High flux positively charged nanofiltration membranes prepared by UV-initiated graft polymerization of methacrylatoethyl trimethyl ammonium chloride (DMC) onto polysulfone membranes

Improving Hemocompatibility of Polysulfone Membrane by UV-Assisted Grafting of Sulfonated Chitosan

The most prevalent type of hemodialysis membrane is polysulfone (PSf). However, due to inadequate biocompatibility, it significantly compromises the safety of dialysis for patients. In this study, we modify the surface of the PSf membrane with 2,4-dihydroxybenzophenone (DBPh) groups to serve as anchoring sites during UV irradiation. Subsequently, a tailored sulfonated dihydroxy propyl chitosan (SDHPCS) is grafted onto the modified PSf membrane to compensate for the deficiencies in hydrophilic additives. The modified PSf membrane exhibits outstanding hydrophilicity and stability, as demonstrated by its characterization and evaluation. This paper focuses on investigating the interaction between platelet membrane formation, protein adsorption, and anticoagulant activity. The results show that the modified PSf membrane exhibits remarkable enhancement in surface hydrophilicity, leading to a significant reduction in protein and platelet adsorption as well as adhesion.

Fabrication of mixed nanoceramic waste with polymeric matrix membranes for water desalting

Mixed matrix membranes were prepared by blending technique between nanoceramic powder and polyethersulfone. Nanoceramic powder (NC) as a fine powder was produced from ceramic industries. The effect of NC as an additive on the membrane matrix was studied. Increasing in NC% on polymeric blend enhances the membrane mechanical properties, where the tensile strength was 13.92 MPa with elongation of 23.67 mm for prepared blend membrane with NC 1 wt%. The highest salt rejection was about 89.3% with permeate flux of 34.6 L/m2 h for R1 membrane using NS of percentage 4 wt% and nonwoven polyester support. The increase in NS% to 6 wt % leads to an increase in the salt rejection to 94.2% after 1 h operating time. The coating was achieved using the layer by layer technique which was carried out on the membrane surface to improve the salt rejection percentage. The salt rejection was found to reach about 99.8% after such coating process; but for permeate flux, it shows a certain decrease. The flux of membrane before the coating was 23.4 L/m2 h for R2 membrane (1 wt% NC & 6 wt% NS), while after coating the flux was reduced to reach 21.6 L/m2 h.

Positively charged nanofiltration membrane synthesis, transport models, and lanthanides separation

The design and understanding of rejection mechanisms for both positively and negatively charged nanofiltration (NF) membranes are needed for the development of highly selective separation of multivalent ions. In this study, positively charged nanofiltration membranes were created via an addition of commercially available polyallylamine hydrochloride (PAH) by conventional interfacial polymerization technique. Demonstration of real increase in surface zeta potential, along with other characterization methods, confirmed the addition of weak basic functional groups from PAH. Both positively and negatively charged NF membranes were tested for evaluating their potential as a technology for the recovery or separation of lanthanide cations (neodymium and lanthanum chloride as model salts) from aqueous sources. Particularly, the NF membranes with added PAH performed high and stable lanthanides retentions, with values around 99.3% in mixtures with high ionic strength (100 mM, equivalent to ~6,000 ppm), 99.3% rejection at 85% water recovery (and high Na+/La3+ selectivity, with 0% Na+ rejection starting at 65% recovery), and both constant lanthanum rejection and permeate flux at even pH 2.7. Donnan steric pore model with dielectric exclusion elucidated the transport mechanism of lanthanides and sodium, proving the potential of high selective separation at low permeate fluxes using positively charged NF membranes.

