Decomposition of gas-phase toluene by the combination of ozone and photocatalytic oxidation process (TiO2/UV, TiO2/UV/O3, and UV/O3)

The gas-phase toluene removal efficiencies by photocatalytic oxidation (TiO2/UV), the combination of ozone and photocatalytic oxidation (TiO2/UV/O3), and the UV/O3 reaction were tested using a quartz tube photoreactor. The experiments were conducted under various ozone concentrations (3.3–15ppm), toluene concentrations (1–9ppm), relative humidity (5–80%), and gas flow rates (200–1200mL/min). The toluene oxidation rates (TORs) of TiO2/UV/O3, and UV/O3 reactions were proportional to the ozone concentrations. The TORs of TiO2/UV, TiO2/UV/O3, and UV/O3 reactions increased with toluene concentration. However, there were negative correlations between the toluene removal efficiencies of these three kinds of reactions and the toluene concentrations. The order of the TORs and the CO2 yield rates of these three reactions were TiO2/UV/O3>TiO2/UV>UV/O3. The kinetics of TiO2/UV, and TiO2/UV/O3 reactions fit the Langmuir–Hinshelwood rate form. The rate constants (k) and Langmuir adsorption constants (K) are as follows: TiO2/UV: k=0.0102ppmm/s, K=0.146ppm−1; TiO2/UV/O3: k=0.0268ppmm/s, K=0.0796ppm−1. The reciprocal of UV/O3 reaction rate showed a positive linear relationship with the reciprocals of humidity and of toluene concentration. Ozone, also an air pollutant, was removed in the TiO2/UV/O3, and UV/O3 reactions. The ozone removal efficiency of TiO2/UV/O3 reaction in the presence and absence of toluene ranged from 61.1 to 99.5% and 38.1 to 95.1%, respectively.