Electrostatic Transparent Air Filter Membranes Composed of Metallized Microfibers for Particulate Removal

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 membranes filtering 100 nm particles from air flow by means of the van der Waals and Coulomb forces

Nonwoven fibrous filter membranes are widely used in filtration because of their low cost. They are less effective in intercepting airborne particles of the order of 100 nm, which is of the SARS-CoV-2 (COVID-19) virus's size. Many diseases, including COVID-19, predominantly spread by droplets released by breathing, coughing, sneezing, or medical procedures. It was shown that the smallest droplets can evaporate in air before settling, thus, making viruses airborne and easily penetrating even the best masks and filters. As a result, air-filtering membranes, which are capable of effective interception of ∼100 nm nanoparticles are highly desirable. A traditional way to improve filtration efficiency by overlapping several layers of nonwoven fabrics increases the required pressure drop, and thus, should be avoided as much as possible. Here, we propose and demonstrate an innovative approach to enhance performance of filtration membranes based on (i) a dramatic reduction in the fiber size, and (ii) metal coating of the fibers. The first component of this approach allows one to incorporate a novel physical mechanism of filtration, the short-range van der Waals forces, whereas the second one adds the long-range electric Coulomb forces if the oncoming nanoparticles are pre-charged and the metal-plated membrane grounded. In the present work, the ∼100 nm aluminum nanoparticles are filtered as a model of commensurate airborne single COVID-19 viruses, and Platinum is used as the sputter-coated material for the fiber coating. The resulting filtration efficiency enhanced by the electric Coulomb forces alone is increased by the factor of 1.77, while the filtration efficiency additionally facilitated by the van der Waals forces increased by the factor of 2.44. In comparison to the filter membranes with ∼500 nm fibers without the electric forces involved, the van-der-Waals-electric filter membrane with fibers ∼90 nm is 2.24 × 1.77 = 3.96 times more effective. The quality factor of a membrane which combines the van der Waals and Coulomb forces is 10.6 psi^-1, which is almost three times that of a comparable membrane without the electric Coulomb force (with only van der Waals forces being used).

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.

Stretchable and Compressible Si3 N4 Nanofiber Sponge with Aligned Microstructure for Highly Efficient Particulate Matter Filtration under High-Velocity Airflow

Particulate matter (PM) is one of the most severe air pollutants and poses a threat to human health. Air filters with high filtration efficiency applied to the source of PM are an effective way to reduce pollution. However, many of the present filtration materials usually fail because of their high pressure drop under high-velocity airflow and poor thermal stability at high temperatures. Herein, a highly porous Si₃ N₄ nanofiber sponge (Si₃ N₄ NFS) assembled by aligned and well-interconnected Si₃ N₄ nanofibers is designed and fabricated via chemical vapor deposition (CVD). The resulting ultralight Si₃ N₄ NFS (2.69 mg cm^-3 ) processes temperature-invariant reversible strechability (10% strain) and compressibility (50% strain), which enables its mechanical robustness under high-velocity airflow. The highly porous and aligned microstructure result in a Si₃ N₄ NFS with high filtration efficiency for PM_2.5 (99.97%) and simultaneous low pressure drop (340 Pa, only <0.33% of atmospheric pressure) even under a high gas flow velocity (8.72 m s^-1 ) at a high temperature (1000 °C). Furthermore, the Si₃ N₄ NFS air filter exhibits good long-term service ability and recyclability. Such Si₃ N₄ NFS with aligned microstructures for highly efficient gas filters provides new perspectives for the design and preparation of high-performance filtration materials.

