Design strategy of poly(vinylidene fluoride) membranes for water treatment

Slight-Crosslinking: Opening a New Journey for the Intrinsic Elastification of Ferroelectric Polymers

Elastic electronic materials are essential components in the next generation of wearable devices and soft robots. However, the development of elastic ferroelectric materials has lagged behind that of conductive and semiconductive materials. The successful realization of intrinsically elastic ferroelectrics through slight-crosslinking has opened a new path for making ferroelectric materials elastic. Given the critical need for materials that combine excellent elasticity with robust ferroelectric properties in the field of elastic electronics, we explore various crosslinking techniques and their performance characteristics. We believe that this cutting-edge research direction holds substantial value for both fundamental studies and practical applications.

Fabrication and Performance of PVAc-Incorporated Porous Self-Standing Zeolite-Based Geopolymer Membranes for Lead (Pb(II)) Removal in Water Treatment

This study explores the fabrication, structural characteristics, and performance of an innovative porous geopolymer membrane made from waste natural zeolite powder for Pb(II) removal, with potential applications in wastewater treatment. A hybrid geopolymer membrane incorporating polyvinyl acetate (PVAc) (10, 20, and 30 wt.%) was synthesized and thermally treated at 300 °C to achieve a controlled porous architecture. Characterization techniques, including Fourier-transform infrared spectroscopy (FTIR), revealed the disappearance of characteristic C=O and C-H stretching bands (~1730 cm-1 and ~2900 cm-1, respectively), confirming the full degradation of PVAc. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) indicated a total mass loss of approximately 14.5% for the sample with PVAc 20 wt.%, corresponding to PVAc decomposition and water loss. Energy-dispersive spectroscopy (EDS) elemental mapping showed the absence of carbon residues post-annealing, further validating complete PVAc removal. X-ray diffraction (XRD) provided insight into the crystalline phases of the raw zeolite and geopolymer structure. Once PVAc removal was confirmed, the second phase of characterization assessed the membrane's mechanical properties and filtration performance. The thermally treated membrane, with a thickness of 2.27 mm, exhibited enhanced mechanical properties, measured with a nano-indenter, showing a hardness of 1.8 GPa and an elastic modulus of 46.7 GPa, indicating improved structural integrity. Scanning electron microscopy (SEM) revealed a well-defined porous network. Filtration performance was evaluated using a laboratory-scale dead-end setup for Pb(II) removal. The optimal PVAc concentration was determined to be 20 wt.%, resulting in a permeation rate of 78.5 L/(m2·h) and an 87% rejection rate at an initial Pb(II) concentration of 50 ppm. With increasing Pb(II) concentrations, the flux rates declined across all membranes, while maximum rejection was achieved at 200 ppm. FTIR and EDS analyses confirmed Pb(II) adsorption onto the zeolite-based geopolymer matrix, with elemental mapping showing a uniform Pb(II) distribution across the membrane surface. The next step is to evaluate the membrane's performance in a multi-cation water treatment environment, assessing the sorption kinetics and its selectivity and efficiency in removing various heavy metal contaminants from complex wastewater systems.

Membrane-based adsorbent materials for uranium extraction from seawater: recent progress and future prospects

The global energy shortage is becoming increasingly severe, making it urgent to address the energy deficit. Nuclear energy is considered a green, efficient and clean energy source. The reserves of uranium, an essential strategic nuclear fuel resource, have become pivotal in addressing the energy crisis. Compared to uranium resources on land, the ocean is rich in uranium. Therefore, uranium extraction from seawater has become an ideal choice. However, the variety of competing ions in seawater, its high salinity and the complex marine environment make uranium extraction from seawater a huge challenge. In the context of assessing the economics and sustainability of the entire uranium separation process, membrane-based adsorbents are considered ideal materials for large-scale uranium extraction from seawater due to their ease of collection and reuse. This review discusses different types of membrane-based adsorbent materials, including modified non-woven membranes, phase conversion membranes, and other types of membrane materials. In addition, this review summarizes recent studies on the use of membrane-based adsorbents for extracting uranium from seawater and the prospects for their development. With the rapid development of membrane-based adsorbents for uranium extraction from seawater, this review also discusses the challenges and future prospects of this frontier field.

Transfiguration of discarded PVDF ultrafiltration membranes: Optimization of pyrolysis parameters for high-value char production

Disposing vast amounts of non-biodegradable wastes presents engineering and economic challenges to environmental management globally. Concomitantly, recycling and upcycling of non-biodegradable materials can play a crucial role in sustainable waste management, reducing the need for raw material extraction and energy-intensive manufacturing. Accordingly, this study aimed to explore the utilization of discarded polyvinylidene fluoride (PVDF) ultrafiltration membranes for char production via optimized pyrolysis. The Generalized Reduced Gradient (GRG) optimization method was applied to predict the optimal final temperature (T) and residence time (t) to achieve the maximum membrane char (MC) iodine number under reasonable conditions. Factorial analysis revealed curvature in the model with a p-value of 0.001 at a 95 % confidence interval, indicating the potential applicability of the response surface method (RSM). The optimized pyrolysis (584 °C; 111 min) achieved an average yield of 31.3 ± 2.6 % of MC with an iodine number of 242.35 mg/g. The structural, surface, and textural properties of PVDF fibers and MC were extensively characterized. Thermal analysis of discarded PVDF confirmed the oxidative breakdown of the fluorinated polymer and the revocation of the C-F bond. Moreover, the Raman and FTIR spectral analysis revealed the coexistence of β- and γ- crystalline phases in the PVDF fiber. Consequently, the produced MC demonstrated superior carbon properties and high potential application for various industrial and environmental purposes, aligning with the circular economy approach for reutilizing discarded PVDF membranes.

