Aerosol Filtration Application Using Fibrous Media-An Industrial Perspective

A Review of the Fabrication Methods, Testing, and Performance of Face Masks

Improvement in the performance and compatibility of face masks has remained the focus of researchers in recent years, especially after the emergence of the COVID pandemic. Although a lot of progress in the design, tolerability, and comfort of the mask has been reported, there are certain limitations, requiring further improvement. The present review aims to highlight the filtration efficacy, comfort, and associated characteristic of various types of face masks and respirators as a function of their design and structure. In addition, the air pollutants, their adverse effects on health, certified respirators, and face masks are also discussed. The present review also provides an insight into different types of commercially available face masks in terms of their materials, filtration efficiency, and limitations. The role of emerging trends (such as nanotechnology and high-performance polymers) in the improvement and development of face masks and respirators is also discussed.

Mass Production of Hierarchically Designed Engine-Intake Air Filters by Multinozzle Electroblow Spinning

Particulate matter damages engines of vehicles when blown into the ventilation system. Conventional engine-intake filter is cellulose microfiber board with an average diameter larger than ten microns, which has low removal efficiency of ultrafine particular matter. In this work, we apply ultrafine polyurethane nanofibers (∼122.8 nm) onto pleated cellulose board using scalable multinozzle electroblow spinning technology, which improves filtration efficiency of particulate matter with a diameter of less than 0.3 μm PM_0.3 greatly. The thermoplastic polyurethane 85A nanofiber membranes are transparent, and display superior filtration performance which meets up with the 95% filtration efficiency standard in GB 19083-2010 technical requirements for protective face mask for medical use. The lightweight pleated thermoplastic polyurethane/cellulose composites intercept ∼90% ultrafine PM_0.3 under airflow velocity of 32 L min^-1 and possess great resistance to shock. These hierarchically designed filters follow a mechanical mechanism and can be used in on-road and off-road cars in the long run.

Facile fabrication of reinforced sub-micron fibrous media with hierarchical structure compounded thermally for effective air purification in application

Air pollution has steadily worsened in recent years, and the coronavirus disease 2019 has been spreading since 2020. The electrospun fibrous filters present superior filtration performance, while the low mechanical property and yield of them limit their applications, which must be addressed urgently. Herein, polyacrylonitrile (PAN) sub-micron fibrous membrane with hierarchical structure was easily manufactured using free surface electrospinning in mass production for air purification. The "sandwich" structured fibrous filter was thermally bonded with bi-component nonwoven through traditional bonding procedures, due to melting and bonding of the cortex of bi-component fibers, in which the electrospun fibrous web as the mid layer with tortuous channels showed superior filtration performance for aerosol particles with diameter of 260 nm, which could effectively intercept different-sized particles suspended in the air. In addition, the impact of the processing parameters on the characteristics and filtration mechanisms of thermally bonded composite materials was thoroughly investigated. The results showed that composite material with "dendrites" and "axon" morphologies presented the best formability, outstanding peeling strength and breaking strength, and steady filtration performance, following an easy through-air bonding procedure, making it useful for post-processing in air purification. The reinforced composite filter, which is thermally bonded with sub-micron fibers with high yield and nonwoven, is save-energy and has a low operation cost, indicating its promising commercial possibilities.

Electrospun Nanofiber Membranes for Air Filtration: A Review

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

Facemask Global Challenges: The Case of Effective Synthesis, Utilization, and Environmental Sustainability

Coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a rapidly spreading pandemic and is severely threatening public health globally. The human-to-human transmission route of SARS-CoV-2 is now well established. The reported clinical observations and symptoms of this infection in humans appear in the range between being asymptomatic and severe pneumonia. The virus can be transmitted through aerosols and droplets that are released into the air by a carrier, especially when the person coughs, sneezes, or talks forcefully in a closed environment. As the disease progresses, the use and handling of contaminated personal protective equipment and facemasks have become major issues with significant environmental risks. Therefore, providing an effective method for treating used/contaminated facemasks is crucial. In this paper, we review the environmental challenges and risks associated with the surge in facemask production. We also discuss facemasks and their materials as sources of microplastics and how disposal procedures can potentially lead to the contamination of water resources. We herein review the potential of developing nanomaterial-based antiviral and self-cleaning facemasks. This review discusses these challenges and concludes that the use of sustainable and alternative facemask materials is a promising and viable solution. In this context, it has become essential to address the emerging challenges by developing a new class of facemasks that are effective against the virus, while being biodegradable and sustainable. This paper represents the potentials of natural and/or biodegradable polymers for manufacturing facemasks, such as wood-based polymers, chitosan, and other biodegradable synthetic polymers for achieving sustainability goals during and after pandemics.