Reusable Filters Augmented with Heating Microfibers for Antibacterial and Antiviral Sterilization

Numerous threats to human health and ecosystems on earth exist due to air pollution and the spread of fatal diseases. Airborne pollutants and particulate matter (PM) pose serious public health risks. In addition, the emergence and spread of bacterial and viral diseases constantly threaten public health and safety. Although various approaches have been implemented thus far to protect humans from air pollution and exposure to diseases, several challenges remain to be addressed. In this study, we developed a hybrid air filter consisting of filtration, heating, and thermal insulation layers. The air filtration layer can effectively capture airborne PM₁ particles (less than 1.0 μm in diameter). Furthermore, the heating layer enables the hybrid air filter to generate temperatures above 100 °C, and the insulation layer prevents the heat from being transferred to the other side (e.g., the human skin, if the hybrid air filter is used in a facemask). Since several bacteria and viruses are incapacitated under high temperatures, this hybrid air filter holds great promise for antibacterial and antiviral protection.

Electrospun Wrinkled Porous Polyimide Nanofiber-Based Filter via Thermally Induced Phase Separation for Efficient High-Temperature PMs Capture

Benefiting from its superior thermal stability, polyimide (PI) fiber-based composites have attracted wide attention in the field of high-temperature filtration and separation. However, the trade-off between filtration efficiency and pressure drop of traditional PI filters with single morphology and structure still remains challenging. Herein, the electrospun PI high-temperature-resistant air filter was fabricated via thermal-induced phase separation (TIPS), employing polyacrylonitrile (PAN) as a template. The PI nanofibers exhibited special wrinkled porous structure, and the filter possessed a high specific surface area of 304.77 m²/g. The removal of PAN changed the chemical composition of the fiber and induced PI molecules to form complex folds on the surface of the fiber, thus forming the wrinkled porous structure. Additionally, the wrinkled porous PI nanofiber filter displayed a high PM0.3 removal efficiency of 99.99% with a low pressure drop of 43.35 Pa at room temperature, and the filtration efficiency was still over 97% after being used for long time. Moreover, the efficiency of the filter could even reach 95.55% at a high temperature of 280 °C. The excellent filtration performance was attributed to the special wrinkled porous surface, which could limit the Brownian motion of PMs and reinforce the mechanical interception effect to capture the particulate matters (PMs) on the surface of the filter. Therefore, this work provided a novel strategy for the fabrication of filters with special morphology to cope with increasingly serious air pollution in the industrial field.

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

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

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.

Filtration Efficiency of Electret Air Filters Reinforced by Titanium Dioxide

In this study, titanium dioxide (TiO2), a mineral with a potential and supercapacitor, is used as the reinforcing material to improve the filtration efficacy of electret melt-blown fabrics. Next, the electret melt-blown fabrics are evaluated in terms of surface voltage and filtration efficiency, thereby examining the influences of the TiO2 ratio and electric field intensity. The test results indicate that the filtration efficiency is proportional to the ratio of TiO2 and electric field intensity. In particular, with a TiO2 ratio of 3 wt% and an electric field intensity of 2.5 kV/cm, the electret melt-blown fabrics demonstrate a maximal filtration efficiency of 96.32%, a lowest pressure drop of 40 Pa, and an optimal quality factor of 0.083 Pa−1.

Electrospun Environment Remediation Nanofibers Using Unspinnable Liquids as the Sheath Fluids: A Review

Electrospinning, as a promising platform in multidisciplinary engineering over the past two decades, has overcome major challenges and has achieved remarkable breakthroughs in a wide variety of fields such as energy, environmental, and pharmaceutics. However, as a facile and cost-effective approach, its capability of creating nanofibers is still strongly limited by the numbers of treatable fluids. Most recently, more and more efforts have been spent on the treatments of liquids without electrospinnability using multifluid working processes. These unspinnable liquids, although have no electrospinnability themselves, can be converted into nanofibers when they are electrospun with an electrospinnable fluid. Among all sorts of multifluid electrospinning methods, coaxial electrospinning is the most fundamental one. In this review, the principle of modified coaxial electrospinning, in which unspinnable liquids are explored as the sheath working fluids, is introduced. Meanwhile, several typical examples are summarized, in which electrospun nanofibers aimed for the environment remediation were prepared using the modified coaxial electrospinning. Based on the exploration of unspinnable liquids, the present review opens a way for generating complex functional nanostructures from other kinds of multifluid electrospinning methods.