Photocatalytic VOC degradation : comparision between commercial nano and micro-sized TiO2

Using TiO2 as a photocatalyst to oxidized volatile organic compounds (VOCs) have been extensively studied. The photooxidation processes originate from band-gap excitation of TiO2 by UV radiation to generate electrons and holes which reduce and oxidize respectively, generating hydroxyl radicals (OH•). These radicals oxide organic contaminant leading them to the complete mineralization or to the formation of less harmful products. In particular, in the last years there is been an accurate study on the application of TiO2 photocatalyst with particles larger because of many problems such as the catalyst-recovering typical of nanoparticles, that can damages both environment and human safety. So, in this paper it is reported a study on photooxidation of VOCs, using both nano- (P25 by Evonik) and micro-sized (1077 by Kronos) TiO2 samples as photocatalysts comparing the results. Photocatalytic degradations were performed in a Pyrex glass cylindrical reactor of 5 L with 0.5 g of photocatalyst. The gaseous mixture in the reactor was obtained by mixing hot chromatography air and an initial concentration of pollutant of 500 ppmV verified by an online micro-GC. The irradiation is carried out by an iron halogenide lamp (Jelosil, model HG 500) emitting in the 315-400 nm wavelength range (UV-A) with an irradiation power of 30 W/m2 [1]. As an example it is reported in Figure 1 the degradation of toluene with micro-TiO2 comparing with that of the nano-sized one. It is evident that the catalytic activity of micro-sized samples is very similar to that obtained by nano- compounds, confirming the possibility of use of micro-sized particles as photocatalysts. Powder samples were also characterized by FTIR-ATR analysis, performed with FTS-40 BIO RAD to evaluate the by-products adsorbed onto the photocatalyst surface. Furthermore, HR-TEM images were reported to observe the difference of size between P25 and 1077 powders, whose diameter is 25 nm and 300 nm respectively. In conclusion, observing these results the use of micrometric TiO2 instead of nano-sized as photocatalyst becomes a possibility for environmental and human protection.