The degradation of paracetamol was studied by sonolysis, photocatalysis and sonophotocatalysis in the presence of homogeneous (Fe3+) and heterogeneous (TiO2) photocatalysts using 213 kHz ultrasound (US). The degradation rates obtained for sonolysis, photocatalysis and sonophotocatalysis using TiO2 (1 g/L) were about 8.3, 30.2 and 40.2 x 10(-7) M min(-1), respectively. In the case of reactions involving Fe3+, the degradation rates obtained were 26.1, 18.6 and 46.7 x 10(-7) M min(-1) for US + Fe3+, UV + Fe3+ and US + UV + Fe3+, respectively. The above results indicate that the combination of sonolysis with photocatalysis (TiO2 or Fe3+) results in an additive effect from combining the two processes, with a synergy index value of similar to 1.0. There was no synergistic effect in total organic carbon (TOC) removal in sonophotocatalysis with TiO2, whereas the mineralization process was synergistic when sonophotolysis was carried out in the presence of Fe3+. Further studies with electrospray mass spectrometry analysis revealed the formation of a hydroxylated derivative of paracetamol during sonolysis. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.