High performance ultrafiltration membrane based on modified chitosan coating and electrospun nanofibrous PVDF scaffolds

Biodegradable Electrospun Membranes for Sustainable Industrial Applications

The escalating demand for sustainable industrial practices has driven the exploration of innovative materials, prominently exemplified by biodegradable electrospun membranes (BEMs). This review elucidates the pivotal role of these membranes across diverse industrial applications, addressing the imperative for sustainability. Furthermore, a comprehensive overview of biodegradable materials underscores their significance in electrospinning and their role in minimizing the environmental impact through biodegradability. The application of BEMs in various industrial sectors, including water treatment, food packaging, and biomedical applications, are extensively discussed. The environmental impact and sustainability analysis traverse the lifecycle of BEMs, evaluating their production to disposal and emphasizing reduced waste and resource conservation. This review demonstrates the research about BEMs toward an eco-conscious industrial landscape for a sustainable future.

Efficacy of Electrospun Nanofiber Membranes on Fouling Mitigation: A Review

Despite the advantages of high contaminant removal, operational flexibility, and technical advancements offered, the undesirable fouling property of membranes limits their durability, thus posing restrictions on their usage. An enormous struggle is underway to conquer this major challenge. Most of the earlier reviews include the basic concepts of fouling and antifouling, with respect to particular separation processes such as ultrafiltration, nanofiltration, reverse osmosis and membrane bioreactors, graphene-based membranes, zwitterionic membranes, and so on. As per our knowledge, the importance of nanofiber membranes in challenging the fouling process has not been included in any record to date. Nanofibers with the ability to be embedded in any medium with a high surface to volume ratio play a key role in mitigating the fouling of membranes, and it is important for these studies to be critically analyzed and reported. Our Review hence intends to focus on nanofiber membranes developed with enhanced antifouling and biofouling properties with a brief introduction on fabrication processes and surface and chemical modifications. A summary on surface modifications of preformed nanofibers is given along with different nanofiller combinations used and blend fabrication with efficacy in wastewater treatment and antifouling abilities. In addition, future prospects and advancements are discussed.

3D Printed Piezoelectric Wound Dressing with Dual Piezoelectric Response Models for Scar-Prevention Wound Healing

During the long process of wound defect repair, the bioelectric stimulation around the wound gradually decreases, which can cause gradual down-regulation of the wound healing cascade response, disordered deposition of collagen fibers, and abnormal remodeling of the extracellular matrix (ECM). All these combined will eventually result in delayed wound healing and scar tissue formation. To resolve these issues, a novel ZnO nanoparticles modified PVDF/sodium alginate (SA) piezoelectric hydrogel scaffold (ZPFSA) is prepared by 3D printing technology. The prepared ZPFSA scaffold has dual piezoelectric response models, mainly consisting of vertical swelling and horizontal friction, which can be used to simulate and amplify endogenous bioelectricity to promote wound healing and prevent scar formation. Compared with other composite scaffolds, ZPFSA 0.5 (contain 0.5% ZnO nanoparticles) exhibits good biocompatibility, excellent antimicrobial properties, and stable piezoelectric response, so that it can significantly accelerate the wound healing and effectively prevent the scar tissue formation within 2 weeks thanks to the cascade regulation in wound healing, including cell migration, vascularization, collagen remodeling, and the expression of related growth factors. The proposed dual piezoelectric response models will provide a new solution to accelerate wound healing process, prevent scar formation, and extend new application range of piezoelectric materials in wound dressing.

Synergistic process using calcium peroxide and ferrous iron for enhanced ultrafiltration of Microcystis aeruginosa-laden water

