Towards Sustainable and Multifunctional Air-Filters: A Review on Biopolymer-Based Filtration Materials

Scalable pilot production of highly efficient 5-ply respiratory masks enhanced by bacterial cellulose nanofibers

This study presents the pilot-scale production of highly efficient real respiratory masks enhanced by bacterial cellulose nanofibers (BCNFs). The BCNFs suspension was deposited onto tissue paper substrates using fog spray technique with three BCNFs grammage levels of 0.5, 1, and 2 g/m2, followed by freeze drying. Also, two continuous and batch welding processes have been used to construct the core structure of the masks. Field emission scanning electron microscopy (FE-SEM) confirmed the uniform distribution and size of fog-sprayed BCNFs and their pore networks. With increase in BCNFs grammage, the adsorption efficiency of masks increased in both continuous and batch production methods. The mask produced through batch processing showed the highest efficiency of 99.2 % (N99) for the particulate matter of 0.3 μm, while the maximum corresponding efficiency value in continuous processing was 95.4 % (N95). The pressure drops of the masks increased with the increase in BCNFs grammage in both methods. The maximum pressure drops of N95 and N99 masks obtained were 112 ± 10 Pa and 128 ± 8 Pa, respectively. Notably, the filtration efficacy of masks was preserved when subjected to relative humidity fluctuations ranging from 30 % to 70 %. The successful findings of this study offer significant promise for future air filtration applications.

Gel-confined fabrication of fully bio-based filtration membrane for green capture and rapid detection of airborne microbes

Air filtration has become a desirable route for collecting airborne microbes. However, the potential biotoxicity and sterilization of current air filtration membranes often lead to undesired inactivation of captured microbes, which greatly limits microbial non-traumatic transfer and recovery. Herein, we report a gel-confined phase separation strategy to rationally fabricate a fully bio-based filtration membrane (SGFM) using soluble soybean polysaccharide and gelatin. The versatile SGFM features fascinating honeycomb micro-nano architecture and hierarchical interconnected porous structures for microbial capture, and achieves a lower pressure drop, higher interception efficiency (99.3%), and superior microbial survivability than commercial gelatin filtration membranes. Particularly, the water-dissolvable SGFM can greatly simplify the elution and extraction process after bioaerosol sampling, thereby bringing about maximum sample transfer and vigorous recovery of collected microbes. Meanwhile, green capture coupled with ATP bioluminescence endows the SGFM with rapid and quantitative detection capability for airborne microbes. This work may pave the way for designing green protocols for the detection of bioaerosols.

Nanoporous air filtering systems made from renewable sources: benefits and challenges

There is a crucial need for air purification systems due to increasing air contamination, while conventional air-filtering materials face challenges in eliminating gaseous and particulate pollutants. This review examines the development and characteristics of nanoporous polymeric materials developed from renewable resources, which have rapidly advanced in recent years. These materials offer more sustainable alternatives for nanoporous structures made out of conventional polymers and significantly impact the properties of porous polymers. The review explores nanoporous materials' production from renewable sources, filtering mechanisms, physicochemical makeup, and sensing capabilities. The recent advancements in this field aim to enhance production techniques, lower pressure drop, and improve adsorption efficiency. Currently, supporting approaches include using adsorbent layers and binders to immobilize nanoporous materials. Furthermore, the prospects and challenges of nanoporous materials obtained from renewable sources used for air purification are discussed.

Versatile filter membrane for effective sampling and real-time quantitative detection of airborne pathogens

Construction of air filter membranes bearing prominent collecting and transferring capability is highly desirable for detecting airborne pathogens but remains challenging. Here, a hyaluronic acid air filter membrane (HAFM) with tunable heterogeneous micro-nano porous structures is straightforwardly constructed through the ethanol-induced phase separation strategy. Airborne pathogens can be trapped and collected by HAFM with high performance due to the ideal trade-off between removal efficiency and pressure drop. By exempting the sample elution and extraction processes, the HAFM after filtration sampling can not only directly disperse on the agar plate for colony culture but also turn to an aqueous solution for centrifugal enrichment, which significantly reduces the damage and losses of the captured microorganisms. The following combination with ATP bioluminescence endows the HAFM with a real-time quantitative detection function for the captured airborne pathogens. Benefiting from high-efficiency sampling and non-traumatic transfer of airborne pathogens, the real-world bioaerosol concentration can be facilely evaluated by the HAFM-based ATP assay. This work thus not only provides a feasible strategy to fabricate air filter membranes for efficient microbial collection and enrichment but also sheds light on designing advanced protocols for real-time detection of bioaerosols in the field.

