Photocatalytic oxidation of propene in gas phase at low concentration by optimized TiO₂ nanoparticles

In the present study, nanocrystalline titanium dioxide (TiO₂) was prepared by sol-gel method at low temperature from titanium tetraisopropoxide (TTIP) and characterized by different techniques (gas adsorption, XRD, TEM and FTIR). Variables of the synthesis, such as the hydrolyzing agent (acetic acid or isopropanol) and calcination temperatures (300-800°C), were analyzed to get uniform size TiO₂ nanoparticles. The effect that these two variables have on the structure of the resultant TiO₂ nanoparticles and on their photocatalytic activity is investigated. The photocatalytic activities of TiO₂ nanoparticles were evaluated for propene oxidation at low concentration (100ppmv) under two different kinds of UV light (UV-A∼365nm and UV-C∼257.7nm) and compared with Degussa TiO₂ P-25, used as reference sample. The results show that both hydrolyzing agents allow to prepare TiO₂ nanoparticles and that the hydrolyzing agent influences the crystalline structure and its change with the thermal treatments. Interestingly, the prepared TiO₂ nanoparticles possess anatase phase with small crystalline size, high surface area and higher photocatalytic activity for propene oxidation than commercial TiO₂ (Degussa P-25) under UV-light. Curiously, these prepared TiO₂ nanoparticles are more active with the 365nm source than with the 257.7nm UV-light, which is a remarkable advantage from an application point of view. Additionally, the obtained results are particularly good when acetic acid is the hydrolyzing agent at both wavelengths used, possibly due to the high crystallinity, low anatase phase size and high surface oxygen groups' content in the nanoparticles prepared with it, in comparison to those prepared using isopropanol.