Polyamide‐imide nanofiltration hollow fiber membranes with elongation‐induced nano‐pore evolution

A critical review with emphasis on the rheological behavior and properties of polymer solutions and their role in membrane formation, morphology, and performance

Considering the importance of asymmetric membrane morphology in controlling the performance of various membrane systems as well as the rapid development of membrane technologies in different industries, the control of membrane manufacturing processes and effective parameters is considered an outstanding subject. Therefore, it seems that investigating the rheological properties of polymer solutions, including gelation behavior, viscoelasticity, and their effect on membrane formation, as well as the morphological structure of membranes, such as hollow fiber and flat sheet membranes, is a requirement for the production of asymmetric membranes with desirable properties. One of the most widely used techniques for the preparation of asymmetric membranes is phase separation. Its two main mechanisms are liquid-liquid demixing and solid-liquid demixing, which can affect the morphology of the membranes in the membrane formation process. Therefore, the membrane morphology can be greatly influenced by controlling the phase separation in the early stages. In this study, an attempt has been made to investigate the rheological behavior of polymer solutions and other factors during the membrane fabrication process, affecting the morphological structure of membranes. The principles governing the rheology of polymer solutions, such as shear, elongation, viscosity, and viscoelasticity have a vital role in determining the membrane morphology and separation performance. Due to the interaction of the rheology of polymer solutions and phase separation, the effects of changes in the rheological properties of the phase separation and the formation of membranes with different structures and morphologies are studied. Furthermore, in addition to the analysis of the effect of the relaxation time and gelation mechanisms, discussions are provided for the determination of the final membrane morphology considering the competition between the domain growth and gelation rates. Finally, the effect of controlling the rheological behavior and phase separation on the membrane structure and performance was investigated in several membrane applications.

Nanomaterials as a Sustainable Choice for Treating Wastewater: A Review

The removal of dyes from textile effluents utilizing advanced wastewater treatment methods with high efficiency and low cost has received substantial attention due to the rise in pollutants in water. The purpose of this work is to give a comprehensive analysis of the different treatments for removing chemical dyes from textile effluents. The capability and potential of conventional treatments for the degradation of dyeing compounds in aqueous media, as well as the influence of multiple parameters, such as the pH solution, initial dye concentration, and adsorbent dose, are presented in this study. This study is an overview of the scientific research literature on this topic, including nanoreductive and nanophotocatalyst processes, as well as nanoadsorbents and nanomembranes. For the purpose of treating sewage, the special properties of nanoparticles are currently being carefully researched. The ability of nanomaterials to remove organic matter, fungus, and viruses from wastewater is another benefit. Nanomaterials are employed in advanced oxidation techniques to clean wastewater. Additionally, because of their small dimensions, nanoparticles have a wide effective area of contact. Due to this, nanoparticles' adsorption and reactivity are powerful. The improvement of nanomaterial technology will be beneficial for the treatment of wastewater. This report also offers a thorough review of the distinctive properties of nanomaterials used in wastewater treatment, as well as their appropriate application and future possibilities. Since only a few types of nanomaterials have been produced, it is also important to focus on their technological feasibility in addition to their economic feasibility. According to this study, nanoparticles (NPs) have a significant adsorption area, efficient chemical reactions, and electrical conductivity that help treat wastewater effectively.

Removing miscellaneous heavy metals by all-in-one ion exchange-nanofiltration membrane

The composition of wastewater containing heavy metal mixtures is often complex and poses a serious threat to human and environmental health. Effective removal of a variety of heavy metal ions with a single technology is challenging, and the conventional split integrated technologies require multi-step processing and a massive footprint. For the first time, we achieve hierarchically integrating ion exchange and nanofiltration into all-in-one "iNF" membranes. The iNF membrane has a hierarchical structure with an interfacial polymerization layer and an ion exchange layer, which can achieve highly efficient indiscriminate heavy metal ion removal, overcoming the defect that traditional nanofiltration membranes can only remove single metal cations or oxyanions. The ion exchange layer can remove heavy metal ions through sulfonic acid groups and quaternary amine groups. In addition, the ion exchange layer can be regenerated by electro-deionization, which is meaningful for sustainable membrane usage. This facile, scalable, and compact integrated process shows outstanding potential and universal applicability in complex wastewater treatment.