A Novel Delayed Phase Inversion Strategy Enables Green PVDF Membranes for Membrane Distillation

Polyvinylidene fluoride (PVDF) membranes are extensively utilized in membrane distillation (MD) for water treatment. However, traditional methods easily form asymmetrical membranes with dense skin layers that are detrimental to membrane flux. Herein, an eco-friendly PVDF membrane was fabricated by utilizing a delayed phase separation process without using any pore-forming agents. In addition, methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean) was used as a green solvent without posing risks to humans and the environment. It was demonstrated that the PVDF concentration is crucial in influencing the microstructures and performance of the resulting membranes. As the PVDF concentration increased, the morphology changed significantly, resulting in a reduction of pore size. When feeding the device with NaCl solution at a concentration of 35 g/L, the MD water vapor flux reached 18.49 kg·m-2·h-1, while maintaining a salt rejection of over 99.97% during the continuous operation for 24 h. This work presented a method for producing green PVDF membranes via delayed phase inversion with satisfactory water vapor flux and salt rejection, highlighting their prospect for effective applications in MD for water treatment.

Wastewater treatment by algae-based membrane bioreactors: a review of the arrangement of a membrane reactor, physico-chemical properties, advantages and challenges

Reducing wastewater contaminants is an emerging area of particular concern for many industrialized and developing countries in improving the ecological quality of their water sources. In this case, the use of algae-based microbial reactors for wastewater treatment has attracted increasing attention in recent years. The advantages of both conventional microbial membrane bioreactors (MBRs) and algae-based treatment are combined in algae-based MBRs. According to the literature, previous studies did not fully discuss the techniques and performance of algae-based bioreactor systems in the treatment of wastewater. In particular, little attention has been paid to the types of waste, their consequences, and the ways in which they are treated. This makes it more difficult to develop and scale up efficient systems to treat waste discharge from industry, agriculture, and urban areas. Thus, the objective of this study is to critically evaluate algae as a valuable biological resource for wastewater treatment, with the goal of reducing emerging contaminants and increasing the chemical oxygen demand (COD) in wastewater. The most common wastewater treatment techniques employed for addressing these wastes are examined together with a brief discussion on contaminants in wastewater. Furthermore, algae-based wastewater treatment arrangements, particularly hybrid configurations, are carefully studied in relation to techniques for removing contaminants using algae. After analysing the key physicochemical characteristics that affect the ability of algal-bioremediation to remove developing contaminants, the benefits of algal-bioremediation systems are compared to those of other techniques. Lastly, an investigation is conducted into the technological difficulties associated with employing algal-bioremediation systems to eliminate emerging contaminants.

Multienzyme Immobilization on PVDF Membrane via One-Step Mussel-Inspired Method: Enhancing Fouling Resistance and Self-Cleaning Efficiency

Immobilizing different enzymes on membranes can result in biocatalytic active membranes with a self-cleaning capacity toward a complex mixture of foulants. The membrane modification can reduce fouling and enhance filtration performance. Protease, lipase, and amylase were immobilized on poly(vinylidene fluoride) (PVDF) microfiltration membranes using a polydopamine coating in a one-step method. The concentrations of polydopamine precursor and enzymes were optimized during the immobilization. The higher hydrolytic activities were obtained using 0.2 mg/mL of dopamine hydrochloride and 4 mg/mL of enzymes: 0.90 mgstarch/min·cm2 for amylase, 10.16 nmoltyrosine/min·cm2 for protease, and 20.48 µmolp-nitrophenol/min·cm2 for lipase. Filtration tests using a protein, lipid, and carbohydrate mixture showed that the modified membrane retained 41%, 29%, and 28% of its initial water permeance (1808 ± 39 L/m2·h·bar) after three consecutive filtration cycles, respectively. In contrast, the pristine membrane (initial water permeance of 2016 ± 40 L/m2·h·bar) retained only 23%, 12%, and 8%. Filtrations of milk powder solution were also performed to simulate dairy industry wastewater: the modified membrane maintained 28%, 26%, and 26% of its initial water permeance after three consecutive filtration cycles, respectively, and the pristine membrane retained 34%, 21%, and 7%. The modified membrane showed increased fouling resistance against a mixture of foulants and presented a similar water permeance after three cycles of simulated dairy wastewater filtration. Membrane fouling is reduced by the immobilized enzymes through two mechanisms: increased membrane hydrophilicity (evidenced by the reduced water contact angle after modification) and the enzymatic hydrolysis of foulants as they accumulate on the membrane surface.

