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Biodegradable Electroactive Nanofibrous Air Filters for Long-Term Respiratory Healthcare and Self-Powered Monitoring
Abstract
The concept of triboelectric nanogenerator (TENG)-based fibrous air filters, in which the electroactive fibers are ready to enhance the electrostatic adsorption by sustainable energy harvesting, is appealing for long-term respiratory protection and in vivo real-time monitoring. This effort discloses a self-reinforcing electroactivity strategy to confer extreme alignment and refinement of the electrospun poly(lactic acid) (PLA) nanofibers, significantly facilitating formation of electroactive phases (i.e., β-phase and highly aligned chains and dipoles) and promotion of polarization and electret properties. It endowed the PLA nanofibrous membranes (NFMs) with largely increased surface potential and filtration performance, as exemplified by efficient removal of PM0.3 and PM2.5 (90.68 and 99.82%, respectively) even at the highest airflow capacity of 85 L/min. With high electroactivity and a well-controlled morphology, the PLA NFMs exhibited superior TENG properties triggered by regular respiratory vibrations, enabling 9.21-fold increase of surface potential (-1.43 kV) and nearly 68% increase of PM0.3 capturing (94.3%) compared to those of conventional PLA membranes. The remarkable TENG mechanisms were examined to elaborately monitor the personal respiration characteristics, particularly those triggered large and rapid variations of output voltages like coughing and tachypnea. Featuring desirable biocompatibility and degradability, the self-powered PLA NFMs permit promising applications in the fabrication of ecofriendly air filters toward high-performance purification and intelligent monitoring.
In many countries and regions, air pollution has become an environmental problem that cannot be ignored. Therefore, air filters with high efficiency, low resistance and strong antibacterial activity should be developed. In this study, carboxymethyl chitosan was impregnated on the surface of PP melt-blown layer to enhance the adsorption of copper ions on PP non-woven fabric. The porous nanomaterial Cu-BTC nanoparticles were loaded on the fibre surface of PP non-woven fabric by in-situ growth method. The micro–nano-composite membrane was prepared by electrospinning TPU on the surface of PP@Cu-BTC. The micro–nano-composite membrane could capture PM2.5 efficiently, and the filtration efficiency of PM2.5 particles was 97.7%. The composite membrane also exhibited excellent antibacterial properties. The inhibition rate of the composite membrane to Staphylococcus aureus and Escherichia coli reached 99.9%. In addition, the composite membrane demonstrated strong stability, and the corresponding inhibition rate did not decrease after washing and drying five times. The membrane featured high-efficiency filtration, excellent antibacterial performance and stability. The PP@Cu-BTC/TPU composite membrane provides a new idea for preparing stable, efficient and antibacterial air filtration membranes.
Polylactic acid (PLA) is a biodegradable plastic with good tensile strength and can be produced from biomass. But there are some defects, such as poor ductility, low barrier properties and poor-UV resistance, which may limit the application and development of PLA. To increase the ductility of PLA, bio-based poly(butylene succinate-butylene furandicarboxylate) (PBSF) was combined with PLA to obtain the blends with different PBSF contents. The blend’s compatibility, crystallinity, thermal, mechanical and rheological properties were determined. The addition of PBSF inhibited the cold crystallization of PLA. Wide-angle X-ray diffractometry (WAXD) showed that the tensile sample of PBSF was semi-crystalline, and the tensile samples of PLA and the blends were almost amorphous. A substantial shift in the stretching vibration of C=O was observed in the FTIR spectra, indicating that the oxygen atom in the furan ring improves the intermolecular interaction between PLA and PBSF. The fracture surfaces of the blends varied from typical brittle morphology to ductile morphology as a result of the addition of PBSF. At 180 °C, the complex viscosity decreased as the PBSF concentration increased. Tensile strength was 31.5 MPa and elongation-at-break was 390% when the amount of PBSF in the blend reached 30% (by weight). The findings demonstrate that PBSF can improve the ductility and processability of PLA.
Intelligent face masks play crucial roles in health monitoring and disease prevention, having attracted huge attention in recent years. However, most of the current intelligent face masks focus on monitoring single physical signal, which were unable to provide comprehensive information. Herein, an intelligent face mask with airflow and temperature sensing abilities, high-efficiency filtration and excellent antibacterial activity was proposed. The real-time airflow monitoring was realized by a triboelectric nanogenerator (TENG), which was composed of electrospun nanofibrous membrane and polydimethylsiloxane (PDMS) composite film. The fabricated electrospun nanofibrous membrane simultaneously played roles as tribo-positive material, filter and antibacterial membrane. The PDMS composite film prepared by co-blending and surface modification was applied as tribo-negative material. It was found that the combination of co-blending and surface modification enhanced the tribo-negative property of the PDMS film, resulting in an increment of output performance of triboelectric nanogenerator. The triboelectric nanogenerator integrated into a face mask could monitor respiratory rate and respiration intensity in real time. Additionally, the temperature sensing was achieved by a serpentine polydimethylsiloxane/laser-induced graphene (PDMS-LIG) temperature sensor. The temperature sensor exhibited a temperature coefficient of resistance of 0.316% °C-1, which could detect subtle temperature variations. Furthermore, the electrospun nanofibrous membrane exhibited excellent filtration performance and antibacterial activity. Therefore, the prepared intelligent face mask showed promising potential for healthcare applications.
Designing wound dressings necessitates the crucial considerations of maintaining a moist environment and implementing effective bacterial control. Furthermore, developing a three-dimensional framework emulating the extracellular matrix (ECM) confers advantages in...
To understand microplastic–nanomaterial interactions in agricultural systems, a randomized block 90-day pot experiment was set up to cultivate ryegrass seedings in a typical red sandy soil amended with compost (1:9 ratio). Polyvinyl chloride (PVC) and polyethylene (PE) microplastic (MP) contaminants were added into pot soils at 0.1 and 10%, whereas nano-Fe3O4 (as nanoenabled agrochemicals) was added at 0.1% and 0.5% in comparison with chemical-free controls. The combination of nano-Fe3O4 and MPs significantly increased the soil pH (+3% to + 17%) but decreased the total nitrogen content (−9% to – 30%; P < 0.05). The treatment group with both nano-Fe3O4 and PE had the highest total soil C (29 g kg–1 vs 20 g kg–1 in control) and C/N ratio (13 vs 8 in control). Increased rhizosphere nano-Fe3O4 concentrations promoted ryegrass growth (+42% dry weight) by enhancing the chlorophyll (+20%) and carotenoid (+15%) activities. Plant leaf and root peroxidase enzyme activity was more significantly affected by nano-Fe3O4 with PVC (+15%) than with PE (+6%). Nano-Fe3O4 significantly changed the ryegrass bacterial community structure from belowground (the rhizoplane and root endosphere) to aboveground (the phylloplane). Under MP contamination, the addition of nano-Fe3O4 increased bacterial diversity (+0.35%) and abundance (+30%) in the phylloplane and further intensified the connectivity of ryegrass aboveground bacterial networks (positive association increased 17%). The structural equation model showed that the change in the plant microbiome was associated with the rhizosphere microbiome. Overall, these findings imply the positive influences of nano-Fe3O4 on the soil–microbe–plant system and establish a method to alleviate the harmful effects of MP accumulation in soils.
