|Title||Efficiency of clay-TiO2 nanocomposites on the photocatalytic elimination of a model hydrophobic air pollutant|
|Publication Type||Journal Article|
|Year of Publication||2009|
|Authors||Kibanova, D., Javiera Cervini-Silva, and Hugo Destaillats|
|Secondary Title||Environmental Science and Technology|
|Keywords||1:1 and 2:1 phyllosilicates, air cleaning, air contaminant, environmental chemistry, exposure & risk group, indoor air quality, indoor environment department, photocatalysis, pollutant fate and transport modeling, titania|
Clay-supported TiO2 photocatalysts can potentially improve the performance ofair treatment technologies via enhanced adsorption and reactivity of target volatileorganic compounds (VOCs). In this study, a bench-top photocatalytic flow reactor wasused to evaluate the efficiency of hectorite-TiO2 and kaolinite-TiO2, two novelcomposite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realisticconcentrations, and reacted under UVA (λmax = 365 nm) or UVC (λmax = 254 nm)irradiation. The UVC lamp generated secondary emission at 185 nm, leading to theformation of ozone and other short-lived reactive species. Performance of clay-TiO2composites was compared with that of pure TiO2 (Degussa P25), and with UVirradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO2 composites and of P25 were prepared by a dip-coating method on the surface of Raschigrings, which were placed inside the flow reactor. An upstream toluene concentration of~170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33 and 66 % relative humidity (RH). Toluene concentrations were determined by collecting Tenax-TA ® sorbent tubes downstream of the reactor, with subsequent thermal desorption – GC/MS analysis. The fraction of toluene removed, %R, and the reaction rate, Tr, were calculated for each experimental condition from the concentration changes measured with and without UV irradiation. Use of UVC light (UV/TiO2/O3) led to overall higher reactivity, which can be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, Tr/Iλ, the UV/TiO2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO2 (P25 and Hecto-TiO2), but not for Kao-TiO2. In all cases, reaction rates peaked at 10% RH, with Tr values between 10 and 50% higher than those measured under dry air. However, a net inhibition was observed as RH increased to 33% and 66%, indicating that water molecules competed effectively with toluene for reactive surface sites and limited the overall photocatalytic conversion. Compared to P25, inhibition by co-adsorbed water was less significant for Kao-TiO2 samples, but was more dramatic for Hecto-TiO2 due to the high water uptake capacity of hectorite.
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