Cyclodextrin-modified PVDF membranes with improved anti-fouling performance

The design of hydrophilic polyvinylidene fluoride (PVDF) membranes with anti-fouling properties has been explored for decades. Surface modification and blending are typical strategies to tailor the hydrophilicity of PVDF membranes. Herein, cyclodextrin was used to improve the antifouling performance of PVDF membranes. Cyclodextrin-modified PVDF membranes were prepared by coupling PVDF amination (blending with branched polyethyleneimine) and activated cyclodextrin grafting. The blending of PEI in the PVDF casting solution preliminarily aminated the PVDF, resulting in PEI-crosslinked/grafted PVDF membranes after phase inversion. Aldehydes groups on cyclodextrin, introduced by oxidation, endow cyclodextrin to be grafted on the aminated PVDF membrane by the formation of imines. Borch reduction performed on the activated cyclodextrin-grafted PVDF membrane converted the imine bonds to secondary amines, ensuring the membrane stability. The resulting membranes possess excellent antifouling performance, with a lower protein adsorption capacity (5.7 μg/cm2, indicated by Bovine Serum Albumin (BSA)), and a higher water flux recovery rate (FRR = 96%). The proposed method provides a facial strategy to prepare anti-fouling PVDF membranes.

Piezoceramic membrane with built-in ultrasound for reactive oxygen species generation and synergistic vibration anti-fouling

Piezoceramic membranes have emerged as a prominent solution for membrane fouling control. However, the prevalent use of toxic lead and limitations of vibration-based anti-fouling mechanism impede their wider adoption in water treatment. This study introduces a Mn/BaTiO3 piezoceramic membrane, demonstrating a promising in-situ anti-fouling efficacy and mechanism insights. When applied to an Alternating Current at a resonant frequency of 20 V, 265 kHz, the membrane achieves optimal vibration, effectively mitigating various foulants such as high-concentration oil (2500 ppm, including real industrial oil wastewater), bacteria and different charged inorganic colloidal particles, showing advantages over other reported piezoceramic membranes. Importantly, our findings suggest that the built-in ultrasonic vibration of piezoceramic membranes can generate reactive oxygen species. This offers profound insights into the distinct anti-fouling processes for organic and inorganic wastewater, supplementing and unifying the traditional singular vibrational anti-fouling mechanism of piezoceramic membranes, and potentially propelling the development of piezoelectric catalytic membranes.

In Situ-Grown Al2O3 Nanoflowers and Hydrophobic Modification Enable Superhydrophobic SiC Ceramic Membranes for Membrane Distillation

Membrane distillation (MD) is considered a promising technology for desalination. In the MD process, membrane pores are easily contaminated and wetted, which will degrade the permeate flux and salt rejection of the membrane. In this work, SiC ceramic membranes were used as the supports, and an Al2O3 micro-nano structure was constructed on its surface. The surface energy of Al2O3@SiC micro-nano composite membranes was reduced by organosilane grafting modification. The effective deposition of Al2O3 nanoflowers on the membrane surface increased membrane roughness and enhanced the anti-fouling and anti-wetting properties of the membranes. Simultaneously, the presence of nanoflowers also regulated the pore structures and thus decreased the membrane pore size. In addition, the effects of Al2(SO4)3 concentration and sintering temperature on the surface morphology and performance of the membranes were investigated in detail. It was demonstrated that the water contact angle of the resulting membrane was 152.4°, which was higher than that of the pristine membrane (138.8°). In the treatment of saline water containing 35 g/L of NaCl, the permeate flux was about 11.1 kg⋅m-2⋅h-1 and the salt rejection was above 99.9%. Note that the pristine ceramic membrane cannot be employed for MD due to its larger membrane pore size. This work provides a new method for preparing superhydrophobic ceramic membranes for MD.

Hydrophilic Modification of Polytetrafluoroethylene (PTFE) Capillary Membranes with Chemical Resistance by Constructing Three-Dimensional Hydrophilic Networks

Polytetrafluoroethylene (PTFE) capillary membranes, known for the great chemical resistance and thermal stability, are commonly used in membrane separation technologies. However, the strong hydrophobic property of PTFE limits its application in water filtration. This study introduces a method whereby acrylamide (AM), N, N-methylene bisacrylamide (MBA), and vinyltriethoxysilane (VTES) undergo free radical copolymerization, followed by the hydrolysis-condensation of silane bonds, resulting in the formation of hydrophilic three-dimensional networks physically intertwined with the PTFE capillary membranes. The modified PTFE capillary membranes prepared through this method exhibit excellent hydrophilic properties, whose water contact angles are decreased by 24.3-61.2%, and increasing pure water flux from 0 to 1732.7-2666.0 L/m2·h. The enhancement in hydrophilicity of the modified PTFE capillary membranes is attributed to the introduction of hydrophilic groups such as amide bonds and siloxane bonds, along with an increase in surface roughness. Moreover, the modified PTFE capillary membranes exhibit chemical resistance, maintaining the hydrophilicity even after immersion in strong acidic (3 wt% HCl), alkaline (3 wt% NaOH), and oxidative (3 wt% NaClO) solutions for 2 weeks. In conclusion, this promising method yields modified PTFE capillary membranes with great hydrophilicity and chemical resistance, presenting substantial potential for applications in the field of water filtration.