Particles with diameters smaller than 2.5 μm (PM2.5) can penetrate the respiratory system and have negative impacts on human health. Filter media with a porous surface and nanofiber/nanonet structure demonstrate superior filtration performance compared to traditional nano- and microfiber-based filters. In this study, nanostructured filters were produced using the electroblowing method from solutions containing different ratios of poly(vinylidene fluoride) (PVDF) and polyethylene glycol (PEG) polymers for the first time. By increasing the water-soluble PEG ratio in PVDF/PEG blend nanofibers and employing a water bath treatment to the produced mat afterward, a more porous fibrous structure was obtained with a lower average fiber diameter. Notably, the removal of PEG from the PVDF/PEG (3–7) sample, which had the highest PEG content, exhibited clustered nanofiber-/nanonet-like structures with average diameters of 170 and 50 nm at the points where the fibers intersect. Although this process resulted in a slight decrease in the filtration efficiency (−1.3%), the significant reduction observed in pressure drop led to a 3.2% increase in the quality factor (QF). Additionally, by exploiting the polarizability of PVDF under an electric field, the filtration efficiency of the nanostructured PVDF filters enhanced with a ratio of 3.6% after corona discharge treatment leading to a 60% improvement in the QF. As a result, the PVDF/PEG (3–7) sample presented an impressive filtration efficiency of 99.57%, a pressure drop (ΔP) of 158 Pa, and a QF of 0.0345 Pa–1.
The rapid rise of triboelectric nanogenerators (TENGs), which are emerging energy conversion devices in advanced electronics and wearable sensing systems, has elevated the interest in high-performance and multifunctional triboelectric materials. Among them, cellulosic materials, affording high efficiency, biodegradability, and customizability, are becoming a new front-runner. The inherently low dielectric constant limits the increase in the surface charge density. However, owing to its unique structure and excellent processability, cellulose shows great potential for dielectric modulation, providing a strong impetus for its advanced applications in the era of Internet of Things and artificial intelligence. This review aims to provide comprehensive insights into the fabrication of dielectric-enhanced cellulosic triboelectric materials via dielectric modulation. The exceptional advantages and research progress in cellulosic materials are highlighted. The effects of the dielectric constant, polarization, and percolation threshold on the charge density are systematically investigated, providing a theoretical basis for cellulose dielectric modulation. Typical dielectric characterization methods are introduced, and their technical characteristics are analyzed. Furthermore, the performance enhancements of cellulosic triboelectric materials endowed by dielectric modulation, including more efficient energy harvesting, high-performance wearable electronics, and impedance matching via material strategies, are introduced. Finally, the challenges and future opportunities for cellulose dielectric modulation are summarized.
The shortage of fossil energy and global climate change have driven humankind to find a new type of renewable, accessible, and clean energy. The triboelectric nanogenerator (TENG) is a new energy technology relying on the coupling of triboelectrification and electrostatic induction. To alleviate the issues of low current density and requirements for complex management circuits, direct-current triboelectric nanogenerators (DC-TENGs) based on the tribovoltaic effect have emerged, exhibiting DC output signals with higher current density and simpler structure design. In this review, the development progress and microscopic mechanisms of DC-TENGs based on the tribovoltaic effect are elaborately summarized for the first time, which is of great significance for designing high-performance DC-TENGs and advancing energy-harvesting technology. The reported DC-TENGs are scientifically classified and the corresponding working mechanisms are explained in detail. The output performances of different types of devices are systematically compared from the aspects of current density, peak power density, open-circuit voltage, short-circuit current, peak power output, and internal resistance. Furthermore, this review delivers a constructive discussion on how to improve the output performance from three perspectives, namely, materials and structures, external parameters, and multiple energy harvesting strategies. Finally, the potential application fields and development prospects of DC-TENGs are discussed. It is expected that the diversified DC-TENGs will bring about revolutionary development in high-efficiency energy harvesting and broaden the applications in intelligent IoTs.
As an on‐skin electronic device, artificial skin shows great potential in medical monitoring and personal electronics, which also holds promise to develop human‐machine merging interfaces. However, merging artificial skins with human bodies is largely restricted by the dissimilarity of material compositions in existing artificial skins and biological tissues. Naturally conductive protein is a potential material candidate for artificial skins, nevertheless, it suffers from the critical issue of dehydration which harms its proton conductivity. Inspired by the sebum membrane of human skin, herein, a protein‐based bioprotonic hydrogel (PBH) with reliable water retention ability is reported for artificial skins. The bovine serum albumin with natural proton conductivity is utilized in the PBH, and the glycerol that originally presents on human skin surface is used as an artificial sebum membrane to retain water. The PBH can act as a bioprotonic skin (B‐skin) for collecting electrophysiological signals and self‐powered sensing. Based on the B‐skin, intelligent robot and cellphone control systems are demonstrated. Compared with present artificial skins, this B‐skin is all made out of biological materials that are consistent with material components of human skin tissues including proteins, endogenous glycerol, and water. Such a B‐skin may enable the development of next‐generation human‐machine merging interfaces.
Aerosol particles, such as the widespread COVID-19 recently, have posed a great threat to humans. Combat experience has proven that masks can protect against viruses; however, the epidemic in recent years has caused serious environmental pollution from plastic medical supplies, especially masks. Degradable filters are promising candidates to alleviate this problem. Degradable nanofiber filters, which are developed by the electrospinning technique, can achieve superior filtration performance. This review focuses on the basic introduction to air filtration, the general aspects of face masks, and nanofibers. Furthermore, the progress of the state of art degradable electrospun nanofiber filters have been summarized, such as silk fibroin (SF), polylactic acid (PLA), chitosan, cellulose, and zein. Finally, the challenges and future development are highlighted.
Controlled incorporation of bioactive hydroxyapatite (HA) into poly(lactic acid) (PLA) signifies a promising approach to design and development of biomedical-adaptive materials. Here we unravel a microwave-assisted biomineralization approach to synthesis of HA nanowhiskers (HANWs), which were characterized by well-controlled diameter (∼30 nm) and length (80 − 120 nm), combined with a desirable calcium − phosphorus ratio (Ca/P) of 1.67. A high-shear liquid dispersion (HSLD) method that provided a combination of high pressure (up to 50 kPa) and high shear rate approaching 10000 s⁻¹ was established to fabricate homogeneous PLA/HANWs composites. In particular, upon incorporation of 30 wt % HANWs the tensile strength and elastic modulus of PLA-HA30 (76.7 MPa and 3.3 GPa) were elevated by 48% and 84% compared to those of pure PLA, respectively, as accompanied by a nearly 2-fold increase in the cell viability. This work paves a facile yet effective roadway to strong and osteoconductive PLA composites appealing for bone tissue repairing.
