Photooxidation of prometryn and prometon in aqueous solution by hydrogen peroxide on photocatalytic membranes immobilising titanium dioxide

The TiO2-mediated photooxidation of prometryn and prometron in aqueous solution by PAOTOPERM(R) CPP/313 membranes containing immobilized 30+/-3 wt.% TiO2 and by employing hydrogen peroxide was studied. This oxygen donor was used as a substitute of dissolved oxygen or ozone by which complete mineralization of s-triazines had been attained on photocatalytic membranes as reported previously. Solutions containing 5.2.10(-6) - 1.0.10(-4) M prometryn and 7.8.10(-6) - 2.0.10(-4) M prometon were photodegraded successfully. Experiments were carried out in a PHOTOPERM(R) WP pilot-plant using monochromatic irradiation (254 nn) in the absorption range of semiconductor with an absorbed power of 11 +/- 1 W. For the disappearance of both substrates, pseudo-first order kinetics were observed and the results could be interpreted by the Langmuir-Hinshelwood treatment. Cyanuric acid, however, resulted as final product under the experimental conditions. This behaviour is compared with that of the use of oxygen or ozone as oxygen donors. Furthermore, based on HPLC and HPIC analysis, a mechanism of photodegradation is proposed for both substrate molecules. (C) 1998 Elsevier Science Ltd. All rights reserved.