Coupling of heterogeneous photocatalysis and photosensitized oxidation for diclofenac degradation : role of the oxidant species

Abstract

The present work focused on the coupling of heterogeneous photocatalysis and photosensitized oxidation processes using TiO2 and ZnO as catalysts and dye perinaphthenone as a sensitizer. The influence of the dye sensitizer adsorbed onto catalyst surface was studied by Raman spectroscopy, UV-Vis diffuse reflectance, and FT-IR analysis. It was found that the sensitizer increases the absorbance of the catalysts in both region of the solar spectrum, ultraviolet and visible. The performance of the prepared materials was investigated on the decomposition of diclofenac (DCF) solution. DCF degradation was higher by using the coupled process compared with only photocatalysis and photosensitized oxidation. The analysis of the reactive oxygen species (ROS) suggested that the superoxide anion radical (O2•-2) was the predominant species that most intervenes in the DCF degradation followed by hydroxyl radical (OH•), whereas singlet oxygen O2 (1Δg) and triplet-excited sensitizer play a minor role in the degradation. The role of such oxidative species in the coupled process was described. Additionally, the analysis of the generated inorganic ions during the diclofenac degradation revealed that ClO−2, Cl−, NO−3, and NH+4, were produced which have an inhibitory effect on the degradation of the pharmaceutical compound.