Biodegradable and multifunctional surgical face masks: A brief review on demands during COVID-19 pandemic, recent developments, and future perspectives

Providing the greater public with the current coronavirus (SARS-CoV-2) vaccines is time-consuming and research-intensive; intermediately, some essential ways to reduce the transmission include social distancing, personal hygiene, testing, contact tracing, and universal masking. The data suggests that universal masking, especially using multilayer surgical face masks, offers a powerful efficacy for indoor places. These layers have different functions including antiviral/antibacterial, fluid barrier, particulate and bacterial filtration, and fit and comfort. However, universal masking poses a serious environmental threat since billions of them are disposed on a daily basis; the current coronavirus disease (COVID-19) has put such demands and consequences in perspective. This review focuses on surgical face mask structures and classifications, their impact on our environment, some of their desirable functionalities, and the recent developments around their biodegradability. The authors believe that this review provides an insight into the fabrication and deployment of effective surgical face masks, and it discusses the utilization of multifunctional structures along with biodegradable materials to deal with future demands in a more eco-friendly fashion.

Assessing effectiveness of air purifiers (HEPA) for controlling indoor particulate pollution

The present study deals with an evaluation of the air purifier's effectiveness in reducing the concentration of different sized particulate matter (PM) and ions in the real-world indoor environment. Two types of air purifiers (API and APII) mainly equipped with High-Efficiency Particulate Air (HEPA) filters that differed in other specifications were employed in general indoor air and the presence of an external source (candles and incense). The gravimetric sampling of PM was carried out by SKC Cascade Impactor and further samples were analyzed for determining ions' concentration while real-time monitoring of different sized PM was done through Grimm Aerosol Spectrometer (1.109). The result showed that API reduced PM levels of different sizes ranged from 12-52% and 29–53% in general indoor air and presence of external source respectively. Concerning the APII, a higher decrease percent in PM level was explored in presence of an external source (52–68%) as compared to scenarios of general indoor air (37–64%). The concentrations of the ions were noticed to be decreased in all three size fractions but surprisingly some ions' (not specific) concentrations increased on the operation of both types of air purifiers. Overall, the study recommends the use of air purifiers with mechanical filters (HEPA) instead of those which release ions for air purification.

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Efficiency of air purifier (AP) in removing indoor air pollutants was observed.

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AP was more effective on small-sized particles than large ones.

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AP of large Clean Air Delivery Rate removed particulate and ions more effectively.

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APs with mechanical filters must be employed instead of ions generators.

Free-Standing Ultrafine Nanofiber Papers with High PM0.3 Mechanical Filtration Efficiency by Scalable Blow and Electro-Blow Spinning

Particulate matter of 0.3 μm in diameter (PM_0.3) poses a serious threat to the environment and human beings. Ultrathin and -light nanofibrous filters with excellent filtration properties can significantly prevent the detrimental effects of these particles. Here, we develop free-standing polyamide PA-66 ultrafine nanofiber papers for PM_0.3 filtration using effective and scalable blow and electro-blow spinning techniques. The smallest average fiber diameter is 61.7 nm, which is 2-3 orders of magnitude smaller than that of conventional textiles. Poly(ethylene terephthalate) nonwovens are selected to fabricate free-standing nanofiber papers of various polymers, including polyamide, poly(methyl methacrylate), poly(vinylpyrrolidone), and poly(ethylene oxide) owing to the smooth surfaces of the nonwovens. This underlying principle can be used to create similar free-standing nanofiber papers from other commodity polymers in the future. Mechanisms of capturing particulate matter with different nanofiber morphologies are discussed. Salt and oil particulates are used to characterize the filtration properties. PA-66 papers are promising reusable filters owing to their mechanical particle-capture mechanism. The blow-spun PA-66 papers show filtration performance of 98.75% efficiency and a pressure drop of 125.44 Pa owing to the "slip" effect caused by the ultrasmall diameter. In the electro-blow spinning process, a supplementary voltage supply is conducive to separating nanofiber bundles into random-oriented nanofibers. Electro-blown spun papers possess an ultrahigh efficiency of 99.99% with a reduced areal density of 0.9 g m^-2. These PA-66 papers can be used in a variety of applications, such as reusable personal protective equipment, industrial waste gas treatment, and central ventilation purification systems.

