Nanofiber Air Filter Research Articles

Electrospinning and Partial Etching Behaviors of Core-Shell Nanofibers Directly Electrospun on Mesh Substrates for Application in a Cover-Free Compact Air Filter.

The exposure of workers to propylene glycol monomethyl ether acetate (PGMEA) in manufacturing environments can result in potential health risks. Therefore, systems for PGMEA removal are required for indoor air quality control. In this study, core-shell zeolite socony mobil-5 (ZSM-5)/polyvinylpyrrolidone-polyvinylidene fluoride nanofibers were directly electrospun and partially wet-etched on a mesh substrate to develop a cover-free compact PGMEA air filter. The electrospinning behaviors of the core-shell nanofibers were investigated to optimize the electrospinning time and humidity and to enable the manufacture of thin and light air-filter layers. The partial wet etching of the nanofibers was undertaken using different etching solvents and times to ensure the exposure of the active sites of ZSM-5. The performances of the ZSM-5/PVDF nanofiber air filters were assessed by measuring five consecutive PGMEA adsorption-desorption cycles at different desorption temperatures. The synthesized material remained stable upon repeated adsorption-desorption cycles and could be regenerated at a low desorption temperature (80 °C), demonstrating a consistent adsorption performance upon prolonged adsorption-desorption cycling and low energy consumption during regeneration. The results of this study provide new insights into the design of industrial air filters using functional ceramic/polymer nanofibers and the application of these filters.

Fabrication of Poly(Lactic Acid)@TiO2 Electrospun Membrane Decorated with Metal-Organic Frameworks for Efficient Air Filtration and Bacteriostasis.

The development of high-performance filtration materials is essential for the effective removal of airborne particles, and metal-organic frameworks (MOFs) anchored to organic polymer matrices are considered to be one of the most promising porous adsorbents for air pollutants. Nowadays, most air filters are generally based on synthetic fiber polymers derived from petroleum residues and have limited functionality, so the use of MOFs in combination with nanofiber air filters has received a lot of attention. Here, a conjugated electrostatic spinning method is demonstrated for the one-step preparation of poly(lactic acid) (PLA) nanofibrous membranes with a bimodal diameter distribution and the anchoring of Zeolitic Imidazolate Framework-8 (ZIF-8) by the introduction of TiO2 and in situ generation to construct favorable multiscale fibers and rough structures. The prepared PLA/TZ maintained a good PM2.5 capture efficiency of 99.97%, a filtration efficiency of 96.43% for PM0.3, and a pressure drop of 96.0 Pa, with the highest quality factor being 0.08449 Pa-1. Additionally, ZIF-8 was uniformly generated on the surface of PLA and TiO2 nanofibers, obtaining a roughened structure and a larger specific surface area. An enhanced filtration retention effect and electrostatic interactions, as well as active free radicals, can be generated for the deep inactivation of bacteria. Compared with the unmodified membrane, PLA/TZ prepared antibacterial characteristics induced by photocatalysis and Zn2+ release, with excellent bactericidal effects against S. aureus and E. coli. Overall, this work may provide a promising approach for the development of efficient biomass-based filtration materials with antimicrobial properties.

TriboNano shield – Scalable manufacturing anti-smog multi-level structured nanofiber air filter with co-enhanced purification performance towards self-powered window screen

Nanofiber air filter has garnered tremendous attention due to large specific surface area, large porosity, highly interconnected aperture channels, etc. However, its unitary interlayer structural construction encounters limitation of filtration performance with a low yield. Here, we architect a triboelectric-induced multi-level interlaminar composite structure-based nanofiber window screen (T-MLNS), manufactured continuously utilizing free surface electrospinning. Subjoined with triboelectric charges (active type), T-MLNS possesses co-enhanced adsorption capacity of aerosols. Additionally, MLNS is constructed with finer fibrous layers for precise filtration and coarser fibrous layers in the middle facilitating airflow passing, under physical filtration mechanisms (passive type). Significantly, three-dimensional theoretical models are innovatively employed with numerical simulation findings that multi-level structures present superb filtration performance than uni-structure ones. In the synergistic effect of the active and passive typed mechanisms, T-MLNS is prolonged service life for precise capture of ultrafine aerosols (Diameter: 0.26 µm) with enhanced filtration efficiency up to 99.9%. The integrated multi-zone structure design creates a pattern-shape fiber mesh, resulting in prominent air permeability (∼100 mm s−1), optical light transmission (> 60%), and robust mechanical properties. This combination of active and passive filtering self-powered window screens offers a unique concept for revolutionising interior air quality in industrialization.

