Reusable Polybenzimidazole Nanofiber Membrane Filter for Highly

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Reusable Polybenzimidazole Nanofiber Membrane Filter for Highly Breathable PM2.5 Dust Proof Mask Sol Lee, A Ra Cho, DaeHoon Park, Jae Kyeom Kim, Kyung Seok Han, Ick-Jae Yoon, Min Hyung Lee, and Junghyo Nah ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b19741 • Publication Date (Web): 07 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019

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ACS Applied Materials & Interfaces

Reusable Polybenzimidazole Nanofiber Membrane Filter for Highly Breathable PM2.5 Dust Proof Mask Sol Lee1, A Ra Cho2, Daehoon Park1, Jae Kyeom Kim2, Kyung Seok Han,1 Ick-Jae Yoon1, Min Hyung Lee2,*, Junghyo Nah1,* 1

Department of Electrical Engineering, Chungnam National University, Daejeon, 34134,

Korea 2

Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi, 17104, Korea

*Corresponding authors : [email protected], [email protected]

Keywords: particulate matters, polybenzimidazole nanofibers, air filters, electrospinning, dust proof mask.

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ABSTRACT Ultrafine particulate matters (PMs) are imminent threat to the human respiratory system as their sizes are comparable to and even smaller than human tissues. To cope with this situation, various personal dust proof masks have been developed and commercialized. However, due to relatively thick filter membrane to guarantee filtering efficiency, a huge pressure drop across the active filter layer is inevitable and breathing through it becomes uncomfortable.

In

this

work,

we

investigated

the

performance

of

electrospun

polybenzimidazole (PBI) nanofiber membrane filters that can potentially be used for dust proof masks or other high performance filters. Thanks to its high dipole moment (6.12) as confirmed by density functional theory (DFT) calculation, the surface potential of the PBI nanofiber air filter, measured by KPFM, was higher than that of other commercially available mask filters. The filter developed in this work provides high PM filtering efficiency of ~98.5% at much reduced pressure drop (130 Pa) in comparison to those used in commercially available masks (386 Pa) with similar filtering efficiencies. Consequently, approximately 3-fold higher quality factor (~0.032), evaluated for PM2.5, in comparison to that of commercial ones (~0.011) was achieved by using PBI nanofiber. Furthermore, we developed a cleaning method effective for the filter contaminated by both inorganic and organic PMs. Even after several cycles of cleaning, the PBI filter membrane demonstrated negligible damage and retained its original performance owing to its mechanical, thermal, and chemical durability.


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INTRODUCTION With the rapid industrialization and urbanization in recent years, the concentration of both organic and inorganic ultrafine particulate matters (PM2.5) in the air has reached above the air quality guidelines (AQG) provided by World Health Organization (WHO), where they present environment policies for health for all human beings in the world, in many developing countries.1 In particular, air pollution due to PM2.5 severely degrades the quality of life and has become an imminent threat to human health.2-6 Therefore, it is advised to wear personal air-purifying equipment such as dust proof masks in areas with high PM2.5 concentration.7,8 To date, extensive research efforts have been made to develop high-performance air filter media, focusing on the enhancement of filtering efficiency.9-16 Indeed, we empirically confirmed that many commercially available dust proof masks demonstrate high filtering efficiencies (η) over 98%. Although high filtering efficiency has been achieved, air permeability, one of the most important features essential for frequent and convenient use in daily life, is still insufficient. Achieving both high breathability and high PM2.5 removal efficiency is challenging because of the trade-off between filtering efficiency and air pressure drop. In particular, difficulties in breathing through PM2.5 filter masks can be a serious problem for asthmatic patients as well as old and young people. Furthermore, most filter membranes for dust-proof mask are disposed after single use because their reuse severely degrades their filtering efficiency. However, careless disposal of these masks associated with their widespread use may cause other environmental problems as well. Therefore, it is necessary to further investigate material systems to develop high-performance and reusable PM2.5 filter



