Al-Coated Conductive Fibrous Filter with Low Pressure Drop for Efficient Electrostatic Capture of Ultrafine Particulate Pollutants

Exploring the versatility of biodegradable biomass aerogels: In-depth evaluation of Firmiana simplex bark microfibers depolymerized by deep eutectic solvent

In this study, we investigated the use of deep eutectic solvents (DESs) at different molar ratios and temperatures as a green and efficient approach for microfibers (MFs) extraction. Our approach entailed the utilization of Firmiana simplex bark (FSB) fibers, enabling the production of different dimensions of FSB microfibers (FSBMFs) by combining DES pretreatment and mechanical disintegration technique. The proposed practice demonstrates the simplicity and effectiveness of the method. The morphology of the prepared microfibers was studied using the Scanning electron microscopic (SEM) technique. Additionally, the results revealed that the chemical and mechanical treatments did not significantly alter the well-preserved cellulose structure of microfibers, and a crystallinity index of 56.6 % for FSB fibers and 63.8 % for FSBMFs was observed by X-ray diffraction (XRD) analysis. Furthermore, using the freeze-drying technique, FSBMFs in water solutions produced effective aerogels for air purification application. In comparison to commercial mask (CM), FSBMF aerogels' superior hierarchical cellular architectures allowed them to attain excellent filtration efficiencies of 94.48 % (PM10) and 91.51 % (PM2.5) as well as excellent degradation properties were analyzed. The findings show that FSBMFs can be extracted from Firmiana simplex bark, a natural cellulose-rich material, using DES for environmentally friendly aerogel preparation and applications.

MXene-Decorated Nylon Mesh Filters for Improvement of Indoor Air Quality by PM2.5 Filtration

Air pollution is a problem that is increasing day by day and poses a threat on a global scale. Particulate matter (PM) is one of the air pollutants that is the biggest concern regarding air quality. In order to control PM pollution, highly effective air filters are required. This is especially necessary for PM with a diameter of less than 2.5 micrometers (PM_2.5), which poses a health risk to humans. In this study, we demonstrate for the first time the use of a two-dimensional titanium carbide (Ti₃C₂) MXene nanosheets-decorated nylon mesh (MDNM) as a low cost and highly efficient PM_2.5 filter. This study develops a proof-of-concept method to capture PM_2.5. Thanks to their high specific surface area and active surface-terminating groups, conductive MXene nanosheets have made nylon mesh filters promising candidates for air filtration. The developed filters used electrostatic force to capture PM_2.5 and showed high removal efficiency (90.05%) when an ionizer was used and under an applied voltage of 10 V, while a commercial high-efficiency particulate air (HEPA) filter had a removal efficiency of 91.03% measured under identical conditions. The proposed filters, which stand out with their low energy consumption, low pressure drop (∼14 Pa), and cost-effectiveness, have the potential to be a strong competitor to conventional PM filter systems used in many fields.

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.

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

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

Electrostatic Polydopamine-Interface-Mediated (e-PIM) filters with tuned surface topography and electrical properties for efficient particle capture and ozone removal

Ambient particulate matter (PM) poses severe environmental health risks to the public globally, and efficient filtration technologies are urgently needed for air ventilation. In this contribution, to overcome the efficiency-resistance trade-off for fibrous filtration, we introduced an electrostatic polydopamine-interface-mediated (e-PIM) filter utilizing a combined effect of particle pre-charging and filter polarizing. After delineating the PM-fiber interactions in electrostatic filtration, we designed a composite fiber structure and fabricated the filters by a two-step dip-coating. The surface topography and electrical potential of the polyester (PET) coarse substrates were regulated by successively coating polydopamine (PDA) layers and manganese oxide clusters. By this means, an 8-mm-thick Mn-P @ P-100 filter possessed improved efficiency of 96.05%, 97.60%, and 99.14% for 0.3-0.5 µm, 0.5-1 µm, and 1-3 µm particles, the ultralow air resistance of 10.4 Pa at a filtration velocity of 0.5 m/s, and steady ozone removal property. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. We expect e-PIM filters and the filtration prototype will be potential candidates as effective and low-cost air cleaning devices for a sustainable and healthy environment.