PVDF-Based Piezo-Catalytic Membranes-A Net-Zero Emission Approach towards Textile Wastewater Purification

Among the various water purification techniques, advancements in membrane technology, with better fabrication and analysis, are receiving the most research attention. The piezo-catalytic degradation of water pollutants is an emerging area of research in water purification technology. This review article focuses on piezoelectric polyvinylidene difluoride (PVDF) polymer-based membranes and their nanocomposites for textile wastewater remediation. At the beginning of this article, the classification of piezoelectric materials is discussed. Among the various membrane-forming polymers, PVDF is a piezoelectric polymer discussed in detail due to its exceptional piezoelectric properties. Polyvinylidene difluoride can show excellent piezoelectric properties in the beta phase. Therefore, various methods of β-phase enhancement within the PVDF polymer and various factors that have a critical impact on its piezo-catalytic activity are briefly explained. This review article also highlights the major aspects of piezoelectric membranes in the context of dye degradation and a net-zero approach. The β-phase of the PVDF piezoelectric material generates an electron-hole pair through external vibrations. The possibility of piezo-catalytic dye degradation via mechanical vibrations and the subsequent capture of the resulting CO2 and H2 gases open up the possibility of achieving the net-zero goal.

Enhanced management and antifouling performance of a novel NiFe-LDH@MnO2/PVDF hybrid membrane for efficient oily wastewater treatment

Layered double hydroxides (LDHs) have gained significant recognition for their facile synthesis and super-hydrophilic two-dimensional (2D) structure to fabricate antifouling membranes for oily wastewater separation. However, conventional PVDF membranes, due to their hydrophobic nature and inert matrix, often exhibit insufficient permeance and compatibility. In this study, a novel NiFe-LDH@MnO2/PVDF membrane was synthesized using ultrasonic, redox, and microwave-hydrothermal processes. This innovative approach cultivated grass-like NiFe-LDH@MnO2 nanoparticles within an inert PVDF matrix, promoting the growth of highly hydrophilic composites. The presence of NiFe-LDH@MnO2 resulted in pronounced enhancements in surface morphology, interfacial wettability, and oil rejection for the fabricated membrane. The optimal NiFe-LDH@MnO2/PVDF-2 membrane exhibited an extremely high pure water flux (1364 L m-2•h-1), and increased oil rejection (from 81.2% to 93.5%) without sacrificing water permeation compared to the original PVDF membrane. Additionally, the NiFe-LDH@MnO2/PVDF membrane demonstrated remarkable antifouling properties, evident by an exceptional fouling resistance ratio of 96.8% following slight water rinsing. Mechanistic insights into the enhanced antifouling performance were elucidated through a comparative "semi-immersion" investigation. The facile synthesis method, coupled with the improved membrane performance, highlights the potential application prospects of this hybrid membrane in emulsified oily wastewater treatment and environmental remediation.

Modified polymer membranes for the removal of pharmaceutical active compounds in wastewater and its mechanism-A review

Membrane technology can play a suitable role in removing pharmaceutical active compounds since it requires low energy and simple operation. Even though membrane technology has progressed for wastewater applications nowadays, modifying membranes to achieve the strong desired membrane performance is still needed. Thus, this study overviews a comprehensive insight into the application of modified polymer membranes to remove pharmaceutical active compounds from wastewater. Biotoxicity of pharmaceutical active compounds is first prescribed to gain deep insight into how membranes can remove pharmaceutical active compounds from wastewater. Then, the behavior of the diffusion mechanism can be concisely determined using mass transfer factor model that represented by β and B with value up to 2.004 g h mg-1 and 1.833 mg g-1 for organic compounds including pharmaceutical active compounds. The model refers to the adsorption of solute to attach onto acceptor sites of the membrane surface, external mass transport of solute materials from the bulk liquid to the membrane surface, and internal mass transfer to diffuse a solute toward acceptor sites of the membrane surface with evidenced up to 0.999. Different pharmaceutical compounds have different solubility and relates to the membrane hydrophilicity properties and mechanisms. Ultimately, challenges and future recommendations have been presented to view the future need to enhance membrane performance regarding fouling mitigation and recovering compounds. Afterwards, the discussion of this study is projected to play a critical role in advance of better-quality membrane technologies for removing pharmaceutical active compounds from wastewater in an eco-friendly strategy and without damaging the ecosystem.

