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Visible light activation of persulfate and H2O2 by TiO2/Fe2O3 composites for degradation of amoxicillin: Degradation Mechanism, transformation pathways and toxicity assessment

The occurrence of trace amounts of antibiotics in various bodies of water was directly linked to the development of antibiotic resistant pathogens. Recently, Amoxicillin (AMX) was added on the second EU “watch list” based on the proposed European Decision 2018/840/EU. Its presence in drinking water samples and wastewater effluents is related to limited removal by common municipal wastewater treatment plants. As such, new remediation techniques must be applied to remove these substances. One of the promising solutions is the application of advanced oxidation technologies, e.g. visible light-assisted TiO2- based photocatalysis. In this study, TiO2/Fe2O3 nanocomposites were fabricated via facile impregnation method of commercial TiO2 (P25 Aeroxide) and different amounts iron (III) nitrate in ethanol solution. The as-prepared TiO2/Fe2O3 nanocomposites were inspected for their structure, morphology, composition, surface, electrochemical and optical properties by XRD, XPS, SEM/EDXS, BET, EIS, PL and DRS analysis methods yielding the following results: Anatase, rutile, and hematite crystalline structure of TiO2/Fe2O3 nanocomposites, extended visible light absorption of prepared composites and improved inhibition of photoelectron hole recombination rate. Photocatalytic activity under visible-light irradiation was assessed by treating targeted pharmaceutical pollutant AMX in the presence and absence of additional oxidants ; hydrogen peroxide (H2O2) and persulfate (S2O82-). In the absence of any oxidant, 5% (w/w) Fe2O3/TiO2 achieved the fastest degradation of AMX among all as-prepared composites. The influence of pH and persulfate salt on AMX degradation rate was establish by the means of statistical planning and response surface modeling. Results revealed optimum condition of [S2O82-]=1.874 mM and pH=4.808 ; and these conditions were also utilized in presence of H2O2 instead of persulfate. Photocatalysis+ persulfate, achieve fastest degradation of AMX possessing first order rate constant of 8.49 x 10-3 min-1, higher comparing to photocatalysis+ H2O2 (4.28 x 10-3 min-1), and photocatalyis alone(7.59 x 10-4 min-1). AMX degradation pathway was established and formed intermediates evolution/degradation were correlated with the changes in toxicity toward Vibrio fischeri bioassay, while Reactive Oxygen Species (ROS) scavenging was also employed for further understanding of AMX degradation mechanism.

Degradation, amoxicilin, transformation pathways, toxicity assessment

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