Fabrication of mixed matrix nanofibers with electrospraying and electrospinning techniques and their application to gas toluene removal

This study describes the fabrication and characterization of mixed matrix nanofiber air filters having adsorptive and photocatalytic properties. Two fabrication techniques were applied as (i) single electrospinning (SE) and (ii) successive electrospinning and electrospraying (SEE) for doping of photocatalyst (TiO2) in nanofiber structure. Polyacrylonitrile (PAN) was used as main polymer, the nanoclay (NC) was used with ratios of 0.5%, 1.0% and 2.0% (w/w) as nanoadsorbent and TiO2 was used as photocatalytic oxidation agent. TiO2 was integrated to the nanofiber structure with two doping methods (blended in solution and sprayed) providing as same TiO2 mass (0.2 g TiO2/g PAN) in unit area of final nanofiber structure. The water vapor transmission rate (WVTR) values showed a decreasing trend with the addition of NC and varies between 80 and 150 g/m2h. The presence of NC played a critical role in increasing of toluene adsorption capacity of nanofiber from 15% to 40% with increasing of NC amount. The maximum toluene degradation rates of mixed matrix nanofiber were found as 0.09 ppm/min for the NC2.0-TiO2-S coded nanofiber and 0.05 ppm/min for the NC2.0-TiO2 coded nanofiber. The integration of TiO2 to nanofibers with SEE was found as more effective for toluene oxidation than SE. With the electrosprayed TiO2, the contact area of nanofiber is further increased and the UVA light more easily activates TiO2 onto nanofiber. Among all nanofibers, NC2.0-TiO2-S coded nanofiber (doped TiO2 with SEE) is promising for air filter considering its filtration properties in general, as it has high toluene adsorption and oxidation efficiency, good air permeability, 93% particulate matter filtration efficiency and low pressure drop.

Synergistic Enhancement of Filtering Efficiency and Antibacterial Performance of a Nanofiber Air Filter Decorated with Electropolarized Lithium-Doped ZnO Nanorods.

According to clinical case reports, bacterial co-infection with COVID-19 can significantly increase mortality, with Staphylococcus aureus (S. aureus) being one of the most common pathogens causing complications such as pneumonia. Thus, during the pandemic, research on imparting air filters with antibacterial properties was actively initiated, and several antibacterial agents were investigated. However, air filters with inorganic nanostructures on organic nanofibers (NFs) have not been investigated extensively. This study aimed to demonstrate the efficiency of electropolarized poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) NFs decorated with Li-doped ZnO nanorods (NRs) to improve the filtering ability and antibacterial activity of the ultrathin air filter. The surfactant was loaded onto the ZnO─known for its biocompatibility and low toxicity─nanoparticles (NPs) and transferred to the outer surface of the NFs, where Li-doped ZnO NRs were grown. The Li-doped ZnO NR-decorated NF effectively enhanced the physical filtration efficiency and antibacterial properties. Additionally, by exploiting the ferroelectric properties of Li-doped ZnO NRs and PVDF-TrFE NFs, the filter was electropolarized to increase its Coulombic interaction with PMs and S. aureus. As a result, the filter exhibited a 90% PM1.0 removal efficiency and a 99.5% sterilization rate against S. aureus. The method proposed in this study provides an effective route for simultaneously improving the air filter performance and antibacterial activity.

