Vacuum Ultraviolet Photocatalysis for the Inactivation of Ozone and MS2 Bacteriophage Aerosols on Palladium Deposited TiO2 Catalyst

Abstract

Increasing concerns about airborne pathogens such as Middle East respiratory syndrome coronavirus and swine influenza virus have attracted public attention to clean indoor environment and spurred the development of air purification techniques for the removal of gaseous and biological pollutants. Recently, 185 nm vacuum ultraviolet (VUV) photocatalysis has attracted much attention in the purification of gaseous pollutants because the high-energy photon, although residual ozone is generated by dissociation of oxygen. In this study, we have synthesized titanium dioxide (TiO2) and palladium deposited titanium dioxide (Pd/TiO2) with four kinds of catalyst shapes (i.e., 2 mm and 5 mm pleated type, screw and flat sheet type) and investigated their effects on simultaneous inactivation of airborne MS2 bacteriophages and ozone under VUV irradiation. In addition, to investigate the role of 185 nm VUV light on MS2 bacteriophage inactivation, the comparative experiment, i.e., O3+UV (254 nm) was also conducted. Palladium nanoparticles (Pd NPs) were deposited on TiO2 sheet via a low-temperature electrostatic self-assembly method. A VUV lamp, i.e. ozone-producing low pressure mercury lamp with λ max at 254 nm and a minor emission (ca. 5%) at 185 nm, was perpendicularly placed in the center of the reactor. The aerosol particles produced by each photoreaction were collected using an SKC BioSampler and particle size distribution was determined using a scanning mobility particle sizer. 2 mm pleated Pd-TiO2 catalyst exhibited the highest activity for both MS2 bacteriophage and ozone inactivation because of the large catalyst area and well dispersed Pd NPs. This may be because the deposited Pd NPs promotes a photocatalytic reaction by acting as mediators for the charge transfer between Pd NPs and TiO2, and improves the generation of reactive species such as hydroxyl radicals for inactivation of MS2 bacteriophage.