Smart Nanostructured Materials for SARS-CoV-2 and Variants Prevention, Biosensing and Vaccination

The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has raised great concerns about human health globally. At the current stage, prevention and vaccination are still the most efficient ways to slow down the pandemic and to treat SARS-CoV-2 in various aspects. In this review, we summarize current progress and research activities in developing smart nanostructured materials for COVID-19 prevention, sensing, and vaccination. A few established concepts to prevent the spreading of SARS-CoV-2 and the variants of concerns (VOCs) are firstly reviewed, which emphasizes the importance of smart nanostructures in cutting the virus spreading chains. In the second part, we focus our discussion on the development of stimuli-responsive nanostructures for high-performance biosensing and detection of SARS-CoV-2 and VOCs. The use of nanostructures in developing effective and reliable vaccines for SARS-CoV-2 and VOCs will be introduced in the following section. In the conclusion, we summarize the current research focus on smart nanostructured materials for SARS-CoV-2 treatment. Some existing challenges are also provided, which need continuous efforts in creating smart nanostructured materials for coronavirus biosensing, treatment, and vaccination.

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

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

Multilevel structured PASS nanofiber filter with outstanding thermal stability and excellent mechanical property for high-efficiency particulate matter removal

Particulate matter (PM) pollution from industrialization poses a great threat to people's health. Although fiber-based filters are used effectively to capture PM, the traditional filters with large diameter suffer from low filtration efficiency, high pressure drop and low temperature resistance. In this study, multilayer poly arylene sulfide sulfone (M-PASS) composite filter was designed and fabricated via electrospinning technology. The M-PASS composite filter is sandwich-structure. Due to the unique structure and composition, the M-PASS filter exhibited outstanding removal efficiency of 99.97 ± 0.0050%, extremely low air resistance of 44.3 ± 0.7 Pa, excellent quality factor (QF) of 0.19 ± 0.0019 Pa^-1, and desirable mechanical strength of 7.0 ± 0.2 MPa. Furthermore, the as-prepared M-PASS filter can remain outstanding filtration performance at 200.0 ℃ due to the high thermal stability of PASS and the removal efficiency was still above 95.2 ± 0.4% after long-term filtration test. These results demonstrate that the structure of filter is the important one for air filtration and the M-PASS nanofiber filters have great potential in PM removal, especially under high temperature conditions.

Facile nanostructured zinc oxide coating technique for antibacterial and antifouling air filters with low pressure drop

Air filters effectively filtrate external contaminants including pathogenic bioaerosols; however, they also act as culture sites for the pathogenic bacteria captured in nutrient organic pollutants. Although many researchers have applied various antibacterial coatings to filters, the coating application inevitably increased the pressure drop, leading to the low efficiency and high energy consumption of the purification system. Herein, we report a simple nanostructured zinc oxide (ZnO) coating technique to confer a polypropylene nonwoven filter with superior antibacterial, antifouling and anti-biofilm properties without an additional pressure drop. For aerodynamic coating designs, filters were directly immersed into low concentration precursor solutions to enable the sedimentation of the ZnO sol-gel particles on the filter fibers according to fluid dynamic. The precursor concentration affected the surface topology and so properties of the as-fabricated coating. 0.07 M precursor solution produced a rose-like nanostructured coating exhibiting no pressure-drop increase. The large specific surface area and hydrophobic surface killed and then repelled the attached bacteria effectively. As a result, the bare filter promoted the growth and consequent biofilm formation of the surface bacteria in a favorable environment for the growth of microorganisms, while the coated filter successfully suppressed biofilm development.

Materials, Preparation Strategies, and Wearable Sensor Applications of Conductive Fibers: A Review

The recent advances in wearable sensors and intelligent human-machine interfaces have sparked a great many interests in conductive fibers owing to their high conductivity, light weight, good flexibility, and durability. As one of the most impressive materials for wearable sensors, conductive fibers can be made from a variety of raw sources via diverse preparation strategies. Herein, to offer a comprehensive understanding of conductive fibers, we present an overview of the recent progress in the materials, the preparation strategies, and the wearable sensor applications related. Firstly, the three types of conductive fibers, including metal-based, carbon-based, and polymer-based, are summarized in terms of their principal material composition. Then, various preparation strategies of conductive fibers are established. Next, the primary wearable sensors made of conductive fibers are illustrated in detail. Finally, a robust outlook on conductive fibers and their wearable sensor applications are addressed.