Electrospinnability analysis of natural cellulose nanofibers for use in high-efficiency particulate matter capture based on rheological behaviors

To aid the development of air filters with high-efficiency fine particulate matter (PM) capture properties, the electrospinnabilities of natural cellulose nanofibers, which considerably affect filter performance, were investigated via rheological behavior analysis. The cellulose nanofibers were prepared by mixing trifluoroacetic acid (to dissolve cellulose) and 1,2-dichloroethane (to improve electrospinnability) with various types of cellulose. The rheological behavior of the precursor solution was analyzed according to mixing time via large amplitude oscillatory shear studies. The electrospinnability of the cellulose precursor solution was investigated based on the flow-induced structural anisotropy characteristics and the storage-loss moduli plot obtained by varying the frequencies. The precursor solution with hardwood pulp (HP) exhibited the highest specific surface area and the lowest combined content of hemicellulose and lignin, and thus, the optimal electrospinnability. The electrospun HP nanofiber sample with an HP content of 1.5 wt% displayed the optimal electrospinnability and the highest specific surface area of 1021 m2/g. It also exhibited high-efficiency PM capture characteristics, such as a PM2.5 capture efficiency and quality factor and an air permeability of 98.99%, 0.27, and 309 cm3/cm2 s, respectively. This study suggests the potential for the development of next-generation green nanofiber air filters using cellulose nanofibers.

Electrospinning synthesis of CuBTC/TiO2/PS composite nanofiber on HEPA filter with self-cleaning property for indoor air purification

In this study, we have developed a cure for indoor air pollution. Herein, we have fabricated CuBTC metal-organic framework MOF combined with TiO2 nanoparticle hybrid material by solvothermal method and obtained it in powder form. The CuBTC/TiO2 hybrid material absorbed toluene higher than TiO2 and CuBTC. CuBTC/TiO2 powder hinders its practical application, however, for the first time, CuBTC/TiO2/PS-based nanofibers were electrospun on a commercial HEPA filter using the electrospinning process in order to examine their air-filtering capabilities. This air filter exhibited 98.6% adsorption efficiency and 129.45 mg g-1 toluene gas adsorption capacity, although pristine HEPA was incapable of absorbing toluene. After the saturated point, a self-cleaning strategy was employed under UV light for regeneration purposes. In addition, the CuBTC/TiO2/PS nanofiber demonstrated superior PM2.5 removal performance, with a 99.82% filtration rate. Compared to a pure HEPA filter, the CuBTC/TiO2/PS-C nanofiber-based HEPA filter has a very high filtration rate and negligible pressure drop when evaluated at various airflow velocities. This study gives significant insight into the design of a self-cleaning nanofiber air filter to protect public health from indoor air pollution and save lives in the near future.

Correction to: Adaptive Electrospinning System Based on Reinforcement Learning for Uniform-Thickness Nanofiber Air Filters

Correction to: Adaptive Electrospinning System Based on Reinforcement Learning for Uniform-Thickness Nanofiber Air Filters

Adaptive Electrospinning System Based on Reinforcement Learning for Uniform-Thickness Nanofiber Air Filters

Adaptive Electrospinning System Based on Reinforcement Learning for Uniform-Thickness Nanofiber Air Filters

Tailoring bimodal protein fabrics for enhanced air filtration performance

Natural material-based nanofiber air filters promise to minimize any adverse impacts on the environment after use, but the nanofiber structure causes poor airflow performance, i.e. high airflow resistance. Constructing bimodal structures reduces airflow resistance without compromising removal efficiency but has been rarely studied for natural nanofiber air filters. In this study, we fabricate bimodal protein fabric air filters and carefully tailor their bimodal structure to achieve higher removal efficiency with significantly lowered airflow resistance. The bimodal structures are generated by co-spinning of denatured zein protein in two solvent systems, via controlling the protein denaturation degree and fiber shape/size. The bimodal structures with bimodal diameter distributions are then carefully adjusted by varying the feed rates. It is revealed that a bimodal fabric shows an optimized filtration performance when the fiber diameters locate at 2.44 and 0.13 μm, reducing the airflow resistance by up to 56.47 Pa (from 84.97 Pa to 28.5 Pa) with a high PM2.5 removal efficiency of 98.43%. The bimodal fabric treated with TX-100 shows a further improved filtration performance of filtering PM0.3 of 97.01% and PM2.5 of 99.15% at an ultralow airflow resistance of 21.1 Pa. Moreover, the treated bimodal fabric presents better long-term performance and higher removal efficiency in a humid environment. This work develops a simple and viable method for fabricating and tailoring bimodal air filters made of abundant natural protein for broad applications.

