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Article: Enhanced nano-aerosol loading performance of multilayer PVDF nanofiber electret filters.

Sun, Qiangqiang / Leung, Wallace Woon-Fong

2020 Volume 240, Page(s) 116606

Abstract: Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure drop and ... ...

Abstract	Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure drop and distribution of deposited aerosols in the filters all having the same fiber basis weight (3.060 gsm). Through the filtration efficiency variations of uncharged/charged, single-/multi-layer filters with aerosol loading, it was observed that mechanical PVDF filters had continuously increasing filtration efficiency, while PVDF electret filters had initially decreasing and subsequently increasing filtration efficiency until reaching 100% due to diminishing electrostatic effect and enhancing mechanical effect. By combining the pressure drop evolution of different filters during aerosol loading and detailed SEM images of the loaded filters, we have demonstrated that multilayer PVDF filters, especially the electret ones, could significantly slow down the pace of filter clogging (skin effect) and increase significantly the aerosol holding capacity during depth filtration. Generally, the multilayer nanofiber filters received the most aerosol deposit during depth filtration, whereas the single-layer nanofiber filters with the same basis weight of fibers received the most deposit during cake filtration. The multilayer nanofiber filters had approximately 70% aerosol deposit in the filter during depth filtration fully utilizing the full filter thickness, especially for the electret filters that had charged fibers, and only 30% deposit in the cake. On the contrary, the single-layer uncharged/charged nanofiber filters were exactly the reverse due to persistency of the skin effect with only 30% deposit in the filter mostly located in the upstream layer, yet 70% deposit in the cake. During depth filtration, the pressure drop per added mass deposit for the multilayer electret filter was very low at 11 Pa gsm
Keywords	covid19
Language	English
Publishing date	2020-01-25
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	2022535-0
ISSN	1383-5866
ISSN	1383-5866
DOI	10.1016/j.seppur.2020.116606
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Charged PVDF multilayer nanofiber filter in filtering simulated airborne novel coronavirus (COVID-19) using ambient nano-aerosols.

Leung, Wallace Woon-Fong / Sun, Qiangqiang

Separation and purification technology

2020 Volume 245, Page(s) 116887

Abstract: The novel coronavirus (COVID-19), average size 100 nm, can be aerosolized by cough, sneeze, speech and breath of infected persons. The airborne carrier for the COVID-19 can be tiny droplets and particulates from infected person, fine suspended mists ( ... ...

Abstract	The novel coronavirus (COVID-19), average size 100 nm, can be aerosolized by cough, sneeze, speech and breath of infected persons. The airborne carrier for the COVID-19 can be tiny droplets and particulates from infected person, fine suspended mists (humidity) in air, or ambient aerosols in air. To-date, unfortunately there are no test standards for nano-aerosols (≤100 nm). A goal in our study is to develop air filters (e.g. respirator, facemask, ventilator, medical breathing filter/system) with 90% capture on 100-nm airborne COVID-19 with pressure drop of less than 30 Pa (3.1 mm water). There are two challenges. First, this airborne bio-nanoaerosol (combined virus and carrier) is amorphous unlike cubic NaCl crystals. Second, unlike standard laboratory tests on NaCl and test oil (DOP) droplets, these polydispersed aerosols all challenge the filter simultaneously and they are of different sizes and can interact among themselves complicating the filtration process. For the first time, we have studied these two effects using ambient aerosols (simulating the bio-nanoaerosols of coronavirus plus carrier of different shapes and sizes) to challenge electrostatically charged multilayer/multimodule nanofiber filters. This problem is fundamentally complicated due to mechanical and electrostatic interactions among aerosols of different sizes with induced charges of different magnitudes. The test filters were arranged in 2, 4, and 6 multiple-modules stack-up with each module having 0.765 g/m
Keywords	covid19
Language	English
Publishing date	2020-04-22
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	2022535-0
ISSN	1383-5866
ISSN	1383-5866
DOI	10.1016/j.seppur.2020.116887
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Electrostatic charged nanofiber filter for filtering airborne novel coronavirus (COVID-19) and nano-aerosols.

Leung, Wallace Woon Fong / Sun, Qiangqiang

Separation and purification technology

2020 Volume 250, Page(s) 116886

Abstract: The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within four months since outbreak in December 2019, over 2.6 million people have been infected across 210 countries around the globe with ... ...