Exposure to ambient particulate matter (PM2.5) currently contributes to millions of global premature deaths every year. Here, we assess the pollution and health futures in five 2015–2100 scenarios using an integrated modelling framework. On the basis of a global Earth System Model (GFDL-ESM4.1), we find lower ambient PM2.5 concentrations, both globally and regionally, in future scenarios that are less fossil fuel-dependent and with more stringent pollution controls. Across the five scenarios, the global cumulative PM2.5-related deaths vary by a factor of two. However, the projected deaths are not necessarily lower in scenarios with less warming or cleaner air. This is because while reducing PM2.5 pollution lowers the exposure level, increasing the size of vulnerable populations can significantly increase PM2.5-related deaths. For most countries, we find that changes in socio-demographic factors (for example, ageing and declining baseline mortality rates) play a more important role than the exposure level in shaping future health burden.
Human‐machine interfaces (HMIs) play important role in the communication between humans and robots. Touchless HMIs with high hand dexterity and hygiene hold great promise in medical applications, especially during the pandemic of coronavirus disease 2019 (COVID‐19) to reduce the spread of virus. However, current touchless HMIs are mainly restricted by limited types of gesture recognition, the requirement of wearing accessories, complex sensing platforms, light conditions, and low recognition accuracy, obstructing their practical applications. Here, an intelligent noncontact gesture‐recognition system is presented through the integration of a triboelectric touchless sensor (TTS) and deep learning technology. Combined with a deep‐learning‐based multilayer perceptron neural network, the TTS can recognize 16 different types of gestures with a high average accuracy of 96.5%. The intelligent noncontact gesture‐recognition system is further applied to control a robot for collecting throat swabs in a noncontact mode. Compared with present touchless HMIs, the proposed system can recognize diverse complex gestures by utilizing charges naturally carried on human fingers without the need of wearing accessories, complicated device structures, adequate light conditions, and achieves high recognition accuracy. This system could provide exciting opportunities to develop a new generation of touchless medical equipment, as well as touchless public facilities, smart robots, virtual reality, metaverse, etc.
Human-machine interfaces (HMIs) are important windows for a human to communicate with the outside world. The current HMI devices such as cellphones, tablets, and computers can be used to help people with aphasia for language expression. However, these conventional HMI devices are not friendly to some particular groups who also lose their abilities of physical movements like in the intensive care unit (ICU) or vegetative patients to realize language expression. Herein, we report a breath-driven triboelectric nanogenerator (TENG) acting as a HMI sensor for language expression through human breathing without voice controls or manual operations. The TENG is integrated within a mask and fabricated via a three-dimensional (3D) printing method. When wearing the mask, the TENG can produce responsive electric signals corresponding to the airflow from breathing, which is capable of recognizing human breathing types with different intensities, lengths, and frequencies. On the basis of the breathing recognition ability, a breathing-based language expressing system is further developed through introducing the Morse code as a communication protocol. Compared with conventional language expressing devices, this system can extract subjective information of a person from breathing behaviors and output corresponding language text, which is not relying on voices or physical movements. This research for the first time introduces the self-powered breathing-based language expressing method to the field of HMI technology by using a 3D printed TENG, and could make HMI interactions become more friendly and fascinating.
Face masks, which serve as personal protection equipment, have become ubiquitous for combating the ongoing COVID-19. However, conventional electrostatic-based mask filters are disposable and short-term effective with high breathing resistance, causing respiratory ailments and massive consumption (129 billion monthly), intensifying global environmental pollution. In an effort to address these challenges, the introduction of a piezoelectric polymer was adopted to realize the charge-laden melt-blown via the melt-blowing method. The charge-laden melt-blown could be applied to manufacture face masks and to generate charges triggered by mechanical and acoustic energy originated from daily speaking. Through an efficient and scalable industrial melt-blown process, our charge-laden mask is capable of overcoming the inevitable electrostatic attenuation, even in a high-humidity atmosphere by long-wearing (prolonging from 4 to 72 h) and three-cycle common decontamination methods. Combined with outstanding protective properties (PM2.5 filtration efficiency >99.9%), breathability (differential pressure <17 Pa/cm2), and mechanical strength, the resultant charge-laden mask could enable the decreased replacement of masks, thereby lowering to 94.4% of output masks worldwide (∼122 billion monthly) without substituting the existing structure or assembling process.
Particulate matter (PM) pollution has posed a huge health and economic burden worldwide. Most existing air filters used to remove PMs are structurally monotonous, cumbersome, and inevitably suffer from the compromise between removal efficiency and air permeability; developing an advanced air filter that can overcome these limitations is of significance but highly challenging. Herein, a novel strategy to create ultrathin, high‐performance air filters based on fluffy dual‐network structured polyacrylonitrile nanofiber/nets, via a humidity‐induced electrospinning/netting technique, is reported. By tailoring the ejection and phase separation of the charged liquids, this approach causes 2D ultrafine (≈20 nm) nanonets tightly bonded with fluffy pseudo‐3D nanofiber scaffolds to form dual‐network structures, with controllable pore size and stacking density on a large scale. The resultant nanofiber/net filters possess the integrated features of small pore size (<300 nm), high porosity (93.9%), low packing density, combined with desirable surface chemistry (4.3‐D dipole moment), resulting in high‐efficiency PM0.3 removal (>99.99%), low air resistance (only <0.11% of atmosphere pressure), and promising long‐term PM2.5 purification. The synthesis of such materials may provide new insights into the design and development of high‐performance filtration and separation materials for various applications. For the first time, fluffy dual‐network structured polyacrylonitrile nanofiber/nets are prepared by a novel humidity‐induced electrospinning/netting technique, where 2D ultrafine (≈20 nm) nanonets tightly bond with pseudo‐3D nanofiber scaffolds. As an ultrathin, high‐performance air filter, such nanofiber/net membranes demonstrate both high efficiency and low air resistance, and show a facile operation and rejuvenation capacity for real‐world applications.
In this study, we use density functional theory (DFT) calculations to investigate the effect of moisture on the performance of three types of nanofiber (NF)-based air-filter media prepared by electrospinning polyvinyl alcohol, polyvinylidene fluoride, and polyacrylonitrile (PAN). Based on the DFT calculations of the intermolecular interactions between the NF-based filter media and water molecules, the PAN-NF filter is expected to exhibit the best performance in the wet state. Experiment studies also successfully demonstrate that the PAN-NF filter medium has better performance in the filtration of particulate matter (PM) than a commercial semi-high efficiency particulate air filter under wet conditions, and these results are in good agreement with the DFT calculation. The PAN-NF filter shows better performance because of its hydrophilic nature and the relatively low thickness the filter medium that allowed fast recovery of its PM-filtration performance.
Recent advances in materials, manufacturing, biotechnology, and microelectromechanical systems (MEMS) have fostered many exciting biosensors and bioactuators that are based on biocompatible piezoelectric materials. These biodevices can be safely integrated with biological systems for applications such as sensing biological forces, stimulating tissue growth and healing, as well as diagnosing medical problems. Herein, the principles, applications, future opportunities, and challenges of piezoelectric biomaterials for medical uses are reviewed thoroughly. Modern piezoelectric biosensors/bioactuators are developed with new materials and advanced methods in microfabrication/encapsulation to avoid the toxicity of conventional lead‐based piezoelectric materials. Intriguingly, some piezoelectric materials are biodegradable in nature, which eliminates the need for invasive implant extraction. Together, these advancements in the field of piezoelectric materials and microsystems can spark a new age in the field of medicine.
