RE: Nano Material2 Dec 2020 10:35
2.2 Nanotechnology-Enabled PPE and Filter Systems
A special concern about COVID-19 surrounds the question of aerial infection via circulation of SARS-CoV-2 in aerosols.[10-12] There are empirical observations that in communities with obligation to wearing face masks (e.g., Hong Kong), the COVID-19 outbreak is significantly lower than in mask-off countries (e.g., Italy, Germany, US, Brazil, etc., at the time of writing that study[75]), which has been ascribed to the reduced transmission of virion-laden respiratory droplets.[75] This lays the focus on the filter efficiency of face masks and fabrics. Konda et al.[76] tested several common fabrics from cotton, silk, flannel, chiffon, and synthetic textiles for filter efficiency toward 300 nm aerosols. Interestingly, the combination of fabric layers affording mechanical filtration (cotton) and electrostatic filtration (silk, chiffon, flannel) showed >90% efficiency for <300 nm aerosols, albeit at much lower pressure drops and air flows than typically used in such tests. Nevertheless, this result may hint at the potential of natural fibers in wider PPE applications and may open a new research line for biodegradable PPE materials to mitigate the huge plastic disposal common to conventional protective gear. Functionalized cellulose fibers and other biopolymers are promising candidates for antimicrobial PPE.[77] An alternative approach to improve PPE fabrics was explored by Bhattacharjee et al.,[53] who reviewed graphene as functional additive for lending mechanical, antibacterial, barrier, UV protective, fire ******ant, light-weight, and conductive properties to a wide range of woven and non-woven textiles used in PPEs.
Another crucial issue in pandemics caused by respiratory viruses is their transmission through ventilation systems, for instance, in hospitals, care homes, ambulances, aircraft cabins, or commercial buildings.[78] Also here, due to the small size of virus particles (50–130 nm), nanotechnology can provide solutions with ultra-fine glass fiber air filters (ultra low penetration air [ULPA] filter) with up to 99.99999% filter efficiency for 0.1 µm particles.[79, 80] High-efficiency particle air (HEPA) filters are commonly employed in buildings and transportation and show high efficiency for larger (>0.3 µm) particles,[79] the typical size range of respiratory droplets.[78] These filters can also be modified with photocatalytic TiO2 NP for combined filtration and destruction of retained microbes.[79] On the other hand, activated carbon in the form of granulated powder or fibers has been successfully tested for adsorption of bacteria and virus particles in conjunction with biocidal Ag and CuO NP for enhanced efficiency.[81]
Air filter may also be equipped with antimicrobial Ag, Ag-hybrid, or Zn-MOF nanoparticles for in situ inactivation of filtered pathogens, thus, minimizing the risk from filter handling.[57, 82, 83] Like air filters, water treatment membranes play an importan
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