Decomposition of endocrine-disrupting chemicals in water by use of TiO2 photocatalysts immobilized on polytetrafluoroethylene mesh sheets

Abstract

We examined the photocatalytic decomposition of 17β-estradiol (E2), bisphenol-A (BPA), and 2,4-dichlorophenol (2,4-DCP) in aqueous solutions by use of TiO2 particulate photocatalysts immobilized on polytetrafluoroethylene (PTFE) mesh sheets and black-light fluorescent lamps. These organic compounds are known to be endocrine-disrupting chemicals (EDCs). These EDCs absorb little of the light from black-light fluorescent lamps. The TiO2-modified PTFE mesh sheets were stacked with 5mm gaps in a 2-l glass cylinder in which the solution was circulated by use of a rotary pump. In the case of this reactor, a first-order rate constant of ca. 0.033min−1 was obtained at 10°C for all of the compounds (initial concentration was 90μgl−1 each). This relatively fast reaction rate was obtained repeatedly in cycling tests under UV illumination. The TiO2-modified PTFE mesh sheets were attached to a bar-rotator in a fan-type arrangement being rotated at 60rpm. In the case of the latter reactor, a higher first-order rate constant (ca. 0.050min−1) was obtained for the decomposition of both E2 and 2,4-DCP. The apparent mass-transfer rate of the EDCs to the TiO2 was able to be increased by a factor of ca. 4.5 by use of the latter reactor (i.e. with rotation of the PTFE mesh sheets themselves) compared to the use of the former reactor (conventional circulation of the aqueous solution only). Based on these results, we conclude that this rotation technique of the TiO2-modified PTFE mesh sheets has the potential to become one of the most effective and efficient procedures for the removal of EDCs from water.