Efficient removal of particulate matter (PM) is the major goal for various air cleaning technologies due to its huge impact on human health. Here, a washable high-efficiency triboelectric air filter (TAF) that can be used multiple times is presented. The TAF consists of five layers of the polytetrafluoroethylene (PTFE) and nylon fabrics. Compared with traditional electrostatic precipitator, which requires a high-voltage power supply, the TAF can be charged by simply rubbing the PTFE and nylon fabrics against each other. The electrical properties of the TAF are evaluated through the periodic contacting–separating of the PTFE and nylon fabrics using a linear motor, and an open-circuit voltage of 190 V is achieved. After charging, the TAF has a removal efficiency of 84.7% for PM0.5, 96.0% for PM2.5, which are 3.22 and 1.39 times as large as the uncharged one. Most importantly, after washing several times, the removal efficiency of the TAF maintains almost the same, while the commercial face mask drops to 70% of its original efficiency. Furthermore, the removal efficiency of the PM2.5 is very stable under high relative humidity. Therefore, the TAF is promising for fabricating a reusable and high-efficiency face mask.
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 PM0.3 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.
High-performance air filtration materials are important for addressing the airborne pollutants. Herein, we propose an unprecedented access to biodegradable poly(lactic acid) (PLA)-based MOFilters with excellent filtering performance and antibacterial activity. The fabrication involved a stepwise in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals at the surface of microfibrous PLA membranes, followed by mechanical polarization under high pressure and low temperature (5 MPa, 40 °C) to trigger the ordered alignment of dipoles in PLA chains and ZIF-8. The unique structural features allowed these PLA-based MOFilters to achieve an exceptional combination of excellent tensile properties, high dielectric constant (up to 2.4 F/m), and enhanced surface potential as high as 4 kV. Arising from the remarkable surface activity and electrostatic adsorption effect, a significant increase (from over 12% to nearly 20%) in PM0.3 filtration efficiency was observed for the PLA-based MOFilters compared to that of pure PLA counterparts, with weak relation to the airflow velocities (10-85 L/min). Moreover, the air resistance was controlled at a considerably low level for all the MOFilters, that is, below 183 Pa even at 85 L/min. It is worth noting that distinct antibacterial properties were achieved for the MOFilters, as illustrated by the inhibitive rates of 87 and 100% against Escherichia coli and Staphylococcus aureus, respectively. The proposed concept of PLA-based MOFilters offers unprecedented multifunction integration, which may fuel the development of biodegradable versatile filters with high capturing and antibacterial performances yet desirable manufacturing feasibility.
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 PM0.3 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.
To develop intelligent wearable protection systems is of great significance to human health engineering. An ideal intelligent air filtration system should possess reliable filtration efficiency, low pressure drop, healthcare monitoring function, and man-machine interactive capability. However, no existing intelligent protection system covers all these essential aspects. Herein, we developed an intelligent wearable filtration system (IWFS) via advanced nanotechnology and machine learning. Based on the triboelectric mechanism, the fabricated IWFS exhibits a long-lasting high particle filtration efficiency and bacteria protection efficiency of 99% and 100%, respectively, with a low-pressure drop of 5.8 mmH2O. Correspondingly, the charge accumulation of the optimized IWFS (87 nC) increased to 3.5 times that of the pristine nanomesh, providing a significant enhancement of the particle filtration efficiency. Theoretical principles, including the enhancement of the β-phase and the lower surface potential of the modified nanomesh, were quantitatively investigated by molecular dynamics simulation, band theory, and Kelvin probe force microscopy. Furthermore, we endowed the IWFS with a healthcare monitoring function and man-machine interactive capability through machine learning and wireless transmission technology. Crucial physiological signals of people, including breath, cough, and speaking signals, were detected and classified, with a high recognition rate of 92%; the fabricated IWFS can collect healthcare data and transmit voice commands in real time without hindrance by portable electronic devices. The achieved IWFS not only has practical significance for human health management but also has great theoretical value for advanced wearable systems.
The COVID-19 pandemic has caused serious social and public health problems. In the field of personal protection, the facial masks can prevent infectious respiratory diseases, safeguard human health, and promote public safety. Herein, we focused on preparing a core filter layer for masks using electrospun polyvinyl butyral/apocynum venetum extract nanofibrous membranes (PVB/AVE NMs), with durable interception efficiency and antibacterial properties. In the spinning solution, AVE acted as a salt to improve electrical conductivity, and achieve long-lasting interception efficiency with adjustable pore size. It also played the role of an antibacterial agent in PVB/AVE NMs to achieve win-win effects. The hydrophobicity of PVB-AVE-6% was 120.9° whereas its filterability reached 98.3% when the pressure drop resistance was 142 Pa. PVB-AVE-6% exhibited intriguing properties with great antibacterial rates of 99.38% and 98.96% against S. aureus and E. coli, respectively. After a prolonged usability test of 8 h, the filtration efficiency of the PVB/AVE masks remained stable at over 97.7%. Furthermore, the antibacterial rates of the PVB/AVE masks on S. aureus and E. coli were 96.87% and 96.20% respectively, after using for 2 d. These results indicate that PVB/AVE NMs improve the protective performance of ordinary disposable masks, which has certain application in air filtration.
The outbreak of COVID-19 provided a warning sign for society worldwide: that is, we urgently need to explore effective strategies for combating unpredictable viral pandemics. Protective textiles such as surgery masks have played an important role in the mitigation of the COVID-19 pandemic, while revealing serious challenges in terms of supply, cross-infection risk, and environmental pollution. In this context, textiles with an antivirus functionality have attracted increasing attention, and many innovative proposals with exciting commercial possibilities have been reported over the past three years. In this review, we illustrate the progress of textile filtration for pandemics and summarize the recent development of antiviral textiles for personal protective purposes by cataloging them into three classes: metal-based, carbon-based, and polymer-based materials. We focused on the preparation routes of emerging antiviral textiles, providing a forward-looking perspective on their opportunities and challenges, to evaluate their efficacy, scale up their manufacturing processes, and expand their high-volume applications. Based on this review, we conclude that ideal antiviral textiles are characterized by a high filtration efficiency, reliable antiviral effect, long storage life, and recyclability. The expected manufacturing processes should be economically feasible, scalable, and quickly responsive.
Polylactic acid (PLA) melt-blown nonwovens are attractive candidates for existing non-degradable air filtration materials due to their unique balance between durability in use and biodegradability at their end-of-life. However, owing to the charge instability caused by conventional corona electret treatment, the filtration performance of PLA melt-blown nonwovens is insufficient to be utilized in practical applications. Herein, we presented an effective hydro-charging treatment strategy to prepare biodegradable PLA melt-blown nonwovens with efficient PM0.3 removal. In this process, a large amount of unstable charge was generated by friction between pressurized deionized water and PLA melt-blown microfibers under the influence of negative pressure suction. Then, the unstable charge on microfibers was transformed into stable charge by hot air drying. Through the adjustment of water pressure, conveyer belt speed and drying temperature, we optimized the hydro-charging treatment process. The resulting hydro-charging PLA melt-blown nonwovens (HC-PLA) shown improved PM0.3 removal efficiency (94.63%), a lower pressure drop (11.74 Pa) and a reasonable quality factor (0.249 Pa⁻¹). After experiencing a hydro-charging treatment, PLA melt-blown nonwovens appear to carry more stable and plentiful charges, according to the surface potential and thermally stimulated discharge (TSD). In addition, plausible charge generation and stable storage mechanisms were proposed based on the optimal performance, which provide promising benefits for the development of long-term and highly efficient filtration materials.
