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Review
. 2021 Feb 25;14(5):1075.
doi: 10.3390/ma14051075.

Effect of UV Irradiation and TiO2-Photocatalysis on Airborne Bacteria and Viruses: An Overview

Nina Bono  1 , Federica Ponti  1   2 , Carlo Punta  3   4 , Gabriele Candiani  1   4
Affiliations
Review

Effect of UV Irradiation and TiO2-Photocatalysis on Airborne Bacteria and Viruses: An Overview

Nina Bono et al. Materials (Basel). .

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.

Keywords: UV light; antibacterial; antiviral; disinfection; photocatalysis; titanium dioxide.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic representation of pyrimidine dimers formation after DNA exposure to UV light. Formation of (a) cyclobutane pyrimidine dimers (CPDs) and (b) pyrimidine-6,4-pyrimidone photoproducts (6,4PP) between two adjacent thymine (T) nitrogenous bases. In the case of RNA, similar reactions may occur for uracil (U).
Figure 2
Figure 2
Schematic representation of a photoactivated surface and the mechanism of photocatalysis of a semiconductor (SC). A SC is characterized by a relatively low energetic band gap between the lower entirely occupied valence band (VB) and the higher unoccupied conduction band (CB). The adsorption of a photon by the SC, with a minimum energy at least equal to the band gap, promotes the excitation of an electron (e−) from the VB to the CB.
Figure 3
Figure 3
Mechanism of photocatalytic inactivation of (a) bacteria and (b) viruses. (a) Reactive oxygen species (ROS), namely, hydroxyl radicals (•OH) and superoxide anions (O2−•), generated after UV-irradiation of TiO2 first damage the cell wall layers, thus allowing the leakage of small molecules such as ions. ROS can thus further penetrate the cell, such that the degradation of the internal components may occur, followed by complete mineralization. The degradation process may occur progressively from the side of the cell in contact with the catalyst. (b) •OH and O2−• generated at the UV-activated TiO2 surface are able to degrade the capsid and envelope proteins, and phospholipids of non-enveloped and enveloped viruses, respectively. Besides, the leakage and consequent NAs degradation occurs, ultimately leading to the inactivation of the viral particles. Image is created with BioRender.com.
See this image and copyright information in PMC

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