Resultant Nanofiltration Membranes Research Articles

Precisely Patterned Nanostrand Surface of Cucurbituril[n]-Based Nanofiltration Membranes for Effective Alcohol–Water Condensation

Low concentration alcohols produced by the state-of-art biological fermentation restrict the subsequent purification processes for chemical, pharmaceutical, biofuel and other applications. Herein, a rarely reported cucurbituril[n] (n=6, 8) is employed to pattern the thin-film composite membranes with controllable and quantifiable nanostrand structures through host-guest strategy. The resulting nanofiltration membrane with such morphology is the first report that exhibits excellent separation performance for isopropanol (IPA) and water, condensing initial 0.5 wt% IPA aqueous solution to 9.0 wt%. This not only provides a novel strategy for patterning nanostructural morphology, but also makes nanofiltration membranes promising for alcohol condensation in the biological fermentation industry that may reduce the energy consumption and post-processing costs.

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricarbonyl trichloride on polysulfone (PSf) support membranes blended with K+-responsive poly(N-isopropylacryamideco-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that: (1) Under K+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections; (2) With K+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic; (3) After a curing treatment at 95 °C, the improved NF membrane achieved an even higher pure water permeability of 10.97 L⋅m-2⋅h-1⋅bar-1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.

End-of-life RO membranes recycling: Reuse as NF membranes by polyelectrolyte layer-by-layer deposition

Nowadays, end-of-life (EoL) reverse osmosis (RO) membranes are considered as waste, hence they are incinerated or discarded in landfills. Due to the environmental problem of disposed membranes, their reuse as nanofiltration (NF) membranes was investigated in this study. At first, the fouling of EoL membrane was cleaned and then the effect of sodium hypochlorite (NaOCl) on removing the polyamide (PA) layer and pure water permeability (PWP) of EoL membranes was investigated. With regard to NaOCl exposure intensities, three groups of EoL membranes with PWP of about 10, 20, and 30 L/(m2h bar) were selected as substrates to convert them to NF membranes by deposition of polyelectrolyte (PE) multilayers. The effects of PE type, substrate permeability, and the charge of outer layer on the performance of the resultant NF membranes were studied. As one of the best results, NF membrane composed of eight bilayers of SC498/KE253 polyelectrolytes on substrates with PWP of 18 L/(m2h bar) had salt water permeability (SWP) of 11 L/(m2h bar) and 94% rejection of MgSO4. Other results are also competitive with commercial NF membranes. The maximum NaCl and MgSO4 rejection of prepared membranes were 92% and 98%, respectively, at a feed pressure of 10 bar. In addition, the stability test showed that the prepared membranes are stable over a long period of filtration.

Surface enriched sulfonated polyarylene ether benzonitrile (SPEB) that enhances heavy metal removal from polyacrylonitrile (PAN) thin-film composite nanofiltration membranes

This study aims to develop a new strategy to fabricate nanofiltration (NF) membranes with high removal efficiency for heavy metal ions in wide acidic pH range. Unlike conventional polyacrylonitrile (PAN) based thin film composite (TFC) membranes that requires multiple coating steps, the new NF membrane was fabricated through direct interfacial polymerization with positively charged polyethyleneimine (PEI) on PAN substrates blended with sulfonated polyarylene ether benzonitrile (SPEB). The unique surface migration effect of SPEB led to a smoother, more hydrophilic surface and sponge-like structure of the substrate. Such a modified structure was found to be crucial to achieve smaller pore size as well as better adhesion of the selective layer and the substrate of the modified TFC membrane. The resultant NF membrane has a reasonably high pure water permeability of 7.62 ± 0.81 LMH·bar−1, and a molecular weight cut-off of 300 Da. It achieved a reasonably high rejection towards heavy metal cations such as Pb2+, Cd2+, Ni2+ over 93.0% in a wide acidic pH range. This work may provide insightful guidelines for upgrading current NF membranes for heavy metal removals in harsh acidic environments.