The massive production of polymer-based respiratory masks during the COVID-19 pandemic has rekindled the issue of environmental pollution from nonrecyclable plastic waste. To mitigate this problem, conventional filters should be redesigned with improved filtration performance over the entire operational life while also being naturally degradable at the end. Herein, we developed a functional and biodegradable polymeric filter membrane consisting of a polybutylene adipate terephthalate (PBAT) matrix blended with cetyltrimethylammonium bromide (CTAB) and montmorillonite (MMT) clay, whose surface properties have been modified through cation exchange reactions for good miscibility with PBAT in an organic solvent. Particularly, the spontaneous evolution of a partial core-shell structure (i.e., PBAT core encased by CTAB-MMT shell) during the electrospinning process amplified the triboelectric effect as well as the antibacterial/antiviral activity that was not observed in naive PBAT. Unlike the conventional face mask filter that relies on the electrostatic adsorption mechanism, which deteriorates over time and/or due to external environmental factors, the PBAT@CTAB-MMT nanofiber membrane (NFM)-based filter continuously retains electrostatic charges on the surface due to the triboelectric effect of CTAB-MMT. As a result, the PBAT@CTAB-MMT NFM-based filter showed high filtration efficiencies (98.3%, PM0.3) even at a low differential pressure of 40 Pa or less over its lifetime. Altogether, we not only propose an effective and practical solution to improve the performance of filter membranes while minimizing their environmental footprint but also provide valuable insight into the synergetic functionalities of organic-inorganic hybrid materials for applications beyond filter membranes.
Wearable electronics with high-efficiency particulate matters (PMs) filtration and real-time respiratory monitoring offer everyone the opportunity to own a personal healthcare system. However, the power supply, breathability, and filtration performance of wearable electronics still have many challenges that need to be overcome. Herein, a self-powered air filter based on a respiration-driven triboelectric nanogenerator (R-TENG) was integrated with facemask for efficiently filtering submicron particles and respiration monitoring. The conductive cellulose aerogel/MOF composite, regarded as filtration and triboelectric material, was designed by in-situ and green synthesis method. The R-TENG was fabricated using conductive cellulose aerogel/MOF composite and polyvinylidene fluoride (PVDF) film as positive and negative triboelectric materials, respectively. Enabled by its desirable porous network structure and unique electricity generation feature, the air filter is capable of removing PM1.0 and PM0.5 and PM0.3 with high efficiency of 98.4%, 97.3% and 95.0%, while maintaining a relatively low pressure drop of 86 Pa. Moreover, the air filter system can monitor breathing status without using an external power supply for disease prevention and medical diagnosis. This work designs a self-powered mask filter based on conductive cellulose aerogel/MOF composite with both PMs filtration and respiratory monitoring capabilities, which has excellent potential for air purification and healthcare applications.
Here, a multifunctional poly (lactic acid)/copper-based metal-organic framework (PLA/CuMOF) degradable composite membrane featuring superior antibacterial and self-cleaning properties was fabricated via a simple electrospinning process for high- efficiency filtration/separation. Benefiting from the decrease of fiber diameter, the improved surface roughness and the surface charge of CuMOF, PLA/CuMOF fibrous membrane achieved excellent capture ability for ultra-fine particles and superb purification capability for real PM2.5 smoke. The differences of filtration capacity between PLA membrane and PLA/CuMOF membrane was further explored using analogue simulation with dynamic particle capture and airflow field distribution. Impressively, PLA/CuMOF fibrous membrane combines robust self-cleaning ability, effective antibacterial effect, and thermal management capability. Moreover, owing to the special selective wettability and chemical stability, PLA/CuMOF membrane possessed the stable oil-water separation performance under harsh environment (e.g., high acid, alkali, and salt). This degradable multifunctional filtration/separation fibrous membrane emerges a broad application prospect ranging from environmental governance, industrial security to personal protection.
Particulate matters (PMs) pollution and bacteria severely affect human health. Fibrous filters have shown great potential in intercepting PMs and bacteria. However, developing a novel respirator material endowed with multi-functions, such as efficient filtration, antibacterial activity, directional moisture transport and biodegradability is still challenging. Herein, a multifunctional air filtration membrane with hierarchical structure was fabricated by sequentially electrospinning poly (ε-caprolactone) (PCL) fibrous membrane, PCL/gelatin fibrous membrane and PCL/gelatin/ε-poly (L-lysine) (ε-PL) fibrous membrane. The fabricated trilayered fibrous membrane exhibited high PM filtration efficiency and a low pressure drop. Moreover, the fibrous membrane possessed excellent antibacterial activity due to the incorporation of ε-PL. In addition, the trilayered fibrous membrane provided directional water transport performance by the combination of hydrophobic fibrous layer and hydrophilic fibrous layer, thus improving the comfort of the wearer. Importantly, benefiting from the biodegradability property of PCL, gelatin and ε-PL, the fibrous membrane was biodegradable, which could decrease the burden on the environment. The fabricated trilayered fibrous membrane not only shows promising potential as a highly efficient, antibacterial, moisture-wicking and biodegradable air filtration membrane, but also offers a versatile strategy to design a multifunctional face mask.
Smoke generated in moxibustion process, which is physiotherapy in traditional Chinese medicine, includes various organic compounds bearing particulate matter. In this paper, according to the composition analysis of moxa smoke, a breathable filter was introduced to reform the moxibustion box for reducing potential respiratory risk and environmental pollution. The breathability, smoke filtration performance, and reuse stability of the filters were systematically evaluated. PTFE membrane with its pore size around 1.44 μm can effectively filtrate (99.99%) the smoke aerosols with the gas permeance of 1257 m³ m⁻² h⁻¹∙kPa⁻¹, while that of Cambridge filter is 469 m³ m⁻² h⁻¹∙kPa⁻¹ (filtration efficiency 99.98%). Most of the organic substances such as o-cresol, phenol, stearic acid amide, 2-Pyrrolidinone, etc. can be captured by the PTFE membrane, indicating its excellent protection role. The regeneration performance of the filters and the filtration mechanism of the PTFE membrane were then revealed to verify the applicability of the filters. This PTFE reformed moxibustion box exhibits good application performance and can be well used in clinical practice.