Electrospinning in personal protective equipment for healthcare work

Protection in many service areas is mandatory for good performance in daily activities of workers, especially health areas. Personal protective equipment (PPE) is used to protect patients and health workers from contamination by harmful pathogens and body fluids during clinical attendance. The pandemic scenario caused by SARS-CoV-2 has shown that the world is not prepared to face global disease outbreaks, especially when it comes to the PPE of healthcare workers. In the last years, the world has faced a deficiency in the development of advanced technologies to produce high-quality PPE to attend to the exponential increasing demand. Electrospinning is a technology that can be used to produce high-quality PPE by improving the protective action of clothing. In the face of this concern, this manuscript presents as focus the potential of electrospinning to be applied in protective clothing. PPE mostly used by healthcare workers are also presented. The physico-chemical characteristics and production processes of medical textiles for PPE are addressed. Furthermore, an overview of the electrospinning technique is shown. It is important to highlight most research about electrospinning applied to PPE for health areas presents gaps and challenges; thus, future projections are also addressed in this manuscript.

Electrospun transparent nanofibers as a next generation face filtration media: A review

The development of fascinating materials with functional properties has revolutionized the humankind with materials comfort, stopped the spreading of diseases, relieving the environmental pollution pressure, economized government research funds, and prolonged their serving life. The outbreak of Coronavirus Disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has triggered great global public health concern. Face masks are crucial tools to impede the spreading of SARS-CoV-2 from human to human. However, current face masks exhibit in a variety of colors (opaque), like blue, black, red, etc., leading to a communication barrier between the doctor and the deaf-mute patient when wearing a mask. High optical transparency filters can be utilized for both personal protection and lip-reading. Thus, shaping face air filter into a transparent appearance is an urgent need. Electrospinning technology, as a mature technology, is commonly used to form nanofiber materials utilizing high electrical voltage. With the alteration of the diameters of nanofibers, and proper material selection, it would be possible to make the transparent face mask. In this article, the research progress in the transparent face air filter is reviewed with emphasis on three parts: mechanism of the electrospinning process and light transmission, preparation of transparent face air filter, and their innovative potential. Through the assessment of classic cases, the benefits and drawbacks of various preparation strategies and products are evaluated, to provide general knowledge for the needs of different application scenarios. In the end, the development directions of transparent face masks in protective gear, particularly their novel functional applications and potential contributions in the prevention and control of the epidemic are also proposed.

Nude and Modified Electrospun Nanofibers, Application to Air Purification

Air transports several pollutants, including particulate matter (PM), which can produce cardiovascular and respiratory diseases. Thus, it is a challenge to control pollutant emissions before releasing them to the environment. Until now, filtration has been the most efficient processes for removing PM. Therefore, the electrospinning procedure has been applied to obtain membranes with a high filtration efficiency and low pressure drop. This review addressed the synthesis of polymers that are used for fabricating high-performance membranes by electrospinning to remove air pollutants. Then, the most influential parameters to produce electrospun membranes are indicated. The main results show that electrospun membranes are an excellent alternative to having air filters due to the versatility of the process, the capacity for controlling the fiber diameter, porosity, high filtration efficiency and low-pressure drop.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Electrospun Nanofibers Containing Natural Deep Eutectic Solvents Exhibiting a 3D Rugose Morphology and Charge Retention Properties