Potential and Design Parameters of Polyvinylidene Fluoride in Gear Applications

(1) Background: With the ever-increasing number of polymer materials and limited data on polymer gear calculations, designers are often required to perform extensive experimental testing in order to establish reliable operational data for specific gear applications. This research investigates the potential of a Polyvinyldene fluoride (PVDF) polymer material in gear applications, considering various loading conditions and different types of gear transmission configurations, including both self-mated mesh and steel/PVDF mesh. (2) Methods: PVDF gear samples were tested on a specially designed test rig that enables active torque control and temperature monitoring in order to obtain the necessary design parameters and failure modes. Each test for certain load conditions was repeated five times, and to fully investigate the potential of PVDF gear samples, comparative testing was performed for Polyoxymethylene (POM) gear. (3) Results: Tribological compatibility, tooth load capacity, and lifespan assessment, along with the types of failure, which, for some configurations, include several types of failures, such as wear and melting, were determined. Temperature monitoring data were used to estimate the coefficient of friction at the tooth contact of analyzed gear pairs, while optical methods were used to determine a wear coefficient. (4) Conclusions: The tribological compatibility of polymer gear pairs needs to be established in order to design a gear pair for a specific application. PVDF gear samples mated with steel gear showed similar lifespan properties compared to POM samples. Temperature monitoring and optical methods serve as a basis for the determination of the design parameters. PVDF is an appropriate material to use in gear applications, considering its comparable properties with POM. The particular significance of this research is reflected in the establishment of the design parameters of PVDF gear, as well as in the analysis of the potential of the PVDF material in gear applications, which gives exceptional significance to the current knowledge on polymer gears, considering that the PVDF material has not previously been analyzed in gear applications.

Adsorption of Diclofenac and Its UV Phototransformation Products in an Aqueous Solution on PVDF: A Molecular Modeling Study

The presence of pharmaceuticals in drinking water has generated considerable scientific interest in potential improvements to polymeric membranes for water purification at the nanoscale. In this work, we investigate the adsorption of diclofenac and its ultraviolet (UV) phototransformation products on amorphous and crystalline poly(vinylidene difluoride) (PVDF) membrane surfaces at the nanoscale using molecular modeling. We report binding affinities by determining the free energy landscape via the extended adaptive biasing force method. The high binding affinities of the phototransformation products found are consistent with qualitative experimental results. For diclofenac, we found similar or better affinities than those for the phototransformation products, which seems to be in contrast to the experimental findings. This discrepancy can only be explained if the maximum adsorption density of diclofenac is much lower than that of the products. Overall, negligible differences between the adsorption affinities of the crystalline phases are observed, suggesting that no tuning of the PVDF surfaces is necessary to optimize filtration capabilities.

Microfluidic-Based Continuous Fabrication of Ultrathin Hydrogel Films with Controllable Thickness

Ultrathin hydrogel films composed of cross-linked polymer networks swollen by water, with soft and moisturized features similar to biological tissue, play a vital role in flexible biosensors and wearable electronics. However, achieving efficient and continuous fabrication of such films remains a challenge. Here, we present a microfluidic-based strategy for the continuous fabrication of free-standing ultrathin hydrogel films by using laminar flow, which can be precisely controlled in the micrometer scale. Compared with conventional methods, the microfluidic-based method shows advantages in producing hydrogel films with a high homogeneity as well as maintaining the structural integrity, without the need of supporting substrates and sophisticated equipment. This strategy allows the precise control over the thickness of the hydrogel films ranging from 15 ± 0.2 to 39 ± 0.5 μm, by adjusting the height of the microfluidic channels, with predictable opportunities for scaling up. Therefore, our strategy provides a facile route to produce advanced thin polymer films in a universal, steerable, and scalable manner and will promote the applications of thin polymer films in biosensors and wearable electronics.

Modified poly(vinylidene fluoride) nanomembranes for dye removal from water - A review

Water contamination due to soluble synthetic dyes has serious concerns. Membrane-based wastewater treatments are emerging as a preferred choice for removing dyes from water. Poly(vinylidene fluoride) (PVDF)-based nanomembranes have gained much popularity due to their favorable features. This review explores the application of PVDF-based nanomembranes in synthetic dye removal through various treatments. Different fabrication methods to obtain high performance PVDF-based nanomembranes were discussed under surface coating and blending methods. Studies related to use of PVDF-based nanomembranes in adsorption, filtration, catalysis (oxidant activation, ozonation, Fenton process and photocatalysis) and membrane distillation have been elaborately discussed. Nanomaterials including metal compounds, metals, (synthetic/bio)polymers, metal organic frameworks, carbon materials and their composites were incorporated in PVDF membrane to enhance its performance. The advantages and limitations of incorporating nanomaterials in PVDF-based membranes have been highlighted. The influence of nanomaterials on the surface features, mechanical strength, hydrophilicity, crystallinity and catalytic ability of PVDF membrane was discussed. The conclusion of this literature review was given along with future research.

A Competitive Study Using Electrospinning and Phase Inversion to Prepare Polymeric Membranes for Oil Removal

Polyacrylonitrile (PAN) is a popular polymer that can be made into membranes using various techniques, such as electrospinning and phase inversion. Electrospinning is a novel technique that produces nonwoven nanofiber-based membranes with highly tunable properties. In this research, electrospun PAN nanofiber membranes with various concentrations (10, 12, and 14% PAN/dimethylformamide (DMF)) were prepared and compared to PAN cast membranes prepared by the phase inversion technique. All of the prepared membranes were tested for oil removal in a cross-flow filtration system. A comparison between these membranes' surface morphology, topography, wettability, and porosity was presented and analyzed. The results showed that increasing the concentration of the PAN precursor solution increases surface roughness, hydrophilicity, and porosity and, consequently, enhances the membrane performance. However, the PAN cast membranes showed a lower water flux when the precursor solution concentration increased. In general, the electrospun PAN membranes performed better in terms of water flux and oil rejection than the cast PAN membranes. The electrospun 14% PAN/DMF membrane gave a water flux of 250 LMH and a rejection of 97% compared to the cast 14% PAN/DMF membrane, which showed a water flux of 117 LMH and 94% oil rejection. This is mainly because the nanofibrous membrane showed higher porosity, higher hydrophilicity, and higher surface roughness compared to the cast PAN membranes at the same polymer concentration. The porosity of the electrospun PAN membrane was 96%, while it was 58% for the cast 14% PAN/DMF membrane.