High-performance fibers generally require both plastic deformation resistance (strength) and high damage tolerance (toughness). Nevertheless, strength and toughness are inherently incompatible because of the unsatisfied supramolecular structure of polymer fibers. Herein, the principle of coordinating chain crystallinity and orientation by electrospinning technique is shown to resolve the conflict between super toughness and high strength. Using polyethylene terephthalate (PET) as the model system, chain crystallinity and alignment can be simultaneously and dynamically manipulated with polymer ultrafine fibers (UFFs) by precisely controlling the electrical stretching of a spinning jet. The obtained PET UFFs, characterized by loosely packed but highly aligned chain stacks, possessed a true strength of 853 MPa (similar to that of spider dragline silk), super toughness of 415 MJ/m³ (2.5 times higher than that of spider dragline silk), and extraordinary true strain of 210% (four times higher than that of spider dragline silk and exceeding that of highly elastic Spandex filaments). This facile strategy may offer a new paradigm for the development of advanced super-tough and robust materials.
The ultrafine particle matters (PMs) are an imminent threat to the global climate and public health because of their easy penetration through the respiratory tract and blood vessel. Tremendous efforts have been devoted by researchers on design and development of electrospun nanofibrous membranes (ENMs) for PM filtration. However, most existing ENMs suffer from the trade-off effect between removal efficiency and pressure drop, as well as non-degradability or non-recyclability, which must be settled urgently due to the ever-growing need of energy-efficient and environmentally friendly technology. Here, we report a degradable and environmentally friendly PLA bead-on-string ENM, by electrospinning with relatively green EA/DMF mixture solvent, in which the EA/DMF mixture solvent plays the role of “Killing Two Birds with One Stone”. The mixture solvent not only endows the ENM with bead-on-string structure but also improves the greenness of the ENM-making process. The air index (Ψiai) and GlaxoSmithKline (GSK) Solvent Sustainability Guide have been calculated to quantitatively illustrate the greenness of ENM-making processes. Polymer solubility experiments combined with molecular dynamics simulation (MD) demonstrate that the solvent composition plays an important role in manipulating the morphology and structure of ENM. Benefiting from the well-defined bead-on-string structure, the PLA bead-on-sting ENM could easily achieve an excellent removal efficiency over 98% for aerosol particles with an extremely low pressure drop of 29.3 Pa. Filtration progress simulation reveals that the existing beads in nanofibers are able to reduce the packing density and alleviate the pressure drop while guaranteeing the PM removal efficiency. More importantly, compared to commercial masks, the prepared PLA bead-on-string ENM (E7D3-10) presents higher filtration efficiency (PM2.5-92.6% and PM10-95.4%) in real hazy environment, which results in relatively safer PM index value (below 50 μg/m³). This work provides a platform for the design of bead-on-string ENMs via green method, thus giving access to their versatile architectural design and applications.
Piezoelectric materials have long been investigated for their ability to convert mechanical energy to electrical energy (or vice versa). Piezoelectric polymers, while they may not exhibit as excellent properties as ceramics, are non-toxic and highly flexible, allowing them to be utilized in a wider range of applications, including those that require eco-friendly, biocompatibility, biodegradability, and flexibility. While polymer thin films have demonstrated the potential to meet some of the requirements, the significantly inferior piezoelectric properties compared to ceramic counterparts inhibited their exploitation. Electrospinning process not only provides in-situ poling and stretching of the piezoelectric polymer that are typically done post-synthesis to induce the electroactive phase of the polymer, but also allows for various process controls before, during, and after the process to enhance the piezoelectric properties of electrospun nanofibers. Herein, an overview of piezoelectric properties of various electrospun organic nanofibers are provided, and recent progress in its enhancement and optimization is discussed. Additionally, energy- and bio-related applications of electrospun piezoelectric polymer nanofibers are reviewed.
Composite electrospun membranes of polyacrylonitrile (PAN) with contents of cellulose nanocrystals (CNCs) of 5–20 wt% were prepared. The increase in cellulose content improved the mechanical properties of the materials up to approximately 2-fold in the tensile strength and 6-fold in elastic modulus compared to the PAN membrane. Filtration performance of the composite membranes against aerosolized salt nanoparticles was evaluated under conditions relevant to their use as active layers in Filtering Facepiece Respirators (FFR), such as N95s. In general, all composite membranes presented values of filtration efficiency (FE) superior to 90%. Pressure drop (Δp) values of the materials, in general, decreased with increasing content of CNCs. In general, an increase of the quality factor (QF) was observed with increasing content of CNCs in the membrane compositions, possibly due to a trend for the porosity of the composite materials to increase. The membrane containing 20 wt% of CNCs presented the highest QF (0.034 ± 0.002 Pa⁻¹), one of the highest FE of 95.97 ± 0.62%, particle penetration (P) of 4.03 ± 0.62%, and the lowest Δp of 9.60 ± 1.04 mmH2O. Thus, it is possible to prepare composite membranes of PAN reinforced with high content of natural, biodegradable, and abundant CNCs, and to evaluate comprehensively their potential to be used in air filtration applications such as respirators and cleanroom filters.
As a newly emerging hazardous material, airborne nanoplastics are easily inhaled and accumulated in human and animal alveoli. We previously found that polystyrene nanoplastics (PS-NPs) induced apoptosis and inflammation of human alveolar epithelial A549 cells, implying they increase the risk of pulmonary fibrosis. In this study, we investigated whether PS-NPs induce epithelial-to-mesenchymal transition (EMT), the prelude to lung fibrosis, in A549 cells. A549 cells treated with PS-NPs of different sizes and surface charges exhibited increased migration and EMT markers accompanied with up-regulation of reactive oxygen species (ROS) and NADPH oxidase 4 (NOX4), an ROS generator located in the mitochondria and endoplasmic reticulum (ER). Moreover, PS-NPs caused mitochondrial dysfunction as demonstrated by membrane potential changes and impaired cellular energy metabolism. PS-NPs also activated ER stress as indicated by the up-regulated ER stress markers. As expected, smaller PS-NPs with a positive surface charge had stronger effects. Furthermore, the effects of PS-NPs on A549 cells were reversed by NOX4 gene knock-down, which verified the involvement of NOX4. Our results suggest that PS-NPs induce EMT in A549 cells through multiple mechanisms, and NOX4 is a key mediator in this process. Our findings contribute to understanding the toxicological mechanisms of nanoplastics on the respiratory system.
Particulate matter (PM) poses a severe health threat to the public, and fibrous filtration is a powerful method for efficient PM removal. Arming the fibers with electrostatic effect is a gold rush to promote PM-fiber interaction, thus reaching high PM removal efficiency, decreasing airflow resistance, and achieving multifunctional applications simultaneously. In this study, we are to provide a comprehensive overview of electrostatic fibrous filters, including the principles, fabrication process, electrical properties, and applications. Firstly, PM-fiber adhesion forces during the filtration were analyzed according to the electrified principle for the filters. Furthermore, electrostatic filters were classified into monopolar-charged and dipolar-induced filters in the dimension of charging characteristics. Compared with other PM removal techniques, the electrical properties, comprehensive performance, and applications for various electrostatic filters are systematically stated and discussed. In the end, we highlighted that the electrostatic fibrous filters would be a competitive candidate for PM removal owing to their durability, versatility, and plasticity. We also discussed the importance of conducting rigorous filtration tests to report accurate performance for electrostatic filters. In an interdisciplinary view between environmental engineering and material engineering, we hope this work could provide a better understanding of the PM-fiber electrostatic interactions and practical insights for designing next-generation air filters.
