Abstract
The beneficial photocatalytic properties of UV light activated TiO2 powder are well-known and have been demonstrated with various pollutants and pathogens. However, traditionally observed photocatalytic activity of visible light activated pristine TiO2 is insignificant but there are a few studies which have reported that under some specific conditions commercially available TiO2 powder could at least partially disinfect microorganisms even under visible light. To better understand this phenomenon, in the current study we focused on bacteria response to the treatment by visible light and P25 TiO2 powder. More specifically, we analyzed the relationship between the bacteria viability, outer membrane permeability, metabolism, and its capacity to generate intracellular reactive oxygen species. During the study we assayed the viability of treated bacteria by the spread plate technique and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction method. Changes in bacterial outer membrane permeability were determined by measuring the fluorescence of N-phenyl-1-naphthylamine (NPN). To detect intracellular reactive oxygen species formation, the fluorescence of dichlorodihydrofluorescein diacetate (DCFH-DA) was assayed. Results of our study indicated that TiO2 and wide spectrum visible light irradiation damaged the integrity of the outer membrane and caused oxidative stress in the metabolizing bacteria. When favorable conditions were created, these effects added up and unexpectedly high bacterial inactivation was achieved.
Highlights
Accumulating scientific reports and increasing weather extremes have forced society to recognize man made climate change [1]
In order to evaluate the effects of combined light and activated TiO2 treatment on bacteria, initially we determined the individual effects of these factors on S
The results of experiments show, that under certain conditions TiO2 and visible light can affect the integrity of their outer membrane
Summary
Accumulating scientific reports and increasing weather extremes have forced society to recognize man made climate change [1] This issue is attracting most of the public attention, but it is not the only environmental problem causing big concern. Photocatalytic water treatment is arguably the most widely investigated AOP method. With this method a photocatalyst (mainly comprised of a semiconductor material with a specific electron level structure) is irradiated by intensive ultraviolet (UV) or visible (vis) light. In comparison to the traditional wastewater treatment methods like UV irradiation and chlorination, photocatalytic water treatment has superior oxidation power [5], does not form carcinogenic disinfection by-products [6], and can be used for the treatment of pathogens which are resistant to chlorine [7]
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