Variable-valence metals catalyzed solid NaBiO 3 nanosheets for oxidative degradation of norfloxacin, ofloxacin and ciprofloxacin: Efficiency and mechanism

In this work, we report metal ions catalyzed oxidative degradation of three typical fluoroquinolones norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP) by using NaBiO nanosheets. It was found that variable-valence metal ions such as Cu , Fe , Mn , Ce , Ag and Co could obviously enhanced degradation of NOR, OFL and CIP by NaBiO . The pseudo-first-order kinetic rate for the degradation of 20 μmol L NOR by NaBiO (2 mmol L ) in the presence of 0.1 mmol L Cu , Fe , Mn , Ce , Ag and Co was 0.021, 0.084, 0.019, 0.23, 0.25 and 0.28 min , 2.1, 8.4, 19, 23, 25 and 28 times that by NaBiO without any metal ions. In comparison, Ca and Fe exhibited no obviously promotive or depressive effect for the degradation of NOR by NaBiO . Singlet oxygen ( O ) was suggested as the main reactive species from NaBiO in the presence of metal ions by electron spin resonance technology and radicals scavenging experiments. The evolution of NaBiO was tracked with scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that the metal ions were embedded into the crystal structure of NaBiO through ion-exchange between Na in NaBiO and metal ions. In the subsequent step, an electron transformation from lattice oxygen to Bi(V) sites was mediated by embedded variable-valence metal species, resulting in an enhanced generation of O from the crystal structure of NaBiO . These results can shed light on the application of NaBiO for the organic pollutant decontamination.