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

Abstract 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.