membranes17-23, which can simultaneously satisfy the requirements of high breathability, high filtering efficiency, and reusability. In this work, we report the performance of electrospun24 polybenzimidazole (PBI) nanofiber membranes,25,26 which can be potentially employed for PM2.5 dust proof masks. Since polymer nanofiber filters with inherently high electric dipole moment can more effectively capture PMs owing to intermolecular electrostatic interaction,10,27-29 and thus PBI with high electric dipole moment (6.12D) can be an optimal platform to develop high performance filter membrane. Indeed, the fabricated PBI filter demonstrated high filtering efficiency (~98.5%) at considerably low pressure drop (130 Pa) as compared to other commercial dust-proof mask filters made of polypropylene (PP) (~98%, 386 Pa). With its high dipole moment, PBI nanofibers can achieve high PM filtering efficiency at lower fiber packing density compared to other filters, leading to reduced pressure drop. Consequently, the breathability of PBI nanofiber membrane dust-proof masks can be greatly improved, enhancing overall quality factor (QF) of the mask for 3-fold. Besides owing to the superior mechanical, chemical and thermal stability of PBI,30,31 the PBI filter membrane has demonstrated negligible damage and retained its original performance even after the proposed cleaning process.

EXPERIMENTAL METHODS

Fabrication of PBI-based nanofibrous filter. The 26 g of PBI (Performance products) solution was dissolved in (100, 89, 53 ml) dimethylacetamide (Samchun chemicals) (12 ~ 18 wt%) weight ratio, respectively, which were stirred for 12 h at 60 °C. The fabrication of nanofibrous membrane air filter that was electrospun on the polyester (PE) mesh by using


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electrospinning equipment (ESR200R2, NanoNC). The PBI solution was loaded in a 10-ml syringe and 23-gauge metal needle tip was used. The syringe was located at a distance of 10 cm between metal tip and collector, injecting a PBI solution at an injection rate 0.2 mL/h. The high voltage of 14 kV was applied between the metal tip and the collector. Afterwards, as-spun nanofibrous membrane was laminated with a separate PE mesh using laminator (330R6, TOFO) at 140 °C. For the formation of Nylon 6 nanofiber filter membrane, Nylon 6 solution (18 wt%) is prepared by adding 1.34 g of Nylon 6 pellets (Sigma Aldrich) to 5 mL of formic acid (Thermo Fisher Scienticfic) and stirring at 50 ℃ for 2 h. The Nylon 6 solution is then loaded in the syringe and injected at a rate of 0.1 mL/h and a high voltage of 15 kV is applied to fabricate the Nylon 6 nanofibers. Characterization and Measurement. The electric dipole moment of each polymer was calculated by Density Functional Theory (DFT). The air flow measured by differential pressure transmitter (CP 210, KIMO). The PM was generated by atomizer (AGK 2000, PALAS). The captured PM was measured by aerosol spectrometer (11-A, GRIMM). The custom-built filtration measuring equipment was installed in the wind tunnel to measure the filtration efficiency. The scanning electron micrograph (SEM) and Electron dispersive X-ray spectroscopy (EDS) were obtained using S-4800 (Hitachi) and Zeiss (Merlin), respectively. The Fourier-transform Infrared Spectroscopy (FTIR) spectroscopy were performed with Vertex 80/80v (Bruker). The X-ray Photoelectron Spectrometer (XPS) was obtained using KAlpha+ (ThermoFisher Scientific). The transmittance was performed with spectrophotometer (Cary 5000, Varian). The surface potential was measured by noncontact mode Kelvin probe force microscopy (XE-7, Park systems). Commercial filters of #1, #2, and #3 were obtained from dust proof masks manufactured by Dongkook, FTENE and Aju Pharm, respectively. The active filter membranes of all three commercial filters are made of polypropylene (PP). The



PM generation procedure is described as the following. First, 2 wt% KCl aqueous solution is connected to the aerosol generator nozzle. The air compressor connected to the nozzle is set to 1 bar. The KCl aqueous solution is soaked up and injected into the cyclone part of the equipment. Due to the centrifugal force of the cyclone, large droplets go back to KCl aqueous solution, and the remaining droplets are generated as KCl particles in aerosol form. The particle size can vary depending on the KCl solution concentration and the compressor pressure. Using 0.5% dioctyl phthalate (DOP) solution (dissolved in ethanol), DOP PMs are also generated by the same mechanism. The flow rate of 0.35 m/s was maintained for all the test samples in this work.

