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Flumequine (FLU) is one of the most used fluoroquinolone antibiotics in intensive aquaculture, however, it has become a typical pollutant in water environment at present due to inappropriate use. Therefore, it is necessary to develop facile techniques for efficient degradation of FLU. In this work, three N-doped TiO2 photocatalysts were synthesized for degradation of FLU. The obtained photocatalysts were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum and UV-Vis diffuse reflection spectra (UV-Vis-DRS). The XRD and XPS results from NH4NO3-doped catalyst (TiO2/AN) confirmed that NO3^- ions were successfully incorporated into the lattice of TiO2. The TiO2/AN sample exhibited higher photocatalytic performance than other N-doped catalysts under simulated sunlight irradiation, and 100% removal efficiency of FLU was achieved after 4 hours of illumination. The photogenerated holes (h⁺) and hydroxyl radicals (^•OH) are main reactive species involved in the photocatalytic degradation of FLU. Eight intermediates for photocatalytic degradation of FLU were detected and their toxicities to aquatic organisms were predicted. This study might have important implications for further research on the removal of fluoroquinolone antibiotics in wastewater.

effect. Radical scavenger experiments indicated that hydroxyl radicals (HO • ) are prevailing active species responsible for SMP removal in UV/Co(II)/PMS system. The degradation of SMP in UV/Co(II)/PMS system was accomplished mainly by hydroxylation of the aromatic ring, extrusion of SO 2 , oxidation of NH 2 group, and N − S bond cleavage. Eight intermediates for SMP degradation were identified, and their toxicities to aquatic organisms were predicted by using the ECOSAR program based on the structure − activity relationships (SARs), which suggested that the chronic toxicities of SMP and its degradation intermediates are more significant than their acute toxicities. The present research indicates that UV/Co(II)/ PMS system is applicable for SMP degradation in aqueous solutions and may be helpful to understand the transformation behavior of SAs.

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