Indoor air quality improvement in COVID-19 pandemic: Review

INTRODUCTION

The advent of COVID-19 has impinged millions of people. The increased concern of the virus spread in confined spaces due to meteorological factors has sequentially fostered the need to improve indoor air quality.

OBJECTIVE

This paper aims to review control measures and preventive sustainable solutions for the future that can deliberately help in bringing down the impact of declined air quality and prevent future biological attacks from affecting the occupant's health.

METHODOLOGY

Anontology chart is constructed based on the set objectives and review of all the possible measures to improve the indoor air quality taking into account the affecting parameters has been done.

OBSERVATIONS

An integrated approach considering non-pharmaceutical and engineering control measures together for a healthy indoor environment should be contemplated rather than discretizing the available solutions. Maintaining social distance by reducing occupant density and implementing a modified ventilation system with advance filters for decontamination of viral load can help in sustaining healthy indoor air quality.

CONCLUSION

The review paper in the main, provides a brief overview of all the improvement techniques bearing in mind thermal comfort and safety of occupants and looks for a common ground for all the technologies based on literature survey and offers recommendation for a sustainable future.

Ultrafine PVDF Nanofibers for Filtration of Air-Borne Particulate Matters: A Comprehensive Review

The ongoing global pandemic has bestowed high priority uponthe separation of air-borne particulate matters (PMs), aerosols, etc. using nonwoven fibrous materials, especially for face masks as a means of personal protection. Although spunbond or meltblown nonwoven materials are amongst the forerunners for polymer microfiber-based face mask or air filter development in mass scale, relatively new process of nonwoven manufacturing such as electrospinning is gaining a lot of momentum amongst the filter membrane manufacturers for its scalability of nanofiber-based filter membrane fabrication. There are several nanofiber-based face masks developing industries, which claim a very high efficiency in filtration of particulate matters (PM0.1-10) as well as other aerosols for their products. Polyvinylidene fluoride (PVDF), which is commonly known for its use of tactile sensors and energy harvesters, due to its piezoelectric property, is slowly gaining popularity among researchers and developers as an air filter material. Electrospun PVDF nanofibers can be as fine as 50 nm in mass scale, which allows the membrane to have large surface area compared to its volume, enhancing nanofiber-PM interaction. At the same time, the breathability index can be improved through these PVDF nanofiber membranes due to their architectural uniqueness that promotes slip flow around the fibers. The conductive nature of PVDF makes it advantageous as a promising electret filter allowing better capturing of ultrafine particles. This review aims to provide a comprehensive overview of such PVDF nanofiber-based filter membranes and their roles in air filtration, especially its application in filtrate of air-borne PMs.

Multistructured Electrospun Nanofibers for Air Filtration: A Review

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

Present cum future of SARS-CoV-2 virus and its associated control of virus-laden air pollutants leading to potential environmental threat - A global review