Antibacterial Activity of Electrospun Polyacrylonitrile Copper Nanoparticle Nanofibers on Antibiotic Resistant Pathogens and Methicillin Resistant Staphylococcus aureus (MRSA)

Bacteria induced diseases such as community-acquired pneumonia (CAP) are easily transmitted through respiratory droplets expelled from a person’s nose or mouth. It has become increasingly important for researchers to discover materials that can be implemented in in vitro surface contact settings which disrupt bacterial growth and transmission. Copper (Cu) is known to have antibacterial properties and have been used in medical applications. This study investigates the antibacterial properties of polyacrylonitrile (PAN) based nanofibers coated with different concentrations of copper nanoparticles (CuNPs). Different concentrations of copper sulfate (CuSO₄) and polyacrylonitrile (PAN) were mixed with dimethylformamide (DMF) solution, an electrospinning solvent that also acts as a reducing agent for CuSO₄, which forms CuNPs and Cu ions. The resulting colloidal solutions were electrospun into nanofibers, which were then characterized using various analysis techniques. Methicillin-Resistant isolates of Staphylococcus aureus, an infective strain that induces pneumonia, were incubated with cutouts of various nanocomposites using disk diffusion methods on Luria-Bertani (LB) agar to test for the polymers’ antibacterial properties. Herein, we disclose that PAN-CuNP nanofibers have successfully demonstrated antibacterial activity against bacteria that were otherwise resistant to highly effective antibiotics. Our findings reveal that PAN-CuNP nanofibers have the potential to be used on contact surfaces that are at risk of contracting bacterial infections, such as masks, in vivo implants, or surgical intubation.

General synthesis of ultrafine metal oxide/reduced graphene oxide nanocomposites for ultrahigh-flux nanofiltration membrane

Graphene-based membranes have great potential to revolutionize nanofiltration technology, but achieving high solute rejections at high water flux remains extremely challenging. Herein, a family of ultrafine metal oxide/reduced graphene oxide (rGO) nanocomposites are synthesized through a heterogenous nucleation and diffusion-controlled growth process for dye nanofiltration. The synthesis is based on the utilization of oxygen functional groups on GO surface as preferential active sites for heterogeneous nucleation, leading to the formation of sub-3 nm size, monodispersing as well as high-density loading of metal oxide nanoparticles. The anchored ultrafine nanoparticles could inhibit the wrinkling of the rGO nanosheet, forming highly stable colloidal solutions for the solution processing fabrication of nanofiltration membranes. By functioning as pillars, the nanoparticles remarkably increase both vertical interlayer spacing and lateral tortuous paths of the rGO membranes, offering a water permeability of 225 L m-2 h-1 bar-1 and selectivity up to 98% in the size-exclusion separation of methyl blue.

Interaction-determined extraction capacity between rare earth ions and extractants: taking lanthanum and lutetium as models through theoretical calculations

Extractant plays an important role in the separation and purification of rare earth elements (REEs), whereas, extraction performance is the most effective tactic to evaluate whether an extractant is complete...

Mixed-Matrix Membrane Fabrication for Water Treatment

In recent years, technology for the fabrication of mixed-matrix membranes has received significant research interest due to the widespread use of mixed-matrix membranes (MMMs) for various separation processes, as well as biomedical applications. MMMs possess a wide range of properties, including selectivity, good permeability of desired liquid or gas, antifouling behavior, and desired mechanical strength, which makes them preferable for research nowadays. However, these properties of MMMs are due to their tailored and designed structure, which is possible due to a fabrication process with controlled fabrication parameters and a choice of appropriate materials, such as a polymer matrix with dispersed nanoparticulates based on a typical application. Therefore, several conventional fabrication methods such as a phase-inversion process, interfacial polymerization, co-casting, coating, electrospinning, etc., have been implemented for MMM preparation, and there is a drive for continuous modification of advanced, easy, and economic MMM fabrication technology for industrial-, small-, and bulk-scale production. This review focuses on different MMM fabrication processes and the importance of various parameter controls and membrane efficiency, as well as tackling membrane fouling with the use of nanomaterials in MMMs. Finally, future challenges and outlooks are highlighted.

