Photocatalytic Activity of TiO2 Thin Films for the Degradation of Organic Pollutants and the Inactivation of Bio-Aerosols

IMOBERDORF, GUSTAVO EDUARDO; CASSANO, ALBERTO ENRIQUE; ALFANO, ORLANDO MARIO; IRAZOQUI, HORACIO ANTONIO

Bariloche, Argentina

Workshop; 2006 Pan American Advanced Studies Institutes on Bio and Nanotechnology (2006 PASI); 2006

Nacional Science Foundation - Centro Atomico Bariloche

Microporous titanium dioxide (TiO2) can be used in photocatalytic reactors for the elimination of contaminants and micro-organisms present in liquid and gas streams (Fujishima et al., J Photochem Photobiol C, Vol. 1, 1-21, (2000)). TiO2 nano-particles can be deposited as porous films on adequate supporting materials. Near ultraviolet light is used to activate these semiconducting metal oxide particles. When illuminated, this material oxidizes the undesirable organic compounds present in the fluid streams, eventually degrading these compounds to water and carbon dioxide (Hoffman et al., Chemical Review, Vol. 95, 69-96, (1995)). Applications of immobilized TiO2 nanoparticles used as photocatalysts include decontamination of wastewater streams (which may be polluted with organics and heavy metals); the elimination of volatile organic compounds present in air streams (i.e., trichloroethylene, benzene, formaldehyde, etc.), and the inactivation of micro-organisms (spores, bacteria, viruses and fungi). We have studied and tested some alternative sol-gel immobilization techniques in order to achieve TiO2 nano-particle films of high homogeneity; photocatalytic activity and stability. In this stage we have decided on several aspects of the TiO2 films preparation, such as the selection of the precursors, the immobilization conditions and final thermal treatment. We concluded that the most appropriate  technique for this application is based on the use of water as the dispersant medium of the TiO2 particles. Peptization was carried out at 80 ºC with addition of nitric acid and a surfactant agent. The films thus obtained were very thin, uniformly distributed and well adhered to the supporting borosilicate glass plane surface. The photocatalytic films were applied for the degradation of a model pollutant (perchloroethylene or PCE) in an air stream. The kinetic of PCE was studied in a laboratory scale reactor for different values of PCE feed concentrations, relative humidity levels and light intensities (Imoberdorf et al., Ind Eng Chem Res, Vol. 44, 6075-6085, (2005)). The kinetic expression developed was used in the physical modeling and mathematical simulation of a multi-annular, bench-scale reactor (Imoberdorf et al., AIChE J, Vol. 52, 1814-1823, (2006)). On the other hand, we recently started a work line (complementary to the study of photocatalytic reactors for the elimination of chemical pollutants) to study the interaction of different micro-organisms (viruses and spores) with photo-catalytic surface films irradiated with near UV. The effect of significant variables (i.e., humidity, time of radiation exposure, radiation flow, etc) on the inactivation rate of micro-organisms is being determined. For this, different borosilicate glass plates covered with TiO2 have been prepared by means of our adapted sol-gel technique, on which the micro-organisms were immobilized and exposed to near UV radiation under different conditions. Their viability before and after irradiation has been determined.