The world is presently infected by the biological fever of COVID-19 caused by SARS-CoV-2 virus. The present study is mainly related to the airborne transmission of novel coronavirus through airway. Similarly, our mother planet is suffering from drastic effects of air pollution. There are sufficient probabilities or evidences proven for contagious virus transmission through polluted airborne-pathway in formed aerosol molecules. The pathways and sources of spread are detailed along with the best possible green control technologies or ideas to hinder further transmission. The combined effects of such root causes and unwanted outcomes are similar in nature leading to acute cardiac arrest of our planet. To maintain environmental sustainability, the prior future of such emerging unknown biological hazardous air emissions is to be thoroughly researched. So it is high time to deal with the future of hazardous air pollution and work on its preventive measures. The lifetime of such an airborne virus continues for several hours, thus imposing severe threat even during post-lockdown phase. The world waits eagerly for the development of successful vaccination or medication but the possible outcome is quite uncertain in terms of equivalent economy distribution and biomedical availability. Thus, risk assessments are to be carried out even during the post-vaccination period with proper environmental surveillance and monitoring. The skilled techniques of disinfection, sanitization, and other viable wayouts are to be modified with time, place, and prevailing climatic conditions, handling the pandemic efficiently. A healthy atmosphere makes the earth a better place to dwell, ensuring its future lifecycle.

Nanofiber-Based Face Masks and Respirators as COVID-19 Protection: A Review

Wearing face masks, use of respirators, social distancing, and practicing personal hygiene are all measures to prevent the spread of the coronavirus disease (COVID-19). This pandemic has revealed the deficiency of face masks and respirators across the world. Therefore, significant efforts are needed to develop air filtration and purification technologies, as well as innovative, alternative antibacterial and antiviral treatment methods. It has become urgent—in order for humankind to have a sustainable future—to provide a feasible solution to air pollution, particularly to capture fine inhalable particulate matter in the air. In this review, we present, concisely, the air pollutants and adverse health effects correlated with long- and short-term exposure to humans; we provide information about certified face masks and respirators, their compositions, filtration mechanisms, and the variations between surgical masks and N95 respirators, in order to alleviate confusion and misinformation. Then, we summarize the electrospun nanofiber-based filters and their unique properties to improve the filtration efficiency of face masks and respirators.

Flexible and reusable carbon nano-fibre membranes for airborne contaminants capture

Airborne aerosol pollutants generated from combustion vehicles exhausts, industrial facilities and microorganisms represent serious health challenges. Although membrane separation has emerged as a technique of choice for airborne contaminants removal, allowing for both size exclusion and surface adsorption. Here, electrospun carbon nanofibre mats were formed from poly(acrylonitrile) by systematic stabilization and carbonization processes to generate flexible and self-standing membranes for air filtration. The great mechanical flexibility of the electrospun carbon-nanofibre membranes was achieved through extreme quenching conditions on a carbon fibre processing line, allowing for complete carbonization in just 3 min. The carbonized nanofibre membranes, with fibre diameters in the range of 218 to 565 nm exhibited modulus of elasticity around 277.5 MPa. The samples exhibited air filtration efficiencies in the range of 97.2 to 99.4% for aerosol particle in the size of 300 nm based on face velocity, higher than benchmark commercial glass fibre (GF) air filters. The carbonized electrospun nanofibre membranes also yielded excellent thermal stability withstanding temperatures up to 450 °C, thus supporting the development of autoclavable and recyclable membranes. This significant and scalable strategy provides opportunities to mass-produce reusable air filters suitable for otherwise complex airborne pollutants, including volatile organic carbons and bio-contaminants, such as viruses.

Effectiveness and Eco-Costs of Air Cleaners in Terms of Improving Fungal Air Pollution in Dwellings Located in Southern Poland—A Preliminary Study

Epidemiological evidence shows that air pollution is responsible for several million premature deaths per year. By virtue of being responsible for these deaths, economic evidence shows that air pollution also imposes a so-called economic cost to society of several trillion dollars per year. The diseases caused by biological air pollutants are of primary global concern for both social and economic reasons, and given that people may spend more than 90% of their time in enclosed spaces, the investigation into methods to remove indoor air pollutants is of paramount importance. One of the methods to improve indoor air quality (IAQ) is to use air cleaners (ACLs) with high-efficiency particulate air filters (HEPA) that remove biological indoor air pollutants from indoor environments. This work presents the results of a study of fungal aerosol samples collected during the summer season from inside two dwellings (DG1 and DG2) before and after starting the use of ACLs. The fungal aerosol samples collected from each of the six stages of the sampler were incubated on agar plates at 26 °C, and the colony forming units (CFU) were manually counted and statistically corrected. The concentration of living airborne fungi was expressed as the CFU in the volume of air (CFU·m−3). The average concentration of fungal aerosol decreased the most when the ACLs were active for 24 min. The reduction was from 474 CFU·m−3 to 306 CFU·m−3, and from 582 CFU·m−3 to 338 CFU·m−3 in DG1 and DG2, respectively. The use of ACLs was assessed by the life cycle assessment (LCA) methodology. This study highlights the benefits of controlling biological air pollutants in order to keep occupants of buildings happy and healthy.