Abstract	The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within four months since outbreak in December 2019, over 2.6 million people have been infected across 210 countries around the globe with over 180,000 deaths. COVID-19 has a size of 60-140 nm with mean size of 100 nm (i.e. nano-aerosol). The virus can be airborne by attaching to human secretion (fine particles, nasal/saliva droplets) of infected person or suspended fine particulates in air. While NIOSH has standardized N95, N99 and N100 respirators set at 300-nm aerosol, to-date there is no filter standards, nor special filter technologies, tailored for capturing airborne viruses and 100-nm nano-aerosols. The latter also are present in high number concentration in atmospheric pollutants. This study addresses developing novel charged PVDF nanofiber filter technology to effectively capture the fast-spreading, deadly airborne coronavirus, especially COVID-19, with our target aerosol size set at 100 nm (nano-aerosol), and not 300 nm. The virus and its attached aerosol were simulated by sodium chloride aerosols, 50-500 nm, generated from sub-micron aerosol generator. PVDF nanofibers, which were uniform in diameter, straight and bead-free, were produced with average fiber diameters 84, 191, 349 and 525 nm, respectively, with excellent morphology. The fibers were subsequently electrostatically charged by corona discharge. The amounts of charged fibers in a filter were increased to achieve high efficiency of 90% for the virus filter but the electrical interference between neighbouring fibers resulted in progressively marginal increase in efficiency yet much higher pressure drop across the filter. The quality factor which measured the efficiency-to-pressure-drop kept decreasing. By redistributing the fibers in the filter into several modules with lower fiber packing density, with each module separated by a permeable, electrical-insulator material, the electrical interference between neighboring charged fibers was reduced, if not fully mitigated. Also, the additional scrim materials introduced macropores into the filter together with lower fiber packing density in each module both further reduced the airflow resistance. With this approach, the quality factor can maintain relatively constant with increasing fiber amounts to achieve high filter efficiency. The optimal amounts of fiber in each module depended on the diameter of fibers in the module. Small fiber diameter that has already high performance required small amounts of fibers per module. In contrast, large diameter fiber required larger amounts of fibers per module to compensate for the poorer performance provided it did not incur significantly additional pressure drop. This approach was applied to develop four new nanofiber filters tailored for capturing 100-nm airborne COVID-19 to achieve over 90% efficiency with pressure drop not to exceed 30 Pa (3.1 mm water). One filter developed meeting the 90% efficiency has ultralow pressure drop of only 18 Pa (1.9 mm water) while another filter meeting the 30 Pa limit has high efficiency reaching 94%. These optimized filters based on rigorous engineering approach provide the badly needed technology for protecting the general public from the deadly airborne COVID-19 and other viruses, as well as nano-aerosols from air pollution which lead to undesirable chronic diseases.
Keywords	covid19
Language	English
Publishing date	2020-04-22
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	2022535-0
ISSN	1383-5866
ISSN	1383-5866
DOI	10.1016/j.seppur.2020.116886
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Electrostatic charged nanofiber filter for filtering airborne novel coronavirus (COVID-19) and nano-aerosols

Leung, Wallace Woon Fong / Sun, Qiangqiang

Separation and Purification Technology

2020 Volume 250, Page(s) 116886

Keywords	Filtration and Separation ; Analytical Chemistry ; covid19
Language	English
Publisher	Elsevier BV
Publishing country	us
Document type	Article ; Online
ZDB-ID	2022535-0
ISSN	1383-5866
ISSN	1383-5866
DOI	10.1016/j.seppur.2020.116886
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Charged PVDF multilayer nanofiber filter in filtering simulated airborne novel coronavirus (COVID-19) using ambient nano-aerosols

Leung, Wallace Woon-Fong / Sun, Qiangqiang

Separation and Purification Technology

2020 Volume 245, Page(s) 116887

Keywords	Filtration and Separation ; Analytical Chemistry ; covid19
Language	English
Publisher	Elsevier BV
Publishing country	us
Document type	Article ; Online
ZDB-ID	2022535-0
ISSN	1383-5866
ISSN	1383-5866
DOI	10.1016/j.seppur.2020.116887
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Introduction of Graphene Nanofibers into the Perovskite Layer of Perovskite Solar Cells.

