Unlike water applications, the photocatalytic technique utilizing light-emitting-diodes as an alternative light source to conventional lamp has rarely been applied for low-level indoor air purification. Accordingly, this study investigated the applicability of UV-LED to annular-type photocatalytic reactor for removal of indoor-level benzene and toluene at a low concentration range associated with indoor air quality issues. The characteristics of photocatalyst was determined using an X-ray diffraction meter and a scanning electron microscope. The photocatalyst baked at 350 ℃ exhibited the highest photocatalytic degradation efficiencies(PDEs) for both benzene and toluene, and the photocatalysts baked at three higher temperatures(450, 550, and 650 ℃) did similar PDEs for these compounds. The average PDEs over a 3-h period were 81% for benzene and close to 100% for toluene regarding the photocatalyst baked at 350 ℃, whereas they were 61 and 74% for benzene and toluene, respectively, regarding the photocatalyst baked at 650 ℃. As the light intensity increased from 2.4 to 3.5 MW cm-1, the average PDE increased from 36 to 81% and from 44% to close to 100% for benzene and toluene, respectively. In addition, as the flow rate increased from 0.1 to 0.5 L min-1, the average PDE decreased from 81% to close to zero and from close to 100% to 7% for benzene and toluene, respectively. It was found that the annular-type photocatalytic reactor inner-inserted with UV-LEDs can effectively be applied for the decomposition of low-level benzene and toluene under the operational conditions used in this study.

Abstract
 1. Introduction
 2. Methodology
  2.1. Experimental set-up and procedures
  2.2. Sampling and analysis
 3. Results and discussion
  3.1. Characterization of photocatalyst
  3.2. Photocatalytic activity dependence on baking temperature
  3.3. Photocatalytic activity dependence on light intensity
  3.4. Photocatalytic activity dependence on flow rate
 4. Conclusions
 Reference

• Wan-Kuen Jo(Department of Environmental Engineering, Kyungpook National University) Corresponding author
• Hyun-Jung Kang(Department of Environmental Engineering, Kyungpook National University)
• Kun-Hwan Kim(Department of Environmental Engineering, Kyungpook National University)