Photocatalytic oxidation of norfloxacin by Zn_0.9Fe_0.1S supported on Ni-foam under visible light irradiation

Norfloxacin (NOR) is an emerging antibiotics contaminant due to its high resistance to microbial degradation and natural weathering. In this study, Fe-doped ZnS photocatalyst (Zn_0.9Fe_0.1S) was deposited on nickel foam (Ni-foam) to improve photocatalytic activity under visible light irradiation. The mass ratio of Zn_0.9Fe_0.1S and Ni-foam was optimized to be 0.03 g catalyst versus per g Ni-foam (0.03 Zn_0.9Fe_0.1S/Ni-foam), which led to the highest removal rate of 95%. The optimal degradation condition for NOR over 0.03 Zn_0.9Fe_0.1S/Ni-foam was pH at 7.0, initial NOR concentration of 5 mg L⁻¹, and initial photocatalyst concentration of 11.7 g L⁻¹, with the highest first-order reaction rate constant of 0.025 min⁻¹ and mineralization rate of 63.1%. The NOR removal rate on 0.03 Zn_0.9Fe_0.1S/Ni-foam photocatalyst (95%) was approximately four times of that obtained on Zn_0.9Fe_0.1S photocatalyst (25%). The increased photocatalytic performance could be attributed to the function of Ni-foam as excellent electron collectors that provided efficient photoinduced charge separation from Zn_0.9Fe_0.1S. The reactive species responsible for the degradation of NOR were photo-generated holes, hydroxyl radical, and superoxide radicals. Nearly 90% of the photocatalytic efficiency was retained over seven cycles and the released metal ion concentrations were <0.3% of the total mass of photocatalyst, suggesting high stability of the photocatalyst during the photocatalytic reactions. The aqueous/solid mass transfer and intraparticle mass transfer for Zn_0.9Fe_0.1S/Ni-foam were not limiting factors for the degradation of NOR. Therefore the Zn_0.9Fe_0.1S/Ni-foam photocatalyst could be applied in the degradation of hazardous pollutants.