One-pot microwave-assisted synthesis of Zn0.9Fe0.1S photocatalyst and its performance for the removal of bisphenol A

Tailoring S-vacancy concentration changes the type of the defect and photocatalytic activity in ZFS

Defect engineering is crucial in the development of semiconductor catalyst activity. However, the influence of defect/vacancy density and states on catalysis remains vague. Thus, the optimized sulfur vacancy (S_V) state is achieved among Fe-ZnS models (ZFS) via a chemical etching strategy for photocatalytic degradation (PD). As the S_V concentration (ρS_V) increases, the predominant state of vacancies changes from isolated defects－a state to a combination of a state and vacancy clusters－e state, as verified by positron annihilation and X-ray absorption fine structure spectra. However, the two types of defect states activated the intrinsic activity of the crystal via radically different mechanisms and exerted different degrees of influence on PD activity, as revealed by first-principles calculations and quantitative structure-activity relationship. Our results suggest that the S_V activity is strongly influenced by its concentration in the ZFS crystal, while the vacancy concentration is not a control parameter for the PD activity, but a defect form. The underlying essence of atomic defects behavior affecting crystal catalytic activity at the atomic level is also revealed in this paper. Uncovering these structural relationships provide a theoretical basis for designing effective catalysts.

Photocatalytic oxidation of norfloxacin by Zn0.9Fe0.1S 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.

Characterization of visible-light photo-Fenton reactions using Fe-doped ZnS (Fex-ZnS) mesoporous microspheres

PNP was efficiently degraded by a Fe_6%-ZnS catalyst through photo-Fenton-like reactions under visible light irradiation.