Effectual removal of indoor ultrafine PM using submicron water droplets

Exposure to ultrafine airborne particulate matter (PM_1.0) poses a significant risk to human health and well-being. Examining the effect of submicron water droplets on the removal of ultrafine PM is timely and important for mitigating indoor ultrafine PM, which is difficult to filter out from incoming air. In this study, submicron water droplets were made by using a nanoporous membrane and an ultrasonic module of a commercial household ultrasonic humidifier (UH) for effectual ultrafine PM removal. The effect of water droplet size on indoor PM removal was experimentally investigated. Variations in the normalized PM concentration, removal efficiency and deposition constants were evaluated by analyzing the temporal variation in PM concentration inside a test chamber. The measured PM deposition constants were compared with the results of other previous studies. As a result, submicron water droplets of 800 nm in mean diameter were generated by ultrasonic module combined passive nanoporous membrane, and PM_1.0 concentration decreased by 30% in the initial 30 min. Compared with micron-sized water droplets, PM_1.0 removal efficiency improved by approximately two times higher. Moreover, the substitution of the experimental results into a theoretical model ascertained that PM collection efficiency is increased by approximately 10³ levels as the size of water droplets decreases. These results would be utilized in the development and implementation of effective strategies for indoor PM removal.

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

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

Electrostatic Charge Retention in PVDF Nanofiber-Nylon Mesh Multilayer Structure for Effective Fine Particulate Matter Filtration for Face Masks

Currently, almost 70% of the world's population occupies urban areas. Owing to the high population density in these regions, they are exposed to various types of air pollutants. Fine particle air pollutants (<2.5 μm) can easily invade the human respiratory system, causing health issues. For fine particulate matter filtration, the use of a face mask filter is efficient; however, its use is accompanied by a high-pressure drop, making breathing difficult. Electrostatic interactions in the filter of the face mask constitute the dominant filtration mechanism for capturing fine particulate matter; these masks are, however, significantly weakened by the high humidity in exhaled breath. In this study, we demonstrate that a filter with an electrostatically rechargeable structure operates with normal breathing air power. In our novel face mask, a filter membrane is assembled by layer-by-layer stacking of the electrospun PVDF nanofiber mat formed on a nylon mesh. Tribo/piezoelectric characteristics via multilayer structure enhance filtration performance, even under air-powered filter bending taken as a normal breathing condition. The air gap between nanofiber and mesh layers increases air diffusion time and preserves the electrostatic charges within the multi-layered nanofiber filter membrane under humid air penetration, which is advantageous for face mask applications.

Ultralow Resistance Two-Stage Electrostatically Assisted Air Filtration by Polydopamine Coated PET Coarse Filter

Airborne particulate matters (PM) pose serious health threats to the population, and efficient filtration is needed for indoor and vehicular environments. However, there is an intrinsic conflict between filtration efficiency, air resistance, and service life. In this study, a two-stage electrostatically assisted air (EAA) filtration device is designed and the efficiency-air resistance-filter life envelope is significantly improved by a thin coating of polydopamine (PDA) on the polyethylene terephthalate (PET) coarse filter by in situ dopamine polymerization. The 8 mm thick EAA PDA-140@PET filter has a high filtration efficiency of 99.48% for 0.3 µm particles, low air resistance of 9.5 Pa at a filtration velocity of 0.4 m s^-1 , and steady performance up to 30 d. Compared with the bare PET filter, the penetration rate for 0.3 µm particles is lowered by 20×. The coated PDA is of submicron thickness, 10^-3  × the gap distance between filter fibers, so low air resistance could be maintained. The filter shows steadily high filtration efficiency and an acceptable increase of air resistance and holds nearly as many particles as its own weight in a 30 day long-term test. The working mechanism of the EAA coarse filter is investigated, and the materials design criteria are proposed.

