The effect of ozone on the removal effectiveness of photocatalysis on indoor gaseous biogenic volatile organic compounds.
ABSTRACT In this study, the degradation of d-limonene by photocatalytic oxidation (PCO) (titanium dioxide [TiO2]/ultraviolet [UV]) and by the combination of PCO and ozone (O3) (TiO2/UV/O3) was investigated to evaluate the enhancement effect of O3. The degradation of d-limonene by UV/O3 was also investigated for comparison. The experiments were conducted with a quartz photoreactor under various gas flow rates (600-1600 mL min(-1)), d-limonene concentrations (0.5-9 parts per million [ppm]), and relative humidity (RH) (20-80%). The d-limonene removal efficiency of TiO2/UV/O3, TiO2/UV, and UV/O3 ranged from 62 to 99%, from 49 to 99%, and from 46 to 75%, respectively. The addition of 120-ppb O3 can enhance the d-limonene removal efficiency of PCO up to 12%. The apparent kinetic parameters (apparent rate constants, kapparent and Langmuir adsorption constants, Kapparent of TiO2/UV and TiO2/UV/O3 reactions obtained from fitting Langmuir-Hinshelwood models are TiO2/UV: kapparent = 1.45 x 10(-3) ppm-m sec(-1), Kapparent = 0.34 ppm(-1); TiO2/ UV/O3: kapparent = 1.83 x 10(-3) ppm-m sec(-1), and Kapparent = 0.35 ppm(-1). When RH was higher than 40%, the residual intermediates yield rates of d-limonene of TiO2/UV/O3, TiO2/UV, and UV/O3 reactions ranged from 0.39 to 0.51 micromol carbon m(-2) sec(-1), 0.56 to 1.96 micromol carbon m(-2) sec(-1), and 157 to 177 micromol carbon m(-3) sec(-1), respectively. In the photocatalytic reaction experiments, the addition of 120-parts per billion (ppb) O3 can reduce the residual intermediates yield rates of d-limonene by up to 1.46 micromol carbon m(-2) sec(-1). These experimental results showed that O3 can enhance the effectiveness of photocatalysis on the removal of d-limonene.