Electrospun Polymer Composite Membrane with Superior Thermal Stability and Excellent Chemical Resistance for High-Efficiency PM2.5 Capture

Biodegradable air filter with electrospun composite nanofibers and cellulose fibers dual network: Enhanced electrostatic adsorption, humidity resistance, and extended service life

Cellulose-based materials have great potential as degradable air filters. Regretfully, the application is limited by their low electrostatic adsorption and hydrophilicity. To meet with the challenge, we designed a composite air filter with dual network. Composite cellulose acetate nanofibers were electrospun on a cellulose-fibers paper substrate, and the resulted multi-scale spider-web-like structure showed high filtration efficiency as well as low resistance. Electrets (silicon nitride and tourmaline) were composited to enhance the electrostatic adsorption for PMs. Hydrophobic modification improved the ability to retain electrostatic charge, promoting the filtration under humid environment. The filtration efficiency for PM0.3 exceeded 99 %, while the pressure drop was only 45.7 Pa. The filtration performance could be maintained for over 12 hours under 90 % relative humidity, and the filter could be completely degraded in natural environment within 80 days.

Hyperbranched polymeric membranes for industrial water purification

This work aims at the preparation and characterization of dual-layer (DL) nano-fibrous mat (NFM) of hydrophobic and mechanical stable polyacrylonitrile (PAN) nano-fibers (NFs), as a supporter, and polyamide 6 (PA)/chitosan (Ch) NFs as a top hydrophilic coating layer. PAN and PA fibers, as residual wastes from textile processes, were collected and dissolved in their proper solvents. PAN was electro-spuned under certain conditions of electro-spinning (voltage, flow rate, and distance between spinneret and collector) to obtain PAN-NFM. Different ratios of PA/Ch composite were prepared and then electro-spun above the PAN-NFM that was previously prepared to obtain hydrophobic/hydrophilic functional dual-layer nano-fibrous membrane (DLNFM). The efficiency of the prepared DLNFM for capturing dye residues and heavy metals from wastewater was investigated. The viscosities of the prepared composite solutions were measured. The prepared dual-layer nano-fiber membranes (DLNFMs) were chemically and physically characterized by Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction, and thermogravimetric analyzer. The potential of the prepared mats for the adsorption of some heavy metal ions, i.e., Cu+2, Cr+3, and Pb+2 cations in addition to dyes from wastewater was evaluated. The effect of using different concentrations of PA/Ch composite as well as the thickness of the obtained DLNFM on the filtration efficiency was studied. The results of this study show the success of functional DLNFM in dye and heavy metal removal. The maximum removal efficiency of acid dyes was reached to 73.4 % and of reactive dye was approximately 61 % for PAN/PA-1.25%Ch DLNFM after 3 days at room temperature. The removal efficiency percent of heavy metal ions reached to 54 % by DLNFM. Additionally, the results showed that 0.08 mm is the ideal thickness for maximum absorption capacity. This value is correlated with the membrane's highest Ch percentage, which is (PAN/PA-1.25%Ch). Furthermore, the results demonstrate that the presence of the Ch polymer strengthened the produced bi-layered membrane to achieve the highest thermal stability when compared to the other nano-fibrous membranes (NFMs), with the breakdown temperature of the Ch functionalized dual-layer membranes (DLMs) reaching approximately 617 °C and a maximum weight loss of 60 %.

Scalable, solvent-free transparent film-based air filter with high particulate matter 2.5 filtration efficiency

Over the course of the COVID-19 pandemic, people have realized the importance of wearing a mask. However, conventional nanofiber-based face masks impede communication between people because of their opacity. Moreover, it remains challenging to achieve both high filtration performance and transparency through fibrous mask filters without using harmful solvents. Herein, scalable transparent film-based filters with high transparency and collection efficiency are fabricated in a facile manner by means of corona discharging and punch stamping. Both methods improve the surface potential of the film while the punch stamping procedure generates micropores in the film, which enhances the electrostatic force between the film and particulate matter (PM), thereby improving the collection efficiency of the film. Moreover, the suggested fabrication method involves no nanofibers and harmful solvents, which mitigates the generation of microplastics and potential risks for the human body. The film-based filter provides a high PM2.5 collection efficiency of 99.9 % while maintaining a transparency of 52 % at the wavelength of 550 nm. This enables people to distinguish the facial expressions of a person wearing a mask composed of the proposed film-based filter. Moreover, the results of durability experiments indicate that the developed film-based filter is anti-fouling, liquid-resistant, microplastic-free and foldability.