A Novel Thin-Film Nanocomposite Nanofiltration Membrane by Incorporating 3D Hyperbranched Polymer Functionalized 2D Graphene Oxide.

In order to develop a high-performance thin-film nanocomposite (TFN) nanofiltration (NF) membrane, the functionalized graphene-based nanomaterial (GO-HBE-COOH) was synthesized by combining two-dimensional graphene oxide (GO) with a three-dimensional hyperbranched polymer, which was used as the novel nanofiller and successfully embedded into the polypiperazine-amide (PPA) active layers on polysulfone (PSU) substrates via interfacial polymerization (IP) process. The resultant NF membranes were characterized using ATR-FTIR, SEM, and AFM, while their performance was evaluated in terms of water flux, salt rejection, antifouling ability, and chlorine resistance. The influence of GO-HBE-COOH concentration on the morphologies, properties, and performance of TFN NF membranes was investigated. With the addition of 60 ppm GO-HBE-COOH, the TFN-GHC-60 NF membrane exhibited the optimal water flux without a sacrifice of the salt rejection. It was found that the introduction of GO-HBE-COOH nanosheets favored the formation of a thinner and smoother nanocomposite active layer with an enhanced hydrophilicity and negative charge. As a result, TFN NF membranes demonstrated a superior permeaselectivity, antifouling ability, and chlorine resistance over the conventional PPA thin-film composite (TFC) membranes.

Novel chitosan-piperazine composite nanofiltration membranes for the desalination of brackish water and seawater

A novel chitosan (CS)-piperazine (PIP) composite nanofiltration (NF) membrane with satisfied characteristics for brackish water and seawater desalination was successfully developed. PIP was mixed with CS during the interfacial polymerization (IP) process to enhance the NF membrane permeate flux. The resultant NF membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), contact angle. Effects of CS concentration, trimesoyl chloride (TMC) concentration, reaction time and the mixing ratio of CS/PIP on NF membrane performance were investigated thoroughly. When PIP in the aqueous phase monomers reached to 25% (w/w), the PWF (60.6 L·m−2·h−1) was synergistically improved by nearly 2 times without a significant reduction of Na2SO4 rejection (89.1%). Moreover, the NF membranes possessed excellent performance for the desalination of brackish water and seawater, which showed high potential to be applied in the desalination process for water treatment.

Positively charged capillary nanofiltration membrane with high rejection for Mg2 + and Ca2 + and good separation for Mg2 + and Li +

High water permeability and good separation property are greatly desired in water production due to energy concerns. To explore nanofiltration (NF) membrane with high permeability for cations separation, a positively charged NF membrane was fabricated via interfacial polymerization using polyethersulfone (PES) three-channel capillary ultrafiltration (UF) membrane as substrate, polyethyleneimine (PEI) as the aqueous precursor. The NF membrane preparation conditions were optimized. To enhance the permeability of the prepared NF membrane, modified hydroxyl contained multi-walled carbon nanotubes (MWCNTs-OH), grafting with piperazine (PIP), were utilized. The resultant NF membrane showed increased water flux from 20.8L·m−2·h−1 to 56.1L·m−2·h−1 at 4bar after adding 0.01wt% modified MWCNTs-OH in aqueous solution. Interestingly, MgCl2 rejection of the membrane also increased from 94.2% to 96.9%. The positively charged NF membrane exhibited above 97% rejection for divalent cations (Mg2+ and Ca2+) and low rejection (<70%) for monovalent cations (Na+ and Li+), and it also showed long durability and good separation for Mg2+ and Li+ when the membrane was used to separate mixed salts solution simulated the composition of salt lake brine. The fabricated membrane would have potential for effective water softening and for reclamation of lithium from brine or seawater with high Mg2+/Li+ ratio.