Novel Fe3O4-poly(methacryloxyethyltrimethyl ammonium chloride) adsorbent for the ultrafast and efficient removal of anionic dyes

The removal of anionic dyes from wastewater has attracted global concern. In this work, a novel Fe₃O₄-poly(methacryloxyethyltrimethyl ammonium chloride) (Fe₃O₄-pDMC) adsorbent for the efficient removal of anionic dyes from wastewater was successfully synthesized by grafting methacryloxyethyltrimethyl ammonium chloride (DMC) on the surfaces of Fe₃O₄. Various characterization analyses confirmed that the obtained Fe₃O₄-pDMC possessed numerous functional groups on its surfaces and retained good magnetic separation properties. Fe₃O₄-pDMC showed ultrafast removal for acid orange 7 (AO7, 58.6%, 1 min) and direct blue 15 (DB15, 98.1%, 1 min), and the maximum adsorption capacity was high (266.8 and 336.5 mg g^-1 for AO7 and DB15, respectively). In addition, the adsorption process was in accordance with pseudo-second-order kinetics and the Langmuir isotherm. The mechanism underlying the adsorption of Fe₃O₄-pDMC on anionic dyes was mainly dependent on electrostatic interaction. This study illustrated that Fe₃O₄-pDMC has great potential applications as an environmentally friendly, desirable adsorbent for the efficient removal of anionic dyes from wastewater.

Tailoring Charged Nanofiltration Membrane Based on Non-Aromatic Tris(3-aminopropyl)amine for Effective Water Softening

High-performance positively-charged nanofiltration (NF) membranes have a profound significance for water softening. In this work, a novel monomer, tris(3-aminopropyl)amine (TAEA), with one tertiary amine group and three primary amine groups, was blended with trace amounts of piperazine (PIP) in aqueous solution to fabricate a positively-charged NF membrane with tunable performance. As the molecular structures of TAEA and PIP are totally different, the chemical composition and structure of the polyamine selective layer could be tailored via varying the PIP content. The resulting optimal membrane exhibited an excellent water permeability of 10.2 LMH bar⁻¹ and a high rejection of MgCl₂ (92.4%), due to the incorporation of TAEA/PIP. In addition, this TAEA NF membrane has a superior long-term stability. Thus, this work provides a facile way to prepare a positively charged membrane with an efficient water softening ability.

Recovery of hydrochloric acid using positively-charged nanofiltration membrane with selective acid permeability and acid resistance

An acid-recovering nanofiltration (NF) membrane with both acid resistance and selective acid permeability was fabricated via a water-based coating process for the recovery of hydrochloric acid. To achieve this, a thermally cross-linked branched-polyethyleneimine (b-PEI) layer was introduced to a loose polyethersulfone NF membrane by dip-coating of b-PEI and an epoxy linker and heat treatment in a sealed oven with a high-humidity atmosphere. The resulting membrane displayed a positive surface charge with a zeta potential, and exhibited a rejection performance order of MgCl₂> MgSO₄> NaCl > Na₂SO₄ characteristic of positive-charge-separation membranes. Mg rejection and Cl permeation experiments showed that the selective permeation of hydrochloric acid was achieved with Mg rejection above 95% and Cl permeation above 70%, and this allowed the acid to be recovered by obtaining permeate at the same pH as the feed. Moreover, the NF membrane maintained selective separation performance and flow rate for a month.

A nanofiltration membrane prepared by PDA-C3N4 for removal of divalent ions

In this study, a positively charged nanofiltration (NF) membrane was prepared by interfacial polymerization for separation of divalent cations, whereby a nanomaterial (modified graphitic carbon nitride (g-C₃N₄) with poly(dopamine), PDA-C₃N₄) was incorporated into the active layer of the NF membrane. PDA-C₃N₄ sheets were synthesized from g-C₃N₄ sheets prepared by thermal oxidation of melamine, and the preparation conditions of NF membrane were also optimized. The results show that the roughness of PDA-C₃N₄ embedded NF membrane decreases, and the hydrophilicity and the permeation increase. The membrane also shows high rejection for divalent cations (Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺ and Zn²⁺) but low rejection (36.8%) for monovalent cation (Li⁺), as well as good fouling resistance performance. The fabricated membrane has the potential for treatment of industrial wastewater.

