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Photocatalytic removal of indoor level of toluene in the gas phase was performed in a tubular reactor by TiO 2 -based photocatalysts under illumination of UV and visible light, respectively. Two types of TiO 2 suspensions were employed in the whole experiments: one prepared by a sol–gel route (designated as SG-TiO 2 ) and the other by applying a commercial Degussa P25 TiO 2 (designated as P25-TiO 2 ). All photocatalysts were dip coated on the inner surface of a Pyrex glass tube and followed by a post-annealing process. For visible-type photocatalysts, the above TiO 2 films were sensitized by tetrakis (4-carboxyphenyl) porphyrin (TCPP) and designated as TCPP/SG-TiO 2 and TCPP/P25-TiO 2 , respectively. The photocatalytic destruction of gaseous toluene by the four catalysts was evaluated. For the UV-type photocatalysts, toluene was decomposed significantly by both types of TiO 2 films at lower toluene concentrations, [T] o . However, the overall removal efficiency (RE) was decreased dramatically as the initial concentration of was elevated to 6.5 ppm for P25-TiO 2 and 4.0 ppm for P25-TiO 2 , respectively. A plot of toluene elimination capacity (EC) versus toluene loading rate indicated that the limiting EC for the SG-TiO 2 and P25-TiO 2 was 4.9 and 2.7 mg/h/m 2 , respectively. In contrast, either type of dye-sensitized TiO 2 photocatalysts evaluated under illumination of visible light showed relatively low toluene RE as compared to the UV-type photocatalysts under identical conditions. After pre-soaking in HCl solution, the activity of the acid-pretreated TCPP/P25-TiO 2 [designated as TCPP/P25-TiO 2 (ACT)] was improved considerably under the identical conditions. The kinetics of photocatalytic decomposition of gaseous toluene in our study generally would follow the Langumuir–Hinshelwood (L–H) model. The rate constant k , as fitted by L–H model, for the SG-TiO 2 -based catalysts is larger than that of P25-TiO 2 -based catalysts while the absorption constant K , on the contrary, follows the different trend. The higher activity of SG-TiO 2 could be attributed to the smaller grain size (4.6–8.1 nm) of anatase crystals as evaluated in XRD diffraction pattern. |
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