The use of TiO2 as a photocatalyst to oxidize volatile organic compounds (VOCs) has been extensively studied. The photooxidation processes originate from band-gap excitation of TiO2, carried out by UV radiation which generates electrons and holes: these species respectively reduce and oxidize, leading to the formation of hydroxyl radicals (OH•). These radicals oxidize organic contaminants present at the semiconductor surface, leading to their complete mineralization or at least to the formation of less harmful products. Photocatalysis is almost always associated to the use of nanoparticles (NPs) notwithstanding the typical problems due to the catalyst-recovering, and more recently to the possibility that NPs may be potentially dangerous for both environment and human safety. In the present study, photoactivity towards the photooxidation of VOCs such as acetone, acetaldehyde and toluene, was verified comparing nano-sized (P25 by Evonik and PC105 by CrystalGlobal) and micro-sized (1077 by Kronos and Tiona AT-1 by CrystalGlobal) TiO2 powdered samples. Photocatalytic tests were performed in a Pyrex glass cylindrical reactor of 5 L with 0.5 g of photocatalyst working in batch mode. The gaseous mixture in the reactor was obtained by mixing hot chromatography air and the pollutant in order to reach a starting pollutant amount of 500 ppmV verified by an online micro-GC. The irradiation was 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]. All samples were fully characterized by both surface and structural techniques. In particular, FE-SEM and HR-TEM images were collected to confirm particles’ sizes and to exclude the presence of ultra-fine particles in the micro-sized powders. Moreover, fringes analyses confirmed the polymorphs distribution. Samples were also analyzed by HR-XPS to evaluate the surface chemical species taking into account both the Ti2p region and the O1s one: this latter region allows the investigation on both quality and abundance of OH surface species, which are fundamental in the photocatalytic process [2]. Powdered samples were also characterized by FTIR analysis, performed with a Bruker IFS28 spectrophotometer (equipped with MCT cryodetector), both before and after the photocatalytic VOCs degradation to evaluate the presence and the kind of by-products adsorbed onto the photocatalyst surface. In conclusion, the use of micrometric TiO2 instead of nano-sized one as photocatalyst seems to be very promising as both samples characterization and the catalytic activity results of micro-sized samples are (almost) fully comparable to those obtained for the nano-sized compounds, confirming the possible employment of the formers as photocatalysts.

PHOTOCATALYTIC VOC DEGRADATION: COMPARISION BETWEEN COMMERCIAL NANO AND MICRO-SIZED TiO2

CERRATO, Giuseppina;CROCELLA', VALENTINA;
2012-01-01

Abstract

The use of TiO2 as a photocatalyst to oxidize volatile organic compounds (VOCs) has been extensively studied. The photooxidation processes originate from band-gap excitation of TiO2, carried out by UV radiation which generates electrons and holes: these species respectively reduce and oxidize, leading to the formation of hydroxyl radicals (OH•). These radicals oxidize organic contaminants present at the semiconductor surface, leading to their complete mineralization or at least to the formation of less harmful products. Photocatalysis is almost always associated to the use of nanoparticles (NPs) notwithstanding the typical problems due to the catalyst-recovering, and more recently to the possibility that NPs may be potentially dangerous for both environment and human safety. In the present study, photoactivity towards the photooxidation of VOCs such as acetone, acetaldehyde and toluene, was verified comparing nano-sized (P25 by Evonik and PC105 by CrystalGlobal) and micro-sized (1077 by Kronos and Tiona AT-1 by CrystalGlobal) TiO2 powdered samples. Photocatalytic tests were performed in a Pyrex glass cylindrical reactor of 5 L with 0.5 g of photocatalyst working in batch mode. The gaseous mixture in the reactor was obtained by mixing hot chromatography air and the pollutant in order to reach a starting pollutant amount of 500 ppmV verified by an online micro-GC. The irradiation was 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]. All samples were fully characterized by both surface and structural techniques. In particular, FE-SEM and HR-TEM images were collected to confirm particles’ sizes and to exclude the presence of ultra-fine particles in the micro-sized powders. Moreover, fringes analyses confirmed the polymorphs distribution. Samples were also analyzed by HR-XPS to evaluate the surface chemical species taking into account both the Ti2p region and the O1s one: this latter region allows the investigation on both quality and abundance of OH surface species, which are fundamental in the photocatalytic process [2]. Powdered samples were also characterized by FTIR analysis, performed with a Bruker IFS28 spectrophotometer (equipped with MCT cryodetector), both before and after the photocatalytic VOCs degradation to evaluate the presence and the kind of by-products adsorbed onto the photocatalyst surface. In conclusion, the use of micrometric TiO2 instead of nano-sized one as photocatalyst seems to be very promising as both samples characterization and the catalytic activity results of micro-sized samples are (almost) fully comparable to those obtained for the nano-sized compounds, confirming the possible employment of the formers as photocatalysts.
2012
V Workshop on oxide based materials
Torino
23-27 Settembre 2012
V Workshop on oxide based materials - Book of abstract
Politeko Editore
P01PHOTO
101
101
9788897862086
Claudia L. Bianchi; Carlo Pirola; Sara Gatto; Alessandro Di Michele; Giuseppina Cerrato; Valentina Crocellà; Valentino Capucci
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/117796
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