Metal-organic framework (MOF), an emerging class of porous hybrid inorganic-organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO2 gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO2 capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.
There is an increasing effort to utilize piezoelectric materials as a self-powered platform to electrically stimulate cells/tissues in regenerative medicine and tissue engineering applications. Poly(l-lactic acid) (PLLA) holds great potential for biological applications due to its biodegradability, especially in a nanofibrous form prepared by electrospinning. However, the mechanism underlying its realization and transformation of piezoelectricity is not well understood. In this study, a design-of-experiment approach was employed to systematically dissect the effects of dimensional control and heat treatment on the piezoelectric performance of electrospun PLLA nanofibers. Specifically, we revealed that the fiber diameter- and heat treatment-dependent phase content change between electrospinning-induced amorphous and crystalline α/α’ phases was responsible for the piezoelectric performance in the transverse and longitudinal directions. Such modulation of piezoelectric properties in PLLA nanofibers was critical in determining the differentiation efficiency of stem cells in a phenotype-specific manner, where neurogenesis and osteogenesis were enhanced by orthogonal and shear piezoelectricity, respectively. Overall, our findings highlight the potential of electrospun PLLA nanofibers with precisely controlled piezoelectric properties through a systematic approach for self-powered stem cell engineering platforms, specific to target tissues.
With the explosive development of sensing systems in miniaturization, intelligence, multi-function and networking, triboelectric nanogenerator (TENG) with simple structure, low cost and self-powering characters has become an excellent candidate for mechanical sensors. However, it remains a great challenge to obtain a stable interface of electrode and triboelectric layers for timely and long-term triboelectric surface charges transfer. In this study, through a simple vacuum-assistant filtration method, we prepared an integrated MXene-PEDOT:PSS/PTFE (MXene-poly(3,4-ethylenedioxythiophene):Poly (styrenesulfonate)/polytetrafluoroethylene) (MPP) film as the electrode and triboelectric layer of TENG for self-powered sensing. The TENG-based sensor has a high sensitivity especially to tiny forces (> 6.05 V·N⁻¹) with short response (52 ms) and recovery (34 ms) time, as well as an excellent stability (over 6000 cycles). The fabrication method is suitable for most conductive nanomaterials, and the triboelectric layer can be replaced with other commercialized filter film, such as cellulose and Mixed fiber resin (MFR). It provides a simple and versatile method for the preparation of stable electrode-triboelectric interface, and has broad prospects in TENG-based wearable sensors.
Smart air filters are beneficial to provide highly efficient particle removal, treat multiple contaminants simultaneously and conserve energy during air filtration processes. Herein, a type of self-supporting smart air filter (SSSAF) was fabricated by sandwiching the VOC-responsive PZT/PVDF electrospun membrane with two metal mesh electrodes. Besides the high filtration efficiency for sub-micron particles, the SSSAF showed good responses to pressure drop in the range of 0 to 500 Pa via the electroactivity of PZT/PVDF membrane. In addition, the SSSAF achieved VOC sensing function via the swelling properties of PZT/PVDF membrane in organic vapors, demonstrated by its signal to 50 to 200 ppm ethanol vapors. The SSSAF was employed to harvest wind energy, which was further applied to inhibit bacterial growth without the need of additional power input. Our SSSAF was designed to take advantage of the energy carried by the filtration air flow, which is necessary in any filtration system thus brings a stable and innate energy source. The results provide new insight into development of all-in-one smart air filters.
Applying triboelectric nanogenerators (TENGs) in air filtration systems to generate electric charges through friction is a major advancement in air cleaning technology. The performance of triboelectric air filter strongly depends on the properties of triboelectric materials. In this work, a better triboelectric material, polyvinylidene fluoride (PVDF)/UiO‐66 composite nanofiber membrane (P6‐NFM), is designed and fabricated through electrospinning technology by doping UiO‐66 into PVDF matrix. As the weight ratio of UiO‐66 increases to 1%, PVDF/UiO‐66 composite nanofiber‐based TENG (P6‐TENG) achieves the maximum current, voltage, and triboelectric charge of 4.29 µA, 52.8 V, and 22.02 nC, which are 6.5 times, 5.1 times, and 8.0 times as large as those of pure PVDF‐based TENG (P‐TENG). Therefore, the triboelectric air filter based on P6‐NFM can be easily charged by slapping the fiber membrane and spun‐bond fabric. After charging, the removal efficiency of P6‐NFM is 92% for PM0.5 and 98% for PM2.5, which are 2.8 and 1.2 times those of the uncharged one. More importantly, the filtration efficiency of this air filter keeps stable after the membrane is washed four times. This method of loading UiO‐66 on the triboelectric fiber material shows tremendous potential in self‐charging and reusable air purification applications.
The World Health Organization and the United States Centers for Disease Control have recommended universal face masking by the general public to slow the spread of COVID-19. A number of recent studies have evaluated the filtration efficiency and pressure differential (an indicator of breathability) of various, widely available materials that the general public can use to make face masks at home. In this review, we summarize those studies to provide guidance for both the public to select the best materials for face masks and for future researchers to rigorously evaluate and report on mask material testing. Of the tested fabric materials and material combinations with adequate breathability, most single and multilayer combinations had a filtration efficiency of <30%. Most studies evaluating commonly available mask materials did not follow standard methods that would facilitate comparison across studies, and materials were often described with too few details to allow consumers to purchase equivalent materials to make their own masks. To improve the usability of future study results, researchers should use standard methods and report material characteristics in detail.
Particulate matter (PM) pollution is a significant burden on global economies and public health. Most present air filter is heavy, bulky, nontransparent, and typically has inevitable compromise between removal efficiency and air permeability. We report a scalable strategy to create ultra-light, thin, rubbery, self-assembled nanoarchitectured networks (nano-networks) with high-efficiency and transparency (ULTRA NET) air filters using capacitive-like electronetting technology. By controlling the ejection, deformation, and phase separation of charged droplets from a Taylor cone, our approach allows continuously welded two-dimensional nano-networks (~20 nm fiber diameter) to assemble into filters on a large scale. The resulting ULTRA NET filters exhibit integrated properties of desirable pore structure yet maintaining strikingly low thickness (~350 nm) and free-standing capability, 99.98% removal efficiency, <0.07% of atmosphere pressure for PM0.3 filtration at ~85.6% transmittance; which enable to serve as a multifunctional filter against PMs either in rigid solid or in soft oil forms and even biohazard pathogens. This work should serve as a source of inspiration for the design and development of high-performance fibrous materials for various filtration and separation applications.
