osmosis (RO) polymeric membranes were examined with the aim of recovering the iron used as catalyst in former secondary treatment based on the Fenton-like advanced oxidation of olive mill wastewater (OMW). Results highlight that both membranes exhibit a good performance towards the rejection of iron (99.1% for the NF membrane vs. 100% for the low-pressure RO membrane) in the secondary-treated OMW effluent, thus permitting the recovery of iron in the concentrate stream in order to recycle it back into the oxidation reactor to reduce catalyst consumption. Finally, the permeate streams could be re-used for irrigation. Major productivity was observed by the selected NF membrane, about 47.4 L/hm 2 upon 9 bar, whereas 30.9 L/hm 2 could be yielded with the RO membrane under an operating pressure of 8 bar. Moreover, a sensibly lower fouling index was measured on the NF membrane (0.0072 in contrast with 0.065), which ensures major steady-state performance on this membrane and a longer service lifetime. This also results in lower required membrane area and membrane plant over dimension (4 modules in case of RO operation whereas only 2 modules for NF).

Preparation of loose polypiperazine amide membranes. Effect of the nanocomposite sublayer on the NF process performance

Novel nanofiltration (NF) membranes were prepared by interfacial polymerization using four different nanocomposite membranes as sublayers. The nanocomposite sublayers were prepared by immersion precipitation method, dispersing nanoparticles such as TiO2, SBA-15 and functionalized SBA-15 with carboxylic groups (SBA-15(COOH)). The physico-chemical properties of the sublayers were studied by means of cross section morphology, pore diameter, pore density, contact angle and roughness by SEM and FEG-SEM. The successful incorporation of the thin film layer was evaluated by FT-IR. The addition of the nanoparticles increased the pore density and hydrophilic character of the ultrafiltration (UF) sublayers. Results showed that the nanocomposite sublayers can improve the process performance of the thin film composite membrane. In this study, the most significant performance improvement was observed on the NF with SBA-15(COOH) doped sublayer, achieving permeability values in the UF range (56.3dm3/m2hbar) and successful MgSO4 rejection coefficients (68.3%). Results also show that there is no strong influence between the physical parameters of the sublayers and NF process performance. Therefore, it was concluded that the COOH functional group of the nanoparticle SBA-15(COOH) might have interfered in the interfacial polymerization process, leading to more permeable and selective NF membranes.

Upgrading coagulation with hollow-fibre nanofiltration for improved organic matter removal during surface water treatment

Rising organic matter concentrations in surface waters in many Nordic countries require current drinking water treatment processes to be adapted. Accordingly, the use of a novel nanofiltration (NF) membrane was studied during a nine month period in pilot scale at a large drinking water treatment plant in Stockholm, Sweden. A chemically resistant hollow-fibre NF membrane was fed with full scale process water from a rapid sand filter after aluminum sulfate coagulation. The combined coagulation and NF process removed more than 90% of the incoming lake water dissolved organic carbon (DOC) (8.7 mg C L−1), and 96% of the absorbance at 254 nm (A254) (0.28 cm−1 incoming absorbance). Including granulated active carbon GAC) filter, the complete pilot plant treatment process we observed decreases in DOC concentration (8.7–0.5 mg C L−1), SUVA (3.1–1.7 mg−1 L m−1), and the average nominal molecular mass (670–440 Da). Meanwhile, water hardness was practically unaffected (<20% reduction). Humic substances (HS) and biopolymers were almost completely eliminated (6510–140 and 260 to 10 μg C L−1 respectively) and low molecular weight (LMW) neutrals decreased substantially (880–190 μg C L−1). Differential excitation emission matrices (EEMs), which illustrate the removal of fluorescing organic matter (FDOM) over a range of excitation and emission wavelengths, demonstrate that coagulation removed 35 ± 2% of protein-like material and 65 ± 2% of longer emission wavelength, humic-like FDOM. The subsequent NF treatment was somewhat less selective but still preferentially targeted humic-like FDOM (83 ± 1%) to a larger extent than protein-like material (66 ± 3%). The high selectivity of organic matter during coagulation compared to NF separation was confirmed from analyses with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and liquid chromatography with organic carbon detection (LC-OCD), as coagulation exclusively targeted oxidized organic matter components while NF removed both chemically reduced and oxidized components. DOC removal and change in DOC character in the GAC filters showed marked differences with slower saturation and more pronounced shifts in DOC character using NF as pre-treatment. Fluorescence derived parameters showed a similar decrease over time of GAC performance for the first 150 days but also indicated ongoing change of DOM character in the post NF GAC filtrate over time even after LC-OCD indicated steady state with respect to outgoing carbon. During our trial iron concentrations were low (<30 ppb) and thus A254 could be directly related to the concentration of HS (R2 = 0.9). The fluorescence derived freshness index (β:α) proved to be an excellent variable for estimating the fraction of HS present in all samples. Given the recommended limit of 4 mg L−1 for chemical oxygen demand (COD) for Swedish drinking water, coagulation will need to be supplemented with one or more treatment steps irrespective whether climate change will lead to drier or wetter conditions in order to maintain sufficient DOC removal with the current increasing concentrations in raw waters.