A Hierarchical Structure of Flower-Like Zinc Oxide and Poly(Vinyl Alcohol-co-Ethylene) Nanofiber Hybrid Membranes for High-Performance Air Filters.

In this article, we reported a hierarchical structure of flower-like zinc oxide (ZnO) and poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofiber (ZnO@NF) hybrid membranes for high-performance air filters. Monodispersed flower-like ZnO superstructures were fabricated using a template-free and surfactant-free hydrothermal method, and PVA-co-PE nanofiber yarns were prepared using a melt extrusion phase separation approach. The PVA-co-PE nanofiber yarns were subjected to high-speed shearing in a mixed aqueous solution of isopropanol and water to obtain a stably dispersed nanofiber suspension. The ZnO@NF hybrid air filter was obtained by coating the mixture of flower-like ZnO superstructures and the PVA-co-PE nanofiber suspension on the surface of the polypropylene (PP) meltblown nonwoven with the electret charge eliminated. The filtration efficiency of the ZnO@NF hybrid air filter increases with increasing loading amount of the flower-like ZnO superstructures, while the pressure drop decreases. The flower-like ZnO superstructures were incorporated into the nanofiber-interconnected networks, which significantly reduces the pressure drop of the pure PVA-co-PE nanofiber air filter. The filtration efficiency of the ZnO@NF hybrid air filter is much higher than that of PP meltblown nonwoven with eliminated electret charge, solving the hidden problem of electret charge dissipation during the protection process. It is demonstrated that these nanofiber hybrid air filters have great application potential in some special areas such as high-temperature and high-humidity environments.

Inorganic-organic nanofiber networks with antibacteria properties for enhanced particulate filtration: The critical role of amorphous titania

The demand for air filter media at indoor and outdoor is increasing tremendously due to air pollution and especially for problems related to airborne particulate matter (PM). To realize that, here a class nanofiber air filter media with strong antibacterial activity, hydrophobic nature, high filtration efficiency with low pressure drop is prepared. Novel organic-inorganic nanocomposite nanofibers used in this work benefited for the multifunctional performance. Amorphous titanium dioxide (mTiO2) is utilized for air filtration application which exhibits excellent enhancement of PM2.5 filtration properties and antibacterial activity. The unique Poly (vinylpyrrolidone) (PVP)-mTiO2 nanofiber air filter media acquired hydrophobic nature with a large increase in water contact angle of 127° from 36°. The resulting free-standing nanofiber filters exhibit high PM2.5 filtration efficiency of >99.9% and low pressure drop of 39 Pa. Antibacterial activity of nanofibrous membrane has been rationally engineered by titanium oxide as the barrier to bacterial ingression. A long term of 160 h filtration test has proved PVP-mTiO2 nanofibers air filter media holds outstanding 99% filtration efficiency for PM2.5. This work takes forward a significant lead in design and production of high performance and very low pressure drop air filter media with a wide range of functional properties.

Nanofiber Air Filters with High-Temperature Stability and Superior Chemical Resistance for the High-Efficiency PM2.5 Removal

In this work, an original oxidized poly(arylene sulfide sulfone)/UiO-66 (O-PASS-U) nanofiber filter was successfully prepared through electrospinning technology, followed by oxidation treatment. As a consequence, the O-PASS-U nanofiber filter exhibited excellent comprehensive properties for the high-temperature PM2.5 filtration. Benefiting from the advantageous structure of UiO-66, the O-PASS-U nanofiber filter achieved a high separation efficiency (99.97%), and low pressure drop (55.25 Pa) with enhanced interfiber voids. The excellent properties of the O-PASS-U nanofiber filter, such as good tensile strength (2 MPa), high thermal stability (400 °C), and hydrophobicity, make it a promising candidate for filtration. To display the correlation relationship between the filtration performance and fiber structure of the nanofiber filter, the filtration processes of three nanofiber filter structures were comprehensively investigated through simulation. In particular, the O-PASS-U nanofiber filter still maintained a high filtration efficiency of PM2.5 removal after the treatment of solvents (e.g., acid, alkali, and strong polar solvents) or high temperature. Overall, the O-PASS-U nanofiber filter could be a high-performance filter material for dust removal, particularly under harsh high-temperature conditions.