Porous Zr-Based Metal-Organic Frameworks (Zr-MOFs)-Incorporated Thin-Film Nanocomposite Membrane toward Enhanced Desalination Performance

Four different thin-film nanocomposite (TFN) membranes were prepared by adding different concentrations of porous Zr-metal-organic frameworks (MOFs) (UiO-66 and UiO-66-NH₂) to piperazine aqueous solution (aqueous phase) or 1,3,5-benzenetricarbonyl trichloride-n-hexane solution (organic phase) by interfacial polymerization. The main purpose is to study the specific effects of different addition methods and addition amounts of nanoparticles on the structure and performance of the TFN membranes by interfacial polymerization. All four TFN membranes exhibited a higher water permeability while maintaining high salt rejection compared to thin-film composite membrane. On the one hand, the TFN membranes behave differently, which are prepared by adding the same kind of nanoparticles to the aqueous phase or organic phase, respectively. The TFN membrane prepared by adding 0.2 w/v% UiO-66 to the organic phase had a high water flux of 87.86 L m^-2 h^-1, compared to 46.31 L m^-2 h^-1 of the membrane prepared by adding 0.3 w/v% UiO-66 in the aqueous phase. This is due to the fact that UiO-66 greatly slows the interfacial polymerization rate when UiO-66 is added to the organic phase, resulting in a thinner and wider-aperture polyamide thin-film layer, reducing the water transmission resistance during filtration. Therefore, it is more economical by adding nanoparticles to organic phase than aqueous phase under the same filtering effect. On the other hand, different nanoparticles can also cause differences in performance and structure of the TFN membranes even in the same preparation manner. TFN membrane with UiO-66-NH₂ in the aqueous phase has higher water permeance than the one with UiO-66 in the aqueous phase, owing to the good hydrophilicity of the amino group, which improves the water dispersibility of UiO-66-NH₂ so that the TFN membrane is more uniform. In addition, UiO-66-NH₂ slows down the process of interface polymerization, making the membrane more porous. The monomers in the aqueous phase and organic phase can be adsorbed in the pores of Zr-MOFs, which makes the interfacial polymerization occur both in the pores and on the surface of the pores. Thus, the compatibility between the polyamide and MOFs was enhanced and less defects were formed in the thin-film layer, resulting in a high salt rejection even when the concentration of Zr-MOFs increased. This is the first time to explain that polyamide membrane has not obvious salt rejection attenuation with increasing porous material content using pore adsorption reaction monomer principle. Also, the Zr-MOFs-based TFN membrane exhibited good heat resistance and antifouling property. This work shows that porous Zr-MOFs nanomaterials have significant advantages in the development of nanofiltration membranes with high water flux and rejection.

Ink-Jet Printing-Assisted Modification on Polyethersulfone Membranes Using a UV-Reactive Antimicrobial Peptide for Fouling-Resistant Surfaces

Antimicrobial peptides (AMPs) are promising candidates for surface coatings to control biofilm growth on water treatment membranes because of their broad activity and the low tendency of bacteria to develop resistance to AMPs. However, general and convenient surface modification methods are limited, and a deeper understanding of the antimicrobial mechanism of action is needed for surface-attached AMPs. Here, we show a method for covalently attaching AMPs on porous ultrafiltration membranes using ink-jet printing and provide insight into the mode of action for the covalently tethered peptide RWRWRWA-(Bpa) (Bpa, 4-benzophenylalanine) against Pseudomonas aeruginosa. AMP-coated ultrafiltration membranes showed surface antibacterial activity and reduced biofilm growth. Fluorescence microscopy analysis revealed that the modified surfaces could cause cell membrane disruption, which was seen by live uptake of propidium iodide stain, and scanning electron microscopy images showed compromised cell membranes of attached bacteria. This study indicated that the mode of action of covalently tethered AMPs was similar to that of freely soluble AMPs. The deeper understanding of the mode of action of AMPs covalently attached to surfaces could lead to a more rational approach for designing surfaces with antibacterial activity.

