Phototransformation of model micropollutants in water samples by photocatalytic singlet oxygen production in heterogeneous medium

The combination of photosensitized production of singlet oxygen (1O2) and solar energy is gaining increasing interest, as disinfection and water remediation technology. In this work, we have investigated the elimination of three common micropollutants such as, ibuprofen, paracetamol and bisphenol A using a photosensitizing material consisting of tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) chloride, immobilized in a porous poly(dimethylsiloxane) inert support. The influence of variables such as, the radiation dose, hydrophobicity, ionization state of the micropollutant and water composition has been discussed. The process has led to effective removal of ibuprofen and bisphenol A in ultra-pure water with conversion rates of 100% and 80%, respectively; whereas elimination of paracetamol was rather limited (35%). Experiments performed in natural water samples have evidenced reduced effectiveness of the 1O2 photosensitized degradation process, due to water matrix composition. Thus, conversion rates of ibuprofen may decrease until 20% (depending on the water matrix) when other inorganic anions (e.g. bicarbonate, sulphate, etc.) are present in the water samples. On the other hand, identification of the main transformation products of ibuprofen and bisphenol A has been achieved by the use of ultra-high-performance liquid chromatography-time-of-flight mass spectrometry (UHPLC/QTOF-MS). The phototransformation pathway of ibuprofen includes hydroxylation, decarboxylation and demethylation processes, while the degradation of bisphenol A mainly proceeded via fragmentation of the isopropylidene bridge between the two phenyl groups leading to different para substituted phenolic compounds.