Super-hydrophobic Cellulose Nanofiber Air Filter with Highly Efficient Filtration and Humidity Resistance.

High-air humidity, especially condensation into droplets under the influence of temperature, can pose a serious threat to air purification filters. This report introduces the use of methyltrimethoxysilane (MTMS) for the silanization hydrophobic modification of cellulose nanofibers (CNFs) and obtains an air filter with super-hydrophobicity (CA = 152.4°) and high-efficiency filtration of particulate matter (PM) through the freeze-drying technology. The antihumidity performance of CNFs filters that undergo hydrophobic modification in high-humidity air is improved. Especially in the case of high-humidity air forming condensed water droplets, the increase in the rate of filtration resistance of the hydrophobically modified CNFs filter is much lower than that of the unmodified filter. In addition, the water-vapor-transmission rate of the hydrophobically modified filter is improved. More importantly, adding MTMS can regulate the porous structure of CNFs filters and improve the filtration performance. The specific surface area and the porosity of the filter are 26.54 m2/g and 99.21%, respectively, and the filtering effects of PM1.0 and PM2.5 reach 99.31 and 99.75%, respectively, while a low-filtration resistance (42 Pa) and a quality factor of up to 0.122 Pa-1 are achieved. This work has improved the application potential of high-performance air-purification devices to remove particulate pollution and may provide useful insights to design next-generation air filters suitable for application in high-air humidity.

Laminated polyacrylonitrile nanofiber membrane codoped with boehmite nanoparticles for efficient electrostatic capture of particulate matters

Particulate matters (PMs) air pollution is identified as the major threat to public health and climate. High-performance air filter technology based on various electrospun nanofibers is considered as an effective strategy to eliminate the effects of PMs air pollution. However, to date, nearly all the existing micro-/nanofibers are hard to meet both requirements of high PMs removal efficiency and long service life. In this work, we reported the production of laminated polyacrylonitrile(PAN)-boehmite nanoparticles (BNPs) nanofiber structured membrane by the electrospinning process. The dimension of PAN-BNPs nanofiber can be tunable from (0.09 ± 0.03) μm to (0.81 ± 0.11) μm by controlling the PAN and BNPs concentrations in precursors. The optimized PAN-BNPs nanofiber air filter with a basis weight of 1 g m−2 demonstrates the attractive attributes of high PM2.5 removal efficiency up to 99.962% and low pressure drop of 58 Pa. Most importantly, after introducing the BNPs as electret, the removal efficiency is very stable under the air flow rate of 6 l min−1. This PAN-BNPs nanofiber with a long electrostatic duration time offers an approach for fabricating future high-performance air filters.

High-temperature bearable polysulfonamide/polyacrylonitrile composite nanofibers for high-efficiency PM2.5 filtration

Polymer nanofibers have a great potential in PM2.5 filtration, but they generally cannot remove particulate matter (PM) particles directly from high-temperature sources due to their vulnerable structure. Polysulfonamide (PSA)/polyacrylonitrile (PAN) composite nanofibers that can withstand a temperature up to 400 °C, were fabricated by a simple electrospinning method. The interactions between PSA and PAN defined the resulting microarchitecture and shape of the nanofibers when suffering heating. The PSA/PAN composite nanofibers exhibited above 99.7% removal efficiency for the PM2.5. More importantly, such a high PM2.5 removal efficiency was well retained even after heating the nanofibers at temperatures ranging between 100 °C and 400 °C. The nanofiber air filter could continuously work for 100 h in an environment with the concentration of PM2.5 approaching 380 μg/m3. The good thermal stability and high filtration efficiency of PSA/PAN nanofibers make them attractive in various applications, especially when high-temperature bearable polymer components are needed.