MODs vs. NPs: Vying for the Future of Printed Electronics

This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution-based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.

Toward the Biophilic Residential Regeneration for the Green New Deal

As climate changes and species extinction accelerate, the global community focuses on Green New Deal plans to promote economic development based on environmental sustainability. The Green New Deal should encourage sustainable resilience in the environment and strengthen the community’s innate ties with natural resources and biodiversity. This study describes biophilic design for sustainable and resilient residential regeneration from the perspective of the Green New Deal, and suggests potential possibilities for these approaches on a residential regeneration scale. A case study clarifies the applicable features of biophilic design in various fields, such as architectural planning and design, technology, and services, and is subdivided according to the scale of residential regeneration (unit, building, and complex). The results of this study suggest new values for existing Green New Deal policies and contribute to the segmentation of residential regeneration projects and the expansion of related industries.

Assessment of Pollution and Health Risks of Heavy Metals in Particulate Matter and Road Dust Along the Road Network of Dhanbad, India

BACKGROUND

The rise in particulate matter (PM) concentrations is a serious problem for the environment. Heavy metals associated with PM₁₀, PM_2.5, and road dust adversely affect human health. Different methods have been used to assess heavy metal contamination in PM₁₀, PM_2.5, and road dust and source apportionment of these heavy metals. These assessment tools utilize pollution indices and health risk assessment models.

OBJECTIVES

The present study evaluates the total mass and average concentrations of heavy metals in PM₁₀, PM_2.5, and road dust along selected road networks in Dhanbad, India, analyzes the source apportionment of heavy metals, and assesses associated human health risks.

METHODS

A total of 112 PM samples and 21 road dust samples were collected from six stations and one background site in Dhanbad, India from December 2015 to February 2016, and were analyzed for heavy metals (iron (Fe), lead (Pb), cadmium (Cd), nickel (Ni), copper (Cu), chromium (Cr), and zinc (Zn)) using atomic absorption spectrophotometry. Source apportionment was determined using principal component analysis. A health risk assessment of heavy metal concentrations in PM₁₀, PM_2.5, and road dust was also performed.

RESULTS

The average mass concentration was found to be 229.54±118.40 μg m^-3 for PM₁₀ and 129.73 ±61.74 μg m^-3 for PM_2.5. The average concentration of heavy metals was found to be higher in PM_2.5 than PM₁₀. The pollution load index value of PM₁₀ and PM_2.5 road dust was found to be in the deteriorating category. Vehicles were the major source of pollution. The non-carcinogenic effects on children and adults were found to be within acceptable limits. The heavy metals present in PM and road dust posed a health risk in the order of road dust> PM₁₀> and PM_2.5. Particulate matter posed higher health risks than road dust due to particle size.

CONCLUSIONS

The mass concentration analysis indicates serious PM₁₀ and PM_2.5 contamination in the study area. Vehicle traffic was the major source of heavy metals in PM₁₀, PM_2.5, and road dust. In terms of non-carcinogenic risks posed by heavy metals in the present study, children were more affected than adults. The carcinogenic risk posed by the heavy metals was negligible.

COMPETING INTERESTS

The authors declare no competing financial interests.

Sustainable Personal Protective Clothing for Healthcare Applications: A Review

Personal protective equipment (PPE) is critical to protect healthcare workers (HCWs) from highly infectious diseases such as COVID-19. However, hospitals have been at risk of running out of the safe and effective PPE including personal protective clothing needed to treat patients with COVID-19, due to unprecedented global demand. In addition, there are only limited manufacturing facilities of such clothing available worldwide, due to a lack of available knowledge about relevant technologies, ineffective supply chains, and stringent regulatory requirements. Therefore, there remains a clear unmet need for coordinating the actions and efforts from scientists, engineers, manufacturers, suppliers, and regulatory bodies to develop and produce safe and effective protective clothing using the technologies that are locally available around the world. In this review, we discuss currently used PPE, their quality, and the associated regulatory standards. We survey the current state-of-the-art antimicrobial functional finishes on fabrics to protect the wearer against viruses and bacteria and provide an overview of protective medical fabric manufacturing techniques, their supply chains, and the environmental impacts of current single-use synthetic fiber-based protective clothing. Finally, we discuss future research directions, which include increasing efficiency, safety, and availability of personal protective clothing worldwide without conferring environmental problems.