RESULT AND DISCUSSION Before we examine the roles of high electric dipole moment on the performance of PBI nanofiber filter membranes, we have investigated a number of commercially available dust-proof masks and categorized them into three representative types based on their filter structures: COM #1, COM #2, and COM #3 (Figure S1). All of the commercial filters examined were found to be made of PP but with different fiber diameters and layer structures. In addition, Nylon 6 filter was also prepared to demonstrate the role of electric dipole moment on the filtering performance. For these three polymers, the electric dipole moment was obtained by DFT calculation. Figure 1a shows the calculated dipole moments of each polymer: PBI, Nylon 6, and PP. The calculated electric dipole moment (D) of PBI, Nylon 6, and PP are 6.12D, 3.31D, and 0.35D, respectively, where much higher dipole moment was obtained from PBI. Figure 1b (left) schematically represents the electrospinning process for the formation of the nanofibrous PBI and Nylon 6 membrane on the PE mesh on the metal collector. While appling electric field between the tip of the syringe and the metal collector, PBI or Nylon 6 nanofibers


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were piled up on the PE mesh with a size of 4 cm  4 cm placed on the metal ground collector. As shown in the scanning electron micrograph (SEM) of electrospun PBI nanofibers, densely packed nanofiber layer is formed on the PE mesh (Figure 1b). Since the nanofiber layer formed on the PE mesh can be easily damaged, we developed the lamination process, where the electrospun nanofiber layer is laminated with another PE mesh at 140 °C under an applied pressure. Through the lamination process as shown in Figure 1c (top), the nanofibers are physically immobilized between the PE nets and are protected even if the filter membrane is bent or stressed. Figure 1c (bottom) shows a photograph of the laminated nanofibrous membrane filter. Next, using the prepared filter layers and active filter layers separated from commercial dust-proof masks, surface potential of each filter was scanned over an area of 5 m  5 m by using Electrostatic Force Microscope (EFM, Park Systems) (Figure 1d). Surface potential was measured over different locations and averaged. The surface potential of PBI and Nylon 6 nanofiber layer were measured as 0.77 V and 0.492 V, respectively, and those of commercial PP membranes were distributed from -0.253 to -0.374 V. Indeed, much higher surface potential with respect to the reference (Pt-coated tip) was observed from the surface PBI nanofiber membrane. As shown in Figure 1e, the fabricated filter membrane can be installed in dust proof mask as an active filtering layer, where different PMs in the air can be filtrated through the PBI nanofiber membrane. To determine optimal extraction conditions for PBI nanofibers and evaluate the performance of the filter membranes, a custom-built PM filtration test equipment was installed as shown in Figure 2a. The test setup consists of PM generator, particle counters, pressure gauge, flow meter and blower. The test filters were placed in the center of the chamber. We note that moisture in PMs was removed by passing them through a diffusion dryer. First, to determine optimal solution viscosity for nanofiber formation, three different concentrations of



PBI solutions (12, 15, 18 wt%) were electrospun to form nanofiber layers. Diameter of electrospun PBI nanofiber filter membranes was then analyzed by graphic software (ImageJ, NIH) to find diameter distribution of the nanofibers. The results show that as the wt% of PBI solution increases, the average diameter of the PBI nanofiber gradually increases. Using the filters prepared by three different solutions, the filtering efficiency was examined. Here, filtration efficiency (η) was calculated by measuring the difference in PM concentration between the front and rear of the filter using particle counters #1 and #2. Similarly, the pressure drop ( △ P) was also obtained by measuring the difference between the front and rear of the filter. All the test filters were prepared to have the same initial pressure drop of ~130 Pa for fair comparison. With 12 wt% of PBI solution, the thinnest nanofibers can be formed, which is desirable to enhance the filtering efficiency. However, due to its low viscosity, many beads are observed as marked in Figure 2(b, i), so that η becomes rather slightly smaller than that of the filter made of 15 wt% PBI solution (Figure 2c). On the other hand, the filter made of 18 wt% PBI solution obviously shows the reduced filtering efficiency particularly for PM1 due to thicker diameter of the nanofiber. Therefore, the optimal concentration of PBI solution was determined as 15 wt% (Figure 2c and S2). Using 15 wt% PBI solution, proper fiber density was determined by gradually increasing electrospinning time until the filtering efficiency of 98.5% is reached, requiring 6 min of electrospinning. Figure 2d shows the PM2.5 removal efficiency and pressure drop of the PBI filters as a function of electrospinning time. Using the optimized PBI filter membrane, its performance was compared with Nylon 6 and three different commercial filter membranes: COM #1, #2, and #3 (Figure S1). For a fair comparison, the identical test condition was maintained for all the test samples. In Figure 2e, all the commercial filters and the PBI nanofiber filter demonstrated a high PM removal efficiency above ~98%. However, the filtering efficiency of Nylon 6 filter prepared to have the same pressure drop as