An optimization approach for fabricating electrospun nanofiber air filters with minimized pressure drop for indoor PM2.5 control

Electrospun nanofiber air filters can achieve remarkable particle filtration efficiency with low pressure drop. Therefore, they can potentially be installed in buildings for reducing indoor PM2.5 concentrations. To improve filtration performance, this study developed a design and fabrication approach for electrospun nanofiber air filters with minimized pressure drop under a target PM2.5 filtration efficiency. First, this research developed semi-empirical models for calculating the pressure drop and PM2.5 filtration efficiency of nylon electrospun nanofiber filters using the fabrication parameters of electrospinning time and nylon concentration. With the developed models, this investigation then proposed an optimization approach to minimize the pressure drop under a given PM2.5 filtration efficiency and air velocity. For a given air velocity and PM2.5 filtration efficiency, one can minimize the pressure drop by finding the optimal solution concentration, while the target PM2.5 filtration efficiency can be achieved through adjustment of the electrospinning time. Furthermore, the proposed optimization approach successfully minimized the pressure drop for 110 out of the 125 cases, with an average pressure drop reduction of 32.7%. Finally, this research numerically studied the performance of a window screen coated with the optimized nanofiber filter in reducing indoor PM2.5 of outdoor origin.

Fabrication of Antimicrobial Nanofiber Air Filter Using Activated Carbon and Cinnamon Essential Oil

Recently, air quality is seriously worsening because of micro dust. As a result, respiratory and heart disease patients are also increasing every year. Therefore, the development of a highly efficient air filter media is required. In this study, we developed an antibacterial air filter media with activated carbon (AC) and cinnamon essential oil (CO). 12 wt.% polyurethane (PU) solution mixed with CO and AC was electrospun to prepare the AC+CO+PU nanofiber mat. We studied various characteristics of the AC+CO+PU nanofibrous mat. The surface morphology of mats in different concentration ratios was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We confirmed the antimicrobial activity of the nanofibrous mat using zone of inhibition test with Staphylococcus aureus and Escherichia coli. Air filter test was carried out to observe air filtration efficiency and pressure drop. This data was used to calculate the quality factor of the fabricated nanofiber air filter media. The fabricated antimicrobial nanofiber air filter media can be applied to various fields such as personal masks, air purification devices and bio applications.

Polybenzimidazole-Benzophenone Composite Nanofiber Window Air Filter with Superb UV Resistance and High Chemical and Thermal Durability.

There is a growing interest in window air filters to protect indoor air quality from ultrafine particulate matter (PM) in outdoor air. The filters for this purpose must achieve high filtering efficiency without compromising the original functions of the window, such as high air permeability and visibility. Several filters meeting these requirements have been developed and demonstrate a high PM2.5 filtering efficiency. However, these filters are installed outside the window or on the window screen guard, thereby requiring high levels of ultraviolet (UV), chemical, and thermal resistance. These requirements have been overlooked so far. In this study, we examine the fabrication and performance of a polybenzimidazole-benzophenone (PBI-BP) composite nanofiber air filter that demonstrates superb UV resistance and chemical and thermal durability. Because of the UV absorbance of the BP in the nanofibers, the filter membrane is robust even under prolonged UV exposure, which is essential for filters for this purpose. The filter membrane is not damaged even after treatment in strong acids or annealing at high temperature up to 400 °C. Thus, the PBI-BP composite filter is suitable for practical application in window air filters and can be adapted to develop filters used under other harsh environments.

Patterned nanofiber air filters with high optical transparency, robust mechanical strength, and effective PM2.5 capture capability.

PM2.5, due to its small particle size, strong activity, ease of the attachment of toxic substances and long residence time in the atmosphere, has a great impact on human health and daily production. In this work, we have presented patterned nanofiber air filters with high optical transparency, robust mechanical strength and effective PM2.5 capture capability. Here, to fabricate a transparency air filter by a facile electrospinning method, we chose three kinds of patterned wire meshes with micro-structures as negative receiver substrates and directly electrospun polymer fibers onto the supporting meshes. Compared with randomly oriented nanofibers (named “RO NFs” in this paper) and commercially available facemasks, the patterned air filters showed great mechanical properties, and the water contact angles on their surfaces were about 122–143° (the water contact angle for RO NFs was 81°). In addition, the patterned nanofibers exhibited high porosity (>80%), and their mean pore size was about 0.5838–0.8686 μm (the mean pore size of RO NFs was 0.4374 μm). The results indicate that the transparent patterned air filters have the best PM2.5 filtration efficiency of 99.99% at a high transmittance of ∼69% under simulated haze pollution.