Photocatalytic degradation of organophosphorus pesticides using floating photocatalyst TiO2 ÆSiO2/beads by sunlight

In this paper, the floating TiO2 ÆSiO2 photocatalyst beads are prepared by the dip-coating method, which use hollow glass microbeads as the carrier and titanium tetraisopropoxide [Ti(iso-OC3H7)4] and ethyl silicate as the raw materials. The feasibility of photocatalytic degradation of organophosphorus pesticides using TiO2 ÆSiO2 beads as a floating photocatalyst by sunlight is studied. The results show that the best heat treatment condition for TiO2 ÆSiO2 beads is at 650 C for 5 h. Apart from heat treatment temperature and time, the amount of SiO2 also influences the photocatalytic activity of TiO2 ÆSiO2 beads. The optimum amount of SiO2 is 0.20 (molecular fraction). 0.65 · 10 4 mol/dm3 of four organophosphorus pesticides of three structures can be completely photocatalytically degraded into PO3 4 after 420 min illumination by sunlight. The effects of parameters such as the amount of TiO2 ÆSiO2 beads, initial pH and metal ions on the photocatalytic degradation of the organophosphorus pesticides are also studied. The possible mechanisms of photocatalytic degradation of phosphate ester pesticides are proposed. After 120 h illumination by sunlight, there is no significant loss of the photocatalytic activity of TiO2 ÆSiO2 beads. 2004 Elsevier Ltd. All rights reserved