Boundary conditions for exhaled airflow from a cough with a surgical or N95 mask.

Wearing surgical or N95 masks is effective in reducing the infection risks of airborne infectious diseases. However, in the literature there are no detailed boundary conditions for airflow from a cough when a surgical or N95 mask is worn. These boundary conditions are essential for accurate prediction of exhaled particle dispersion by computational fluid dynamics (CFD). This study first constructed a coughing manikin with an exhalation system to simulate a cough from a person. The smoke visualization method was used to measure the airflow profile from a cough. To validate the setup of the coughing manikin, the results were compared with measured data from subject tests reported in the literature. The validated coughing manikin was then used to measure the airflow boundary conditions for a cough when a surgical mask was worn and when an N95 mask was worn, respectively. Finally, this study applied the developed airflow boundary conditions to calculate person-to-person particle transport from a cough when masks are worn. The calculated exhaled particle patterns agreed well with the smoke pattern in the visualization experiments. Furthermore, the calculated results indicated that, when the index person wore a surgical and a N95 mask, the total exposure of the receptor was reduced by 93.0% and 98.8%, respectively.

Investigating the Influence of Metal-Organic Framework Loading on the Filtration Performance of Electrospun Nanofiber Air Filters.

Integrating metal-organic frameworks (MOFs) into electrospun nanofiber filters has become an effective method for improving particle filtration efficiency. This study hypothesized that there is an optimal amount of MOFs that can be integrated into electrospun nanofiber filters to achieve the maximum particle removal efficiency while minimizing the corresponding MOF synthesis time. To test the hypothesis, this study systematically explored the influence of the time-dependent in situ growing process of zeolitic imidazolate framework-67 (ZIF-67), a typical type of MOFs, on the filtration performance of polyacrylonitrile (PAN) electrospun nanofibers. The results show that the surface morphology and chemical composition of the PAN/ZIF-67 hybrid nanofiber filters gradually changed with the reaction time. For PAN/ZIF-67 hybrid nanofiber filters with relatively low initial PM0.3-0.4 filtration efficiency, a reaction time of only 5 min was sufficient for the synthesis of the amount of ZIF-67 that maximized the PM0.3-0.4 filtration efficiency. However, for thick filters with high original PM0.3-0.4 filtration efficiency (>90%), the integration of ZIF-67 was not necessary, because the efficiency enhancement would not be significant. In addition, the enhancement of filtration efficiency for ultrafine particles was positively correlated with the amount of incorporated ZIF-67. In summary, this study shortened the synthesis time of the in situ incorporation of MOFs into electrospun nanofiber filters from more than 10 h (reported in the literature) to only 5 min.

Removal of Size-Dependent Submicron Particles Using Metal-Organic Framework-Based Nanofiber Air Filters.

Particulate matter poses a serious threat to human health. In particular, exposure to submicron particles can result in more severe health effects as they can deposit more deeply into human tissues. Metal-organic framework (MOF)-based nanofiber filters are regarded as promising candidates for efficient particle control. In this study, ZIF-8@PAN nanofiber filters that were developed via an in situ growth strategy were selected for the filtration of submicron particles. The addition of ZIF-8 more effectively enhanced the filtration of particles with smaller sizes. For the most penetrating particle size of around 0.3 µm, the MOF-based nanofiber filter exhibited an 8.9% increase in filtration efficiency compared with that of the pure nanofiber filter. Meanwhile, for particles with large aerodynamic diameters (in the range of 0.7-1 µm, for example), the role of ZIF-8 was negligible. This work provides important insights into the filtration performance of MOF-based nanofiber filters in capturing submicron particles and may aid in designing nanofiber filters for efficient control of particles.

Tribo-charge enhanced hybrid air filter masks for efficient particulate matter capture with greatly extended service life.

Face masks have been an effective and indispensable personal protective measure against particulate matter pollutants and respiratory diseases, especially the novel Coronavirus disease recently. However, disposable surgical face masks suffer from low filtration efficiency for particles ranging from nano- to micro-size, and the limited service life of ~ 4 h. Here, a nano/micro fibrous hybrid air filter mask composing of electrospun nanofibrous network and poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) coated polypropylene (PP) is proposed. Furthermore, the resultant filter is supplied with tribo-charges by a freestanding sliding triboelectric nanogenerator. Through the enhanced synergistic effect of mechanical interception and electrostatic forces, the hybrid air filter demonstrates high filtration efficiency for particle size of 11.5 nm to 2.5 µm, with a 9.3-34.68% enhancement for particles of 0.3-2.5 µm compared to pristine PP, and 48-h stable filtration efficiency of 94% (0.3-0.4 µm) and 99% (1-2.5 µm) with a low pressure drop of ~110 Pa. In addition, sterilization ability of the tribo-charge enhanced air filter is demonstrated. This work provides a facile and cost-effective approach for state-of-the-art face masks toward high filtration performance of nano- to micro- particles with greatly extended service life.