Structure–performance study of polyamide composite nanofiltration membranes prepared with polyethyleneimine

Polyethyleneimine (PEI) of various molecular weights and trimesoyl chloride (TMC) were utilized to prepare composite nanofiltration (NF) membranes via interfacial polymerization. The changes in the surface structure and chemical composition of the prepared membranes were evaluated using SEM, ATR-FTIR, XPS and surface potential measurements. The pure-water flux and rejection rates of the inorganic salts (MgCl2, MgSO4, Na2SO4 and NaCl) through the resultant NF membranes were also investigated. The results showed that the performance of the composite NF membranes was significantly affected by the molecular weight of the PEI. Notably, the permeate flux and rejection rate of the NF membranes increased with the PEI molecular weight. In addition, when the NF membranes were used to treat actual wastewater from the electroplating industry, the NF membranes presented high-efficiency separation properties for heavy metal ions. The rejection rates of the NF membranes at 0.4 MPa for chromium, nickel, zinc and copper ions reached 92.6, 89.6, 89.2 and 86.3%, respectively.

Concurrent Removal of Selenium and Arsenic from Water Using Polyhedral Oligomeric Silsesquioxane (POSS)–Polyamide Thin-Film Nanocomposite Nanofiltration Membranes

With stringent regulations regarding the toxic ions selenium and arsenic on wastewater discharge, various industries such as coal mining and power generation are demanding more efficient and effective treatment methods to remove these two ions. Since the performance of commercially available thin film composite nanofiltration (NF) membranes reported so far has a great room for improvement, a thin-film nanocomposite (TFN) NF membrane comprising polyhedral oligomeric silsesquioxane (POSS) with high efficiency was developed for the concurrent removal of selenium and arsenic from aqueous solutions. The resultant NF membrane has a mean effective pore diameter of 0.65 nm, a molecular weight cutoff of 302 Da, and superior pure water permeability of 5.4 LMH/bar with notably high rejections of SeO32–, SeO42–, and HAsO42– toward 93.9%, 96.5%, and 97.4%, respectively. The TFN membranes also exhibit slightly higher rejection performance when a mixed ion solution separation test was conducted. To the best of our knowledge, this is the first reported NF membrane comprising POSS in the selective layer for the concurrent removal of Se and As ions. The promising results achieved in this study provide promising methodology for the development of novel NF membranes to remove other multiple toxic ions from waste streams.

Incorporating hyperbranched polyester into cross-linked polyamide layer to enhance both permeability and selectivity of nanofiltration membrane

To prepare thin film composite (TFC) nanofiltration (NF) membranes with improved flux and rejection performance at low pressure, hyperbranched polyester (HPE) was selected as the nano-sized macromonomer and successfully incorporated into the skin layers on PVC hollow fiber substrates via interfacial polymerization between trimesoyl chloride and the mixtures of hydroxyl-terminated HPE/piperazine (PIP). The resultant NF membranes were characterized using ATR-FTIR, FESEM, AFM and surface zeta potential, while their performance was evaluated in terms of permeate flux and rejection rates of different inorganic salts and neutral solutes. When the HPE content was lower than 60wt% in HPE/PIP mixtures, the increased membrane surface roughness and the HPE embedded in skin layer effectively enhanced the permeate flux without sacrificing salt rejection for the prepared TFC NF membranes. Further increasing HPE content in HPE/PIP mixtures yielded looser polyamide skin layer, which led to the decline of solute rejection. Due to the larger size and good interfacial compatibility with cross-linked polyamide matrix, the incorporated HPE could exist stably in the skin layer. And thus, the prepared TFC NF membranes showed good flux and rejection stability in a long-term filtration process.