Electroactive, Antibacterial, and Biodegradable Poly(lactic acid) Nanofibrous Air Filters for Healthcare

Poly(lactic acid) (PLA)-based nanofibrous membranes (NFMs) hold great potential in the field of biodegradable filters for air purification but are largely limited by the relatively low electret properties and high susceptibility to bacteria. Herein, we disclosed a facile approach to the fabrication of electroactive and antibacterial PLA NFMs impregnated with a highly dielectric photocatalyst. In particular, the microwave-assisted doping (MAD) protocol was employed to yield Zn-doped titanium dioxide (Zn-TIO), featuring the well-defined anatase phase, a uniform size of ∼65 nm, and decreased band gap (3.0 eV). The incorporation of Zn-TIO (2, 6, and 10 wt %) into PLA gave rise to a significant refinement of the electrospun nanofibers, decreasing from the highest diameter of 581 nm for pure PLA to the lowest value of 264 nm. More importantly, dramatical improvements in the dielectric constants, surface potential, and electret properties were simultaneously achieved for the composite NFMs, as exemplified by a nearly 94% increase in surface potential for 3-day-aged PLA/Zn-TIO (90/10) compared with that of pure PLA. The well regulation of morphological features and promotion of electroactivity contributed to a distinct increase in the air filtration performance, as demonstrated by 98.7% filtration of PM_0.3 with the highest quality factor of 0.032 Pa^-1 at the airflow velocity of 32 L/min for PLA/Zn-TIO (94/6), largely surpassing pure PLA (89.4%, 0.011 Pa^-1). Benefiting from the effective generation of reactive radicals and gradual release of Zn²⁺ by Zn-TIO, the electroactive PLA NFMs were ready to profoundly inactivate Escherichia coli and Staphylococcus epidermidis. The exceptional combination of remarkable electret properties and excellent antibacterial performance makes the PLA membrane filters promising for healthcare.

Bioelectrets in Electrospun Bimodal Poly(lactic acid) Fibers: Realization of Multiple Mechanisms for Efficient and Long-Term Filtration of Fine PMs

Despite the great potential in fabrication of biodegradable and eco-friendly air filters by electrospinning poly(lactic acid) (PLA) membranes, the filtering performance is frequently dwarfed by inadequate physical sieving or electrostatic adsorption mechanisms to capture airborne particulate matters (PMs). Here, using the parallel spinning approach, the unique micro/nanoscale architecture was established by conjugation of neighboring PLA nanofibers, creating bimodal fibers in electrospun PLA membranes for the enhanced slip effect to significantly reduce the air resistance. Moreover, the bone-like nanocrystalline hydroxyapatite bioelectret (HABE) was exploited to enhance the dielectric and polarization properties of electrospun PLA, accompanied by the controlled generation of junctions induced by the microaggregation of HABE (10-30 wt %). The incorporated HABE was supposed to orderly align in the applied E-field and largely promote the charging capability and surface potential, gradually increasing to 7.2 kV from the lowest level of 2.5 kV for pure PLA. This was mainly attributed to HABE-induced orientation of PLA backbone chains and C═O dipoles, as well as the interfacial charges trapped at the interphases of HABE-PLA and crystalline region-amorphous PLA. Given the multiple capturing mechanisms, the micro/nanostructured PLA/HABE membranes were characterized by excellent and sustainable filtering performance, e.g., the filtration efficiency of PM_0.3 was promoted from 59.38% for pure PLA to 94.38% after addition of 30 wt % HABE at a moderate airflow capacity of 32 L/min and from 30.78 to 83.75% at the highest level of 85 L/min. It is of interest that the pressure drop was significantly decreased, mainly arising from the slip effect between the ultrafine nanofibers and conjugated microfibers. The proposed combination of the nanostructured electret and the multistructuring strategy offers the function integration of efficient filtration and low resistance that are highly useful to pursue fully biodegradable filters.

Acid and alkali-resistant fabric-based triboelectric nanogenerator for self-powered intelligent monitoring of protective clothing in highly corrosive environments

The corrosion of materials severely limits the application scenarios of triboelectric nanogenerators (TENGs), especially in laboratories, chemical plants and other fields where leakage of chemically corrosive solutions is common. Here, we demonstrate a chemical-resistant triboelectric nanogenerator (CR-TENG) based on polysulfonamide (PSA) and polytetrafluoroethylene (PTFE) non-woven fabrics. The CR-TENG can stably harvest biological motion energy and perform intelligent safety protection monitoring in a strong corrosive environment. After treatment with strong acid and alkali solution for 7 days, the fabric morphology, diameter, tensile properties and output of CR-TENG are not affected, showing high reliability. CR-TENG integrated into protective equipment can detect the working status of protective equipment in real time, monitor whether it is damaged, and provide protection for wearers working in high-risk situations. In addition, the nonwoven-based CR-TENG has better wearing comfort and is promising for self-powered sensing in harsh environments.

