Photocatalytic Degradation Of Gaseous Toluene By Modified TiO₂ Films Under185 Nm Vacuum UV Light

Volatile organic compounds(VOCs) are common pollutants found in microenvironment. It is a challenge to effectively remove VOCs to improve the indoor air quality. Though Ti O2 photocatalysis can degrade most VOCs, the degradation rate is low and the photocatalyst may deactivate in the Ti O2/UV process. 185 nm vacuum ultraviolet(VUV) photocatalysis exhibits better performance to degrade VOCs with the shortcoming of ozone production. In this thesis, Pd nanoparticles deposited Ti O2 and Ti O2 with high exposure of {001} facets were prepared, and their activities for simultaneous decomposition of gaseous toluene and residual ozone under VUV irradiation were investigated. In addition, a pilot scale system with the flow rate(0.35-0.65 m3/min) was established to evaluate the performance of Pd-Ti O2/VUV and its feasibility for practical use.First, palladium nanoparticles(Pd NPs) were deposited on a Ti O2 film with a low-temperature electrostatic self-assembly method, and their activities for simultaneous removal of toluene and ozone under 185 nm VUV irradiation were investigated. The uniform Pd NPs were uniformly deposited on the Ti O2 film, which was influenced by the immersion time. The Pd-Ti O2 film prepared with an immersion time of 10 min exhibited the highest activity for both toluene and ozone conversion because of the relatively small size(3.0 nm) and high number density(6.67×1011 cm-2)of the as-deposited Pd NPs. Compared with the direct VUV photolysis and the Ti O2/VUV photocatalytic processes, the Pd-Ti O2/VUV process exhibited a better performance in degrading toluene over a range of concentrations with a short retention time(5.7 s), and 90% of the ozone generated by 185 nm VUV was simultaneously decomposed. In addition, approximately 94.1% of the converted toluene was mineralized into CO2 and CO, and only a small amount of degradation intermediates,such as benzaldehyde and formic acid, were detected in the Pd-Ti O2/VUV process with a total yield less than 2%.We also investigated the photocatalytic activity of the Ti O2 catalyst with a highly exposed {001} facet that was prepared by a hydrothermal method. The Ti O2 catalyst prepared with a HF solution of p H 2.5 exhibited the highest percentage of {001} facets(ca. 58%), and showed the better activity than the sol-gel prepared Ti O2 for simultaneous removal of toluene and residual ozone. The deposition of Pd nanoparticles on {001}Ti O2 catalyst only significantly increased the activity for ozone removal, while the activity for toluene can’t be further increased.A pilot scale system with the flow rate of 0.35- 0.65 m3/min was established and used to evaluate the performance of the Pd-Ti O2 catalyst to remove toluene and ozone under 185 nm VUV irradiation. Due to long residence time(72 s), the direct VUV photolysis achieved high conversion(55- 100%) for low concentration toluene under the condition of low specific energy input(1.43- 4.23 Wh/m3). The Pd-Ti O2/VUV also achieved high conversion(52.2- 84.4%) with same specific energy input within much shorter residence time(5.8 s). However, when the residence time and the specific energy input further decreased to 3.1 s and 0.77- 2.28 Wh/m3 respectively, the conversion greatly decreased.