Shifting to the red the absorption edge in TiO2 films: a photoacoustic study

when titanium dioxide in contact with a polluted water sample is irradiated with ultraviolet light, electron-hole pairs can be generated, which can react with oxygen and water producing free radicals that can degrade the pollutants, changing them into harmless compounds for the environment. the ultraviolet component of the solar radiation is around 7%. therefore, it is convenient to modify the tio2 films crystalline structure for obtaining photocatalytical processes with visible light. in this work we report on the growth of tio2 thin films by the sol-gel technique considering the incorporation of agno3 in the initial solution containing the precursor. the concentration of the agno3 saline solution was changed between 5 and 30% to control the grain size of the grown tio2 nanocrystals, impregnating 6 layers over glass slide substrates and using a sintering temperature of 600 °c. the obtained films were characterized structurally by means of x-ray diffraction. the shift in the forbidden energy bandwidth value to the red part of the optical absorption spectrum was evidenced by photoacoustic spectroscopy. the photocatalytic activity was tested on a solution of methylene blue using also the photoacoustic technique.