Dual-Network Structured Nanofibrous Membranes with Superelevated Interception Probability for Extrafine Particles

Airborne particulate matter (PM) pollution has caused a public health threat, including nanoscale particles, especially with emerging infectious diseases and indoor and vehicular environmental pollution. However, most existing indoor air filtration units are expensive, energy-intensive, and bulky, and there is an unavoidable trade-off between low-efficiency PM_0.3/pathogen interception, PM removal, and air resistance. Herein, we designed and synthesized a two-dimensional continuous cellulose-sheath/net with a unique dual-network corrugated architecture to manufacture high-efficiency air filters and even N95 particulate face mask. Combined with its sheath/net structured pores (size 100-200 nm) consisting of a cellulose framework (1-100 nm diameter), the cellulose sheath/net filter offers high-efficiency air filtration (>99.5338%, Extrafine particles; >99.9999%, PM_2.5), low-pressure drops, and a robustness quality factor of >0.14 Pa^-1, utilizing their ultralight weight of 30 mg/m² and physical adhesion and sieving behaviors. Simultaneously, masks prepared with cellulose-sheath/net filters are more likely to capture and block smaller particles than the N95 standard. The synthesis of such materials with their nanoscale features and designed macrostructures may suggest new design criteria for a novel generation of high-efficiency air filter media for different applications such as personal protection products and industrial dust removal.

Fabrication of Glutaraldehyde Vapor Treated PVA/SA/GO/ZnO Electrospun Nanofibers with High Liquid Absorbability for Antimicrobial of Staphylococcus aureus

In this study, we aim to develop organic-inorganic hybrid nanofibers containing high moisture retention and good mechanical performance as an antimicrobial dressing platform. The main theme of this work focuses on several technical tasks including (a) the electrospinning process (ESP) to produce organic polyvinyl alcohol/sodium alginate (PVA/SA) nanofibers with an excellent diameter uniformity and fibrous orientation, (b) the fabrication of inorganic nanoparticles (NPs) as graphene oxide (GO) and ZnO NPs to be added to PVA/SA nanofibers for enhancement of the mechanical properties and an antibacterial function to Staphylococcus aureus (S. aureus), and then (c) the crosslinking process for PVA/SA/GO/ZnO hybrid nanofibers in glutaraldehyde (GA) vapor atmosphere to improve the hydrophilicity and moisture absorption of specimens. Our results clearly indicate that the uniformity nanofiber with 7 wt% PVA and 2 wt% SA condition demonstrates 199 ± 22 nm in diameter using an electrospinning precursor solution of 355 cP in viscosity by the ESP process. Moreover, the mechanical strength of nanofibers was enhanced by 17% after the handling of a 0.5 wt% GO nanoparticles addition. Significantly, the morphology and size of ZnO NPs can be affected by NaOH concentration, where 1 M NaOH was used in the synthesis of 23 nm ZnO NPs corresponding to effective inhibition of S. aureus strains. The PVA/SA/GO/ZnO mixture successfully performed an antibacterial ability with an 8 mm inhibition zone in S. aureus strains. Furthermore, the GA vapor as a crosslinking agent acting on PVA/SA/GO/ZnO nanofiber provided both swelling behavior and structural stability performance. The swelling ratio increased up to 1.406%, and the mechanical strength was 1.87 MPa after 48 h of GA vapor treatment. Finally, we successfully synthesized the hybrid nanofibers of GA-treated PVA/SA/GO/ZnO accompanied with high moisturizing, biocompatibility, and great mechanical properties, which will be a novel multi-functional candidate for wound dressing composites for patients receiving surgical operations and first aid treatments.

Silk fibroin fibers-based shape memory membrane with Janus wettability for multitiered wearable protection

Realizing breathable shape memory fiber-based material with antibacterial and waterproof performances is important for multitiered wearable protection to address the increasing concerns of air pollution. Herein, using an alternating electrospinning-electrospraying technology, we develop a fiber-based membrane with Janus wettability based on a silk fibroin nanofibers-substrate (SFNFs), a polyurethane nanospheres-top layer (PUNSs), and a middle layer of PU nanofibers-mat with in-situ grown silver nanoparticles (PUNFs-AgNPs), which serves separately for skin contact, a self-cleaning physical barrier to resist external aerosol/bacteria (PM2.5 filtration efficiency ~ 98.1%), and a bio-barrier that can sterilize harmful particles and inhibit bacteria proliferation (> 95%). This breathable Janus film (SFNFs/PUNFs-AgNPs/PUNSs, SPAP) with an antibacterial filter shows shape memory stretchability enabled by the thermoplastic PU component, which is mechanically adaptive to human body for wearable protection. This work presents a breathable wearable material for air-filtration and anti-bacteria, promising for applications such as wound dressings, medical masks, protection suits, and multifunctional filters.

GRAPHICAL ABSTRACT

An alternating electrospinning-electrospraying technology was proposed to achieve a silk fibroin-based antibacterial membrane with Janus wettability, as well as good skin affinity and breathability, which serves well as physical and bio-barriers for water resistance, PM2.5 filtration (~98.1%) and bacteria inhibition (efficiency of 95%). This shape memory Janus membrane can adapt mechanically to human body curvatures for functional wearable protections.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43578-022-00805-w.