Development of layer-by-layer assembled polyamide-imide membranes for oil sands produced water treatment

The sustainable expansion of steam-assisted gravity drainage, as one of the most popular enhanced oil recovery methods, strongly depends on the proper management of the produced water. The strict environmental regulations have forced the oil sands industry to treat and reuse the produced water for oil extraction. Membrane separation as a single-step water treatment technique has played an important role in removing multiple-sized contaminants from wastewater. However, fouling limits the widespread application of this technology if the membrane is not modified properly to achieve antifouling propensities. Herein, we used the layer-by-layer assembly technique to sequentially coat the hydrophilic poly(diallyl dimethylammonium chloride) and polyacrylic acid on the surface of the polyamide-imide porous membrane to improve its fouling resistance. The effect of the number of bilayers on fouling and permeation properties was examined. The membrane with the highest fouling resistance and reasonable hydrodynamic permeability of 5.2 LMH/psi was achieved by coating four bilayers. This membrane exhibited a low flux decline of 50.2% and a high flux recovery ratio of 100%, while these numbers for the pristine PAI membrane were 75.9% and 97.8% under similar test conditions. The enhanced antifouling characteristics of the modified membranes indicate the viability of these membranes for oil sands produced water treatment with an easy cleaning procedure. The key parameter that contributed to the enhanced fouling resistance of the bilayer-coated membranes was the improved surface hydrophilicity, which manifests through the reduction of water contact angle from 62° ± 3° for the pristine membrane to 52° ± 2° for surface-modified membranes.

Self-Cleaning Nanofiltration Membranes by Coordinated Regulation of Carbon Quantum Dots and Polydopamine

Performance declination of nanofiltration (NF) membranes caused by concentration polarization (CP) and membrane fouling has severely restricted their practical application in many fields. This work reports the construction of a novel interlayer between the substrate and the selective layer of conventional composite membranes by coordinating regulation of carbon quantum dots (CQDs) and polydopamine (PDA). Unlike traditional methods that treat CP and fouling separately, the new strategy grants the membrane with dual functions at one time. First, the insertion of the PDA-CQDs layer reformulates the interfacial polymerization process that reduces the solute transport resistance and mitigates the CP issue. Second, the sandwiched photoactive CQDs can degrade organic molecules adsorbed on the membrane surface under visible light, which is promising for low-cost fouling remediation. This study may offer valuable insights into the preparation of durable self-cleaning NF membranes for the effective treatment of complex wastewater in various industries.

Phase Inversion Directly Induced Tight Ultrafiltration (UF) Hollow Fiber Membranes for Effective Removal of Textile Dyes

This study has demonstrated the application of tight ultrafiltration (UF) membranes for effective removal of textile dyes from water at a low pressure. Novel UF hollow fiber membranes with well-defined nanopores and surface charges were developed via a single-step spinning process without any post-treatment. The newly developed tight UF hollow fibers not only possess a small mean pore diameter of 1.0-1.3 nm with a molecular weight cutoff (MWCO) of 1000-2000 Da but also have a high pure water permeability (PWP) of 82.5-117.6 L m^-2 h^-1 bar^-1. Through the synergistic effects of size exclusion and charge repulsion, the novel UF hollow fibers can effectively remove various dyes with impressive rejections of 93.2-99.9% at 1 bar. At the same time, more than 92% of inorganic salts (i.e., NaCl and Na₂SO₄) would permeate through the fibers, reducing the detrimental effects of concentration polarization and providing an attracted avenue for salts reuse. The tight UF hollow fibers also exhibit robust performance in a continuous operation of 170 h or at a high feed recovery of 90%. The fouled fibers can be easily regenerated by backwash of water with a flux recovery of larger than 92%. The newly developed tight UF hollow fiber membranes display huge potential for treating textile wastewater and other impaired effluents because of their great separation performance and simple fabrication process.

Dual-Charged Hollow Fiber Membranes for Low-Pressure Nanofiltration Based on Polyelectrolyte Complexes: One-Step Fabrication with Tailored Functionalities

A new nanofiltration (NF) hollow fiber membrane is developed by using two oppositely charged polyelectrolytes coagulating into a polyelectrolyte complex (PEC) onto polyether sulfone base polymer. The particular membrane architecture emerges during a single-step procedure, allowing setting both the porous negatively charged support of the hollow fiber and the separation layer containing also the positive polyelectrolyte (PEI/PDADMAC) through a single layer dry-jet wet spinning process. The novelty is two-pronged: the composition of the hollow fiber membrane itself and its fabrication procedure (one-step fabrication of membranes employing polyelectrolytes). These result in highly permeable hollow fiber membranes with a stable separation layer and performance at par with the membranes reported in literature obtained by multistep processes. More importantly, the membranes are obtained through a simple, very fast (one-step), and less expensive procedure. The best performance among these newly obtained hollow-fiber membranes is achieved by PD5% hollow fiber (MWCO of 300 Da), which showed 7.6 L/m(2)·h·bar permeability and ∼90% rejection of MgCl2, MgSO4, and Na2SO4 at 2 bar pressure. Thus, the resulting membranes not only have the advantages of the hollow-fiber configuration, but perform very well at extremely low pressures (the lowest reported in the literature). The broad impact of the results presented in this Article lies in the potential to dramatically reduce both the fabrication (duration and complexity) and the price and desalination costs of highly performing NF hollow fiber membranes. These might result in interesting potential applications and open new directions toward designing efficient functional NF hollow fibers for water desalination.