Electrostatic Air Filtration by Multifunctional Dielectric Heterocaking Filters with Ultralow Pressure Drop

In air filtration, for creating healthy indoor air, there is an intrinsic conflict between high filtration efficiency and low wind pressure drop. In this study, we overcame this conflict by developing new dielectric heterocaking (HC) filters, in which high relative dielectric constant (ε_r) materials were heterogeneously loaded on traditional polymer fibers. The dielectric HC filters in an electrostatic polarizing field generate a great amount of charges on their surface, leading to a strong attraction to precharged aerosol particles, and result in high filtration efficiency. Observing via a charged coupled device camera, the migration speed of aerosol smoke particles toward the polarized HC fiber exceeded those toward the unpolarized HC fiber by a factor of 6. We loaded high-ε_r HCs including manganese dioxide (MnO₂), activated carbon, zinc oxide (ZnO), copper oxide (CuO), and barium titanate (BaTiO₃) on polyurethane foams using a fast and large-scale roll-to-roll gel squeezing method. Based on the experimental results, when HCs had a ε_r larger than 5.1, an increased ε_r did not benefit electrostatic filtration efficiency for aerosol particles much, but resulted in a larger net ozone production. We suggested a MnO₂-HC filter for efficient and multifunctional filtration of indoor particles, ambient ozone, and formaldehyde with only 3.8 Pa pressure drop at 1.1 m/s filtration velocity. This efficient and cost-effective dielectric HC filter opens a new avenue for the design of multifunctional filters, which will facilitate its large-scale production and commercial application in the ventilation system for healthy buildings.

Transparent Metallized Microfibers as Recyclable Electrostatic Air Filters with Ionization

Air-quality control remains a major environmental concern as polluted air is a threat to public safety and health in major industrialized cities. To filter pollutants, fibrous filters employing electrostatic attraction have been widely used. However, such air filters suffer from some major disadvantages, including low recyclability and a significant pressure drop owing to clogging and a high packing density. Herein, we developed ionization-assisted electrostatic air filters consisting of nonwoven nanofibers. Ionization of particulate matter (PM) using air ionization enhanced the electrostatic attraction, thereby promoting efficient filtration. Metallization of the fibers facilitated strong electrical attraction and the consequent capture of PM of various sizes. The low packing density of the metallized fibers also facilitated efficient filtration of the PM, even at low driving pressures, which in turn reduced the energy consumption of the air-filtration device.

High-performance particulate matter including nanoscale particle removal by a self-powered air filter

Particulate matter (PM) pollutants, including nanoscale particles (NPs), have been considered serious threats to public health. In this work, a self-powered air filter that can be used in high-efficiency removal of PM, including NPs, is presented. An ionic liquid-polymer (ILP) composite is irregularly distributed onto a sponge network to form an ILP@MF filter. Enabled by its unique electrochemical properties, the ILP@MF filter can remove PM_2.5 and PM₁₀ with high efficiencies of 99.59% and 99.75%, respectively, after applying a low voltage. More importantly, the charged ILP@MF filter realizes a superior removal for NPs with an efficiency of 93.77%. A micro-button lithium cell or silicon-based solar panel is employed as a power supply platform to fabricate a portable and self-powered face mask, which exhibits excellent efficacy in particulate removal compared to commercial masks. This work shows a great promise for high-performance purification devices and facile mask production to remove particulate pollutants.