A Review of Filtration Performance of Protective Masks

Masks are essential and effective small protective devices used to protect the general public against infections such as COVID-19. However, available systematic reviews and summaries on the filtration performance of masks are lacking. Therefore, in order to investigate the filtration performance of masks, filtration mechanisms, mask characteristics, and the relationships between influencing factors and protective performance were first analyzed through mask evaluations. The summary of filtration mechanisms and mask characteristics provides readers with a clear and easy-to-understand theoretical cognition. Then, a detailed analysis of influencing factors and the relationships between the influencing factors and filtration performance is presented in. The influence of the aerosol size and type on filtration performance is nonlinear and nonconstant, and filtration efficiency decreases with an increase in the gas flow rate; moreover, fitness plays a decisive role in the protective effects of masks. It is recommended that the public should wear surgical masks to prevent COVID-19 infection in low-risk and non-densely populated areas. Future research should focus on fitness tests, and the formulation of standards should also be accelerated. This paper provides a systematic review that will be helpful for the design of masks and public health in the future.

Electrospun Filtering Membrane Designed as Component of Self-Decontaminating Protective Masks

The 2019 coronavirus outbreak and worsening air pollution have triggered the search for manufacturing effective protective masks preventing both particulate matter and biohazard absorption through the respiratory tract. Therefore, the design of advanced filtering textiles combining efficient physical barrier properties with antimicrobial properties is more newsworthy than ever. The objective of this work was to produce a filtering electrospun membrane incorporating a biocidal agent that would offer both optimal filtration efficiency and fast deactivation of entrapped viruses and bacteria. After the eco-friendly electrospinning process, polyvinyl alcohol (PVA) nanofibers were stabilized by crosslinking with 1,2,3,4-butanetetracarboxylic acid (BTCA). To compensate their low mechanical properties, nanofiber membranes with variable grammages were directly electrospun on a meltblown polypropylene (PP) support of 30 g/m². The results demonstrated that nanofibers supported on PP with a grammage of around only 2 g/m² presented the best compromise between filtration efficiencies of PM_0.3, PM_0.5, and PM_3.0 and the pressure drop. The filtering electrospun membranes loaded with benzalkonium chloride (ADBAC) as a biocidal agent were successfully tested against E. coli and S. aureus and against human coronavirus strain HCoV-229E. This new biocidal filter based on electrospun nanofibers supported on PP nonwoven fabric could be a promising solution for personal and collective protection in a pandemic context.

High-performance multifunctional electrospun fibrous air filter for personal protection: A review

With the increasingly serious air pollution and the rampant coronavirus disease 2019 (COVID–19), preparing high–performance air filter to achieve the effective personal protection has become a research hotspot. Electrospun nanofibrous membrane has become the first choice of air filter because of its small diameter, high specific surface area and porosity. However, improving the filtration performance of the filter only cannot meet the personal needs: it should be given more functions based on high filtration performance to maximize the personal benefits, called, multifunctional, which can also be easily realized by electrospinning technology, and has attracted much attention. In this review, the filtration mechanism of high–performance electrospun air filter is innovatively summarized from the perspective of membrane. On this basis, the specific preparation process, advantages and disadvantages are analyzed in detail. Furthermore, other functions required for achieving maximum personal protection benefits are introduced specifically, and the existing high–performance electrospun air filter with multiple functions are summarized. Finally, the challenges, limitations, and development trends of manufacturing high–performance air filter with multiple functions for personal protection are presented.

Dual-Functional Nanofibrous Patches for Accelerating Wound Healing

Bacterial infections and inflammation are two main factors for delayed wound healing. Coaxial electrospinning nanofibrous patches, by co-loading and sequential co-delivering of anti-bacterial and anti-inflammation agents, are promising wound dressing for accelerating wound healing. Herein, curcumin (Cur) was loaded into the polycaprolactone (PCL) core, and broad-spectrum antibacterial tetracycline hydrochloride (TH) was loaded into gelatin (GEL) shell to prepare PCL-Cur/GEL-TH core-shell nanofiber membranes. The fibers showed a clear co-axial structure and good water absorption capacity, hydrophilicity and mechanical properties. In vitro drug release results showed sequential release of Cur and TH, in which the coaxial mat showed good antioxidant activity by DPPH test and excellent antibacterial activity was demonstrated by a disk diffusion method. The coaxial mats showed superior biocompatibility toward human immortalized keratinocytes. This study indicates a coaxial nanofiber membrane combining anti-bacterial and anti-inflammation agents has great potential as a wound dressing for promoting wound repair.

Fabrication and evaluation of electrospun polyacrylonitrile/silver nanofiber membranes for air filtration and antibacterial activity

Particulate matter and airborne microorganisms are two of the most severe indoor air problems due to their significant risks to human health. Comprehensive research on air filtration with good filtration performance for fine particles and antibacterial function is essential. In this study, after some experimentations and optimization of conditions, polyacrylonitrile (PAN) 10–1% silver nanoparticles (AgNPs) membranes with suitable morphology and uniform diameter distribution are fabricated by an electrospinning method. These electrospun mats exhibited antibacterial activity toward Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria). With its small pore size, high porosity, the high specific surface area of 42 m²/g, and robust mechanical strength of 7.14 MPa properties, the resultant PAN10%-1%Ag membranes exhibit high filtration efficiency of 99.27%, the low pressure drop of 33 Pa, and higher quality factor compared to the two standard commercial masks including, the three-ply surgical mask and the respirator face mask. After 24 h of the filtration process in a simulated living environment, the obtained air filter still displayed a high filtration efficiency and a less pressure drop variation. In addition, the R² value was 0.99, which indicates that the calculation results are in good agreement with the measured results. The fabrication of PAN-Ag membranes will have broad applications, including face masks, indoor air filtration and clean room.