In the present study, electrospun nanofibers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a biodegradable polyester, containing natural deep eutectic solvents (NADES) were obtained and reported for the first time, exhibiting an unreported 3D morphology and enhanced charge retention properties. Choline chloride (ChCl)/urea/water in a molar ratio of 1:2:1 was used as the NADES model system. Electrospun nanofibers were produced from a 10 wt % solution of PHBV containing 26 wt % NADES with respect to the polymer and were deposited on different substrates, that is, aluminum foil and non-woven spunbond polypropylene (PP). The morphology and charge retention ability were characterized under different conditions and on different substrates. The attained fiber morphology for the NADES-containing mats showed an average fiber diameter of around 300 nm, whereas the pure PHBV polymer under the same conditions produced electrospun fibers of around 880 nm. However, the deposition of PHBV/ChCl/urea/water fibers resulted in a surprising macroscopic rugose 3D surface morphology made of aligned nanofibers when processed at 50% relative humidity (RH). The nanofiber grammages above which this 3D morphology, associated with NADES-induced charge retention, formed was found to be dependent on the substrate used and RH. This morphology was not seen at 20% RH nor when pure PHBV was produced. Charge stability studies revealed that PHBV/ChCl/urea/water nanofibers exhibited lasting charge retention, especially when sandwiched between spunbond polypropylene textiles. Finally, such multilayer structures containing a very thin double layer of PHBV/ChCl/urea/water fibers after corona treatment exhibited improved paraffin aerosol penetration, which was ascribed to the combination of thinner fibers and their charge retention capacity. The here-developed electrospun PHBV fibers containing NADES demonstrated for the first time a new potential application as electret filter media.

Smart Mask as Wearable for Post-Pandemic Personal Healthcare

A mask serves as a simple external barrier that protects humans from infectious particles from poor air conditions in the surrounding environment. As an important personal protective equipment (PPE) to protect our respiratory system, masks are able not only to filter pathogens and dust particles but also to sense, reflect or even respond to environmental conditions. This smartness is of particular interest among academia and industries due to its potential in disease detection, health monitoring and caring aspects. In this review, we provide an overlook of the current air filtration strategies used in masks, from structural designs to integrated functional modules that empower the mask's ability to sense and transfer physiological or environmental information to become smart. Specifically, we discussed recent developments in masks designed to detect macroscopic physiological signals from the wearer and mask-based disease diagnoses, such as COVID-19. Further, we propose the concept of next-generation smart masks and the requirements from material selection and function design perspectives that enable masks to interact and play crucial roles in health-caring wearables.

Application of 2D Materials for Adsorptive Removal of Air Pollutants

Air pollution is on the priority list of global safety issues, with the concern of fatal environmental and public health deterioration. 2D materials are potential adsorbent materials for environmental decontamination, owing to their high surface area, manageable interlayer binding, large surface-to-volume ratio, specific binding capability, and chemical, thermal, and mechanistic stability. Specifically, graphene oxide and reduced graphene oxide have been attracting attention, taking advantage of their low cost synthesis, excessive oxygen containing surface functionalities, and intrinsic aqueous dispersibility, making them desirable for the development of cost-effective, high performance air filters. Many different material designs have been proposed to expand their filtration capability, including the functionalization and integration with other metals and metal oxides, which act not only as binding agents to the target pollutants but also as antimicrobial agents. This review highlights the advantages and drawbacks of 2D materials for air filtration and summarizes the interrelationships among various strategies and the resultant filtration performance in terms of structural engineering, morphology control, and material compositions. Finally, potential future directions are suggested toward the idealized designs of 2D material based air filters.

Electrospun-Based Membranes as a Key Tool to Prevent Respiratory Infections

The use of electrospun meshes has been proposed as highly efficient protective equipment to prevent respiratory infections. Those infections can result from the activity of micro-organisms and other small dust particles, such as those resulting from air pollution, that impair the respiratory tract, induce cellular damage and compromise breathing capacity. Therefore, electrospun meshes can contribute to promoting air-breathing quality and controlling the spread of such epidemic-disrupting agents due to their intrinsic characteristics, namely, low pore size, and high porosity and surface area. In this review, the mechanisms behind the pathogenesis of several stressors of the respiratory system are covered as well as the strategies adopted to inhibit their action. The main goal is to discuss the performance of antimicrobial electrospun nanofibers by comparing the results already reported in the literature. Further, the main aspects of the certification of filtering systems are highlighted, and the expected technology developments in the industry are also discussed.

