Dégradation de produits pharmaceutiques photoinduite par les oxychlorures de bismuth et par les ions persulfate dans le compartiment aquatique

Abstract

This work is a contribution to the elimination of three pharmaceutical compounds from different therapeutic classes: carbamazepine (anti-epileptic), diclofenac (antiinflammatory) and venlafaxine (anti-depressor) by photochemical pathways in homogeneous and heterogeneous aqueous environment under simulated sunlight. In this study, we investigated the degradation of diclofenac and venlafaxine in homogeneous medium in the presence of persulfate ion activated by ferrous iron and light. The results have enabled us to deduce a very important efficiency of S2O82- /Fe2+/UV system to degrade these molecules in aqueous media. The complete disappearance of venlafaxine is reachedafter 45 minutes of irradiation and for a molar ratio Fe2+/S2O82- equal to 1/16 and a death rate of 86% in the case of diclofenac for a ratio of 1/1 after 180 minutes of irradiation. In heterogeneous phase, the disappearance of three molecules was performed in aqueous suspensions containing the single bismuth oxychloride and doped with silver chloride (BiOCl/AgCl) and bismuth molybdates (BiOCl/Bi2MoO6). The three types of BiOCl showed a very high adsorption efficiency in the case of diclofenac (about 4.17 mg adsorbed per g of BiOCl). However, the adsorption of the other two compounds revealed to be negligible. The results of the photocatalytic degradation have shown very clearly that bismuth oxychlorides contribute greatly to the elimination of selected pharmaceutical pollutants. In the case of carbamazepine, the best rate of disappearance is obtained in the presence of BiOCl/AgCl, while venlafaxine degrades very quickly in the presence of BiOCl. Identification of carbamazepine transformation products were used to determine the main routes of transformations such as hydroxylation reactions, epoxidation ring contraction and hydroxylation on the aromatic ring. For venlafaxine, formation of hydroxylated derivatives, desmethylvenlafaxine (ODV) and products resulting from the oxidation of a CH3 group of ether function were observed. The use of bismuth oxychlorides in the presence of the simulated sunlight in the degradation of carbamazepine and venlafaxine detected in natural waters showed a very high efficiency, which suggests the use of such systems in the treatment of wastewaters.