Li, Yun / Leung, Wallace Woon-Fong

ChemSusChem

2018 Volume 11, Issue 17, Page(s) 2921–2929

Abstract: Although the application of graphene-derived nanomaterials in the electron transport layer (ETL), hole transport layer (HTL), or top electrode of perovskite solar cells (PSCs) has been thoroughly studied, the effects of inserting such materials into the ... ...

Abstract	Although the application of graphene-derived nanomaterials in the electron transport layer (ETL), hole transport layer (HTL), or top electrode of perovskite solar cells (PSCs) has been thoroughly studied, the effects of inserting such materials into the perovskite layer of PSCs is not well understood. In this study, pristine graphene nanofibers were introduced into the perovskite layer of PSCs for the first time. The quality of the electrospun graphene nanofibers was optimized by controlled centrifugation of graphene sheets in the precursor suspension. Under optimized conditions, the device power conversion efficiency increased from 17.51 % without graphene to 19.83 % with graphene nanofibers, representing a 13 % increase. The introduction of graphene nanofibers into the perovskite layer led to a dramatic increase in the grain size of the perovskite layer to over 2 μm, owing to improved nucleation and crystallization at the nanofiber interface, which led to much higher FF and J
Language	English
Publishing date	2018-07-19
Publishing country	Germany
Document type	Journal Article
ISSN	1864-564X
ISSN (online)	1864-564X
DOI	10.1002/cssc.201800758
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Enhanced nano-aerosol loading performance of multilayer PVDF nanofiber electret filters

Sun, Qiangqiang / Leung, Wallace Woon-Fong

Separation and Purification Technology

Abstract: Abstract Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure ... ...

Abstract	Abstract Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure drop and distribution of deposited aerosols in the filters all having the same fiber basis weight (3.060 gsm). Through the filtration efficiency variations of uncharged/charged, single-/multi-layer filters with aerosol loading, it was observed that mechanical PVDF filters had continuously increasing filtration efficiency, while PVDF electret filters had initially decreasing and subsequently increasing filtration efficiency until reaching 100% due to diminishing electrostatic effect and enhancing mechanical effect. By combining the pressure drop evolution of different filters during aerosol loading and detailed SEM images of the loaded filters, we have demonstrated that multilayer PVDF filters, especially the electret ones, could significantly slow down the pace of filter clogging (skin effect) and increase significantly the aerosol holding capacity during depth filtration. Generally, the multilayer nanofiber filters received the most aerosol deposit during depth filtration, whereas the single-layer nanofiber filters with the same basis weight of fibers received the most deposit during cake filtration. The multilayer nanofiber filters had approximately 70% aerosol deposit in the filter during depth filtration fully utilizing the full filter thickness, especially for the electret filters that had charged fibers, and only 30% deposit in the cake. On the contrary, the single-layer uncharged/charged nanofiber filters were exactly the reverse due to persistency of the skin effect with only 30% deposit in the filter mostly located in the upstream layer, yet 70% deposit in the cake. During depth filtration, the pressure drop per added mass deposit for the multilayer electret filter was very low at 11 Pa gsm−1, which was at least twice below any other nanofiber filters. This was all attributed to the uniform capture of aerosols by electrostatic effect across the entire filter depth from the upstream to downstream layers of the multilayer electret filter. The above conclusion was confirmed by the detailed SEM images taken across the different filter layers for the multilayer filter configuration. The 4-layer electret nanofiber filter with a 3.060-gsm basis weight has 4 times more aerosol holding capacity than the single uncharged/charged nanofiber filter with the same fiber basis weight in depth filtration. Based on the standpoint of highest efficiency and capacity with maximum pressure drop 800 Pa imposed on the filtration operation, the 4-layer nanofiber electret was the best among all 4 filters. It had 52% more aerosol holding capacity than the single layer uncharged nanofiber filter and 38% more capacity than the charged single-layer and the uncharged multilayer nanofiber filters. The multilayer PVDF electret filters have excellent filtration performance for long-term aerosol filtration and also great potential applications in the fields of personal health care and environmental protection.
Keywords	covid19
Publisher	Elsevier
Document type	Article ; Online
DOI	10.1016/j.seppur.2020.116606
Database	COVID19

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Article: Electrostatic Charged Nanofiber Filter for Filtering Airborne Novel Coronavirus (COVID-19) and Nano-aerosols

Woon Fong Leung, Wallace / Sun, Qiangqiang

Sep Purif Technol

Abstract: The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within 3-1/2 months since outbreak in December 2019, over 1.3 million people have been infected across 206 countries with over 70,000 deaths. ...