Synergistic Effect of Co-Delivering Ciprofloxacin and Tetracycline Hydrochloride for Promoted Wound Healing by Utilizing Coaxial PCL/Gelatin Nanofiber Membrane

Combining multiple drugs or biologically active substances for wound healing could not only resist the formation of multidrug resistant pathogens, but also achieve better therapeutic effects. Herein, the hydrophobic fluoroquinolone antibiotic ciprofloxacin (CIP) and the hydrophilic broad-spectrum antibiotic tetracycline hydrochloride (TH) were introduced into the coaxial polycaprolactone/gelatin (PCL/GEL) nanofiber mat with CIP loaded into the PCL (core layer) and TH loaded into the GEL (shell layer), developing antibacterial wound dressing with the co-delivering of the two antibiotics (PCL-CIP/GEL-TH). The nanostructure, physical properties, drug release, antibacterial property, and in vitro cytotoxicity were investigated accordingly. The results revealed that the CIP shows a long-lasting release of five days, reaching the releasing rate of 80.71%, while the cumulative drug release of TH reached 83.51% with a rapid release behavior of 12 h. The in vitro antibacterial activity demonstrated that the coaxial nanofiber mesh possesses strong antibacterial activity against E. coli and S. aureus. In addition, the coaxial mats showed superior biocompatibility toward human skin fibroblast cells (hSFCs). This study indicates that the developed PCL-CIP/GEL-TH nanofiber membranes hold enormous potential as wound dressing materials.

Multi-Component Nanofiber Composite Membrane Enabled High PM0.3 Removal Efficiency and Oil/Water Separation Performance in Complex Environment

Currently, industrial waste gas and oily wastewater are usually at high temperature and contain corrosive components (e.g., acid, alkali, oxidant, or high salt, etc.), presenting great challenges on filtration/separation materials. Here, a multi-purpose Poly(m-phenylene isophthalamide)/polyacrylonitrile/silica (PMIA/PAN/SiO₂) nanofiber composite membrane with a high yield was prepared simply via electrospinning to satisfy the demands of air filtration and oil/water separation in complex environments. Under the synergy of PMIA, PAN and SiO₂, the composite membrane possesses high PM_0.3 removal capacity of 99.69%, robust purification ability against real smoke PM_2.5, effective oil/water separation performance of > 99.6%, superior high temperature stability (about 250 °C) and excellent chemical resistance, showing the potential application in filtration/separation process under complex conditions. Moreover, the influence mechanism of SiO₂ NPs on mechanical properties and filtration performance was systematically investigated through experiments and simulations, paving the way for future intensive research. This study provides an option for the facile and effective preparation of high-performance filtration/separation membranes applied in the field of dust filtration and oily wastewater separation, even in harsh environments.

High-performance Electret and Antibacterial Polypropylene Meltblown Nonwoven Materials Doped with Boehmite and ZnO Nanoparticles for Air Filtration

The current pandemic caused by COVID-19 has intensively triggered the development of high-performance air filters. Polypropylene (PP) is widely used as the raw material of meltblown nonwoven materials and is the core layer in air filters, such as masks. In this study, an electret PP meltblown nonwoven with antibacterial activity was developed, and nano boehmite (AlOOH) and nano-ZnO were employed as electret and antibacterial agents, respectively. AlOOH (0.5–2.0 wt%) and ZnO (1.0 wt%) were doped into the PP matrix using a twin-screw extruder, and the resulting masterbatches were applied as raw materials to produce nonwoven materials via a meltblown process. The as-prepared nonwoven samples were characterized by means of SEM, IR and DSC/TG. After corona charging, the filtration efficiency was determined by a filtration tester, charge decay was measured by an infrared electrostatic tester, and the antibacterial properties were evaluated (evaluation method: AATCC 100–2012). A dosage of AlOOH greater than 1.0 wt% endowed the nonwoven material with high filtration efficiency, and 1.0 wt% ZnO brought about antibacterial activity. Corona charging was an effective means to charge the nonwoven electret, and the charges were quicker to decay in air than in a sealed bag. The as-prepared meltblown nonwoven filter is a remarkably promising filter for air filtration.

Biodegradable and Reusable Cellulose-Based Nanofiber Membrane Preparation for Mask Filter by Electrospinning

Environmentally friendly face masks with high filtration efficiency are in urgent need to fight against the COVID-19 pandemic, as well as other airborne viruses, bacteria and particulate matters. In this study, coaxial electrospinning was employed to fabricate a lithium chloride enhanced cellulose acetate/thermoplastic polyurethanes (CA/TPU-LiCl) face mask nanofiber filtration membrane, which was biodegradable and reusable. The analysis results show that the CA/TPU-LiCl membrane had an excellent filtration performance: when the filtration efficiency reached 99.8%, the pressure drop was only 52 Pa. The membrane also had an outstanding reusability. The filtration performance maintained at 98.2% after 10 test cycles, and an alcohol immersion disinfection treatment showed no effect on its filtration performance. In summary, the CA/TPU-LiCl nanofiber membrane made in this work is a promising biodegradable and reusable filtration material with a wide range of potential applications, including high-performance face mask.