Nanofiltration membranes with dually charged composite layer exhibiting super-high multivalent-salt rejection

State-of-the-art nanofiltration (NF) membranes generally positively or negatively charged could not remove both multivalent cations and anions once and for all according to the Donnan Exclusion. Designing NF membranes with facile approach for effective removal of multivalent-salt without compromising the permeation is still a tough challenge. In this work, we demonstrate a sort of novel NF membrane consists of a positively charged interlayer sandwiched between substrate and negatively charged outermost surface. The restructured NF membranes with dually charged composite layer were fabricated via amination-interfacial polymerization (A-IP) on poly (vinyl chloride) (PVC) substrate. The resultant NF membranes exhibited super high salts rejection of up to 99.0% MgCl2, 99.0% MgSO4, 98.5% CaCl2, 95.7% Pb(NO3)2, and 96.0% Na2SO4. Additionally, reasonably high flux (8.7Lm−2h−1bar−1, (pure water permeability (PWP))) approaching those of commercial NF membranes was obtained due to the relatively loose structure of the composite layer. Furthermore, the transport and separation mechanism of the restructured NF membranes reveals that the significant upgraded separation performance could be attributed to the synergistic effect of the dually charged layer. Moreover, the dually charged composite layer shown none unfavorable interaction and the resultant NF membranes possessed good interfacial stability.

Fabrication of electro-neutral nanofiltration membranes at neutral pH with antifouling surface via interfacial polymerization from a novel zwitterionic amine monomer

A kind of novel electro-neutral nanofiltration (NF) membrane at neutral pH was fabricated by interfacial polymerization from a novel zwitterionic amine monomer PEI-g-SBMA. The zwitterionic amine endowed the resultant NF membrane with an electro-neutral separation layer under neutral condition and enhanced antifouling property via regulation of surface charge balance. The electro-neutral zwitterionic NF membranes (PEI-g-SBMA/TMC) showed a high water flux of 132L/ (m2hMPa), i.e. over 2 times higher than that of the PEI/TMC membranes without grafted SBMA. The PEI-g-SBMA/TMC membrane exhibited a high dye rejection (90.6% for Orange GII) but a low salt rejection (7.1% for NaCl and 50.4% for Na2SO4). Meanwhile, the antifouling property against bovine serum albumin (BSA), sodium alginate (SA) and humic acid (HA) was significantly improved compared with the PEI/TMC membranes. The as-fabricated electro-neutral PEI-g-SBMA/TMC membranes with high organics rejection and low salt rejection as well as good antifouling property may find promising application potential in food, pharmaceutical, chemical industry and membrane bioreactor (MBR) processes.

Novel nanofiltration membranes consisting of a sulfonated pentablock copolymer rejection layer for heavy metal removal.

Facing stringent regulations on wastewater discharge containing heavy metal ions, various industries are demanding more efficient and effective treatment methods. Among the methods available, nanofiltration (NF) is a feasible and promising option. However, the development of new membrane materials is constantly required for the advancement of this technology. This is a report of the first attempt to develop a composite NF membrane comprising a molecularly designed pentablock copolymer selective layer for the removal of heavy metal ions. The resultant NF membrane has a mean effective pore diameter of 0.50 nm, a molecular weight cutoff of 255 Da, and a reasonably high pure water permeability (A) of 2.4 LMH/bar. The newly developed NF membrane can effectively remove heavy metal cations such as Pb(2+), Cd(2+), Zn(2+), and Ni(2+) with a rejection of >98.0%. On the other hand, the membrane also shows reasonably high rejections toward anions such as HAsO4(2-) (99.9%) and HCrO4(-) (92.3%). This performance can be attributed to (1) the pentablock copolymer's unique ability to form a continuous water transport passageway with a defined pore size and (2) the incorporation of polyethylenimine as a gutter layer between the selective layer and the substrate. To the best of our knowledge, this is the first reported NF membrane comprising this pentablock copolymer as the selective material. The promising preliminary results achieved in this study provide a useful platform for the development of new NF membranes for heavy metal removal.