Advanced materials used in wearable health care devices and medical textiles in the battle against coronavirus (COVID-19): A review

The novel coronavirus disease (COVID-19) has generated great confusion around the world, affecting people's lives and producing a large number of deaths. The development of portable and wearable devices is of great importance in several fields such as point-of-care medical applications and environmental monitoring. Wearable devices with an ability to collect various types of physiological records are progressively becoming incorporated into everyday life of people. Physiological indicators are essential health indicators and their monitoring could efficiently enable early discovery of disease. This would also help decrease the number of extra severe health problems, in disease avoidance, and lower the overall public sector health cost. Protective clothing is nowadays a main part of textiles classified as technical or industrial textiles. Protective clothing aims to protect its wearer from the harsh environmental impacts that may result in injury or death. Providing protection for the common population has also been taken seriously considering the anticipated disaster due to virus attacks. This review highlights the properties of the materials that are used in wearable health care device and medical textiles.

Electrospun Nanofiber Membranes for Air Filtration: A Review

Nanomaterials for air filtration have been studied by researchers for decades. Owing to the advantages of high porosity, small pore size, and good connectivity, nanofiber membranes prepared by electrospinning technology have been considered as an outstanding air-filter candidate. To satisfy the requirements of material functionalization, electrospinning can provide a simple and efficient one-step process to fabricate the complex structures of functional nanofibers such as core-sheath structures, Janus structures, and other multilayered structures. Additionally, as a nanoparticle carrier, electrospun nanofibers can easily achieve antibacterial properties, flame-retardant properties, and the adsorption properties of volatile gases, etc. These simple and effective approaches have benefited from the significate development of electrospun nanofibers for air-filtration applications. In this review, the research progress on electrospun nanofibers as air filters in recent years is summarized. The fabrication methods, filtration performances, advantages, and disadvantages of single-polymer nanofibers, multipolymer composite nanofibers, and nanoparticle-doped hybrid nanofibers are investigated. Finally, the basic principles of air filtration are concluded upon and prospects for the application of complex-structured nanofibers in the field of air filtration are proposed.

Mitigation Strategies of Air Pollutants for Mechanical Ventilated Livestock and Poultry Housing—A Review

The fast development of large-scale intensive animal husbandry has led to an increased proportion of atmospheric pollution arising from livestock and poultry housing. Atmospheric pollutants, including particulate matter (PM), ammonia (NH3), hydrogen sulfide (H2S), and greenhouse gases (GHG), as well as other hazardous materials (e.g., gases, bacteria, fungi and viruses), have significant influences upon the local atmospheric environment and the health of animals and nearby residents. Therefore, it is imperative to develop livestock and poultry housing mitigation strategies targeting atmospheric pollution, to reduce its negative effects on the ambient atmosphere and to promote sustainable agricultural production. In this paper, we summarize the various strategies applied for reducing outlet air pollutants and purifying inlet air from mechanical ventilated livestock and poultry housing. This review highlights the current state of knowledge on the removal of various atmospheric pollutants and their relative performance. The potential optimization of processes and operational design, material selection, and other technologies, such as electrostatic spinning, are discussed in detail. The study provides a timely critical analysis to fill the main research gaps or needs in this domain by using practical and stakeholder-oriented evaluation criteria.