Thin Film Nanocomposite Membrane Filled with Metal-Organic Frameworks UiO-66 and MIL-125 Nanoparticles for Water Desalination

Knowing that the world is facing a shortage of fresh water, desalination, in its different forms including reverse osmosis, represents a practical approach to produce potable water from a saline source. In this report, two kinds of Metal-Organic Frameworks (MOFs) nanoparticles (NPs), UiO-66 (~100 nm) and MIL-125 (~100 nm), were embedded separately into thin-film composite membranes in different weight ratios, 0%, 0.05%, 0.1%, 0.15%, 0.2%, and 0.3%. The membranes were synthesized by the interfacial polymerization (IP) of m-phenylenediamine (MPD) in aqueous solution and trimesoyl chloride (TMC) in an organic phase. The as-prepared membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and salt rejection and water flux assessments. Results showed that both UiO-66 and MIL-125 could improve the membranes’ performance and the impacts depended on the NPs loading. At the optimum NPs loadings, 0.15% for UiO-66 and 0.3% for MIL-125, the water flux increased from 62.5 L/m² h to 74.9 and 85.0 L/m² h, respectively. NaCl rejection was not significantly affected (UiO-66) or slightly improved (MIL-125) by embedding these NPs, always at >98.5% as tested at 2000 ppm salt concentration and 300 psi transmembrane pressure. The results from this study demonstrate that it is promising to apply MOFs NPs to enhance the TFC membrane performance for desalination.

Self-Healing Hydrogel Pore-Filled Water Filtration Membranes

Damages to water filtration membranes during installation and operation are known to cause detrimental loss of the product water quality. Membranes that have the ability to self-heal would recover their original rejection levels autonomously, bypassing the need for costly integrity monitoring and membrane replacement practices. Herein, we fabricated hydrogel pore-filled membranes via in situ graft polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto microporous poly(ether sulfone) (PES) substrates and successfully demonstrated their self-healing ability. Covalent attachment of the hydrogel to the substrate was essential for stable membrane performance. The membranes autonomously restore their particle rejection up to 99% from rejection levels as low as 30% after being physically damaged. We attribute the observed self-healing property to swelling of the pore-filling hydrogel into the damage site, strong hydrogen bonding, and molecular interdiffusion. The results of this study show that hydrogel pore-filled membranes are a promising new class of materials for fabricating self-healing membranes.

A Novel Synthesis of Gold Nanoparticles Supported on Hybrid Polymer/Metal Oxide as Catalysts for p-Chloronitrobenzene Hydrogenation

This contribution reports a novel preparation of gold nanoparticles on polymer/metal oxide hybrid materials (Au/P[VBTACl]-M metal: Al, Ti or Zr) and their use as heterogeneous catalysts in liquid phase hydrogenation of p-chloronitrobenzene. The support was prepared by in situ radical polymerization/sol gel process of (4-vinyl-benzyl)trimethylammonium chloride and 3-(trimethoxysilyl)propyl methacrylate in conjunction with metal-alkoxides as metal oxide precursors. The supported catalyst was prepared by an ion exchange process using chloroauric acid (HAuCl4) as gold precursor. The support provided the appropriate environment to induce the spontaneous reduction and deposition of gold nanoparticles. The hybrid material was characterized. TEM and DRUV-vis results indicated that the gold forms spherical metallic nanoparticles and that their mean diameter increases in the sequence, Au/P[VBTACl]-Zr > Au/P[VBTACl]-Al > Au/P[VBTACl]-Ti. The reactivity of the Au catalysts toward the p-CNB hydrogenation reaction is attributed to the different particle size distributions of gold nanoparticles in the hybrid supports. The kinetic pseudo-first-order constant values for the catalysts in the hydrogenation reaction increases in the order, Au/P[VBTACl]-Al > Au/P[VBTACl]-Zr > Au/P[VBTACl]-Ti. The selectivity for all the catalytic systems was greater than 99% toward the chloroaniline target product. Finally the catalyst supported on the hybrid with Al as metal oxide could be reused at least four times without loss in activity or selectivity for the hydrogenation of p-CNB in ethanol as solvent.

