Photodegradation of propranolol by Fe(III)-citrate complexes: Kinetics, mechanism and effect of environmental media

Photogeneration of HO(center dot) was optimized in Fe(III)-citrate solution within the pH range of 3.0-9.0 to investigate its photoreactivity at neutral pH without the addition of H(2)O(2) under simulated sunlight. The generation of HO(center dot) decreased with increasing pH within the range of 6.0-9.0 at the Fe(III)-to-citrate ratio of 10:50 (10(-6) M). However, when the concentration of citrate increased to 1.5 x 10(-4) M, the formation rate of HO(center dot) increased in the order of pH 9.0 < 3.0 < 7.0 < 4.0 < 5.0. The pH-dependent HO(center dot) production was governed by the stability of Fe(II)/Fe(II)-citrate and the amount of O(2) in the solution. Propranolol can be efficiently photodegraded in Fe(III)-citrate system at pH 7.0 with pseudo-first-order constant 3.1 x 10(-4) s(-1). HO(center dot) was verified to be the main reactive oxygen species (ROS) responsible for the photodegradation of propranolol. The presence of metal ions inhibited the Fe(III)-cit-induced photodegradation in the order of Mn(2+) > Cu(2+) > Ca(2+) > Mg(2+). Both humic acid (HA) and fulvic acid (FA) markedly suppressed the degradation of propranolol. Moreover, the iron in Fe(III)-citrate system was reused by a simple addition of citrate to the reaction solution. By GC-MS analysis, the photoproducts of the propranolol were identified and the degradation pathway was proposed. This work suggests that Fe(III)-citrate complexes are good alternative for the advanced treatment of organic pollutants at neutral pH in aqueous solution. (C) 2011 Elsevier B.V. All rights reserved.