Polytetrafluoroethylene/Polyphenylene Sulfide Needle-Punched Triboelectric Air Filter for Efficient Particulate Matter Removal

The demand for air filtration materials in recent years has been substantially increasing on a worldwide scale because people are paying extensive attention to particulate matter (PM) pollution. In this work, we report a type of needle-punched triboelectric air filter (N-TAF) consisting of polytetrafluoroethylene (PTFE) fibers modified by silica nanoparticles and polyphenylene sulfide (PPS) fibers. Compared to conventional electrostatic precipitators, the N-TAF can be charged online by a unique nonwoven processing technology without additional energy consumption and toxic ozone emission. Owing to the triboelectrification effect, a large number of charges were generated during the process of carding and needle-punching, resulting in an increased filtration performance. Benefiting from the addition of silica nanoparticles, the PTFE fibers are endowed with many pores and grooves and substantial surface roughness, which contributes to the enhancement of triboelectrification. As a result, the N-TAF with 2 wt % silica nanoparticles (N-TAF-2) exhibited a high removal efficiency of 89.4% for PM, which is 45% higher than unmodified N-TAF (61.8%), and a low pressure drop of 18.6 Pa. Meanwhile, the decay of the removal efficiency for N-TAF-2 remained at a low level (6.4%) for 60 days. More importantly, N-TAF-2 could realize a high efficiency of 99.7% and a low pressure drop of 55.4 Pa at a high surface density. In addition, the washed N-TAF has an excellent charge regeneration performance via air blowing or manual rubbing, thus recovering the removal efficiency easily and rapidly. Ultimately, the powerful dust holding capacity (227 g m^-2) for N-TAF-2 indicates that the filter has a long service life, which makes it a promising air purification material. The filter reported in this work has the potential to be practically applied to air purification fields because it has excellent filtration performance and is easy to be produced on a large industrial scale.

Hierarchical Porous Poly(l-lactic acid) Nanofibrous Membrane for Ultrafine Particulate Aerosol Filtration

Ultrafine particulate aerosols less than 100 nm diffuse randomly in the air and are hazardous to the environment and human health. However, no technical standards or commercial products are available for filtering particle sizes under 100 nm yet. Here, we report the development of a porous poly(l-lactic acid) (PLLA) nanofibrous membrane filter with an ultra-high specific surface area via electrospinning and a post-treatment process. After PLLA fibres were electrospun and collected, they were treated by acetone to generate a blossoming porous structure throughout each individual fibre. Characterizations of morphology, crystallinity, and mechanical and thermal properties demonstrated that the porous structure can be attributed to the nonsolvent-induced spinodal phase separation during electrospinning and solvent-induced recrystallization during post treatment. The blossoming porous structure with high specific surface area contributed to excellent filtration efficiency (99.99%) for sodium chloride (NaCl) ultrafine aerosol particles (30-100 nm) with a low pressure drop (110-230 Pa). Notably, under 7.8 cm/s air flow rate, the membrane samples performed better for filtering smaller-sized aerosol particles than the larger ones when evaluated by the quality factor (0.07). Finally, this finding demonstrates that the electrospun membrane with a hierarchical pore structure and high specific surface area hold great potential in applications as air-filtering materials.

Moisture Effect on Particulate Matter Filtration Performance using Electro-Spun Nanofibers including Density Functional Theory Analysis

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.

Ecofriendly Electrospun Membranes Loaded with Visible-Light-Responding Nanoparticles for Multifunctional Usages: Highly Efficient Air Filtration, Dye Scavenging, and Bactericidal Activity

Ambient particulate matter pollution has posed serious threats to global environment and public health. However, highly efficient filtration of submicron particles, the so-named "secondary pollution" caused by, e.g., bacterial growth in filters and the use of nondegradable filter materials, remains a serious challenge. In this study, poly(vinyl alcohol) (PVA) and konjac glucomannan (KGM)-based nanofiber membranes, loaded with ZnO nanoparticles, were prepared through green electrospinning and ecofriendly thermal cross-linking. Thus obtained fibrous membranes not only show highly efficient air-filtration performance but also show superior photocatalytic activity and antibacterial activity. The filtration efficiency of the ZnO@PVA/KGM membranes for ultrafine particles (300 nm) was higher than 99.99%, being superior to that of commercial HEPA filters. By virtue of the high photocatalytic activity, methyl orange was efficiently decolorized with a removal efficiency of more than 98% at an initial concentration of 20 mg L^-1 under 120 min of solar irradiation. A multifunctional membrane with high removal efficiency, low flow resistance, superior photocatalytic activity, and superior antibacterial activity was successfully achieved. It is conceivable that the combination of a biodegradable polymer and an active metal particle would form an unprecedented photocatalytic system, which will be quite promising for environmental remediation such as air filtration and water treatment.

