Photocatalytic degradation of acetone, acetaldehyde and toluene in gas-phase : comparison between nano and micro-sized TiO2

Volatile Organic Compounds (VOCs) are widely used in industrial processes and for domestic activities, so generating both water and air pollution. Well-known indoor sources of VOCs include cigarette smoke, building materials, paints, lacquers and cleaning products. The photodegradation of organic compounds by titanium dioxide TiO2 has been proposed as an alternative Advanced Oxidation Process (AOP) for the decontamination of air. In general AOPs based on UV radiation involve TiO2 mostly in nanometric size. However, nanoparticles give rise to many problems such as the catalyst-recovering, hindering their commercial application, other than possible damages on both human safety and environment. In this contribution, a comparative study about the application of nano- (P25 by Evonik) and micro-sized (1077 by Kronos) TiO2 samples as photocatalyst in the degradation of acetone (AC), acetaldehyde (AD) and toluene (TL) is reported, in order to evaluate the feasibility of using micro-sized TiO2 instead of nanometric particles, which results in a greater environmental impact if compared to the former one. Photocatalytic degradations of these pollutants were performed in a Pyrex glass cylindrical reactor of 5 L with 0.05 g of photocatalyst. The gaseous mixture in the reactor was obtained by mixing hot chromatographic air and an initial concentration of pollutant of 400 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 shown in Fig. 1 the activity of the micro-TiO2 is comparable with that of the nano-sized one. In particular, the amount of degraded AC is reported: the trend of degradation of the pollutant obtained with nanometric and micrometric TiO2 samples is quite similar. Powdery samples were also characterized by FTIR-ATR analysis, performed with FTS-40 BIO RAD to evaluate the by-products adsorbed onto the photocatalyst surface. As a consequence, this result demonstrates that micro-sized TiO2 powders are good candidates for the photocatalytic degradation of organic molecules in the gas phase.