A Cleanable Self-Assembled Nano-SiO2/(PTFE/PEI)n/PPS Composite Filter Medium for High-Efficiency Fine Particulate Filtration

A silicon dioxide/polytetrafluoroethylene/polyethyleneimine/polyphenylene sulfide (SiO2/PTFE/PEI/PPS) composite filter medium with three-dimensional network structures was fabricated by using PPS nonwoven as the substrate which was widely employed as a cleanable filter medium. The PTFE/PEI bilayers were firstly coated on the surfaces of the PPS fibers through the layer-by-layer self-assembly technique ten times, followed by the deposition of SiO2 nanoparticles, yielding the SiO2/(PTFE/PEI)10/PPS composite material. The contents of the PTFE component were easily controlled by adjusting the number of self-assembled PTFE/PEI bilayers. As compared with the pure PPS nonwoven, the obtained SiO2/(PTFE/PEI)10/PPS composite material exhibits better mechanical properties and enhanced wear, oxidation and heat resistance. When employed as a filter material, the SiO2/(PTFE/PEI)10/PPS composite filter medium exhibited excellent filtration performance for fine particulate. The PM2.5 (particulate matter less than 2.5 μm) filtration efficiency reached up to 99.55%. The superior filtration efficiency possessed by the SiO2/(PTFE/PEI)10/PPS composite filter medium was due to the uniformly modified PTFE layers, which played a dual role in fine particulate filtration. On the one hand, the PTFE layers not only increase the specific surface area and pore volume of the composite filter material but also narrow the spaces between the fibers, which were conducive to forming the dust cake quickly, resulting in intercepting the fine particles more efficiently than the pure PPS filter medium. On the other hand, the PTFE layers have low surface energy, which is in favor of the detachment of dust cake during pulse-jet cleaning, showing superior reusability. Thanks to the three-dimensional network structures of the SiO2/(PTFE/PEI)10/PPS composite filter medium, the pressure drop during filtration was low.

Self-Supporting Three-Dimensional Electrospun Nanofibrous Membrane for Highly Efficient Air Filtration

High-performance air filtration was the key to health protection from biological and ultrafine dust pollution. A self-supporting, three-dimensional (3D) nanofibrous membrane with curled pattern was electrospun for the filtration, of which the micro-fluffy structure displayed high-filtration efficiency and low-pressure drop. The flow field in the 3D filtration membrane was simulated to optimize the process parameters to increase the filtration performance. The qualification factor increased from 0.0274 Pa⁻¹ to 0.0309 Pa⁻¹ by 12.77% after the optimization of the electrospinning parameters. The best filtration efficiency and pressure drop were 93.6% and 89.0 Pa, separately. This work provides a new strategy to fabricate 3D structures through the construction of fiber morphology and promotes further improvement of air filtration performance of fibrous filters.

High-performance filter membrane composed of oxidized Poly (arylene sulfide sulfone) nanofibers for the high-efficiency air filtration

In this study, a novel, oxidized poly (arylene sulfide sulfone) (O-PASS) nanofibrous membrane filter was successfully fabricated for the effective removal of particulate matter. PASS was electrospun into a nanofibrous membrane with an average nanofiber diameter of 0.31 µm and basis weight of 3 g/m². These specifications were chosen as they showed high particulate matter removal efficiency (99.98%), low pressure drop (68 Pa), and high quality factor Q_F (0.125 Pa^-1). In addition, the filtration mechanism of the PASS nanofibrous membrane was intuitively revealed by simulating the intercepted particular distributions and motion paths of particles. After a simple oxidation treatment, the O-PASS nanofibrous membrane was successfully built up. The microstructure and morphology showed little change compared with the PASS nanofiber, but the oxidation treatment significantly improved the mechanical properties of the membrane from 1.51 MPa to 4.92 MPa. More importantly, the O-PASS nanofibrous membrane still exhibited high removal efficiency after high temperature, acid, alkali, or organic solvent treatments. Overall, O-PASS nanofibrous membranes are promising high-performance filter materials with high temperature and corrosion resistance.