How efficiently can HEPA purifiers remove priority fine and ultrafine particles from indoor air?

More than 1 million premature deaths in Asia annually are estimated to be associated with indoor air quality. HEPA (high-efficiency particulate air) filter air purifiers (APs) are widely used in urban Chinese residences by the growing middle class, as public awareness of air pollution increases. Currently, understanding of how particle size affects particle removal is inconsistent, and the rate at which different particle types are removed remains largely unknown. Therefore, this investigation aimed to determine the relationship between particle size and the removal efficiency of particles, and how efficiently ambient air is filtered compared to particle types which are typically used in standard tests (tobacco smoke, dust and pollen). Three of the most popular AP models in China were tested in China's largest indoor controlled chamber laboratory and the removal efficiencies of particles in the 18-514 nm range were identified. Each AP had a distinct profile of removal efficiency against particle size, but the three APs shared similarities in performance, with removal efficiency consistently lowest at 200-250 nm. This size fraction is important in an exposure context as these particles are abundant in ambient air in mega-cities, can penetrate through building shells effectively, remain airborne for long periods of time and can penetrate the deepest areas of the lungs. Ambient air particles were removed at a similar rate to test particles; this confirms that the Association of Home Appliance Manufacturers' (AHAM) standards are a suitable proxy for "real world" performance.

Facile Approaches of Polymeric Face Masks Reuse and Reinforcements for Micro-Aerosol Droplets and Viruses Filtration: A Review

Since the widespread of severe acute respiratory syndrome of coronavirus 2 (SARS-CoV-2) disease, the utilization of face masks has become omnipresent all over the world. Face masks are believed to contribute to an adequate protection against respiratory infections spread through micro-droplets among the infected person to non-infected others. However, due to the very high demands of face masks, especially the N95-type mask typically worn by medical workers, the public faces a shortage of face masks. Many papers have been published recently that focus on developing new and facile techniques to reuse and reinforce commercially available face masks. For instance, the N95 mask uses a polymer-based (membrane) filter inside, and the filter membrane can be replaced if needed. Another polymer sputtering technique by using a simple cotton candy machine could provide a cheap and robust solution for face mask fabrication. This review discuss the novel approaches of face mask reuse and reinforcement specifically by using membrane-based technology. Tuning the polymeric properties of face masks to enhance filterability and virus inactivity is crucial for future investigation.

Numerical calculation and analysis of filtration performance of an effective novel structural fiber for PM2.5

In this study, a novel fiber with slit-crescent-shaped cross-section is proposed to enhance the filtration performance of PM_2.5 in fibrous filtration. The collection efficiency of this fiber is simulated by using a Brownian dynamics simulation technique, and its filtration pressure drop is obtained by numerically solving Navier-Stokes equation with Fluent software. A parametric study is performed to improve the optimum filtration performance of the slit-crescent-shaped fiber via adjusting its structural parameters (dimensionless center-to-center spacing and slit width). Results indicate that at the optimal condition, i.e., when dimensionless slit width ranges from 0.2 to 0.4, collection efficiency is enhanced by 13.1%–101.1% relative to the circular fiber for particles ranging from 0.1μm to 2.5μm for the slit-crescent-shaped fiber under various dimensionless center-to-center spacing, and filtration pressure drop is reduced by up to 14.4%. In addition, quality factor is introduced to evaluate the comprehensive filtration performance of the slit-crescent-shaped fiber with different structural parameters, and results show that large dimensionless slit width and small dimensionless center-to-center spacing lead to a much higher quality factor than the circular fiber, especially for particles lager than 0.5μm. The numerical results obtained in this work are conducive to designing high efficiency fibrous filters.

