From aromatic rings to aliphatic compounds - Degradation of duloxetine with the use of visible light driven Z-scheme photocatalyst

The growing consumption of antidepressants, associated with their high chemical stability and low biodegradability, become a serious problem for aquatic environment. Many of their components are resistant to conventional water treatment technologies. The photocatalytic processes with the use of semiconductors becoming attractive methods of drugs degradation because the highly reactive species: electrons, holes, hydroxyl radicals (<middle dot>OH) and superoxide anion radicals (O-2(<middle dot>-)) generated under illumination may be involved directly or indirectly in decomposition of complicated organic molecules. In this work we have shown for the first time that Z-scheme photocatalyst, consisted of bismuth vanadate (BiVO4), graphitic-like carbon nitride (g-C3N4) and Au nanoparticles (Au NPs) as a charge transfer mediator, is very efficient in degradation of duloxetine (DLX). We performed the comprehensive evaluation focused not only on degradation rate, mechanism of photocatalytic process, but also identification of decomposition products and the pathways of DLX degradation. Due to application of the elaborated Z-scheme photocatalyst, the degradation rate constant was more than 2-3 times higher than that obtained for photolysis, but more important, the final compounds were mainly aliphatic products, formed by opening of aromatic rings. The chemical structure of the degradation products were determined with the use of HPLC and LC-MS. The toxicity of photoproducts with respect to water organisms was tested by means of Spirotox and Microtox assays. The Microtox test indicated that toxicity of the products after 6 h of the solution irradiation in the presence of Z-scheme photocatalyst is about 4 times lower than that after photolysis.