CONICET | Buscador de Institutos y Recursos Humanos

Pollution of indoor air by pathogen microorganisms represents a major problem in modern societies, where people spend most of their time indoors. Bioaerosols, containing viruses, bacteria, and fungi, can be responsible for infectious diseases, toxic reactions, and allergic responses. Consequently, research on disinfection technologies to control bioaerosols in air constitutes an area of great interest. Photocatalysis with TiO2 has many advantages over conventional technologies to remove microorganisms from air. Mainly, it can effectively destroy biological species, unlike filtration or ventilation. Additionally, it does not produce any hazardous by-products, as it is the case of chemical disinfection, and it can be operated under ambient conditions of temperature and pressure. The present work evaluates the enhancement of the inactivation activity of silver doped TiO2 catalysts compared to TiO2 alone. Bacillus subtilis spores spread over TiO2 films doped with different amounts of silver were irradiated with artificial UV-A light (1.89 mW cm-2). The performances of the coatings were compared by the quantum efficiency parameter, which relates the inactivation rate with the radiation absorption rate by the coating. Spectral diffuse transmittance and reflectance measurements of the films were performed using a spectroradiometer with an integrating-sphere attachment. The net-radiation method was then applied to evaluate the fraction of energy absorbed by the coatings. A notable increase in the photocatalytic inactivation activity was observed by increasing the silver content of the coatings. The highest inactivation rate was obtained with the coating containing 1.09 wt.% Ag/TiO2. A decrease on the spores concentration of more than 3 orders of magnitude (from 3.71  105 to 1.29  102 CFU cm-2) was achieved after 6 h of irradiation. The addition of higher amounts of silver rendered lower inactivation rates, thus indicating the existence of an optimum Ag/TiO2 ratio. The quantum efficiency reached with the sample containing 1.09 wt.% Ag/TiO2. (ηabs = 4.18  10-14 CFU photon-1) was almost twice the efficiency value found with TiO2 without the addition of Ag (ηabs = 2.19  10-14 CFU photon-1). The enhanced antibacterial effect of silver on the photocatalytic activity can be associated to the fact that silver acts as electron trap at the TiO2 surface. Accordingly, the reduction of charge recombination facilitates the reaction of holes with adsorbed water or hydroxyl ions to generate hydroxyl radicals.