Enhancement of the photostability and visible photoactivity of ZnO photocatalyst used for reduction of Cr(VI) ions

Abstract

In this present study, the enhancement of ZnO stability toward photo-corrosion was conducted by incorporating onto natural zeolite (NZ), followed by improvement of the photocatalytic activity under visible light through doping Ag into ZnO/NZ. The prepared photocatalysts were characterized by using X-ray diffraction, ultraviolet diffuse reflection, surface area analyzer, and transmission electron microscope machines. The modified ZnO photocatalyst was examined for photoreduction of Cr(VI) under visible light through batch experiments. The research results reveal that ZnO was successfully incorporated in the zeolite, generating a larger surface area and higher photostability, thereby increasing its activity in the photoreduction of Cr(VI) under UV light. Furthermore, the doping Ag into the ZnO/NZ photocatalyst can narrow the band gap to 2.85 eV, greatly increasing the activity undervisible light. The enhancement of the ZnO–Ag/NZ activity under visible light in the photoreduction of Cr(VI) was controlled by Ag content, ZnO–Ag/NZ with medium Ag content (⁓10 mg g−1) showed the highest activity. The best photoreduction of Cr(VI) 10 mg L−1 in 20 mL of the solution, under visible light over ZnO–Ag/NZ containing 10 mg g−1 of Ag, could be reached within 10 h by 40 mg of the photocatalyst mass at pH 3.0, which is around ⁓60%.