Preparation and characterization of high‐selectivity hollow fiber composite nanofiltration membrane by two‐way coating technique

ABSTRACTA novel coating technique, named as two‐way coating (TWC), was explored to prepare hollow fiber composite (HFC) nanofiltration (NF) membrane through interfacial polymerization from piperazine (PIP) and trimesoyl chloride (TMC) on the lumen side of hollow fiber polysulfone ultrafiltration membrane with an effective membrane area of 0.4 m2. The optimum preparation conditions were systematically investigated and obtained as follows: PIP 0.023 mol/L, TMC 0.0057 mol/L, air blowing rate 2.7 m/s for 30 min after aqueous coating, aqueous coating pressure 0.1 MPa, organic solution flowing rate 0.32 m/s, and heat treating time 3 min. The resultant HFC membrane showed a high selectivity of divalent ion and monovalent ion. Salt rejections of MgSO4 and NaCl were 98.13 and 18.6% with the permeate flux of 32.6 and 40.2 L m−2 h−1 at 0.7 MPa, respectively. Field emission scanning electron microscopy images indicated that composite membrane prepared by TWC technique had a uniform active layer from the upper end to the bottom of the hollow fiber. And the salt rejection and permeate flux showed almost no difference between different membrane sections. Stability results suggested that good reproducibility could be obtained by TWC technique for the preparation of high‐performance HFC NF membrane. The resultant NF membrane showed a high removal rate of chemical oxygen demand and chroma of landfill leachate which were approximately 100%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41187.

Preparation, characterization and performance of ZnCl2 incorporated polysulfone (PSF)/polyethylene glycol (PEG) blend low pressure nanofiltration membranes

Simultaneous use of organic (PEG 200), and inorganic (ZnCl2) additives to polysulfone for casting of nanofiltration (NF) membrane was reported in this work. Dimethylformamide (DMF) was used as the solvent. The membranes were characterized in terms of surface morphology, permeability, porosity, contact angle, molecular weight cut off and zeta potential. The resultant NF membranes were tested with monovalent and divalent electrolytes sucrose, glucose and three dyes in the range of molecular weight from 263 to 697. Both NF membranes showed rejection of salts, NaCl: 40–43% and Na2SO4: 52–54%, at 690kPa and pH11. The corresponding permeate flux were 20 to 22l/m2·h. Among the dyes crystal violet and congo red are rejected more than 98% and chrysoidine more than 95% over the transmembrane pressure range of 276 to 690kPa. Electrostatic interaction was found to play a determinant role in rejection of salts, whereas, size exclusion was the major mechanism for rejection of dyes.

Antifouling, High-Flux Nanofiltration Membranes Enabled by Dual Functional Polydopamine

A facile method for fabricating antifouling and high-flux nanofiltration (NF) membranes was developed based on bioinspired polydopamine (PDA). Polyethersulfone (PES) ultrafiltration membrane as the support was first deposited a thin PDA layer and then chemically modified by a new kind of fluorinated polyamine via Michael addition reaction between fluorinated polyamine and quinone groups of PDA. PDA coating significantly reduced the pore sizes of the PES support membrane and endowed the NF membrane with high separation performance (flux about 46.1 L/(m(2) h) under 0.1 MPa, molecular weight cutoff of about 780 Da). The grafted fluorinated polyamine on the PDA layer could form low free energy microdomains to impede the accumulation/coalescence of foulants and lower the adhesion force between foulants and the membrane, rendering the membrane surface with prominent fouling-release property. When foulant solutions (including bovine serum albumin, oil and humic acid) were filtered, the resultant NF membrane exhibited excellent antifouling properties (the minimal value of total flux decline ratio was ∼8.9%, and the flux recovery ratio reached 98.6%). It is also found that the structural stability of the NF membrane could be significantly enhanced due to the covalent bond and other intermolecular interactions between the PDA layer and the PES support.