Polyacrylonitrile/polyimide composite sub-micro fibrous membranes for precise filtration of PM0.26 pollutants

Particulate matter (PM) pollution has enormously threatened ecosystem and public health. Among various air filtration medium, fibrous ones are very attracting and promising, with an array of advantages such as high specific surface area, and good internal connectivity. Even so, the large-scale fabrication of fibrous filtration materials still remains challenging. Here, three-dimensional polyacrylonitrile/polyimide (PAN/PI) composite sub-micro fibrous membranes were fabricated facilely via free surface electrospinning for precise filtration of PM_0.26 pollutants, where the waste PI short fibers were utilized as raw material. The resultant composite fibrous membranes, featuring thin fiber diameter (~150 nm), low areal density (<0.8 g m^-2), large porosity, and highly tortuous airflow channels with uniform poresize distribution, possessed excellent mechanical property with tensile strength of 4.95 MPa (twice that of pristine PAN), high thermal durability as well as remarkable filtration performance for ultrafine NaCl aerosol particles (≤0.26 µm) even after multiple filtration tests at high airflow velocity of 14.1 cm s^-1. The deepened aperture channels inside three-dimensional sub-micro fibrous membranes are tortuous enough for capturing ultrafine PMs from the airstream mainly via diffusion, interception, and impaction mechanisms, and the reported large-scale fabrication of cost-effective homogeneous PAN/PI fibrous filter media is promising for industrial production and commercial applications.

Multi-Scale Microstructure Investigation for a PM2.5 Air-Filter Efficiency Study of Non-Woven Polypropylene

A N95 face-piece respirator and a 3M air filter composed of non-woven polypropylene filter material were investigated for their multi-scale microstructure and resulting filtration performance. Filtration mechanisms of each system are found and quantified. Both media showed a gradually decrease of the most penetrating particle size with respect to an increase in face velocity or surface charge density. Increasing the face velocity and porosity dramatically degraded the collection efficiency in the 3M filter rather than in the N95 system. We exploited three-dimensional X-ray tomography to characterize the morphological and geometrical properties of the fiber arrangement and deposition of aerosol on the fiber surface. Tuning the most predominant material parameters to achieve a precedence in lower pressure drop or higher collection efficiency in a specifically captured particle size range is of great requisite to a peculiar application of the filter media.

One-pot synthesis of catalytic molybdenum based nanocomposite nano-fiber membranes for aerosol air remediation

The development of fibrous air filters exhibiting high air filtration efficiency, low energy consumption, and self-cleaning properties is a critical challenge to generate the next generation of resilient air filtration systems. Nano-fibrous mats typically exhibit higher particle capture efficiency but may also lead to higher airflow resistance compared to macro-fibrous materials due to their tighter structure. In this paper, novel catalytic membranes mats were fabricated through a one-pot synthesis from ammonium tetrathiomolybdate (ATTM) doped poly(acrylonitrile) (PAN) nanofibers for sub-micron diameter aerosol particle removal. The presence of ATTM as a dopant in conjunction with a PAN polymeric matrix was found to not only enhance the air filtration performance by increasing aerosol particle removal down to 300 nm, but also increase the photocatalytic properties of the PAN material. The enhanced separation properties compared to bare polymeric PAN nanofibrous membranes were attributed to surface nanotexturation of the fibers, leading to protrusions and pores across the nano-fiber structures, thus leading to more permeable and lightweight membranes with higher particle capture capacities. The samples were benchmarked against commercial glass fiber air filters and found to offer higher filtration efficiency, lower pressure drop, and higher quality factor than the commercial filters. Specifically, the quality factors of the catalytic nano-fiber membranes were found to be up to four times higher than that of the benchmarked commercial air filters for PM_2.5 particles, while two times higher for 300 nm sized contaminants. The presence of the ATTM across the PAN matrix was also found to enhance the photocatalytic activity of the membranes by up to 130% compared to the bare PAN reference nanofibers. This novel strategy opens avenues to engineering advanced multifunctional catalytic membranes, to capture toxic particulate matter from air while offering self-cleaning properties when exposed to sunlight.