Preparation of Needleless Electrospinning Polyvinyl Alcohol/Water-Soluble Chitosan Nanofibrous Membranes: Antibacterial Property and Filter Efficiency

Electrospinning is an efficient method of producing nanofibers out of polymers that shows a great potential for the filtration territory. Featuring water-soluble chitosan (WS-CS), a low-pollution process and a self-made needleless machine, PVA/WS-CS nanofibrous membranes were prepared and evaluated for nanofiber diameter, bacteriostatic property, filtration efficiency, pressure drop, and quality factor. Test results indicate that the minimal fiber diameter was 216.58 ± 58.15 nm. Regardless of the WS-CS concentration, all of the PVA/WS-CS nanofibrous membranes attained a high porosity and a high water vapor transmission rate (WVTR), with a pore size of 12.06–22.48 nm. Moreover, the membranes also exhibit bacteriostatic efficacy against Staphylococcus aureus, an optimal quality factor of 0.0825 Pa⁻¹, and a filtration efficiency as high as 97.0%, that is 72.5% higher than that of common masks.

On the design of particle filters inspired by animal noses

Passive filtering is a common strategy to reduce airborne disease transmission and particulate contaminants across scales spanning orders of magnitude. The engineering of high-performance filters with relatively low flow resistance but high virus- or particle-blocking efficiency is a non-trivial problem of paramount relevance, as evidenced in the variety of industrial filtration systems and face masks. Next-generation industrial filters and masks should retain sufficiently small droplets and aerosols while having low resistance. We introduce a novel 3D-printable particle filter inspired by animals' complex nasal anatomy. Unlike standard random-media-based filters, the proposed concept relies on equally spaced channels with tortuous airflow paths. These two strategies induce distinct effects: a reduced resistance and a high likelihood of particle trapping by altering their trajectories with tortuous paths and induced local flow instability. The structures are tested for pressure drop and particle filtering efficiency over different airflow rates. We have also cross-validated the observed efficiency through numerical simulations. We found that the designed filters exhibit a lower pressure drop, compared to commercial masks and filters, while capturing particles bigger than approximately 10 μm. Our findings could facilitate a novel and scalable filter concept inspired by animal noses.

Efficient capture of airborne PM by nanotubular conjugated microporous polymers based filters under harsh conditions

The exploitation of high-performance filters which can capture and remove airborne particulate matter (PM) in harsh conditions is greatly important to limit the serious effect of PM on human health. Herein, we demonstrate a simple approach for the creation of robust and hierarchically porous filters based on conjugated microporous polymers (CMPs) nanotubes for efficient PM capture. Taking advantage of their inherently superhydrophobic wettability, the CMPs-based filters possess high filtration efficiency of higher than 99.4% for PM_0.3 and 99.9% for PM_2.5 and PM₁₀, respectively, even in high humidity environment (RH ≥ 94%). The CMPs-based filters show highly physicochemical and thermal stability, e.g., by calcination at 500 °C for 2 h, the filtration efficiency of the samples still reaches as great as 99.4% for both PM_2.5 and PM₁₀ with a low-pressure drop of only 10 Pa. In addition, these CMPs-based filters can be easily regenerated and their high PM filtration efficiency remains nearly unchanged by a simple methanol washing. More interestingly, the CMPs-based filters also exhibit superior antibacterial performance, which enables them to sterilize or eliminate the bacteria possibly loaded on PM pollutions, thus showing great potential for various applications such as PM removal, air purification and so on.

Hybrid Bead Air Filters with Low Pressure Drops at a High Flow Rate for the Removal of Particulate Matter and HCHO

A tower air filtration system was designed in which bead air filters (BAFs) were actively rotated by a fan motor to remove particulate matter (PM) or HCHO gas. Three types of BAF, hydrophilic, hydrophobic, and hybrid, were prepared and compared for the removal of PM and HCHO gas. A tower air filtration system loaded with hybrid BAFs purified 3.73 L of PM (2500 μg/m³ PM_2.5) at a high flow rate of 3.4 m/s with high removal efficiency (99.4% for PM_2.5) and a low pressure drop (19 Pa) in 6 min. Against our expectations, the PM_2.5 removal efficiency slightly increased as the air velocity increased. The hybrid BAF-200 showed excellent recyclability up to 50 cycles with high removal efficiencies (99.4-93.4% for PM_2.5). Furthermore, hydrophilic BAF-200 could permanently remove 3.73 L of HCHO gas (4.87 ppm) and return the atmosphere to safe levels (0.41-0.31 ppm) within 60 min without any desorption of HCHO gas.

