Effect of Water Vapor on Photocatalytic Air Treatment.
- The effect of water vapor very much depends on the type of pollutant and, obviously, on the partial pressure of water against that of the pollutant.
- On one hand, water can compete with the adsorption of organic pollutants, especially those that are structurally related, such as alcohols.
- On the other hand, water can behave as a reactant in some of the successive steps of the degradation of organics and, in particular, can limit the formation of products that inhibit the photocatalytic activity.
- Water can be at the origin of the formation of hydroxyl radicals; however, the importance of these radicals in gas-phase photocatalytic reactions is being debated on.
- The conclusion is that some humidity seems necessary for optimum photocatalytic activity.
Inactivation of Microorganisms.
- For the inactivation of a variety of microorganisms in water, UV-irradiated TiO2 has been found to be more efficient than the same UV irradiation in the absence of TiO2.
- Cellular membranes and DNA appear to be damaged. This is not surprising because TiO2 photocatalysis is able to degrade nearly all categories of organics, including polymers. Although the effects on a greater number of microorganism families should be tested, the method already appears promising both for water and air treatment.
- These antibacterial properties undoubtedly increase the interest of TiO2 photocatalysis because, simultaneous to disinfection, organic pollutants can be degraded and certain toxic metal cations can be reduced or oxidized.
- Furthermore, the bactericidal activity can be enhanced by spraying an aqueous solution of silver ions on the TiO2 coating during its preparation; under UV irradiation, these cations are reduced to Ag, which also presents antimicrobial properties.