Solar Light Activation of Persulfate by TiO2/Fe2O3 Layered Composite Films for Degradation of Amoxicillin: Degradation Mechanism, Matrix Effects, and Toxicity Assessments

In this study, sandwich-type composites made of commercial TiO2-P25 and α-Fe2O3 are obtained by spin coating thin films with different layer configurations, namely: i) TiO2 layer over α-Fe2O3 (TiO2@α-Fe2O3), ii) α-Fe2O3 layer over TiO2 (α-Fe2O3@TiO2), and iii) physically mixed 50% (w/w) of TiO2/Fe2O3. Photocatalytic activity under simulated solar irradiation of the aforementioned composites and their pure components is investigated for the degradation of amoxicillin (AMX) in the presence and absence of persulfate (PS). In both cases, TiO2@α-Fe2O3 sandwich-type achieve the highest degradation rates of AMX and a marked effect of PS addition on the AMX degradation rate is noted. The influence of pH and PS concentration on AMX degradation rate is established by means of experimental design and response surface modeling. The AMX degradation pathway is studied by means of reactive oxygen species scavenging and identification of intermediates by liquid chromatography with tandem mass spectrometry. Their evolution is directly correlated with an increased toxicity assessed by Daphnia magna and Vibrio fischeri assays. Furthermore, biodegradability changes are correlated with the mineralization profile of AMX solution. The influence of water matrix constituents (Cl−, CO32−, NO3−, PO43− and Suwannee river natural organic matter) on AMX degradation is established as well.