Biodegradable and high-performance multiscale structured nanofiber membrane as mask filter media via poly(lactic acid) electrospinning

The usage of single-use face masks (SFMs) has increased since the outbreak of the coronavirus pandemic. However, non-degradability and mismanagement of SFMs have raised serious environmental concerns. Moreover, both melt-blown and nanofiber-based mask filters inevitably suffer from poor filtration performance, like a continuous decrease in the removal efficiency for particulate matter (PM) and weak breathability. Herein, we report a new method to create biodegradable and reusable fibrous mask filters. The filter consists of a true nanoscale bio-based poly(lactic acid) (PLA) fiber (an average size of 37 ± 4 nm) that is fabricated via electrospinning of an extremely dilute solution. Furthermore, we designed a multiscale structure with integrated features, such as low basis weight (0.91 g m-2), small pore size (0.73 μm), and high porosity (91.72%), formed by electrospinning deposition of true nanoscale fibers on large pore of 3D scaffold nanofiber membranes. The resultant mask filter exhibited a high filtration efficiency (PM0.3-99.996%) and low pressure drop (104 Pa) superior to the commercial N95 filter. Importantly, this filter has a durable filtering efficiency for PM and natural biodegradability based on PLA. Therefore, this study offers an innovative strategy for the preparation of PLA nanofibers and provides a new design for high-performance nanofiber filters.

Bifunctional conjugated microporous polymer based filters for highly efficient PM and gaseous iodine capture

Cross-linked conjugated microporous polymers (CMPs) based air filters obtained by a one-step cross-coupling reaction for effective capture of particulate matter and gaseous iodine from dusty air.

Co-existing "spear-and-shield" air filter: Anchoring proteinaceous pathogen and self-sterilized nanocoating for combating viral pandemic

Infectious pollutants bioaerosols can threaten human public health. In particular, the indoor environment provides a unique exposure situation to induce infection through airborne transmission like SARS-CoV-2. To prevent the infection from spreading, personal protective equipment or indoor air purification is necessary. However, it has been discovered that the conventional filter can become contaminated by pathogen-containing aerosols, meaning that advanced filtering and self-sterilization systems are required. Here, we fabricate a multilayered nanocoating around the fabric using laponite (LAP) with Cu²⁺ ions (LAP-Cu²⁺ nanocoating) two contradictory functions in one system: trapping proteinaceous pathogens and antibacterial effect. Due to the strong LAP-protein interaction, albumin and spike protein (S-protein) are trapped into the fabric when proteins are sprayed using a nebulizer. The protein-blocking performance of the nanocoated fabric is 9.55-fold higher than bare fabric. These trapping capacities are retained after rinsing and repeated adsorption cycles, showing reproducibility for air filtration. Even though the protein-binding occurred, the LAP-Cu²⁺ fabric indicates antibacterial effect. LAP-Cu²⁺ fabric has an equivalent air and water transmittance rate to that of bare fabric with a stability under physiological environment. Therefore, given its excellent "Spear-and-shield" functions, the proposed LAP-Cu²⁺ fabric shows great potential for use in filter and masks during the viral pandemic.

Low-Voltage Bacterial and Viral Killing Using Laser-Induced Graphene-Coated Non-woven Air Filters