Washable antimicrobial polyester/aluminum air filter with a high capture efficiency and low pressure drop

Here, we introduce a reusable bifunctional polyester/aluminum (PET/Al) air filter for the high efficiency simultaneous capture and inactivation of airborne microorganisms. Both bacteria of Escherichia coli and Staphylococcus epidermidis were collected on the PET/Al filter with a high efficiency rate (∼99.99%) via the electrostatic interactions between the charged bacteria and fibers without sacrificing pressure drop. The PET/Al filter experienced a pressure drop approximately 10 times lower per thickness compared with a commercial high-efficiency particulate air filter. As the Al nanograins grew on the fibers, the antimicrobial activity against airborne E. coli and S. epidermidis improved to ∼94.8% and ∼96.9%, respectively, due to the reinforced hydrophobicity and surface roughness of the filter. Moreover, the capture and antimicrobial performances were stably maintained during a cyclic washing test of the PET/Al filter, indicative of its reusability. The PET/Al filter shows great potential for use in energy-efficient bioaerosol control systems suitable for indoor environments.

Al-Coated Conductive Fiber Filters for High-Efficiency Electrostatic Filtration: Effects of Electrical and Fiber Structural Properties

Through the direct decomposition of an Al precursor ink AlH₃{O(C₄H₉)₂}, we fabricated an Al-coated conductive fiber filter for the efficient electrostatic removal of airborne particles (>99%) with a low pressure drop (~several Pascals). The effects of the electrical and structural properties of the filters were investigated in terms of collection efficiency, pressure drop, and particle deposition behavior. The collection efficiency did not show a significant correlation with the extent of electrical conductivity, as the filter is electrostatically charged by the metallic Al layers forming electrical networks throughout the fibers. Most of the charged particles were collected via surface filtration by Coulombic interactions; consequently, the filter thickness had little effect on the collection efficiency. Based on simulations of various fiber structures, we found that surface filtration can transition to depth filtration depending on the extent of interfiber distance. Therefore, the effects of structural characteristics on collection efficiency varied depending on the degree of the fiber packing density. This study will offer valuable information pertaining to the development of a conductive metal/polymer composite air filter for an energy-efficient and high-performance electrostatic filtration system.

Hot-Pressing Method To Prepare Imidazole-Based Zn(II) Metal-Organic Complexes Coatings for Highly Efficient Air Filtration

Particulate matters (PMs) air pollution has become a serious environmental issue due to its great threat to human health. Herein, metal-organic complexes PBM-Zn1 and PBM-Zn2 coatings (noted as PBM-Zn-Filter) have been produced by the hot-pressing method on various substrates for the first time. Layer-by-layer PBM-Zn-Filters were also obtained through varying hot-pressing cycles. The obtained PBM-Zn-Filters with high robustness show excellent performance in PMs removal. In particular, benefiting from thelarger conjugation system, micropore structure, lower pressure drop, higher electrostatic potential ζ, and electron cloud exposed metal center of PBM-Zn2 (DFT calculations), PBM-Zn2@melamine foam-4 gives the highest removal rates, PM2.5:99.5% ± 1.2% and PM10:99.3% ± 1.1%, and the removal efficiency for capture PM2.5 and PM10 particles in cigarette smoke were both retained at high levels (>95.5%) after 24 h tests. More importantly, a homemade mask is made up by imbedding the PBM-Zn2@melamine foam-4 into a commercial breathing mask, which shows higher removal efficiency, lower pressure drop, smaller thickness, and higher quality factor than two commercial breathing masks, the PMs removal efficiencies for both PM2.5 and PM10 are 99.6% ± 0.5% and 99.4% ± 0.8%, and acceptable air resistance are demonstrated.