A Thin Film Nanocomposite Membrane with MCM-41 Silica Nanoparticles for Brackish Water Purification

Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthesized by the interfacial polymerization (IP) process. An m-phenylenediamine (MPD) aqueous solution and an organic phase with trimesoyl chloride (TMC) dissolved in isooctane were used in the IP reaction, occurring on a nanoporous polysulfone (PSU) support layer. Isooctane was introduced as the organic solvent for TMC in this work due to its intermediate boiling point. MCM-41 silica NPs were loaded in MPD and TMC solutions in separate experiments, in a concentration range from 0 to 0.04 wt %, and the membrane performance was assessed and compared based on salt rejection and water flux. The prepared membranes were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, and attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis. The results show that adding MCM-41 silica NPs into an MPD solution yields slightly improved and more stable results than adding them to a TMC solution. With 0.02% MCM-41 silica NPs in the MPD solution, the water flux was increased from 44.0 to 64.1 L/m²·h, while the rejection virtually remained the same at 95% (2000 ppm NaCl saline solution, 25 °C, 2068 kPa (300 psi)).

Potential applications of abandoned aromatic polyamide reverse osmosis membrane by hypochlorite degradation

Reverse osmosis (RO) membranes might experience significant changes in surface structure and performance after disinfection has been applied, or after membrane cleaning, because of hydrolysis and oxidation processes.

Preparation of a novel positively charged nanofiltration composite membrane incorporated with silver nanoparticles for pharmaceuticals and personal care product rejection and antibacterial properties

A novel positively charged N-[(2-hydroxy-3-trimethylammonium)propyl] chloride chitosan (HTCC)-Ag/polyethersulfone (PES) composite nanofiltration membrane was easily prepared by coating the active layer, HTCC, onto PES as the support through epichlorohydrin as the cross-linking reagent and nano-Ag particles as the introduced inorganic components. Scanning election microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray diffraction were employed to characterize the morphology of the resultant membranes, of which the molecular weight cut-off was about 941 Da. At 25 °C, the pure water permeability is 16.27 L/h·m(2)·MPa. Our results showed that the rejection of pharmaceuticals and personal care products (PPCPs) followed the sequence: atenolol > carbamazepine > ibuprofen, confirming that the membranes were positively charged. The antibacterial properties of the membranes were compared to elucidate the existence of Ag nanoparticles which help to improve antibacterial activity against Gram-negative Escherichia coli (DH5α, Rosetta) and Gram-positive Bacillus subtilis. The inhibition zone diameters of HTCC-Ag/PES membranes towards E. coli DH5α, E. coli Rosetta and Bacillus subtilis were 17.77, 16.18, and 15.44 mm, respectively. It was found that HTCC-Ag/PES membrane has a better antibacterial activity against E. coli than against Bacillus subtilis, especially for E. coli DH5α.

A novel positively charged membrane based on polyamide thin-film composite made by cross-linking for nanofiltration

In this paper, a novel positively charged membrane was prepared through interfacial polymerization technique between polyethyleneimine in aqueous phase and trimesoyl chloride in organic phase. Next, cross-linking of polyamide (PA) layer using ρ-xylylene dichloride (XDC) and glutaraldehyde (GA) was studied. The influences of cross-linking concentrations on the separation and permeation performance of membrane were also investigated. Membranes were characterized in terms of their chemical structure, the cross-sectional and surface morphologies, contact angles, molecular weight cut-off (MWCO) and effect of pH feed solution. The salt rejection sequence of CaCl2 >NaCl > Na2SO4 showed a positive charge at the membrane surface after cross-linking reaction. The MWCO of primary PA membrane decreased from 1,135 to 775 and 885 Da for XDC and GA, respectively. XDC membrane shows highest CaCl2 divalent cationic rejection (95.5%) and lowest water flux (21.1 L/m(2).h). This study illustrates a promising method for fabrication of positively charged membrane in cation separation.

Enhanced surface hydrophilicity of thin-film composite membranes for nanofiltration: an experimental and DFT study

In the current study, thin-film composite (TFC) nanofiltration membranes desirable for water softening were successfully developed through interfacial polymerization using N-(2-hydroxyethyl)ethylenediamine (HEDA) as the amine monomer in the aqueous phase.