An efficient green photo-Fenton system for the degradation of organic pollutants. Kinetics of propranolol removal from different water matrices

Abstract

We report on the degradation of aqueous propranolol (PRO) in a heterogeneous system with natural iron oxide (N.I.O.) and oxalic acid (OAA) under near UV–Vis irradiation. Photolysis experiments showed ca. 65% degradation of PRO after 2 h irradiation, and a similar degradation in the presence of N.I.O. A more efficient PRO removal was obtained upon irradiation within a mixture of N.I.O. and OAA. Under the best conditions considered, complete degradation (> 95%) was observed in less than 10 min, and TOC decreased by 60% after 3 h irradiation. The observed processes were adequately fitted by pseudo-first-order kinetics, the corresponding rate constants were determined, and the effect of different variables analyzed. Photodegradation of PRO is accelerated under acidic conditions, and neutralization takes place along the reaction. Hydroxyl radicals play a predominant role in the photodegradation reaction, as shown by the dramatic inhibition observed upon t-butanol addition. Furthermore, HO formation is strongly dependent on the pH of the medium. LC-MS identification of ten different intermediates leads to the proposal of a degradation mechanism. This photocatalytic system has also proven effective, for the first time, in different real aqueous matrices (river water > distilled water > sewage ≫ > seawater, revealing quite efficient in the former) and also employing sunlight, where PRO photodegradation was slower. The results obtained show that N.I.O.-oxalate complexes are a green, cheap choice for removing organic pollutants in aqueous solution.