Versatile Silver-Nanoparticle-Impregnated Membranes for Water Treatment: A Review

Increased affordability, smaller footprint, and high permeability quality that meets stringent water quality standards have accelerated the uptake of membranes in water treatment. Moreover, low pressure, gravity-based microfiltration (MF) and ultrafiltration (UF) membranes eliminate the use of electricity and pumps. However, MF and UF processes remove contaminants by size exclusion, based on membrane pore size. This limits their application in the removal of smaller matter or even harmful microorganisms. There is a need to enhance the membrane properties to meet needs such as adequate disinfection, flux amelioration, and reduced membrane fouling. To achieve these, the incorporation of nanoparticles with unique properties in membranes has potential. Herein, we review recent developments in the impregnation of polymeric and ceramic microfiltration and ultrafiltration membranes with silver nanoparticles that are applied in water treatment. We critically evaluated the potential of these membranes in enhanced antifouling, increased permeability quality and flux compared to uncoated membranes. Despite the intensive research in this area, most studies have been performed at laboratory scale for short periods of time. There is a need for studies that assess the long-term stability of the nanoparticles and the impact on disinfection and antifouling performance. These challenges are addressed in this study and future directions.

Next-generation ultrafiltration membranes: A review of material design, properties, recent progress, and challenges

Membrane technology utilizing ultrafiltration (UF) processes has emerged as the most widely used and cost-effective simple process in many industrial applications. The industries like textiles and petroleum refining are promptly required membrane based UF processes to alleviate the potential environmental threat caused by the generation of various wastewater. At the same time, major limitations such as material selection as well as fouling behavior challenge the overall performance of UF membranes, particularly in wastewater treatment. Therefore, a complete discussion on material design with structural property relation and separation performance of UF membranes is always exciting. This state-of-the-art review has exclusively focused on the development of UF membranes, the material design, properties, progress in separation processes, and critical challenges. So far, most of the review articles have examined the UF membrane processes through a selected track of paving typical materials and their limited applications. In contrast, in this review, we have exclusively aimed at comprehensive research from material selection and fabrication methods to all the possible applications of UF membranes, giving more attention and theoretical understanding to the complete development of high-performance UF systems. We have discussed the methodical engineering behind the development of UF membranes regardless of their materials and fabrication mechanisms. Identifying the utility of UF membrane systems in various applications, as well as their mode of separation processes, has been well discussed. Overall, the current review conveys the knowledge of the present-day significance of UF membranes together with their future prospective opportunities whilst overcoming known difficulties in many potential applications.

Research Progress of Water Treatment Technology Based on Nanofiber Membranes

In the field of water purification, membrane separation technology plays a significant role. Electrospinning has emerged as a primary method to produce nanofiber membranes due to its straightforward, low cost, functional diversity, and process controllability. It is possible to flexibly control the structural characteristics of electrospun nanofiber membranes as well as carry out various membrane material combinations to make full use of their various properties, including high porosity, high selectivity, and microporous permeability to obtain high-performance water treatment membranes. These water separation membranes can satisfy the fast and efficient purification requirements in different water purification applications due to their high filtration efficiency. The current research on water treatment membranes is still focused on creating high-permeability membranes with outstanding selectivity, remarkable antifouling performance, superior physical and chemical performance, and long-term stability. This paper reviewed the preparation methods and properties of electrospun nanofiber membranes for water treatment in various fields, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, and other special applications. Lastly, various antifouling technologies and research progress of water treatment membranes were discussed, and the future development direction of electrospun nanofiber membranes for water treatment was also presented.

Waste to treasure: Superwetting foam enhanced by bamboo powder for sustainable on-demand oil-water separation

Low-cost and sustainable superwetting materials are urgently required for oily wastewater treatment. Many poly(vinylidene fluoride) (PVDF)-based materials have been designed for oil-water separation. However, their fabrication processes frequently require toxic organic solvents and high-cost materials (e.g., carbon tubes and graphene). In this study, a highly porous and superhydrophobic bamboo powders (BP)-enhanced PVDF foam (SBPF) was fabricated via an organic solvent-free process. The SBPF exhibits efficient adsorption and recovery for various oils and organic solvents. Moreover, the SBPF shows high adsorption and separation performance under ultraviolet exposure and turbulent environments. It can also be used for water-in-oil emulsions separation, with a high separation efficiency more than 99.3 % under gravity. Interestingly, the amphiphilic PVDF-BP foam (ABPF) shows underwater superoleophobicity and underoil superhydrophobicity after delignification of SBPF. Owing to the conversion of wettability, it presents a high performance in treatment of both surfactant-stabilied water-in-oil and oil-in-water emulsions with the high separation efficiency achieving more than 99.6 % and 99.5 % respectively under gravity. In addition, the ABPF shows a high separation performance even after ten cycles. Hence, this fabricated organic solvent-free foams are promising candidates for sustainable on-demand separation of oils or organic solvents and water in complex environments.

