Although the relative arrangement of a UV light source and immobilized TiO2 is estimated to strongly affect the photocatalytic decomposition of volatile organic compounds (VOCs), no studies have been published regarding this matter. In the present study, reactor performances were compared between parallel arrangements, where UV lamps are placed in parallel to flat TiO2-PET sheets, and circular arrangements, where each glass tube has a UV lamp and a cylindrical TiO2-PET sheet closely attached to the inside surface of the tube. In the decomposition of isopropanol, acetone was released into air and decomposed after being readsorbed onto TiO2. In the decomposition of toluene, benzaldehyde remained on the surface and inhibited the decomposition. Parallel arrangement generated an area of low UV intensity on TiO2-PET sheets, leaving unconverted intermediates on the sheets. Circular arrangement made it possible to irradiate the whole surface of a TiO2-PET sheet with high intensity UV light and provided higher rates of VOC decomposition such that intermediates could be decomposed efficiently. To completely decompose VOCs including the intermediates, TiO2 must be irradiated with strong UV light above a certain threshold that depends on the kind of VOC. The use of the circular arrangement is recommended for the VOC decomposition.
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