@article{22210,
  keywords = {Air cleaning, Indoor environment department, Titania, Pollutant fate and transport modeling, Indoor Air Quality (IAQ), 1:1 and 2:1 phyllosilicates, Air contaminant, Photocatalysis, Environmental Chemistry, Exposure and Risk Group},
  author = {Daria Kibanova and Javiera Cervini-Silva and Hugo Destaillats},
  title = {Efficiency of clay-TiO2 nanocomposites on the photocatalytic elimination of a model hydrophobic air pollutant},
  abstract = {<p>Clay-supported TiO<sub>2</sub> photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a benchtop photocatalytic flow reactor was used to evaluate the efficiency of hectorite−TiO<sub>2</sub> and kaolinite−TiO<sub>2</sub>, two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (λ<sub>max</sub> = 365 nm) or UVC (λ<sub>max</sub> = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay−TiO<sub>2</sub> composites was compared with that of pure TiO<sub>2</sub> (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay−TiO<sub>2</sub> composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of <img src="http://pubs.acs.org/appl/literatum/publisher/achs/journals/entities/223C.gif" alt="" align="bottom" class="entityA" />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, %<em>R</em>, and the reaction rate, <em>T</em><sub>r</sub>, were calculated for each experimental condition from the concentrations measured with and without UV irradiation. Use of UVC light (UV/TiO<sub>2</sub>/O<sub>3</sub>) 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, <em>T</em><sub>r</sub>/<em>I</em><sub>λ</sub>, the UV/TiO<sub>2</sub> reaction under UVA irradiation was more efficient for samples with a higher content of TiO<sub>2</sub> (P25 and Hecto−TiO<sub>2</sub>), but not for Kao−TiO<sub>2</sub>. In all cases, reaction rates peaked at 10% RH, with <em>T</em><sub>r</sub> 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 coadsorbed water was less significant for Kao−TiO<sub>2</sub> samples, but was more dramatic for Hecto−TiO<sub>2</sub> due to the high water uptake capacity of hectorite.</p>},
  year = {2009},
  journal = {Environmental Science and Technology},
  volume = {43},
  pages = {1500-1506.},
  language = {eng},
}