Study of Membranes with Nanotubes to Enhance Osmosis Desalination Efficiency by Using Machine Learning towards Sustainable Water Management

Water resources management is one of the most important issues nowadays. The necessity of sustainable management of water resources, as well as finding a solution to the water shortage crisis, is a question of our survival on our planet. One of the most important ways to solve this problem is to use water purification systems for wastewater resources, and one of the most necessary reasons for the research of water desalination systems and their development is the problem related to water scarcity and the crisis in the world that has arisen because of it. The present study employs a carbon nanotube-containing nanocomposite to enhance membrane performance. Additionally, the rise in flow brought on by a reduction in the membrane's clogging surface was investigated. The filtration of brackish water using synthetic polyamide reverse osmosis nanocomposite membrane, which has an electroconductivity of 4000 Ds/cm, helped the study achieve its goal. In order to improve porosity and hydrophilicity, the modified raw, multi-walled carbon nanotube membrane was implanted using the polymerization process. Every 30 min, the rates of water flow and rejection were evaluated. The study's findings demonstrated that the membranes have soft hydrophilic surfaces, and by varying concentrations of nanocomposite materials in a prescribed way, the water flux increased up to 30.8 L/m²h, which was notable when compared to the water flux of the straightforward polyamide membranes. Our findings revealed that nanocomposite membranes significantly decreased fouling and clogging, and that the rejection rate was greater than 97 percent for all pyrrole-based membranes. Finally, an artificial neural network is utilized to propose a predictive model for predicting flux through membranes. The model benefits hyperparameter tuning, so it has the best performance among all the studied models. The model has a mean absolute error of 1.36% and an R² of 0.98.

Fluoropolymer Membranes for Membrane Distillation and Membrane Crystallization

Fluoropolymer membranes are applied in membrane operations such as membrane distillation and membrane crystallization where hydrophobic porous membranes act as a physical barrier separating two phases. Due to their hydrophobic nature, only gaseous molecules are allowed to pass through the membrane and are collected on the permeate side, while the aqueous solution cannot penetrate. However, these two processes suffer problems such as membrane wetting, fouling or scaling. Membrane wetting is a common and undesired phenomenon, which is caused by the loss of hydrophobicity of the porous membrane employed. This greatly affects the mass transfer efficiency and separation efficiency. Simultaneously, membrane fouling occurs, along with membrane wetting and scaling, which greatly reduces the lifespan of the membranes. Therefore, strategies to improve the hydrophobicity of membranes have been widely investigated by researchers. In this direction, hydrophobic fluoropolymer membrane materials are employed more and more for membrane distillation and membrane crystallization thanks to their high chemical and thermal resistance. This paper summarizes different preparation methods of these fluoropolymer membrane, such as non-solvent-induced phase separation (NIPS), thermally-induced phase separation (TIPS), vapor-induced phase separation (VIPS), etc. Hydrophobic modification methods, including surface coating, surface grafting and blending, etc., are also introduced. Moreover, the research advances on the application of less toxic solvents for preparing these membranes are herein reviewed. This review aims to provide guidance to researchers for their future membrane development in membrane distillation and membrane crystallization, using fluoropolymer materials.

Designing of nanotextured inorganic-organic hybrid PVDF membrane for efficient separation of the oil-in-water emulsions

The separation of the emulsified oil/water is one of the critical environmental challenges. The PVDF membranes have been found helpful for separation, but rapid fouling makes them less attractive in treating oil-in-water emulsions. The design of antifouling membranes has become an area of deep interest. Herein, developing a novel modified PVDF ultrafiltration membrane was reported by doping the pyrrole and solidifying it in a ferric-containing coagulation bath, resulting in a unique nanotextured PVDF membrane (CCB-Fe/PP_np-PVDF) to separate the oil/water emulsions. The resultant CCB-Fe/PP_np-PVDF membrane was thoroughly characterized using the FTIR, FE-SEM, EDX, mapping, AFM, and contact analyzer. The hydrophilicity of the CCB-Fe/PP_np-PVDF was substantially improved, and the water contact angle was reduced from 81֯ ± 0.9֯ to 44֯ ± 1.7֯. The CCB-Fe/PPnp-PVDF membrane flux increased by 121% compared to the pristine PVDF membrane, with high separation efficiency of 99%. The hydrophilic nanotextured surface of the CCB-Fe/PP_np-PVDF membrane showed good antifouling behavior, with a flux recovery ratio (FRR) of more than 96%. Irreversible flux was just less than 4%. The high flux recovery ratio indicated that the nanotextured surface produced by the Fe/PP_np had prevented the blockage of the membrane pores and compact cake layer formation, which makes it an excellent membrane for oil/water emulsion separation. This strategy can be adopted for designing advanced membranes for separation applications.

