Photocatalytic properties of different TiO2 thin films of various porosity and titania loading

Thin sol–gel titania films with varying porosity but constant mass were coated on SiO2/glass substrate. The mass was kept constant by changing the withdrawal rate of dipping from a titania sol. The porosity properties of the films were determined by the analysis of adsorption isotherms of Kr at ca 77 K. Photocatalytic performance of TiO2 layers in the degradation of Acid orange 7 (AO7) and 4-chlorophenol (4CP) in aqueous solution depends on the mass of titania but not on the porosity/surface area of the films. On the contrary, in the degradation of thin layers of Resazurin (Rz) ink and methyl stearate (MS) deposited on the TiO2 film surface, the activity of the films is clearly enhanced due to the porosity but does not depend on titania mass itself. Obtained data suggest that while in an aqueous solution the reaction rate depends primarily on the mass of titania and amount of absorbed light, in solid thin films test the porosity/surface area together with interfacial area of tested compound with titania layer is significant.