Laser-induced graphene (LIG) is uniquely positioned to advance applications in which electrically conductive carbon coatings are required. Recently, the antifouling, antiviral, and antibacterial properties of LIG have been proven in both air and water filtration applications. For example, an unsupported LIG based filter (pore size: ∼0.3 μm) demonstrated exceptional air filtration properties, while its joule heating effects successfully sterilized and removed unwanted biological components in air despite persisting challenges such as pressure drop, energy consumption, and lack of mechanical robustness. Here, we developed a polyimide (PI) non-woven supported LIG air filter with negligible pressure drop changes compared to the non-woven support material and showed that low electrical current density inactivates aerosolized bacteria. A current density of 4.5 mA/cm² did not cause significant joule heating, and 97.2% bacterial removal was obtained. The low-voltage antibacterial mechanism was elucidated using bacterial inhibition experiments on a titanium surface and on an LIG surface fabricated on dense PI films. Complete sterilization was obtained using current densities of ∼8 mA/cm² applied for 2 min or ∼ 6 mA/cm² for 10 min upon the dense PI-LIG surface. Lastly, >98% bacterial removal was observed using a low-resistance LIG-coated non-woven polyimide air filter at 5 V. However, only very low voltages (∼0.3 V) were needed to remove ∼99% Pseudomonas aeruginosa bacteria and 100% of T4 virus when the LIG-coated filters were hybridized with a stainless steel mesh. Our results show that low current density levels at very low voltages are sufficient for substantial bacterial and viral inactivation, and that these principles might be effectively used in a wide number of air filtration applications such as air conditioners or other ventilation systems, which might limit the spread of infectious particles in hospitals, homes, workplaces, and the transportation industry.

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.

Potential natural polymer-based nanofibres for the development of facemasks in countering viral outbreaks

The global coronavirus disease 2019 (COVID-19) pandemic has rapidly increased the demand for facemasks as a measure to reduce the rapid spread of the pathogen. Throughout the pandemic, some countries such as Italy had a monthly demand of ca. 90 million facemasks. Domestic mask manufacturers are capable of manufacturing 8 million masks each week, although the demand was 40 million per week during March 2020. This dramatic increase has contributed to a spike in the generation of facemask waste. Facemasks are often manufactured with synthetic materials that are non-biodegradable, and their increased usage and improper disposal are raising environmental concerns. Consequently, there is a strong interest for developing biodegradable facemasks made with for example, renewable nanofibres. A range of natural polymer-based nanofibres has been studied for their potential to be used in air filter applications. This review article examines potential natural polymer-based nanofibres along with their filtration and antimicrobial capabilities for developing biodegradable facemask that will promote a cleaner production.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized. (1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

Electrospun Nanofiber Mats for Filtering Applications-Technology, Structure and Materials

Air pollution is one of the biggest health and environmental problems in the world and a huge threat to human health on a global scale. Due to the great impact of respiratory viral infections, chronic obstructive pulmonary disease, lung cancer, asthma, bronchitis, emphysema, lung disease, and heart disease, respiratory allergies are increasing significantly every year. Because of the special properties of electrospun nanofiber mats, e.g., large surface-to-volume ratio and low basis weight, uniform size, and nanoporous structure, nanofiber mats are the preferred choice for use in large-scale air filtration applications. In this review, we summarize the significant studies on electrospun nanofiber mats for filtration applications, present the electrospinning technology, show the structure and mechanism of air filtration. In addition, an overview of current air filtration materials derived from bio- and synthetic polymers and blends is provided. Apart from this, the use of biopolymers in filtration applications is still relatively new and this field is still under-researched. The application areas of air filtration materials are discussed here and future prospects are summarized in conclusion. In order to develop new effective filtration materials, it is necessary to understand the interaction between technology, materials, and filtration mechanisms, and this study was intended to contribute to this effort.

Gelatin/β-Cyclodextrin Bio-Nanofibers as respiratory filter media for filtration of aerosols and volatile organic compounds at low air resistance

Air pollution is a universal concern. The suspended solid/liquid particles in the air and volatile organic compounds (VOCs) are ubiquitous. Synthetic polymer-based air filter media not only has disposal issues but also is a source of air and water pollution at the end of their life cycle. It has been a challenge to filter both particulate matter and VOC pollutants by a common biodegradable filter media having low air resistance. This study reports gelatin/β-cyclodextrin composite nanofiber mats with dual function air filtration ability at reduced air resistance (148 Pa) and low basis weight (1 g/m²). Gelatin/β-cyclodextrin nanofibers captured aerosols (0.3-5 μm) with < 95% filtration efficiency at 0.029/Pa quality factor. They adsorbed great amount of xylene (287 mg/g), benzene (242 mg/g), and formaldehyde (0.75 mg/g) VOCs. VOC adsorption of gelatin/β-cyclodextrin nanofibers is found several times higher than a commercial face mask and pristine powder samples. This study provides a solution for a 'green' dual function respiratory air filtration at low resistance. Gelatin/β-cyclodextrin nanofibers also have the potential to filter nano-sized viruses.