Brief Review of PVDF Properties and Applications Potential

Currently, there is an ever-growing interest in carbon materials with increased deformation-strength, thermophysical parameters. Due to their unique physical and chemical properties, such materials have a wide range of applications in various industries. Many prospects for the use of polymer composite materials based on polyvinylidene fluoride (PVDF) for scientific and technical purposes explain the plethora of studies on their characteristics "structure-property", processing, application and ecology which keep appearing. Building a broader conceptual picture of new generation polymeric materials is feasible with the use of innovative technologies; thus, achieving a high level of multidisciplinarity and integration of polymer science; its fundamental problems are formed, the solution of which determines a significant contribution to the natural-scientific picture of the modern world. This review provides explanation of PVDF advanced properties and potential applications of this polymer material in its various forms. More specifically, this paper will go over PVDF trademarks presently available on the market, provide thorough overview of the current and potential applications. Last but not least, this article will also delve into the processing and chemical properties of PVDF such as radiation carbonization, β-phase formation, etc.

Study on Filtration Performance of PVDF/PUL Composite Air Filtration Membrane Based on Far-Field Electrospinning

At present, the situation of air pollution is still serious, and research on air filtration is still crucial. For the nanofiber air filtration membrane, the diameter, porosity, tensile strength, and hydrophilicity of the nanofiber will affect the filtration performance and stability. In this paper, based on the far-field electrospinning process and the performance effect mechanism of the stacked structure fiber membrane, nanofiber membrane was prepared by selecting the environmental protection, degradable and pollution-free natural polysaccharide biopolymer pullulan, and polyvinylidene fluoride polymer with strong hydrophobicity and high impact strength. By combining two kinds of fiber membranes with different fiber diameter and porosity, a three-layer composite nanofiber membrane with better hydrophobicity, higher tensile strength, smaller fiber diameter, and better filtration performance was prepared. Performance characterization showed that this three-layer composite nanofiber membrane had excellent air permeability and filtration efficiency, and the filtration efficiency of particles above PM 2.5 reached 99.9%. This study also provides important reference values for the preparation of high-efficiency composite nanofiber filtration membrane.

Dielectrophoresis-Based Universal Membrane Antifouling Strategy toward Colloidal Foulants

Membrane fouling compromises the benefits of membrane technology, leading to its performance deterioration and incremental cost. Coupling with an electric field has been attractive but is limited by the electrical dependence of the electrophoresis (EP) mechanism and undesired faradic reactions. This study reports a universal dielectrophoresis-based (DEP) membrane antifouling strategy for electronegative, electropositive, and neutral colloidal foulants, which depends on the particle polarizability rather than its charge. The porous Ni@PVDF model electroconductive membrane was fabricated to construct a nonuniform electric field inducing DEP, while applying a low voltage avoided side electrochemical reactions. For electronegative SiO₂(-) and electropositive Al₂O₃(+) particles with a lower relative permittivity than the medium water (78), the membrane permeability all remarkably increased by 90.1% under AC/DC (±1.0 V) fields. By contrast, serious membrane fouling occurred for the BaTiO₃ colloids with a higher relative permittivity (∼2000). Notably, the permittivity of nearly all colloids in wastewater treatment is much less than that of water, which makes the dielectrophoresis-based antifouling strategy universal. The theoretical simulation systematically analyzed the forces on particles including DEP, EP, and others, indicating that the formed protected area on the membrane pore wall by DEP forces prevented the irreversible membrane blockage of colloids and facilitated loose cake layer formation for alleviating membrane fouling. In brief, this work reported a hopeful concept for dielectrophoresis-based membrane antifouling and verified its antifouling mechanism.

Scale Up and Validation of Novel Tri-Bore PVDF Hollow Fiber Membranes for Membrane Distillation Application in Desalination and Industrial Wastewater Recycling

Novel tri-bore polyvinylidene difluoride (PVDF) hollow fiber membranes (TBHF) were scaled-up for fabrication on industrial-scale hollow fiber spinning equipment, with the objective of validating the membrane technology for membrane distillation (MD) applications in areas such as desalination, resource recovery, and zero liquid discharge. The membrane chemistry and spinning processes were adapted from a previously reported method and optimized to suit large-scale production processes with the objective of translating the technology from lab scale to pilot scale and eventual commercialization. The membrane process was successfully optimized in small 1.5 kg batches and scaled-up to 20 kg and 50 kg batch sizes with good reproducibility of membrane properties. The membranes were then assembled into 0.5-inch and 2-inch modules of different lengths and evaluated in direct contact membrane distillation (DCMD) mode, as well as vacuum membrane distillation (VMD) mode. The 0.5-inch modules had a permeate flux >10 L m−2 h−1, whereas the 2-inch module flux dropped significantly to <2 L m−2 h−1 according to testing with 3.5 wt.% NaCl feed. Several optimization trials were carried out to improve the DCMD and VMD flux to >5 L m−2 h−1, whereas the salt rejection consistently remained ≥99.9%.