Positively charged nanofiltration (NF) membranes via UV grafting on sulfonated polyphenylenesulfone (sPPSU) for effective removal of textile dyes from wastewater

Novel positively charged nanofiltration (NF) membranes have been fabricated using sulfonated polyphenylenesulfone (sPPSU) support with hydrophilic properties and fully sponge-like morphology via UV-induced grafting. The resultant NF membranes with a mean effective pore diameter of 1.13–1.20 nm, molecular weight cut off (MWCO) of 1627–1674 Da and high pure water permeability (PWP) of 9–14 LMH bar −1 can be successfully developed by utilizing two different types of positively charged grafting monomers. In view of salt rejections of the resultant NF membranes, it follows the order R(MgCl 2 )>R(NaCl)>R(MgSO 4 )>R(Na 2 SO 4 ) with high rejections to MgCl 2 of up to 95.20%. Furthermore, the newly developed NF1 and NF2 membranes demonstrate an impressive prospect for the dye removal from wastewater treatment. Due to their positive surface charges, a superior rejection of up to 99.98% to Safranin O dye can be achieved by NF1 and NF2 membranes. Characterizations of the two NF membranes were further done to elucidate the difference in performance and a variety of factors such as pore size, surface roughness, selective layer thickness and zeta potential were established as the controlling factors. ► Novel nanofiltration (NF) membranes based on UV-grafting on sulfonated material. ► Use of positively charged vinyl monomers to induce positive charge on NF membrane. ► High water flux of 9–14 LMH bar −1 and impressive rejection of more than 99% to Safranin O dye molecule.

Cellulose acetate nanofiltration hollow fiber membranes for forward osmosis processes

Abstract Cellulose acetate (CA) nanofiltration (NF) hollow fiber membranes have been fabricated and tested in the forward osmosis (FO) process. A two-step heat-treatment, i.e., 60 min at 60 °C and 20 min at 95 °C, effectively shrinks the membrane mean pore radius from 0.63 to 0.30 nm. The molecular weight cut off (MWCO) of the resultant CA NF membrane is 186 Da. In the NF experiments under 1 bar transmembrane pressure, the newly developed CA NF membrane shows a pure water permeability (PWP) of 0.47 L m −2 bar −1 h −1 and rejection levels of 90.17% to NaCl and 96.67% to MgCl 2 . The water flux and the salt leakage of the CA NF hollow fiber are measured in the FO process using NaCl or MgCl 2 draw solutions. With increasing the draw solution concentration, the water flux increases. However, the increase is almost linear when the draw solution flows in the shell side and is nonlinear when the draw solution flows in the lumen side. With 2.0 M MgCl 2 draw solution (osmotic pressure ≈ 258.3 bar) flowing in the shell side, the water flux and the salt leakage are 7.3 L m −2 h −1 (LMH) and 0.53 g m −2 h −1 (gMH), respectively. When using saline water as the feed solution, the efficiency of the osmotic pressure decreases with increasing feed concentration due to the more severe internal concentrative concentration polarization. These preliminary results indicate that CA NF membrane is a promising candidate for FO processes.

Preparation and characterization of poly(piperazineamide) composite nanofiltration membrane by interfacial polymerization of 3,3′,5,5′-biphenyl tetraacyl chloride and piperazine

Most nanofiltration (NF) membranes are composite and have a polyamide thin film prepared by interfacial polymerization. Their performances mainly correlate the structure of the thin film and monomers used for its preparation. In this work, a novel thin-film composite (TFC) nanofiltration membrane was successfully prepared from 3,3′,5,5′-biphenyl tetraacyl chloride (mm-BTEC) and piperazine (PIP) through interfacial polymerization. Attenuated reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS) were used to characterize the chemical composition of the membrane surface. The membrane performance was optimized by studying preparation parameters including monomer concentration, reaction time, and pH of aqueous phase. The resulting NF membrane exhibited significantly enhanced water permeability while maintaining high rejection to salt. The flux and rejection of NF membrane to Na 2SO 4 (500 ppm) reached to 51.5 L/(m 2 h) and 95% under 0.5 MPa. The streaming potential tests indicated that the TFC membrane surface had high charge density and very low isoelectric point which situated between pH 1 and 2.