Three narrow band-gap semiconductors modified Z-scheme photocatalysts, Er3+:Y3Al5O12@NiGa2O4/(NiS, CoS2 or MoS2)/Bi2Sn2O7, for enhanced solar-light photocatalytic conversions of nitrite and sulfite

Abstract

Three Z-scheme photocatalysts, Er3+:Y3Al5O12@NiGa2O4/NiS/Bi2Sn2O7, Er3+:Y3Al5O12@NiGa2O4/CoS2/Bi2Sn2O7 and Er3+:Y3Al5O12@NiGa2O4/MoS2/Bi2Sn2O7, are designed for synchronous conversions of nitrite and sulfite and fabricated by sol-hydrothermal and calcination methods. In these Z-scheme photocatalysts, three narrow band-gap semiconductors as “conductive ladder” are inserted between Er3+:Y3Al5O12@NiGa2O4 and Bi2Sn2O7 to accelerate the electron transfer from conduction band of Bi2Sn2O7 to valence band of NiGa2O4. Er3+:Y3Al5O12 as an up-conversion luminescence agent (from visible-light to ultraviolet-light) provides enough ultraviolet-light for satisfying the energy demand of wide band-gap NiGa2O4. The prepared photocatalysts are characterized by UV–vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), Fourier transform infrared (FT-IR) spectra and photoluminescence (PL) spectra. The photocatalytic activity of prepared photocatalysts is evaluated via conversions of nitrite and sulfite under simulated solar-light irradiation. The results show that the prepared Er3+:Y3Al5O12@NiGa2O4/NiS/Bi2Sn2O7, Er3+:Y3Al5O12@NiGa2O4/CoS2/Bi2Sn2O7 and Er3+:Y3Al5O12@NiGa2O4/MoS2/Bi2Sn2O7 composites exhibit the high and stable photocatalytic activity during the conversions of nitrite and sulfite. The highest conversion ratios (86.23% and 94.44%) for nitrite and sulfite can be obtained when the Er3+:Y3Al5O12@NiGa2O4/NiS/Bi2Sn2O7 is adopted as photocatalyst under simulated solar-light irradiation. Meanwhile, the effect of simulated solar-light irradiation time and corresponding reaction kinetics on photocatalytic conversions of nitrite and sulfite are also studied. Subsequently, the study of used times shows that the prepared Z-scheme photocatalysts can be effectively reused without an apparent inactivation on photocatalytic activity. These results demonstrate that the Er3+:Y3Al5O12@NiGa2O4/NiS/Bi2Sn2O7 is a potential Z-scheme photocatalyst to be used in actual conversions of nitrite and sulfite under solar-light irradiation.