MOF-Embedded Bifunctional Composite Nanofiber Membranes with a Tunable Hierarchical Structure for High-Efficiency PM0.3 Purification and Oil/Water Separation

Herein, a unique hierarchically structured composite nanofiber membrane, consisting of a zeolitic imidazolate framework-8-embedded polyethersulfone (PES@ZIF8) fiber layer and a polysulfonamide/polyethersulfone (PSA/PES) fiber layer, was successfully developed to cope with the complex environments during the actual filtration/separation process and overcome the conflict between high filtration efficiency and low air pressure resistance. Due to the advantages of the synergistic effect of multicomponents and the bi-layer hierarchical structure, the integrated PES@ZIF8-PSA/PES filter possesses an extremely high air filtration efficiency (up to 99.986%) under a very low pressure drop (only 15 Pa), superior PM_0.3 purification capacity (close to 99.95%), long-term recycling ability for purifying real smoke PM_2.5 from >800 to <10 μg/m³, extremely high temperature resistance (exceed 200 °C), flame retardancy, good chemical stability, satisfactory transmittance, and robust self-cleaning ability. Apart from these, it achieves effective separation of oil-water mixtures and oil-water emulsions as a result of selective wettability including hydrophobicity and superoleophilicity. In particular, the PES@ZIF8-PSA/PES nanofiber membranes maintain outstanding air filtration and oil/water separation properties under the high temperature or strong acid/alkali conditions. This special comprehensive performance gives the PES@ZIF8-PSA/PES-based filtration/separation membranes a wider application prospect ranging from environmental governance to individual protection and industrial security.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Multistructured Electrospun Nanofibers for Air Filtration: A Review

Air filtration materials (AFMs) have gradually become a research hotspot on account of the increasing attention paid to the global air quality problem. However, most AFMs cannot balance the contradiction between high filtration efficiency and low pressure drop. Electrospinning nanofibers have a large surface area to volume ratio, an adjustable porous structure, and a simple preparation process that make them an appropriate candidate for filtration materials. Therefore, electrospun nanofibers have attracted increased attention in air filtration applications. In this paper, first, the preparation methods of high-performance electrospun air filtration membranes (EAFMs) and the typical surface structures and filtration principles of electrospun fibers for air filtration are reviewed. Second, the research progress of EAFMs with multistructures, including nanoprotrusion, wrinkled, porous, branched, hollow, core-shell, ribbon, beaded, nets structure, and the application of these nanofibers in air filtration are summarized. Finally, challenges with the fabrication of EAFMs, limitations of their use, and trends for future developments are presented.

Coaxial electrospun PVA/PCL nanofibers with dual release of tea polyphenols and ε-poly (L-lysine) as antioxidant and antibacterial wound dressing materials

Preparing wound dressing with dual-delivery of antioxidant and antibacterial agents is highly desirable in clinical wound treatment. Herein, a series of coaxial nanofiber membranes loaded with antioxidant tea polyphenols (TP) in the core and antibacterial ε-poly (L-lysine) (ε-PL) in the shell layer were successfully fabricated by coaxial electrospinning. The physicochemical characterizations by transmission electron microscopy, inverted fluorescence microscopy and fourier transform infrared spectroscopy confirmed the formation of core-shell structure. The results of in vitro drug release indicated that ε-PL exhibited a fast release profile while TP released in a sustained manner, which is favorable to the achievement of quick bacteria inhibition in the initial phase as well as long-term antioxidant activity during wound healing. The antioxidant activity of coaxial nanofibers was found to be increased with the increment of TP content and incubation time. The antibacterial assays against Escherichia coli and Staphylococcus aureus demonstrated that the incorporation of ε-PL in the coaxial nanofibers led to strong antibacterial activity. Additionally, all the coaxial nanofibers possessed good cytocompatibility. Therefore, the prepared coaxial nanofibers simultaneously incorporated with ε-PL and TP are promising as potential wound dressing materials.

Three-dimensional composite electrospun nanofibrous membrane by multi-jet electrospinning with sheath gas for high-efficiency antibiosis air filtration

Three-dimensional (3D) composite polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN) electrospun nanofibrous membranes combining both thick and thin nanofibers have been fabricated by the method of multi-jet electrospinning with sheath gas to realize high-efficiency air filtration under a low pressure drop. The thin PAN nanofibers form a dense membrane, with a strong capturing ability on the ultra-fine particles, while the thick PVDF nanofibers play a 3D supporting effect on the thin PAN nanofibers. In this case, the combination results in a fluffy membrane with higher porosity, which could achieve the airflow passing through the membrane without the air pressure drop. The effects of the composite manner of thick nanofibers and thin nanofibers are investigated, in order to optimize the air filtration performance of the 3D composite nanofibrous membrane. As a result, the maximum quality factor for air filtration could reach up to 0.398 Pa^-1. The particle-fiber interaction model was used to simulate the air filtration process as well, and the simulation results were fairly consistent with the experimental results, providing a guidance method for the optimization of composite nanofibrous membrane for high-efficiency air filtration. More interestingly, a cationic poly[2-(N,N-dimethyl amino) ethyl methacrylate] (PDMAEMA) was added in the PVDF solution to obtain a composite air filtration membrane with excellent antibiosis performance, which achieved the highest inhibition rate of approximately 90%. In short, this work provides an effective way to promote antibiosis air filtration performance by using an electrospun nanofibrous membrane, and might also effectively accelerate the biological protection application of current air filtration membranes.

