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

► The relationship between the Fe(III)-to-cit ratio and pH-dependent OH production is investigated. ► The generation rate of OH increased in the order of pH 9.0 < 3.0 < 7.0 < 4.0 < 5.0 at Fe(III)-to-cit ratio of 10:150. ► The presence of metal ions inhibited the Fe(III)–cit-induced photodegradation in the order of Mn 2+ > Cu 2+ > Ca 2+ > Mg 2+. ► Iron in the Fe(III)–cit system is reused to decrease the process cost and colourity of water. Photogeneration of HO 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 2O 2 under simulated sunlight. The generation of HO 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 × 10 −4 M, the formation rate of HO increased in the order of pH 9.0 < 3.0 < 7.0 < 4.0 < 5.0. The pH-dependent HO 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 × 10 −4 s −1. HO 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.