Efficient separation of transition metals from rare earths by an undiluted phosphonium thiocyanate ionic liquid

Efficient separation of transition metal ions from their mixture with rare-earth ions was achieved by extraction with a phosphonium thiocyanate ionic liquid.

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

Bis(2-ethylhexyl)diglycolamic acid (DEHDGA) dissolved in the fluorine-free ionic liquid tetraoctylammonium dodecyl sulphate, [N₈₈₈₈][DS] is an efficient extractant for europium(iii).

Effect of copolymer concentration on the structure and permeability of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane

Temperature-sensitive poly(vinylidene fluoride)-grafted-poly( N-isopropylacrylamide) (PVDF- g-PNIPAAm) copolymer hollow fiber membrane was fabricated by dry–wet spinning technique using N,N-dimethyl formamide as solvent and poly(ethylene glycol) as pore-making agent, respectively. The effect of PVDF- g-PNIPAAm copolymer concentration in the spinning solution on the structure and performance of resultant fiber membranes were investigated by field-emission scanning electronic microscopy, pore size measurements, mechanical tests, and filtration experiments. It was found that the microvoid in the inner cross-section of hollow fiber membrane changed to a finger-like structure with the increase of copolymer concentration from 16 to 20%. The increasing copolymer concentration also led to the increase of the inner diameter, outer diameter, and wall thickness and the decrease of mean pore size and porosity. When the permeation temperature was increased from 20 to 45°C, a remarkable reduction of pure water flux and a drastic increase of the retention of bovine serum albumin were observed around 32°C, indicating an obvious temperature-sensitive permeability.

Outer-selective pressure-retarded osmosis hollow fiber membranes from vacuum-assisted interfacial polymerization for osmotic power generation

In this paper, we report the technical breakthroughs to synthesize outer-selective thin-film composite (TFC) hollow fiber membranes, which is in an urgent need for osmotic power generation with the pressure-retarded osmosis (PRO) process. In the first step, a defect-free thin-film composite membrane module is achieved by vacuum-assisted interfacial polymerization. The PRO performance is further enhanced by optimizing the support in terms of pore size and mechanical strength and the TFC layer with polydopamine coating and molecular engineering of the interfacial polymerization solution. The newly developed membranes can stand over 20 bar with a peak power density of 7.63 W/m(2), which is equivalent to 13.72 W/m(2) of its inner-selective hollow fiber counterpart with the same module size, packing density, and fiber dimensions. The study may provide insightful guidelines for optimizing the interfacial polymerization procedures and scaling up of the outer-selective TFC hollow fiber membrane modules for PRO power generation.

Theoretical Application of Irreversible (Nonequilibrium) Thermodynamic Principles to Enhance Solute Fluxes across Nanofabricated Hemodialysis Membranes

Objective. Nanotechnology has the potential to improve hemodialysis membrane technology. Thus, a major objective is to understand how to enhance toxic solute fluxes across these membranes. The aim of this concept building study is to review the application of irreversible thermodynamic (IT) to solute fluxes. Methods. We expanded the application of the Nernst-Planck equation to include the Kedem-Katchalsky equation, pH, membrane thickness, pore size, and electric potential as variables. Results. (1) Reducing the membrane's thickness from 25 μm to 25 nm increased the flux of creatinine, β₂-microglobulin, and tumor necrosis factor-α (TNF-α) by a thousand times but prevented completely albumin flux, (2) applying an electric potential of 50–400 mV across the membrane enhanced the flux of the respective molecules by 71.167 × 10⁻³, 38.7905 × 10⁻⁸, and 0.595 × 10⁻¹³ mol/s, and (3) changing the pH from 7.35 to 7.42 altered the fluxes minimally. Conclusions. The results supported an argument to investigate the application of IT to study forces of fluxes across membranes. Reducing the membrane's thickness—together with the application of an electrical potential—qualities achievable by nanotechnology, can enhance the removal of uremic toxins by many folds. However, changing the pH at a specific membrane thickness does not affect the flux significantly.