Algal blooms and eutrophication in natural surface water not only pose a threat to human health, but also adversely affect the water purification process. Ultrafiltration (UF) has been proved to be effective for the retention of algal cells, but its further application is still restricted by the relatively limited removal of algal organics and membrane fouling. To enhance the UF performance, a synergistic process using calcium peroxide and ferrous sulfate (CaO₂/FeSO₄) was proposed for the treatment of Microcystis aeruginosa-laden water. The results suggested that the removal of algal cells and organics, fluorescent components were effectively increased with the synergism of CaO₂ and FeSO₄. The particle size distribution and morphology revealed that the size of algal pollutants apparently increased due to the formation of algal flocs. With CaO₂/FeSO₄ pretreatment, the terminal specific flux of polyethersulfone and polyvinylidene fluoride membranes were increased by 75.0% and 56.5%, individually. The fouling resistances were significantly reduced, and the fouling mechanism transition to cake filtration was delayed. The membrane interface properties including morphologies and functional groups were characterized, further verifying the effectiveness. The in-situ formed Fe³⁺ integrated with Ca(OH)₂ showed excellent coagulation effect, thus promoting the agglomeration of algal foulants. Simultaneously, the generated hydroxyl radical could improve the oxidative degradation of algal organics. In conclusion, the CaO₂/FeSO₄ strategy has great advantages and application prospects in enhancing UF performance for Microcystis aeruginosa-laden water treatment.

Decreasing free fatty acid of crude palm oil with polyvinylidene fluoride hollow fiber membranes using a combination of chitosan and glutaraldehyde

Crude palm oil (CPO) has emerged as a significant commodity in the economic and social development of producer nations.

Enhancement of Physical Characteristics of Styrene-Acrylonitrile Nanofiber Membranes Using Various Post-Treatments for Membrane Distillation

Insufficient mechanical strength and wide pore size distribution of nanofibrous membranes are the key hindrances for their concrete applications in membrane distillation. In this work, various post-treatment methods such as dilute solvent welding, vapor welding, and cold-/hot-pressing processes were used to enhance the physical properties of styrene–acrylonitrile (SAN) nanofiber membranes fabricated by the modified electrospinning process. The effects of injection rate of welding solution and a working distance during the welding process with air-assisted spraying on characteristics of SAN nanofiber membranes were investigated. The welding process was made less time-consuming by optimizing system parameters of the electroblowing process to simultaneously exploit residual solvents of fibers and hot solvent vapor to reduce exposure time. As a result, the welded SAN membranes showed considerable enhancement in mechanical robustness and membrane integrity with a negligible reduction in surface hydrophobicity. The hot-pressed SAN membranes obtained the highest mechanical strength and smallest mean pore size. The modified SAN membranes were used for the desalination of synthetic seawater in a direct contact membrane distillation (DCMD). As a result, it was found that the modified SAN membranes performed well (>99.9% removal of salts) for desalination of synthetic seawater (35 g/L NaCl) during 30 h operation without membrane wetting. The cold-/hot-pressing processes were able to improve mechanical strength and boost liquid entry pressure (LEP) of water. In contrast, the welding processes were preferred to increase membrane flexibility and permeation.

Tunable Graphene Oxide Nanofiltration Membrane for Effective Dye/Salt Separation and Desalination

Effective dye separation and desalination are critical for the treatment of highly saline textile wastewater with dye mixtures. In this study, a graphene oxide (GO) membrane with a tunable interlayer distance (d) was fabricated to generate clean water via two-stage filtration, namely, the dye/salt separation and desalination stages. In the first stage, under low pressure (e.g., 0.3 MPa), the membrane with a d value of ca. 7.60 Å was suitable for removing the dye from the saline wastewater. The dye and salt (i.e., Na₂SO₄) rejection rates of >99% and <6.5% were achieved, respectively, indicating the significant potential to recycle the dyes from the highly saline dye wastewater. In the second stage, under a higher pressure (e.g., 0.8 MPa), the d value was reduced to ca. 7.15 Å, bestowing the membrane with a desalination function. The desalination rate of a single filtration process could reach up to 51.8% from 1.0 g/L saline (i.e., Na₂SO₄) water. The as-prepared membrane also exhibited excellent practical advantages, including ultrahigh permeability, significant antifouling (against dye) performance, and excellent stability. Furthermore, with the stacking of multistage filtration systems, the proposed membrane technology will be capable of regenerating dye and producing clean water.