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PBI filter was below 95%. Although equivalent filtering efficiency was achieved, however, all the commercial mask filters demonstrated high pressure drops above ~350 Pa due to their high fiber packing density required for guaranteeing high filtering efficiency. Therefore, high air flow resistance can be experienced through the active filter layer during inhalation. In contrast, the PBI filter exhibited much reduced pressure drop (~130 Pa), while maintaining a similar filtering efficiency (~98.5%). We attribute this to high dipole moment of PBI nanofibers, allowing to achieve high filtering efficiency at much low nanofiber density. In addition, by comparing the filters made of polymers with different dipole moments, the role of dipole moment on the filtering efficiency has also be examined (Figure S3). To further evaluate the performance of the filters, quality factor (QF)12,32-34 was also calculated using the equation, QF = − ln (1-η) / △P, where η denotes a filtering efficiency and △P denotes a pressure drop. QF is a figure of merit (FOM) commonly used to evaluate performance of the filters. Since η and △P are inversely related, it is necessary to optimize them to maximize QF. Consequently, a QF of ~0.032 was achieved for the PBI nanofiber filter, which is 3  higher than that of commercial filter (Figure 2f). Filtering efficiency and pressure drop of the PBI filter were further examined by increasing air flow rate, where we observed a negligible decrease of filtering efficiency even if the pressure drop is increased proportionally (Figure S4). Next, the performance of the PBI air filter was also evaluated using organic PMs. In this test, DOP solution was used as PM source. Figure 3a shows measured organic PM removal efficiencies and pressure drops of each filter. All the filters except Nylon 6 filter demonstrated organic PM filtration efficiencies above 90%, similar to the results observed using inorganic PMs. However, for PBI filter, the filtration efficiency for organic PMs was slightly reduced compared to that for inorganic PMs. In the case of inorganic PMs (KCl), the high dipole



moment of the PBI contributes to the effective trapping of PMs by the electrostatic effect (Figure 2). Thus, high filtration efficiency can be achieved even with a relatively thin filter layer. For organic PMs such as DOP, filtration of PMs using polymer filters can be made by both chemical bonding and electrostatic interactions. According to the surface analysis of PM models using XPS,27 structure of organic PMs can be core-shell like structures with nonpolar hydrocarbons and polar functional groups (C-O, C=O) at the core and the shell, respectively (Figure 3b). Therefore, the electrostatic interactions can be still important factor of filtration for the organic PMs. For the filters with the same pressure drop, the filtering efficiency for organic PMs is also higher for the filters made of the polymer with high dipole moment (Figure S3). Consequently, the calculated QF of the PBI nanofiber air filter was still more than 2  higher than those of the commercial ones (Figure 3c). All the test results obtained using organic PMs in this work are summarized in Table 1. Figure 3d shows Fourier-transform Infrared Spectroscopy (FTIR) results of the PBI filter measured before (black colored line) and after (red colored line) the filtration test with DOP. The main peaks located at 1700, 1245, 1083, and 720 cm-1 indicate molecular bonding of C=O, C-O, C-O, and C-H respectively. After filtration of DOP using the PBI filter, we can clearly notice that the intensities of the main peaks are increased. This indicates that the organic components are attached to the PBI nanofiber membrane. To further investigate general characteristics of organic PMs, we collected soot by burning incense. The FTIR analysis and XPS results are similar to those of DOP but with higher composition of oxygen due to combustion (Figure S5). Thus, we expect similar effect from other organic PMs as well. To understand PM filtering efficiency of polymer filters in the molecular-level, binding affinity between various polymers and surface functional groups of PM were calculated by DFT at the B3LYP 6-31G(d) level (Figure S6).35-38 The binding energy (∆E)