Laminated polyacrylonitrile nanofiber membrane codoped with boehmite nanoparticles for efficient electrostatic capture of particulate matters

Particulate matters (PMs) air pollution is identified as the major threat to public health and climate. High-performance air filter technology based on various electrospun nanofibers is considered as an effective strategy to eliminate the effects of PMs air pollution. However, to date, nearly all the existing micro-/nanofibers are hard to meet both requirements of high PMs removal efficiency and long service life. In this work, we reported the production of laminated polyacrylonitrile(PAN)-boehmite nanoparticles (BNPs) nanofiber structured membrane by the electrospinning process. The dimension of PAN-BNPs nanofiber can be tunable from (0.09 ± 0.03)μm to (0.81 ± 0.11)μm by controlling the PAN and BNPs concentrations in precursors. The optimized PAN-BNPs nanofiber air filter with a basis weight of 1 g m^-2demonstrates the attractive attributes of high PM_2.5removal efficiency up to 99.962% and low pressure drop of 58 Pa. Most importantly, after introducing the BNPs as electret, the removal efficiency is very stable under the air flow rate of 6 l min^-1. This PAN-BNPs nanofiber with a long electrostatic duration time offers an approach for fabricating future high-performance air filters.

New Design Method for Fabricating Multilayer Membranes Using CO2-Assisted Polymer Compression Process

It was verified that deep learning can be used in creating multilayer membranes with multiple porosities using the CO2-assisted polymer compression (CAPC) method. To perform training while reducing the number of experimental data as much as possible, the experimental data of the compression behavior of two layers were expanded to three layers for training, but sufficient accuracy could not be obtained. However, the accuracy was dramatically improved by adding the experimental data of the three layers. The possibility of only simulating process results without the necessity for a model is a merit unique to deep learning. Overall, in this study, the results show that by devising learning data, deep learning is extremely effective in designing multilayer membranes using the CAPC method.

Novel Strategy for Fabricating Multilayer Porous Membranes with Varying Porosity

CO2-assisted polymer compression (CAPC) is a method for fabricating porous polymer materials in which the polymer is plasticized with CO2 and then pressed. In this work, a two-step molding method is adapted, and a porous membrane with multiple layers of varying porosity is fabricated by laminating sheets of a single starting material. A model is constructed in which the expansion owing to CO2 and compression reflected by the longitudinal elastic modulus are considered. The model is constructed based on a two-layer experiment and extended to three layers. From the model simulation, the conditions for fabricating a multilayer porous polymer membrane with three layers of varying porosity (0.6, 0.5, and 0.4) and identical thickness (0.6 mm) are calculated. Finally, a porous membrane with varying porosity is fabricated based on the simulated design.

Flexible and transparent composite nanofibre membrane that was fabricated via a "green" electrospinning method for efficient particulate matter 2.5 capture

Air particulate pollution from ever-increasing industrialization poses an enormous threat to public health. Thus, the development of a green air filter with high efficiency and performance is of urgent necessity. In this study, we introduce a new effective air filtration membrane that can be used for outdoor protection. The air filter's composite nanofibre materials were prepared from polyvinyl alcohol (PVA)-sodium lignosulfonate (LS) via a "green" electrospinning method and thermal crosslinking. The addition of LS helped increase the PM_2.5 removal efficiency compared to that of a pure PVA nanofibre membrane. The pressure drops of the electrospun PVA-LS membranes exceeded those of the pristine PVA air filter. The remarkable air filtration performance was maintained even after 10 cycles of circulation filtration. In addition, the PVA-LS composite nanofibre membrane exhibited excellent mechanical properties and transparency due to the introduction of LS. This study provides new insight into the design and development of high-performance and high-visibility green filter media, which include personal protection and building screens.

Multifunctional composite membrane based on BaTiO3@PU/PSA nanofibers for high-efficiency PM2.5 removal

In this study, a new barium titanate@polyurethane/polysulfonamide (BaTiO₃@PU/PSA) composite nanofibrous membrane with comprehensive properties for high temperature filtration and robust PM2.5 removal was successfully fabricated through the blending spinning of PU and PSA and the introduction of BaTiO₃. As a consequence, the BaTiO₃@PU/PSA membrane achieved the high capture efficiency of 99.99 % for fine particulates, low pressure drop of 39.4 ± 0.2 Pa, good mechanical property (13.27 MPa), sufficient flexibility, high thermal stability (up to 300 °C), favorable flame-retardancy as well as superior chemical resistance against acid and alkali. Especially, to intuitively reveal the relationship between the fiber structure, high temperature environment, gas velocity and filtration performance of the composite membrane, the filtration processes were carefully investigated through the analog simulation. More importantly, the BaTiO₃@PU/PSA membrane exhibited high-efficiency PM2.5 purification capacity, and the removal efficiency kept stable after high temperature, acid or alkali treatment, ascribing to the advantageous structure of PSA, PU and BaTiO₃. Overall, the BaTiO₃@PU/PSA nanofiber membranes with versatility are a promising high-efficiency candidate for dust removal, particularly in harsh conditions.