Highly-efficient PVDF adsorptive membrane filtration based on chitosan@CNTs-COOH simultaneous removal of anionic and cationic dyes

An adsorptive membrane filtration based on polyvinylidene fluoride (PVDF) with chitosan (CS) and carboxylated carbon nanotubes (CNTs-COOH) is prepared by method of phase conversion, and the PVDF-CS@CNTs-COOH membranes can effectively separate anionic and cationic dye wastewater. Compared to pure PVDF membranes, PVDF-CS@CNTs-COOH increases pure water flux from 36.39 (L·m^-2·h^-1) to 85.25 (L·m^-2·h^-1), an increase of nearly 230%. The membrane exhibits excellent rejection performance in the filtration of six types of dye wastewater. The modified membranes also performed well in terms of rejection of mixed anionic and cationic dyes and also have a high performance in recycling, with a flux of over 94% for both anionic and cationic dyes. In addition, the adsorption curve fitting results showed that the adsorption process was more consistent with the pseudo-second-order adsorption kinetic model and Langmuir mode.

Chitosan Nanocomposite Coatings Containing Chemically Resistant ZnO-SnOx Core-shell Nanoparticles for Photocatalytic Antifouling

Functional nanocomposites with biopolymers and zinc oxide (ZnO) nanoparticles is an emerging application of photocatalysis in antifouling coatings. The reduced chemical stability of ZnO in the acidic media in which chitosan is soluble affects the performance of chitosan nanocomposites in antifouling applications. In this study, a thin shell of amorphous tin dioxide (SnO_x) was grown on the surface of ZnO to form ZnO–SnO_x core–shell nanoparticles that improved the chemical stability of the photocatalyst nanoparticles, as examined at pH 3 and 6. The photocatalytic activity of ZnO–SnO_x in the degradation of methylene blue (MB) dye under visible light showed a higher efficiency than that of ZnO nanoparticles due to the passivation of electronic defects. Chitosan-based antifouling coatings with varying percentages of ZnO or ZnO–SnO_x nanoparticles, with or without the glutaraldehyde (GA) crosslinking of chitosan, were developed and studied. The incorporation of photocatalysts into the chitosan matrix enhanced the thermal stability of the coatings. Through a mesocosm study using running natural seawater, it was found that chitosan/ZnO–SnO_x/GA coatings enabled better inhibition of bacterial growth compared to chitosan coatings alone. This study demonstrates the antifouling potential of chitosan nanocomposite coatings containing core–shell nanoparticles as an effective solution for the prevention of biofouling.

Dual Functional Ultrafiltration Membranes with Enzymatic Digestion and Thermo-Responsivity for Protein Self-Cleaning

Controlling surface⁻protein interaction during wastewater treatment is the key motivation for developing functionally modified membranes. A new biocatalytic thermo-responsive poly vinylidene fluoride (PVDF)/nylon-6,6/poly(N-isopropylacrylamide)(PNIPAAm) ultrafiltration membrane was fabricated to achieve dual functionality of protein-digestion and thermo-responsive self-cleaning. The PVDF/nylon-6,6/PNIPAAm composite membranes were constructed by integrating a hydrophobic PVDF cast layer and hydrophilic nylon-6,6/PNIPAAm nanofiber layer on to which trypsin was covalently immobilized. The enzyme immobilization density on the membrane surface decreased with increasing PNIPAAm concentration, due to the decreased number of amine functional sites. An ultrafiltration study was performed using the synthetic model solution containing BSA/NaCl/CaCl2, where the PNIPAAm containing biocatalytic membranes demonstrated a combined effect of enzymatic and thermo-switchable self-cleaning. The membrane without PNIPAAm revealed superior fouling resistance and self-cleaning with an RPD of 22%, compared to membranes with 2 and 4 wt % PNIPAAm with 26% and 33% RPD, respectively, after an intermediate temperature cleaning at 50 °C, indicating that higher enzyme density offers more efficient self-cleaning than the combined effect of enzyme and PNIPAAm at low concentration. The conformational volume phase transition of PNIPAAm did not affect the stability of immobilized trypsin on membrane surfaces. Such novel surface engineering design offer a promising route to mitigate surface⁻protein contamination in wastewater applications.