Pore engineering towards highly efficient electrospun nanofibrous membranes for aerosol particle removal

Electrospun nanofibrous membranes were engineered for aerosol particle removal by controlling the fiber density and alignment across electrospun mats. Electrospun nanofiber membranes were deposited on both, rotatory drum and stationary collectors, to investigate the effect of fiber alignment on filtration performance. Poly(acrylonitrile)/dimethyl formamide (PAN/DMF) solutions were used to produce membranes for applications in air purification. The air filtration performance of as-produced and hot-compacted membranes were systematically evaluated with regard to penetration, pressure drop, and quality factor when subjected to potassium chloride (KCl) aerosol particles in the size-range of 300nm to 12μm. The membranes offered air filtration efficiencies in the range of 77.7% to 99.616% and quality factors between 0.0026 and 0.0204 (1/Pa). The samples were benchmarked against commercial filters and were found to exhibit similar quality factors but higher air filtration efficiencies. These results were correlated to differences in pore morphologies and fiber orientation distributions generated from the different processing techniques, which revealed that the alteration of the fiber density is an effective method for enhancing air filtration performance.

In Situ Investigation on the Nanoscale Capture and Evolution of Aerosols on Nanofibers

Aerosol-induced haze problem has become a serious environmental concern. Filtration is widely applied to remove aerosols from gas streams. Despite classical filtration theories, the nanoscale capture and evolution of aerosols is not yet clearly understood. Here we report an in situ investigation on the nanoscale capture and evolution of aerosols on polyimide nanofibers. We discovered different capture and evolution behaviors among three types of aerosols: wetting liquid droplets, nonwetting liquid droplets, and solid particles. The wetting droplets had small contact angles and could move, coalesce, and form axisymmetric conformations on polyimide nanofibers. In contrast, the nonwetting droplets had a large contact angle on polyimide nanofibers and formed nonaxisymmetric conformations. Different from the liquid droplets, the solid particles could not move along the nanofibers and formed dendritic structures. This study provides an important insight for obtaining a deep understanding of the nanoscale capture and evolution of aerosols and benefits future design and development of advanced filters.

A multifunctional multi-walled carbon nanotubes/ceramic membrane composite filter for air purification

Carbon nanotubes (CNTs) are very small diameter fibers that have the potential to be integrated into filters to further increase particle capture efficiency.

Air filtration in the free molecular flow regime: a review of high-efficiency particulate air filters based on carbon nanotubes

Air filtration in the free molecular flow (FMF) regime is important and challenging because a higher filtration efficiency and lower pressure drop are obtained when the fiber diameter is smaller than the gas mean free path in the FMF regime. In previous studies, FMF conditions have been obtained by increasing the gas mean free path through reducing the pressure and increasing the temperature. In the case of carbon nanotubes (CNTs) with nanoscale diameters, it is possible to filtrate in the FMF regime under normal conditions. This paper reviews recent progress in theoretical and experimental studies of air filtration in the FMF regime. Typical structure models of high-efficiency particulate (HEPA) air filters based on CNTs are introduced. The pressure drop in air filters operated in the FMF regime is less than that predicted by the conventional air filtration theory. The thinnest HEPA filters fabricated from single-walled CNT films have an extremely low pressure drop. CNT air filters with a gradient nanostructure are shown to give a much better filtration performance in dynamic filtration. CNT air filters with a hierarchical structure and an agglomerated CNT fluidized bed air filter are also introduced. Finally, the challenges and opportunities for the application of CNTs in air filtration are discussed.

Composite nonwovens in filters: applications

This chapter discusses the role of composite nonwoven filters in different structural forms such as combining mechanical support and durability with filtration, providing two or more layers of different filtration efficiency and combining different separation technologies/functionality into one filter medium. In many situations, composite nonwovens might fulfill multiple objectives. Applications of composite nonwovens are quite diverse and increasing in the area of air, liquid and engine filtration. The developmental objectives of composite filtering media are lower energy consumption, longer filter life, high filtration capacity, greater dust holding (in depth filtration) and easy cleanability (of surface filter), satisfying more than one functional requirement and easier maintenance.