Efficacy of single pass UVC air treatment for the inactivation of coronavirus, MS2 coliphage and Staphylococcus aureus bioaerosols.

There is strong evidence that SARS-CoV-2 is spread predominantly by airborne transmission, with high viral loads released into the air as respiratory droplets and aerosols from the infected subject. The spread and persistence of SARS-CoV-2 in diverse indoor environments reinforces the urgent need to supplement distancing and PPE based approaches with effective engineering measures for microbial decontamination - thereby addressing the significant risk posed by aerosols. We hypothesized that a portable, single-pass UVC air treatment device (air flow 1254 L/min) could effectively inactivate bioaerosols containing bacterial and viral indicator organisms, and coronavirus without reliance on filtration technology, at reasonable scale. Robust experiments demonstrated UVC dose dependent inactivation of Staphylococcus aureus (UV rate constant (k) = 0.098 m2/J) and bacteriophage MS2, with up to 6-log MS2 reduction achieved in a single pass through the system (k = 0.119 m2/J). The inclusion of a PTFE diffuse reflector increased the effective UVC dose by up to 34% in comparison to a standard Al foil reflector (with identical lamp output), resulting in significant additional pathogen inactivation (1-log S. aureus and MS2, p < 0.001). Complete inactivation of bovine coronavirus bioaerosols was demonstrated through tissue culture infectivity (2.4-log reduction) and RT-qPCR analysis - confirming single pass UVC treatment to effectively deactivate coronavirus to the limit of detection of the culture-based method. Scenario-based modelling was used to investigate the reduction in risk of airborne person-to-person transmission based upon a single infected subject within the small room. Use of the system providing 5 air changes per hour was shown to significantly reduce airborne viral load and maintain low numbers of RNA copies when the infected subject remained in the room, reducing the risk of airborne pathogen transmission to other room users. We conclude that the application of single-pass UVC systems (without reliance on HEPA filtration) could play a critical role in reducing the risk of airborne pathogen transfer, including SARS-CoV2, in locations where adequate fresh air ventilation cannot be implemented.

Use of Selected Scavengers for the Determination of NF-TiO2 Reactive Oxygen Species during the Degradation of Microcystin-LR under Visible Light Irradiation.

Although UV-induced TiO2 photocatalysis involves the generation of several reactive oxygen species (ROS), the formation of hydroxyl radicals are generally associated with the degradation of persistent organic contaminants in water. In this study, a variety of radical scavengers were employed to discriminate the roles of different ROS during visible light activated (VLA) photocatalysis using nitrogen and fluorine doped TiO2 (NF-TiO2) in the degradation of the hepatotoxin, microcystin-LR (MC-LR) in water. The addition of hydroxyl radical scavengers, methanol and tert-butyl alcohol to the reaction mixture resulted in negligible inhibition of VLA NF-TiO2 photocatalytic degradation of MCLR at pH 3.0 and only partial inhibition at pH 5.7. While hydroxyl radicals generally play the primary role in UV TiO2 photocatalysis, the minimal influence of MeOH and t-BuOH on the degradation process under these experimental conditions indicates hydroxyl radicals (•OH) do not play the primary role in VLA NF-TiO2 photocatalysis. However, strong inhibition was observed in VLA NF-TiO2 photocatalytic degradation of MC-LR in the presence of superoxide dismutase, benzoquinone and catalase at pH 3.0 and 5.7 indicating O2•- and H2O2 play critical roles in the degradation process. Similar degradation rates were observed in the presence of singlet oxygen scavenger, deuterium oxide, which enhances singlet oxygen mediated processes further suggesting singlet oxygen does not play a key role in the degradation of MCLR in these system. Formic acid and cupric nitrate were added to probe the roles of the valence band holes and conduction band electrons, respectively. Under UV+vis light irradiation, almost complete inhibition of MC-LR removal is observed with NF-TiO2 in the presence of •OH scavengers at pH 5.7. These results demonstrate that solution pH plays a major role in the formation and reactivities of ROS during VLA NF-TiO2 photocatalysis. The adsorption strength of the scavengers and MCLR onto NF-TiO2 as well as the speciation of the ROS as a function of pH need to be carefully considered since they also play a key role in the efficiency of the process. These results indicate the reduction of molecular oxygen by photo-generated electrons rather than hydroxyl radicals produced by oxidative reactions of photo-generated holes play a key role in the of VLA NF-TiO2 photocatalytic degradation of MC-LR.

Synthesis, characterization and photocatalytic evaluation of visible light activated C-doped TiO2 nanoparticles.

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.

Photocatalytic inactivation of E. coli in surface water using immobilised nanoparticle TiO2 films.

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally contains suspended solids, dissolved inorganic ions and organic compounds (mainly humic substances) which may affect the efficacy of solar photocatalysis. In this work the photocatalytic and photolytic inactivation rates of Escherichia coli using immobilised nanoparticle TiO2 films were found to be significantly lower in surface water samples in comparison to distilled water. The presence of nitrate and sulphate anions spiked into distilled water resulted in a decrease in the rate of photocatalytic disinfection. The presence of humic acid, at the concentration found in the surface water, was found to have a more pronounced affect, significantly decreasing the rate of disinfection. Adjusting the initial pH of the water did not markedly affect the photocatalytic disinfection rate, within the narrow range studied.