2D and 3D Bulk Materials for Environmental Remediation: Air Filtration and Oil/Water Separation

Air and water pollution pose an enormous threat to human health and ecosystems. In particular, particulate matter (PM) and oily wastewater can cause serious environmental and health concerns. Thus, controlling PM and oily wastewater has been a great challenge. Various techniques have been reported to effectively remove PM particles and purify oily wastewater. In this article, we provide a review of the recent advancements in air filtration and oil/water separation using two- and three-dimensional (2D and 3D) bulk materials. Our review covers the advantages, characteristics, limitations, and challenges of air filters and oil/water separators using 2D and 3D bulk materials. In each section, we present representative works in detail and describe the concepts, backgrounds, employed materials, fabrication methods, and characteristics of 2D and 3D bulk material-based air filters and oil/water separators. Finally, the challenges, technical problems, and future research directions are briefly discussed for each section.

Environmentally Friendly Methylcellulose-Based Binders for Active and Passive Dust Control

Particulate matter (PM) is an essential indicator to evaluate air pollution, threatening human health. Although PM control could be achieved by using a variety of polymeric materials, identifying effective and green materials remains elusive in dust control technology. Here, we have employed environmentally friendly cellulose modified by methyl side groups, such as methylcellulose (MC)-based polymers, and evaluated their PM reduction efficiency when utilized in active and passive dust control methods, such as dust suppressants and air filters, respectively. When 25 m/s wind was applied on soil treated by MC-based polymers, PM emissions were reduced 95% or 85% lower than the soil treated by only water or the other cellulose without methyl side groups. The MC-based polymer was also effectively suppressed mineral dust from a local copper mine in Arizona with approximately 50 times lower amounts than a synthetic polymer containing methyl side groups. Furthermore, when MC-based polymers have deposited on filters of commercial face masks, the average filtration efficiency improved to greater than 99% while maintaining airflow resistance. Our results present that environmentally friendly MC-based polymers can act as dust binders that effectively agglomerate air pollutants, preventing the PM emission from dust sources and the inhalation after being suspended in the air; thus, labeling them as essential materials for advanced active and passive dust control technology.

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.

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

To address the challenge of high-temperature air filtration, a novel electreted polysulfonamide/polyacrylonitrile-boehmite (PSA/PAN-B) composite nanofiber based filter was developed via electrospinning for effective high-temperature dust removal. In this study, the spinnability of PSA was greatly improved by adding a small amount of PAN as an auxiliary polymer, and the introduction of a boehmite electret further significantly reinforced the properties of PSA fibers. As a result, the PSA/PAN-B membrane exhibited a high filtration efficiency (up to 99.52 ± 0.32%), low pressure drop (45.16 ± 1.39 Pa), excellent flexibility, good mechanical properties, high thermal stability (up to approximately 300 °C), and superior chemical resistance. Through data analysis and 3D simulation, the important benefits of the boehmite electret in the optimization of the PSA fibrous membrane performance were determined: it increases the charge storage capacity, constructs a rough surface morphology, improves the specific surface area, and enhances the mechanical properties. More importantly, the PSA/PAN-B film possessed a robust PM2.5 purification capacity, and the particulate matter removal efficiency was kept unchanged after high-temperature, acid, or alkali treatment-a performance derived from the intrinsic molecular structure of PSA. The PSA/PAN-B composite fibrous membrane, with excellent comprehensive properties, is a promising candidate for air filters, especially in harsh environments, further broadening the applications of PSA and providing new insight into the design of high-performance filters with high-temperature and corrosion resistance.