Mineralization of paracetamol by ozonation catalyzed with Fe2+, Cu2+ and UVA light

Abstract

Acid solutions containing up to 1gl−1 of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe2+, Cu2+ and/or UVA light at 25.0°C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be efficiently destroyed by the combined action of generated H2O2 and UVA light. In the presence of Fe2+ and UVA light, the process is accelerated due to the production of oxidant hydroxyl radical (OH) and the photodecomposition of Fe3+ complexes. The highest oxidizing power is achieved by combining Fe2+, Cu2+ and UVA light, because complexes of final acids with Cu2+ are more quickly degraded than those competitively formed with Fe3+. For all catalyzed methods, the initial mineralization rate is enhanced and the percent of degradation generally drops with increasing drug concentration. The paracetamol decay always follows a pseudo-first-order reaction with slightly higher rate constant for catalyzed systems than direct ozonation. Aromatic products such as hydroquinone, p-benzoquinone and 2-hydroxy-4-(N-acetyl)aminophenol are identified by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Acetamide is generated when hydroquinone is produced. These products are degraded to oxalic and oxamic acids as ultimate carboxylic acids, as detected by GC–MS and ion-exclusion chromatography. Oxalic acid is generated via glycolic, glyoxylic, tartronic, ketomalonic and maleic acids. While Fe3+-oxalato complexes are photolyzed by UVA light, Cu2+-oxalato, Fe3+-oxamato and Cu2+-oxamato complexes are oxidized with OH. NH4+ and NO3− ions are produced during mineralization.