*4.2. Peroxymonosulfate Activated by the Combination of Perovskites and Light Irradiation (PMS/Catalyst/Light)*

The combination of PMS activation by a perovskite and light irradiation has been applied for the degradation of different pollutants [107–109]. Rhodamine B (RhB) was used as model of organic pollutant for studying the PMS activation by a BiFeO3 microsphere in presence of visible light [107]. To confirm the contribution of the oxidizing radical species, ethanol (EtOH), t-butanol (t-BuOH) and 1,4-benzoquinone (BQ) were employed as radical scavengers. The results indicate that the main generated radical species during the activation of PMS by BiFeO3 were HO• and SO4•<sup>−</sup> radicals. However, the O2•<sup>−</sup> radicals, which are formed at longer reaction times, also play an important role in the degradation of RhB. Authors explained the reaction mechanism as follows. BiFeO3, with narrow band gap energy (1.92 eV), can be easily excited by visible light and the electrons and holes generated by action of light can react with Fe3+ and RhB, respectively. Simultaneously, Fe3+ and Fe2+ can also activate PMS to yield SO4•<sup>−</sup> and SO5•<sup>−</sup> radicals, which degrades RhB. About 63% of RhB was degraded in 40 min by BiFeO3/PMS/vis light system, in contrast to 43% of removal in the absence of perovskite. The catalyst was used in three consecutive cycle runs without significant loss of photocatalytic activity.

The combination of a cobalt perovskite (LaCoO3) with a photocatalyst (TiO2) in different molar ratios (Co:Ti = 0:1–1:0) was used to activate PMS for the oxidation of a mixture of four herbicides (metazachlor, tembotrione, tritosulfuron and ethofumesate) [108]. Same authors had previously tested LaCoO3/PMS system for the degradation of the same herbicides [103]. In general, LaCoO3-TiO2 with Co:Ti ratios in the range 0.1:1 to 0.5:1 showed a higher activity than the rest of solids tested, although a Co/Ti ratio of 0.1:1 was enough to reach enhanced degradation rates when compared to pristine titania or pure perovskite. The number of degraded herbicides by LaCoO3-TiO2/PMS system was 3.5–5 times higher in the presence of UVA-light and the reaction followed a second order kinetic, depending of concentration of both PMS and herbicides. As complete mineralization was not achieved, authors carried out studies to assess the potential phytotoxicity of the accumulated intermediates, concluding that all samples did show no phytotoxicity after 180 min of treatment for PMS concentrations ≥ 0.15 mM.

A double cobalt perovskite, Sr2CoFeO6, was tested in the mineralization of bisphenol F (BPF) in neutral medium by activation of PMS under UV irradiation [109]. Neither direct UV photolysis nor PMS alone degraded the BPF and Sr2CoFeO6 exhibited higher activity (75% of BPF degradation in 2 h) than the corresponding single perovskites, SrCoO3 (60%) and SrFeO3 (35%), caused probably by an accelerated reduction of Fe3+ in the presence of cobalt ions. UV irradiation also improved the

mineralization degree of BPF and values of TOC removal in 6 h increased from 65% to 90% when Sr2CoFeO6/PMS system was irradiated. As a novel aspect of this work, authors studied the influence of chemicals co-existing in the natural water matrix, such as humic acid and inorganic anions (Cl−, HCO3 − and CO3 2-), on the inhibition of degradation of bisphenol.