Surface-Engineered Biocatalytic Composite Membranes for Reduced Protein Fouling and Self-Cleaning

A new biocatalytic nanofibrous composite ultrafiltration membrane was developed to reduce protein fouling interactions and self-clean the membrane surface. The dual-layer poly(vinylidenefluoride)/nylon-6,6/chitosan composite membrane contains a hydrophobic poly(vinylidenefluoride) cast support layer and a hydrophilic functional nylon-6,6/chitosan nanofibrous surface layer where enzymes were chemically attached. The intrinsic surface chemistry and high surface area of the nanofibers allowed optimal and stable immobilization of trypsin (TR) and α-chymotrypsin enzymes via direct covalent binding. The enzyme immobilization was confirmed by X-ray photoelectron spectroscopy and visualized by confocal microscopy analysis. The prepared biocatalytic composite membranes were nanoporous with superior permeability offering stable protein antiadhesion and self-cleaning properties owing to the repulsive mechanism and digestion of proteins into peptides and amino acids, which was quantified by the gel electrophoresis technique. The TR-immobilized composite membranes exhibited 2.7-fold higher permeance and lower surface protein contamination with 3-fold greater permeance recovery, when compared to the pristine membrane after two ultrafiltration cycles with the model feed solution containing bovine serum albumin/NaCl/CaCl₂. The biocatalytic membranes retained about 50% of the enzyme activity after six reuse cycles but were regenerated to 100% activity after enzyme reloading, leading to a simple and cost-effective water remediation operation. Such surface- and pore-engineered membranes with self-cleaning properties offer a viable solution for severe surface protein contamination in food and water applications.

Durable superhydrophobic and superoleophilic electrospun nanofibrous membrane for oil-water emulsion separation

Marinepollution andindustrial wastewater have caused serious environmental pollution, thereby resulting into an alarming damage to public health in the past decades, hence the high demand for, cost effective, energy-efficient oil-water separation technologies for the removal of oil contaminants from such water. Herein, we report a facile method to fabricate superhydrophobic/superoleophilic membrane by immersing a polyimide (PI)-based nanofibrous membrane into a water/ethanol/ammonia/dopamine mixture, followed by modification with 1H, 1H, 2H, 2H-perfluorodecanethiol (PFDT). The PI-based membrane exhibited water contact angle (WCA) above 153°, while the oil contact angle (OCA) approached 0°, thereby promoting an outstanding chemical stability which sustained its superhydrophobicity when immersed in aqueous solutions at different pH values. Additionally, the PI-based membrane possesses ultrahigh flux, high separation efficiency and good reusability in oil-water separation. The aforementioned properties, as well as the easily scale-up preparation process ensure that this promising as-fabricated membrane can be applied for practical environmental applications including treatment of oily wastewater and oil spillage clean-up.

Exploration of polyelectrolyte incorporated with Triton-X 114 surfactant based osmotic agent for forward osmosis desalination

Selection of a proper osmotic agent is important to make the forward osmosis (FO) feasible. The objective of this study was to enhance FO by lowering reverse solute flux and maintaining high water flux. Poly(propylene glycol) with molecular weight of 725 Da (PPG-725) was found to possess high osmolality, making it a strong candidate for using as a draw agent. In addition, to reduce the partial leakage of draw solute, a non-ionic surfactant (Triton X-114) has been incorporated. Typically, when the hydrophobic tails of Triton X-114 interacted with the membrane surface, a layer on the surface of membrane is produced to constrict the pores and thus minimize the reverse solute flux. In this study, different concentrations of PPG-725 incorporated with different concentrations of Triton X-114 (0.2-0.8 mM) were used to evaluate their osmotic potentials as draw solute. The specific reverse solute flux (J_s/J_w) of 40% PPG-725 doped with Triton X-114 was found to be 0.01 g/L, considerably much lesser than the conventional inorganic draw agents. Finally, membrane distillation operation was utilized as the recovery system in which solute rejection of 97% was achieved for 40% PPG-725/Triton X-114. Therefore, the overall performance supported PPG-725/Triton X-114 as being an efficient draw agent for forward osmosis-membrane distillation hybrid process.

R. R, A. S. Tailored design of polyurethane based fouling-tolerant nanofibrous membrane for water treatment

Polyurethane (PU) nanofibers have gained attention due to their good mechanical properties and water resistance.