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between polymers and PM functional groups are estimated by difference in total energy between free PM, polymer molecules, and PM/polymer binders, and optimized geometries of molecular interactions with the lowest binding energy are also modeled and illustrated in the Figure S6. As model PM molecules interacting with different functional groups such as C-O, C=O, and C-N, five saturated hydrocarbons with the functional groups were modeled. We note that the ∆E of polymers/PMs are increased in the order of PBI, Nylon6, and PP for all functional group of PMs. These trends demonstrate that polymers with higher polarity can bind stronger with polar PMs due to electrostatic interactions, matching with PM filtering efficiency test results. Binding energies of DOP also shows similar trends due to partially polar oxygen atoms in the molecules. Lastly, the reusability of the PBI filter was also examined by cleaning the contaminated filter after tests. Figure 4a shows SEM images of the PBI nanofiber filter before the tests, contaminated after the filtration tests using (i) inorganic PMs and (ii) organic PMs, and recovered after the cleaning process. In case of inorganic PMs, a large amount of the particles was physically collected between the nanofibers (Figure 4(a, i)). Electron dispersive X-ray spectroscopy (EDS) of the collected PMs also indicated that the elements corresponded to potassium (K) and chloride (Cl) (Figure 4b). Unlike inorganic PMs, the PBI filter was completely covered with organic compounds after testing with the organic PMs (Figure 4(a, ii)). Supplied organic PMs were initially captured by the PBI nanofibers and became large aggregated PMs.39,40 With a continuous supply of DOP, aggregated PMs merged together, and the entire filter became completely covered with PMs. In order to examine reusability of the filter membranes, we first tested the cleaning process of the filter contaminated with inorganic PMs. For this, the PM captured filter was dipped and washed in deionized (DI) water for 30 s. Afterwards, the filter was dried under ambient conditions. As shown in Figure 4(a, i), all KCl



nanoparticles were completely removed and electrospun nanofibers clearly remained on the PE mesh even after the cleaning process owing to its excellent mechanical strength (Figure S7). EDS of the filter clearly showed the removal of PMs after the cleaning process (Figure 4b). For cleaning of the PBI filter contaminated with organic PMs (Figure 4(a, ii)), we dipped the filter in customized organic PM cleaning solutions based on diluted acetic acid containing various ionic species for 10 s, followed by dipping in DI water and drying under ambient condition. This cleaning solution completely removed all organic PMs over the filter, as shown in Figure 4(a, ii). Optical transmittance test and FTIR analysis of the PBI filter after the cleaning process also confirmed the removal of organic PMs (Figure S8 and S9). Furthermore, the proposed cleaning process only requires a short cleaning time and does not include any harmful chemical elements. Owing to their chemical stability, the PBI nanofibers were not damaged even after dipping in strong the acid solutions (Figure S10, S11). As this cleaning process includes two sequential cleaning steps with acid solution and DI water, it can simultaneously remove both inorganic and organic contaminants. Our method was also found to be effective for cleaning other organic contaminants, such as paraffin oil and smoke from burning incense (Figure S12). To evaluate the filtration efficiency after the cleaning process, we measured the filtering efficiency of the PBI filter after each cleaning cycle. Even after three cleaning cycles, the removal efficiency for both inorganic and organic PMs was maintained. Therefore, the PBI nanofiber air filter can be reused for several cycles after a simple cleaning process, which can extend the life of the dustproof mask. This unique advantage of re-usability of the PBI nanofiber membrane can provide significant benefits in developing filters, and their application can be expanded to other fields. Furthermore, in addition to its mechanical and chemical stability, the PBI polymer is also highly stable even at relatively high temperature compared to


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other polymers used in commercial PM filtering masks. The morphology of the PBI nanofibers was preserved after thermal exposure at 400 °C for one hour, as shown in Figure 4d. Thus, the PBI nanofiber filter can also be used for the applications requiring thermal endurance.

CONCLUSIONS In this work, we have developed high performance PBI nanofiber filter membrane, which can effectively capture ultrafine PMs at reduced pressure drop. Thanks to high electric dipole moment of PBI, high PM removal efficiency of 98.5% was obtained at a pressure drop of 130 Pa, which is approximately ~30% of commercial filter membranes with equivalent filtering efficiency. Thus, highly breathable and high performance dust proof mask can be realized using the PBI filter membranes. Due to enhanced breathability, QF of the PBI filter was also found to be 3  higher than those of other commercial filters. Furthermore, we proposed a simple cleaning method that can simultaneously remove both inorganic and organic PMs. Even after several cyclic cleaning cycles, the performance of the PBI filter was maintained without noticeable degradation. With its mechanical, chemical, and thermal stability, the PBI filter membrane can be widely adopted to develop different filters for various applications. ASSOCIATED CONTENT Supporting Information SEMs and schematic images of the commercial filters; Removal efficiency of DOP at different PBI concentration; Comparison of removal efficiency and surface potential at different dipole moment; PM

2.5

removal efficiency and pressure drop at different air flow; XPS and FTIR

analysis of burning incense; Binding energies of different polymer-PM interactions; SEMs of



PBI nanofibers after cleaning; Before and after cleaning, analysis of the optical transmittance; FTIR analysis of after cleaning; SEMs of PBI nanofiber after dipping in acid; Initial pressure drop change after cleaning; Before and after cleaning, SEM images of the different type organic PMs. AUTHOR INFORMATION Corresponding Authors *E-mail address: [email protected] *E-mail address: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF-2017R1A4A1015744), Creative Materials Discovery Program (NRF-2017M3D1A1039379, and Korea Ministry of Environment (MOE) as "Advanced Technology Program for Environmental Industry Program".


