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Abstract
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Pharmaceuticals are polluting water streams even at low concentrations. In order to address this issue, photocatalysis with peroxydisulfate activation could be used to degrade pharmaceuticals in wastewater. Herein, photocatalytic activation of peroxydisulfate employing coal fly ash as waste–to–material was conducted, for the first time, for ciprofloxacin photodegradation. Initially, the ZnO@NiO heterostructure was obtained by hydrothermal reaction followed by its incorporation onto coal fly ash backbone in a suspension solution, then calcination was performed to obtain coal fly ash/ZnO@NiO. This photocatalyst was characterized by Fourier transform infrared spectroscopy (FTIR), X–ray diffraction (XRD), X–ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), high–resolution transmission electron microscopy (HR–TEM) and selected area (electron) diffraction (SAED). We found that, at pH = 7.0, the degradation efficiencies of ciprofloxacin by coal fly ash, ZnO, NiO, ZnO@NiO and coal fly ash/ZnO@NiO photocatalysts were 23.90, 59.23, 62.15, 74.50, and 94.3 % with degradation rate constant (k) of 0.0051, 0.0276, 0.0339. 0.0356 and 0.0486 min−1, respectively. Through the activation of peroxydisulfate, oxidative reactive species such as sulfate (SO4•−), hydroxyl (•OH) and superoxide radicals (•O2−) were evidenced by trapping tests and electron paramagnetic resonance (EPR). The degraded products of ciprofloxacin were identified by liquid chromatography coupled with mass spectrometry (LC–MS). Density functional theory (DFT) and Fukui index calculations provided insight about the reaction mechanism. Furthermore, the toxicity of the degradation products were estimated employing the toxicity estimation software tool (TEST) and quantitative structure activity relationship (QSAR) mathematical models.
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