Abstract
Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort is being expended to develop ever more powerful technologies to restricting the spread of airborne microorganisms in indoor spaces through the minimization of health- and environment-related risks. In this context, UV-based and photocatalytic oxidation (PCO)-based technologies (i.e., the combined action of ultraviolet (UV) light and photocatalytic materials such as titanium dioxide (TiO2)) represent the most widely utilized approaches at present because they are cost-effective and ecofriendly. The virucidal and bactericidal effect relies on the synergy between the inherent ability of UV light to directly inactivate viral particles and bacteria through nucleic acid and protein damages, and the production of oxidative radicals generated through the irradiation of the TiO2 surface. In this literature survey, we draw attention to the most effective UV radiations and TiO2-based PCO technologies available and their underlying mechanisms of action on both bacteria and viral particles. Since the fine tuning of different parameters, namely the UV wavelength, the photocatalyst composition, and the UV dose (viz, the product of UV light intensity and the irradiation time), is required for the inactivation of microorganisms, we wrap up this review coming up with the most effective combination of them. Now more than ever, UV- and TiO2-based disinfection technologies may represent a valuable tool to mitigate the spread of airborne pathogens.
Highlights
Since the outbreak of respiratory disease in December 2019 and subsequent COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2, great effort has been devoted to the development and widespread use of antimicrobial technologies to mitigate airborne microbial contaminations [1]
Environmental pollution, and airborne contamination is a complex and intriguing issue that involves the presence of contaminants in the form of particulate matter, non-volatile biological agents such as bacteria, molds, and viruses transferred by the bioaerosols, and inorganic gaseous pollutants such as NOx, SOx, CO, CO2, and volatile organic compounds (VOCs) [4]
As a rule of thumb, there are a couple of mechanisms through which the UV radiation can damage microorganisms: (i) the photo-induced reactions resulting from the direct absorption of UV photons by biopolymers, especially nucleic acids (NAs) and proteins, which are the basic constituents in common between bacteria and viruses [39,40], and (ii) the photo-oxidation triggered by reactive oxygen species (ROS) generated after UV irradiation of exogenous and endogenous photosensitizers, i.e., powerful oxidant materials or photosensitive molecules other than NAs and proteins [41]
Summary
Since the outbreak of respiratory disease in December 2019 and subsequent COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), great effort has been devoted to the development and widespread use of antimicrobial technologies to mitigate airborne microbial contaminations [1]. Filtration systems, in which airborne biological particles are collected on the surface of a filter, are great options to overcome the limitations of the aforementioned technologies These antimicrobial materialsembedded filters are generally effective in the short-term because of the accumulation of dust that progressively clog them and cause a large pressure drop, so that they must be replaced regularly to prevent the possible re-introduction of airborne microorganisms into the environment all of a sudden [9]. Another effective approach to prevent the spread of airborne-mediated microbial diseases relies on the inactivation of harmful bacteria and viruses by means of UV light [13,14,15]. Such information would be very helpful to design next-generation air disinfection technologies
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