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Figure 1. (a) Molecular structures and dipole moment of PBI, Nylon 6, and PP calculated by density functional theory (DFT). (b) (left) Fabrication of nanofibrous PBI or Nylon 6 membrane filter by electrospinning on PE mesh at 1.4 kVcm-1. (right) SEM image of as spun PBI nanofibers ; magnified view (scale bar is 1 m). (c) (top) Schematic representation of the lamination of PE mesh over PBI or Nylon 6 nanofiber-coated PE mesh at 140 °C and (bottom) Photograph of the laminated nanofiber membrane after lamination process (right). (d) KPFM images of surface potential of PBI, Nylon 6 nanofiber filters, and three commercial filters made of PP. (e) Schematic representations of PM filtration process and its potential application as a filter membrane for PM2.5 dust proof masks.


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Figure 2. (a) A photograph of the measurement setup for testing PM removal efficiency and pressure drop of the filter, consisting of PM generator, particle counters, pressure gauge, flow meter and blower. (b) Diameter distribution of PBI nanofibers electrospun using the PBI solutions with (i) 12 wt% PBI (red marks indicate beads formed during the electrospinning process) (ii) 15 wt% (iii) 18 wt% (scale bar is 5 m) (c) PBI concentration dependent PM1.0 and PM2.5 removal efficiencies. The optimal PBI concentration is found at 15 wt%. Note: All the test filters were prepared to have the same initial pressure drop of ~130 Pa. (d) KCl (PM2.5) removal efficiencies and pressure drops of the PBI nanofibrous membrane filter prepared by different electrospinning times. (e) Comparison of PM2.5 removal efficiency and pressure drop of PBI, Nylon 6 filters, and the filters separated from the commercial dust proof masks. (f) Quality factors (QFs) of different filters, indicating excellent QF of PBI filter due to enhanced breathability.



Figure 3. (a) Organic PM filtering efficiency and pressure drop of the PBI, Nylon 6, and PPbased commercial dust proof mask filters. (b) XPS analysis of DOP PMs showing the C 1s and O 1s peak analysis and composition ratio, indicating polar functional groups (c) Quality factors of the filters fabricated with different polymers (d) FTIR measurement of the filter before (black colored line) and after (red colored line) the filtration test.


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 (%) KCl

 (%) DOP

ΔP (Pa)

QF (Pa-1) KCl

QF (Pa-1) DOP

Surface potential (V)

Dipole moment (D)

PBI (This work)

98.55

90.2

131.2

0.032

0.0170

0.77

6.12

Nylon 6

94.14

85.74

131.2

0.021

0.015

0.0492

3.31

COM #1

98.14

94.60

350.6

0.014

0.0083

-0.374

0.35

COM #2

98.45

93.98

364.1

0.011

0.0077

-0.253

0.35

COM #3

97.90

95.08

386.4

0.010

0.0078

-0.314

0.35

Table 1. PM2.5 removal efficiencies(, pressure drop(ΔP), QF, surface potential, and dipole moment (D) of different polymer fiber filters for both inorganic (KCl) and organic (DOP) PMs The QFs were calculated using data obtained at an air flow of 0.35 m/s.



Figure 4. Reusability test of the PBI filter contaminated with inorganic and organic PMs. (a) SEMs showing nanofibers of the PBI filter before and after the cleaning process. The filters were tested using i) inorganic PMs (KCl) and ii) organic PMs (DOP), respectively. (b) EDS analysis of the filter contaminated with KCl PMs before (top) and after (bottom) cleaning, indicating complete removal of the PMs. (c) Inorganic (left) and organic (right) PM removal efficiencies of the PBI nanofiber filter after cyclic cleaning steps. (d) Photographs showing thermal stability of the PBI nanofiber filter after applying thermal stress on a hot plate at 400 C for 1h, demonstrating negligible deformation and color change. (inset) SEM showing nanofibers of the PBI after the test (scale bar 2 m).


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TOC

The performance of reusable PBI based nanofiber filter for high PM removal efficiency was investigated by comparing various commercial mask filters.


Reusable Polybenzimidazole Nanofiber Membrane Filter for Highly

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