Removal of paraquat dissolved in a photoreactor with TiO2 immobilized on the glass-tubes of UV lamps.

Experiments were performed to investigate the effects of operating parameters, such as air-inflow rate, UV-light intensity, and film thickness of the photocatalyst, on the photo-decomposition efficiency of paraquat in an immersion-type reactor with TiO2 immobilized by three kinds of methods on the glass tube of UV lamps. As the number of TiO2 coating-time increased from 1 to 4, film thickness on the glass tube by a dip-coating method increased from 355 to 1180 A. The removal efficiency of paraquat using TiO2 prepared by the hydrothermal method was the highest, being 99% in a 12 h operation of 3-type TiO2 immobilized by a sol-gel method and a hydrothermal method, including a commercial product P-25, while that in the absence of TiO2 with only the UV light was the lowest, being 50% in 12 h. The conversion ratios of paraquat at the volumetric flow rates of 5, 10, and 20 mL min(-1) were 46%, 25%, and 17% in 18 h, respectively.