Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)In photocatalysis, controversy still exists over as whether oxidation proceeds via primary oxidants, such as HO center dot radicals, positive holes, electrons, O-2(center dot)-radicals in the photodegradation process. The contribution of the main active species to the photocatalytic degradation of metoprolol (MET) using a solar simulator with Xenon lamp as irradiation source was examined by using different specific scavengers (formic acid, tert-butyl alcohol, rho-benzoquinone and oxygen). According to this, we also compared the effect on the generation of active species, in the MET degradation, of two types of TiO2 catalyst having different physical and chemical properties: pure TiO2 and TiO2 doped with 5% B (w/w), both synthesized by sol-gel method. The scavenger study indicates that HO center dot radicals are the dominant reactive species, contributing around 80% and to a lesser extent by the contribution of O-2(center dot)- radicals and holes in systems using TiO2 doped with 5% B (w/w). However, when pure TiO2 was used as catalyst, experiments carried out in rho-benzoquinone demonstrate that O-2(center dot)-radicals did not participate in the degradation mechanism of MET. Oxygen seems to play an important role during the observed degradation of MET. Additionally, the relation between the intermediates formed during the photocatalytic degradation with TiO2 doped 5% B (w/w) as catalyst, with addition of specific scavengers, was investigated and distinct degradation pathways have been proposed for each active species involved. By-products studies in the presence of scavengers were used as a diagnostic tool for the analysis of the photocatalytic mechanism and it was possible to prove that there is change in the reactions of the degradation process of MET when change the role of any active species generated on the surface of the catalyst. (C) 2016 Elsevier B.V. All rights reserved.194111122Brazilian funding agency CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)Brazilian funding agency CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior)Brazilian funding agency FUNDECT (Fundacao de Apoio ao Desenvolvimento do Ensino, Ciencia e Tecnologia do Estado de Mato Grosso do Sul)Brazilian funding agency INCT-EMA (Institute Nacional de Ciencia e Tecnologia de Estudos do Meio Ambiente)Ministry of Science and Innovation of Spain [CTQ2011-26258, CSD2007-00055]AGAUR-Generalitat de Catalunya [2009SGR 1466]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)