Gas phase photocatalytic efficiency of TiO2 powders evaluated by acetone photodegradation

The photocatalytic efficiency of different TiO2 powders, prepared by a sol–gel method and annealed at different temperatures, has been evaluated through the TiO2 photosensitized degradation (until mineralization) of acetone, as model reaction, in a static gas phase reactor. Two profiles “TiO2 efficiency vs. powders annealing temperature” have been obtained analyzing the produced CO2 by gas-chromatography or by an IR gas sensor. Despite the different operative conditions, that are: (i) acetone initial concentration (2400 or 600 ppm), (ii) relative humidity (40 or 70%) and (iii) reaction time (a test after 7 h or a continuous monitoring until 1 h), the two profiles are similar and show the same TiO2 efficiency maximum (at 700◦C calcination temperature of the powder). The efficiency increase until 700°C could depend on the crystallinity increase of anatase form and on the decreasing amount of physisorbed water at the surface of the semiconductor. The efficiency decrease observed at higher temperatures could be ascribed to the gradual transformation of anatase into rutile form, less reactive. Differently, parameters as specific surface and mesopore volume of TiO2 powders seem to be less important for the powder efficiency.