Abstract	The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within 3-1/2 months since outbreak in December 2019, over 1.3 million people have been infected across 206 countries with over 70,000 deaths. COVID-19 has a size of 60-140nm with mean size of the nano-aerosols, 100nm. The virus can be airborne by attaching to human secretion (fine particles, nasal/saliva droplets) of infected person or suspended fine particulates in air. While NIOSH has standardized N95 and N98 at 300nm, to-date there is no filter standards, nor special filter technologies, tailored for capturing airborne viruses and 100nm nano-aerosols. The latter also are present in high number concentration in atmospheric pollutants. This study addresses developing novel charged PVDF nanofiber filter technology to effectively capture the deadly airborne coronavirus with our target set at 100nm (nano-aerosol), and not 300nm. The virus and its attached particle were simulated by sodium chloride aerosols, 50-500nm, generated from sub-micron aerosol generator. PVDF nanofibers were produced with fiber diameters 84, 191, 349 and 525nm with excellent morphology. The fibers were subsequently charged by corona discharge. The amounts of charged fibers in a filter were increased to achieve high efficiency of 90% for the virus filter but the electrical interference between neighbouring fibers resulted in progressively marginal increase in efficiency and concurrently much higher pressure drop across the filter. The quality factor which measured the efficiency-to-pressure-drop kept decreasing. By redistributing the fibers in the filter into several modules, each separated by a permeable scrim material, the electrical interference was reduced, if not fully mitigated. Also, the additional scrim materials introduced macropores into the filter that further reduced the airflow resistance. With this approach, the quality factor can maintain relatively constant with increasing fiber amounts to achieve high filter efficiency. The optimal amounts of fiber in each module depended on the diameter of fibers in the module. Small fiber diameter that has already high performance required small amount of fibers per module. In contrast, large diameter fiber required more amounts of fiber per module to compensate for the poorer performance without incurring higher pressure drop. This approach was applied to develop four new nanofiber filters tailored for capturing 100nm airborne COVID-19 to achieve over 90% efficiency with pressure drop below 30Pa (3.1mm water). One filter developed meeting the 90% efficiency has ultralow pressure drop of only 18Pa (1.9mm water) while another filter meeting the 30Pa limit has high efficiency reaching 94%. These optimized filters based on rigorous engineering approach provide the badly needed technology for protecting the general public from the deadly airborne COVID-19 and other viruses, and nano-aerosols from air pollution which lead to chronic diseases.
Keywords	covid19
Publisher	WHO
Document type	Article
Note	WHO #Covidence: #108995
Database	COVID19

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Article: Charged PVDF multilayer nanofiber filter in filtering simulated airborne novel coronavirus (COVID-19) using ambient nano-aerosols

Leung, Wallace Woon-Fong / Sun, Qiangqiang

Sep. Purif. Technol.