Recent developments in polymeric electrospun nanofibrous membranes for seawater desalination

Seawater desalination is a promising strategy that offers an abundant and reliable source of clean fresh water. Nanotechnology, in terms of nanoparticles or electrospun nanofibrous membranes, for water-treatment or desalination applications, is a new concept that has rapidly grown in interest as a method for improving performance by enhancing the surface properties of membranes. Here, we report a critical review on recent developments in membrane-fabrication methods for seawater desalination technologies, focusing mainly on the electrospinning technique. High-performance membranes that address ongoing permeability concerns, while maintaining membrane selectivity, need further study and development. Considering that the world today is faced with energy-shortage crises, these membranes also need to be energy efficient. As electrospinning is considered to be a feasible method for the production of desalination membranes, this technique requires appropriate optimization and the structural properties of the membranes produced need to be controlled in order to tailor their properties to those desired for well-known desalination technologies, such as reverse osmosis and membrane distillation. Moreover, there is a need to understand the influence of membrane structure on performance, and the latest trends in their use as high-performance desalination membranes.

Seawater desalination is a promising strategy that offers an abundant and reliable source of clean fresh water.

Facile modification of electrospun fibrous structures with antifouling zwitterionic hydrogels

Electrospinning technology can easily produce different shaped fibrous structures, making them highly valuable to various biomedical applications. However, surface contamination of biomolecules, cells, or blood has emerged as a significant challenge to the success of electrospun devices, especially artificial blood vessels, catheters and wound dressings etc. Many efforts have been made to resist the surface non-specific biomolecules or cells adsorption, but most of them require complex pre-treatment processes, hard-to-remove metal catalysts or rigorous reaction conditions. In addition, the stability of antifouling coatings, especially in complex conditions, is still a major concern. In this work, inspired by the interpenetrating polymer network and reinforced concrete structure, an efficient and facile strategy for modifying hydrophobic electrospun meshes and tubes with antifouling zwitterionic hydrogels has been introduced. The resulting products could efficiently resist the adhesion of proteins, cells, or even fresh whole blood. Meanwhile, they could maintain the shapes and mechanical strength of the original electrospun structures. Furthermore, the hydrogel structures could retain stable in a physiological condition for at least 3 months. This paper provided a general antifouling and hydrophilicity surface modification strategy for various fibrous structures, and could be of great value for many biomedical applications where antifouling properties are critical.

Nanofiber Composite Membrane with Intrinsic Janus Surface for Reversed-Protein-Fouling Ultrafiltration

Janus nanofiber based composite ultrafiltration (UF) membranes were fabricated via a two-step method, i.e., consecutive electrospinning of hydrophilic nylon-6,6/chitosan nanofiber blend and conventional casting of hydrophobic poly(vinylidene difluoride) (PVDF) dope solution. The as-developed PVDF/nylon-6,6/chitosan membranes were investigated for its morphology using Scanning Electron Microscopy (SEM) by which 18 wt % PVDF was chosen as the optimum base polymer concentration due to optimal degree of integration of cast and nanofiber layers. This membrane was benchmarked against the pure PVDF and PVDF/nylon-6,6 membranes in terms of surface properties, permeability, and its ability to reverse protein fouling. The improved hydrophilicity of the PVDF/nylon-6,6/chitosan membrane was revealed from the 72% reduction in the initial water contact angle compared to the pure PVDF benchmark, due to the incorporation of intrinsic hydrophilic hydroxyl and amine functional groups on the membrane surface confirmed by FTIR. The integration of the nanofiber and cast layers has led to altered pore arrangements offering about 93% rejection of bovine serum albumin (BSA) proteins with a permeance of 393 L·m^-2·h^-1·bar^-1 in cross-flow filtration experiments; while the PVDF benchmark only had a BSA rejection of 67% and a permeance of 288 L·m^-2·h^-1·bar^-1. The PVDF/nylon-6,6/chitosan membrane exhibited high fouling propensity with 2.2 times higher reversible fouling and 78% decrease in the irreversible fouling compared to the PVDF benchmark after 4 h of filtration with BSA foulants.