Stability and permeation behavior of a porous membrane modified by polyelectrolyte networks enabled by electro-deposition and cross-linking for water purification

A novel nanofiltration (NF) membrane is developed via polyethyleneimine (PEI) deposition on a hydrolyzed polyacrylonitrile (PAN) substrate enhanced by an electric field and chemical cross-linking to achieve improved desalting properties. Compared to the PEI static-deposition process, dramatic increase in salt rejection and substantial reductions of deposition time and PEI concentration are achieved for the membranes prepared by electro-deposition. What's more, the resulting membrane exhibited both stable flux and salt rejection in filtrating seawater for a relatively long term due to a significant membrane stability attributed to the electro-deposition. Desalting properties in terms of salt rejection and flux were found to be strongly affected by both hydrolysis and electro-deposition conditions. Under the optimal fabricating conditions, the resulting NF membrane exhibited a high flux of 24L/m2h, excellent MgCl2 rejection of ∼92% and low NaCl rejection of ∼39% when filtrating 2000mg/L salt solution at 0.5MPa. Under filtration of raw seawater at 1.8MPa, the resulting membrane exhibited a high flux of 30.2L/m2h and a significant improvement in seawater softening efficiency compared to various commercial NF membranes, which is attributed to its excellent separation efficiency between divalent and univalent ions. The current investigation demonstrated that polyelectrolyte NF membranes fabricated by electro-deposition and cross-linking led to excellent separation performance and satisfactory stability and durability that can be used in seawater softening for a relatively long time.

Preparation and characterization of a composite nanofiltration membrane from cyclen and trimesoyl chloride prepared by interfacial polymerization

ABSTRACTA novel nanofiltration (NF) membrane was prepared with cyclen and trimesoyl chloride by interfacial polymerization on a poly(ether sulfone) ultrafiltration membrane with a molecular weight cutoff of 50,000 Da. The effects of the reaction time, monomer concentration, and heat‐treatment temperature are discussed. The physicochemical properties and morphology of the prepared NF membrane were characterized by Fourier transform infrared spectroscopy–attenuated total reflectance, scanning electron microscopy, energy‐dispersive spectrometry, and atomic force microscopy. The NF performances were evaluated with solutions of Na2SO4, MgSO4, Mg(NO3)2, and NaCl. The salt‐rejection order of the prepared NF membrane was as follows: Na2SO4 &gt; MgSO4 &gt; Mg(NO3)2 &gt; NaCl. The resulting rejection of Na2SO4 and PEG600 (polyethylene glycol with the average molecular weight of 600) were more than 90%, whereas that of NaCl was approximately 10%. After the addition of silica sol in the aqueous phase (silica sol concentration = 0.1% w/v), the salt rejection of the membrane changed slightly. However, the water flux was from 24.2 L·m−2·h−1 (25°C, 0.6 MPa) up to 38.9 L·m−2·h−1 (25°C, 0.6 MPa), and the resulting membrane exhibited excellent hydrophilicity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42345.

Bioinspired fabrication of composite nanofiltration membrane based on the formation of DA/PEI layer followed by cross-linking

This work deals with a facile approach to fabricate a novel nanofiltration (NF) membrane consisting of a dense active layer from polyethyleneimine (PEI) cross-linking on a porous polysulphone (PS) substrate which was modified by self-polymerized dopamine (DA). Inspired by the bioadhesion principle, a composite membrane with a poly(dopamine) (poly(DA)) layer was fabricated by simply dipping the PS substrate into DA aqueous solution. Later, the modified PS substrate was thermal-treated and then impregnated into PEI solution for PEI grafting on the poly(DA) layer. Finally, PEI cross-linking was performed and as a result a composite PS/DA/PEIc membrane with a dense cross-linked DA/PEI layer was obtained, which exhibited a typical NF property. Several parameters such as PEI grafting, thermal treatment, cross-linkers and operating conditions were investigated to obtain the optimum composite membrane with an excellent NF performance. The results showed that the optimum NF membrane yielded a permeation flux of 43.96L/m2h and a rejection of 89.27% when 2000mg/L MgCl2 solution was used as a feed solution at 0.8MPa, whereas a permeation flux of 49.21L/m2h and a rejection of 27.30% were obtained for a feed NaCl concentration of 2000mg/L. These results show the promising use of such NF membranes in water softening.

New type of nanofiltration membrane based on crosslinked hyperbranched polymers

Novel nanofiltration (NF) membrane was developed from hydroxyl-ended hyperbranched polyester (HPE) and trimesoyl chloride (TMC) by in situ interfacial polymerization process using ultrafiltration polysulfone membrane as porous support. Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle (CA) measurements were employed to characterize the resulting membranes. The results indicated that the crosslinked hyperbranched polyester produced a uniform, ultra-thin active layer atop polysulfone (PSf) membrane support. FTIR-ATR spectra indicated that TMC reacted sufficiently with HPE. Water permeability and salts rejection of the prepared NF membrane were measured under low trans-membrane pressures. The resulting NF membranes exhibited significantly enhanced water permeability while maintaining high rejection of salts. The salts rejection increase was accompanied with the flux decrease when TMC dosage was increased. The flux and rejection of NF 1 for Na 2SO 4 (1 g/L) reached to 79.1 l/m 2 h and 85.4% under 0.3 MPa. The results encourage further exploration of NF membrane preparation using hyperbranched polymers (HBPs) as the selective ultra-thin layer.