Abstract	The novel coronavirus (COVID-19), average size 100 nm, can be aerosolized by cough, sneeze, speech and breath of infected persons. The airborne carrier for the COVID-19 can be tiny droplets and particulates from infected person, fine suspended mists (humidity) in air, or ambient aerosols in air. To-date, unfortunately there are no test standards for nano-aerosols (≤100 nm). A goal in our study is to develop air filters (e.g. respirator, facemask, ventilator, medical breathing filter/system) with 90% capture on 100-nm airborne COVID-19 with pressure drop of less than 30 Pa (3.1 mm water). There are two challenges. First, this airborne bio-nanoaerosol (combined virus and carrier) is amorphous unlike cubic NaCl crystals. Second, unlike standard laboratory tests on NaCl and test oil (DOP) droplets, these polydispersed aerosols all challenge the filter simultaneously and they are of different sizes and can interact among themselves complicating the filtration process. For the first time, we have studied these two effects using ambient aerosols (simulating the bio-nanoaerosols of coronavirus plus carrier of different shapes and sizes) to challenge electrostatically charged multilayer/multimodule nanofiber filters. This problem is fundamentally complicated due to mechanical and electrostatic interactions among aerosols of different sizes with induced charges of different magnitudes. The test filters were arranged in 2, 4, and 6 multiple-modules stack-up with each module having 0.765 g/m 2of charged PVDF nanofibers (mean diameter 525 ± 191 nm). This configuration minimized electrical interference among neighboring charged nanofibers and reduced flow resistance in the filter. For ambient aerosol size>80 nm (applicable to the smallest COVID-19), the electrostatic effect contributes 100–180% more efficiency to the existing mechanical efficiency (due to diffusion and interception) depending on the number of modules in the filter. By stacking-up modules to increase fiber basis weight in the filter, a 6-layer charged nanofiber filter achieved 88%, 88% and 96% filtration efficiency for, respectively, 55-nm, 100-nm and 300-nm ambient aerosol. This is very close to attaining our set goal of 90%-efficiency on the 100-nm ambient aerosol. The pressure drop for the 6-layer nanofiber filter was only 26 Pa (2.65 mm water column) which was below our limit of 30 Pa (3.1 mm water). For the test multi-module filters, a high ‘quality factor’ (efficiency-to-pressure-drop ratio) of about 0.1 to 0.13 Pa −1can be consistently maintained, which was far better than conventional filters. Using the same PVDF 6-layer charged nanofiber filter, laboratory tests results using monodispersed NaCl aerosols of 50, 100, and 300 nm yielded filtration efficiency, respectively, 92%, 94% and 98% (qualified for 'N98 standard') with same pressure drop of 26 Pa. The 2–6% discrepancy in efficiency for the NaCl aerosols was primarily attributed to the absence of interaction among aerosols of different sizes using monodispersed NaCl aerosols in the laboratory. This discrepancy can be further reduced with increasing number of modules in the filter and for larger 300-nm aerosol. The 6-layer charged nanofiber filter was qualified as a 'N98 respirator' (98% capture efficiency for 300-nm NaCl aerosols) but with pressure drop of only 2.65-mm water which was 1/10 below conventional N95 with 25-mm (exhaling) to 35-mm (inhaling) water column! The 6-layer charged PVDF nanofiber filter provides good personal protection against airborne COVID-19 virus and nano-aerosols from pollution based on the N98 standard, yet it is at least 10X more breathable than a conventional N95 respirator.
Keywords	covid19
Publisher	WHO
Document type	Article
Note	WHO #Covidence: #102262
Database	COVID19

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Article: Numerical Investigation of Cell Encapsulation for Multiplexing Diagnostic Assays Using Novel Centrifugal Microfluidic Emulsification and Separation Platform.

Ren, Yong / Leung, Wallace Woon Fong

Micromachines

2016 Volume 7, Issue 2

Abstract: In the present paper, we report a novel centrifugal microfluidic platform for emulsification and separation. Our design enables encapsulation and incubation of multiple types of cells by droplets, which can be generated at controlled high rotation speed ... ...

Abstract	In the present paper, we report a novel centrifugal microfluidic platform for emulsification and separation. Our design enables encapsulation and incubation of multiple types of cells by droplets, which can be generated at controlled high rotation speed modifying the transition between dripping-to-jetting regimes. The droplets can be separated from continuous phase using facile bifurcated junction design. A three dimensional (3D) model was established to investigate the formation and sedimentation of droplets using the centrifugal microfluidic platform by computational fluid dynamics (CFD). The simulation results were compared to the reported experiments in terms of droplet shape and size to validate the accuracy of the model. The influence of the grid resolution was investigated and quantified. The physics associated with droplet formation and sedimentation is governed by the Bond number and Rossby number, respectively. Our investigation provides insight into the design criteria that can be used to establish centrifugal microfluidic platforms tailored to potential applications, such as multiplexing diagnostic assays, due to the unique capabilities of the device in handling multiple types of cells and biosamples with high throughput. This work can inspire new development of cell encapsulation and separation applications by centrifugal microfluidic technology.
Language	English
Publishing date	2016-01-25
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2620864-7
ISSN	2072-666X
ISSN	2072-666X
DOI	10.3390/mi7020017
Database	MEDical Literature Analysis and Retrieval System OnLINE

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