In addition to the rapid urbanization and industrialization around the world, air pollution due to particulate matter is a substantial threat to human health. A considerable research effort has been devoted to the development of electrospun polymer nanofibers for air filter applications. Among these new technologies, electrostatic charge‐assisted air filtration is a promising technology for removing small particulate matter (PM). In this investigation, biodegradable electrospun poly(l‐lactic acid) (PLLA) polymer nanofibers are employed for air filter applications. Electrostatic charges generated from the PLLA nanofiber can significantly enhance air filter applications. Compared with a 3M commercial respirator filter, electrospun PLLA fibrous filters exhibit a high efficiency of 99.3%. Even after 6 h of filtration time, the PLLA filtration membrane still exhibits a 15% improvement in quality factor for PM 2.5 particles than the 3M respirator. This is mainly attributed to the electrostatic force generated from the electrospun PLLA nanofibers, which significantly benefit submicron particle absorption. Due to their biodegradability, ease of fabrication, and relatively high efficiency, electrospun PLLA nanofibers show great promise in applications such as air cleaning systems and personal air purifier applications. Biodegradable electrospun poly(l‐lactic acid) (PLLA) polymer nanofibers are investigated for air filter applications. Compared with a 3M filter, the electrospun PLLA fibrous filters exhibit a high efficiency of 99.3% and a 15% improvement in quality factor for PM 2.5 particles. The electrospun PLLA material shows great promise in applications such as air cleaning systems and personal air purifier applications.
Fabrication of multifunctional fiber filters for passive room air purification through filtration, adsorption and catalysis mechanism is critical to cater to urgent needs in the current air filter industry. However, few studies have concentrated on the construction of primary filters or medium efficiency filters with versatile performance. Herein, we constructed a multifunctional composite filter combined with nanocrystalline MnO2 and PE/PP bicomponent fibers by introducing corona charge technology. We utilized a novel redox process to synthesize α-MnO2 and δ-MnO2 with outstanding HCHO catalytic capacity. The δ-MnO2 synthesized via redox method was proved to possess the highest content of manganese vacancies, species and the mobility of adsorbed oxygen. Thereby, the δ-MnO2 showed the best HCHO oxidation performance at low temperature and was further chosen to fabricate carding MnO2/PE/PP filter with filtration, adsorption and catalysis abilities. Benefiting from the through-air bonding procedure, a fluffy PE/PP nonwoven mat with uniform dispersion and anchoring of MnO2 was constructed. The as-prepared MnO2/PE/PP swatch exhibited excellent HCHO catalytic activity including complete oxidation within 60 min and acceptable reversibility in 5 cycles. Moreover, after corona charge, the MnO2/PE/PP sample showed a relatively high filtration efficiency of 71.73%, a low pressure drop of 6.02 Pa and an improved quality factor of 0.2219 Pa-1. Since the manufacture of this MnO2/PE/PP filter does not involve tedious procedures and would easily take into mass production, we expect that the methodology for fabricating MnO2/PE/PP filter with more functionality and charge-retention capacity might enlighten the creation of advanced fiber filters.
We developed a high-efficiency rotating triboelectric nanogenerator (R-TENG)-enhanced multilayered antibacterial polyimide (PI) nanofiber air filters for removing ultrafine particulate matter (PM) from ambient atmosphere. Compared to single-layered PI nanofiber filters, the multilayered nanofiber filter can completely remove all of the particles with diameters larger than 0.54 μm and shows enhanced removal efficiency for smaller PM particles. After connecting with aR-TENG, the removal efficiency of the filer for ultrafine particles is further enhanced.The highest removal efficiency for ultrafine particulate matter is 94.1% at the diameter of 53.3 nm and the average removal efficiency reached 89.9%. Despite an increase in the layer number, the thickness of each individual layer of the film decreased, and hence, the total pressure drop of the filter decreased insteadof increasing. Moreover, the nanofiber film exhibited high antibacterial activity because of the addition of a small amount of silver nanoparticles. This technology with zero ozone release and low pressure drop is appropriate for cleaning air, haze treatment, and bacterial control.
The physical filtration mechanism of traditional face mask has a low removal efficiency of ultrafine particulates in the size range of 10-1000 nm, which are badly harmful to human health. Herein, a novel self-powered electrostatic-adsorption face mask (SEA-FM) based on the Poly (vinylidene fluoride) electrospun nanofiber film (PVDF-ESNF) and triboelectric nanogenerator (TENG) driven by respiration (R-TENG) is developed. The ultrafine particulates are electrostatically adsorbed by the PVDF-ESNF and the R-TENG can continually provide electrostatic charges in this adsorption process by respiration. Based on the R-TENG, the SEA-FM show an removal efficiency of coarse and fine particulates is higher than 99.2wt%, and the removal efficiency of ultrafine particulates is still as high as 86.9wt% after continually wearing for 240 min and a 30-day interval. This work has proposed as a new method of wearable air filtration and may have great prospects in human health, self-powered electronics and wearable devices.
Electrospun electret filter has been regarded as a promising medium to remove particulate matter (PM) from air stream because it could fulfill the requirements for both high filtration efficiencies and low pressure drops. The physico-chemical characteristics of the polymer material have significant effects on the PM collection performance of the electret filter. In this study, polyvinyl chloride (PVC), polyacrylonitrile (PAN), polycarbonate (PC) and polyethyleneimine (PEI) electret filters with similar structures are electrospun using polymers of different permittivity and their collection efficiencies for neutral particles are evaluated experimentally. Then the lattice Boltzmann coupled with discrete element method (DEM) is applied to simulate the particle transport and deposition through the virtual 3-D electret filters, to give further insight into the particle capture mechanisms due to the PM-fiber interaction and the dielectrophoretic attraction. The simulation results compare favorably with the experimental data. Results indicate that the PM collection efficiency of PVC electret filter is the highest, and followed by the PAN, PC and PEI electret filters. It is revealed that the dielectric property of the polymer material is an influential factor shaping the interaction of particles and fiber surfaces, as well as the charge storage abilities of the electrospun electret filters. A higher polymer permittivity would lead to a larger PM-fiber adhesion energy, a larger fiber charge density and then a better PM collection performance.
Nanofiller-tailored stereocomplexation signifies a promising and feasible pathway to develop heat-resistant poly(lactic acid) (PLA) materials. However, this pathway is thwarted by the potential adverse environmental issues of traditional nanofillers and the challenges in facilitating the nanofiller dispersion and selective formation of stereocomplex crystals (SCs). Here we unravel a microwave-assisted approach to exploit biobased quantum dots (QDs) featuring excellent capability to preferably nucleate PLA SCs. The combination of ultrasmall dimension and high oxygenation degree of QDs conferred intimate interactions with stereocomplexed PLA chains, readying complete exfoliation and uniform dispersion of QDs to promote stereocomplexation. The well-dispersed QDs provided perfect UV shielding for PLA composites, while sustaining high transmission to visible light comparable to pure PLA. Strong interfacial interactions and high concentration of SCs were created around the nanoscale surfaces of QDs, accounting for the greatly increased resistance to oxygen permeation, thermal deformation and microwave heating. This was accompanied by substantial rise in tensile modulus and elongation at break (up to 74% and 51%) compared to pure PLA, affording the demonstration of unusual reinforcing and toughening mechanisms imparted by the PLA-affinitive QDs. The robust structural integrity under harsh usage environments, coupled with high gas barrier, prominent light management and evasion of flexibility and extensibility sacrifices, may prompt low-cost and ecofriendly PLA nanocomposites suitable for diverse applications including microwaveable food packaging.