Synthesis, characterization and synergistic photocatalytic properties of yeast-assisted composite La0.7Sr0.3MnO3/TiO2

Abstract

In order to identify a high-efficiency solar-light-driven magnetic photocatalyst, a series of powders such as perovskite La_0.7Sr_0.3MnO₃, yeast-assisted La_0.7Sr_0.3MnO₃ (Y-La_0.7Sr_0.3MnO₃), Y-La_0.7Sr_0.3MnO₃/TiO₂ and TiO₂ were prepared and characterized by photoluminescence spectroscopy (PL), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption–desorption (N₂-BET). The magnetic and photocatalytic properties of the powders were also investigated. The experimental results show that, when the content of TiO₂ in the composite Y-La_0.7Sr_0.3MnO₃/TiO₂ is 3.51 wt%, the Y-La_0.7Sr_0.3MnO₃/TiO₂ exhibits stronger absorption in the UV-Vis light region. A composite p–n heterojunction was formed and had the lowest photoluminescence (PL) intensity, indicating a higher separation efficiency of photogenerated charge carriers and an enhancement of the photocatalytic activity of the Y-La_0.7Sr_0.3MnO₃/TiO₂ composite. Under solar irradiation, Y-La_0.7Sr_0.3MnO₃/TiO₂ shows an obvious synergistic photocatalytic effect on orange (MO) wastewater, and the synergetic index is calculated to be 1.79. Furthermore, it still exhibits high photocatalytic activity after being reused 8 times. Moreover, Y-La_0.7Sr_0.3MnO₃/TiO₂ displays soft ferromagnetic behavior, has much higher magnetization and lower coercivity and remanence. Therefore, Y-La_0.7Sr_0.3MnO₃/TiO₂ can be recycled by an external magnetic field more easily and can be used repeatedly. Radical trapping experiments confirmed that the main reactive oxygen species (ROS) involved in the process of the photocatalytic reaction are the superoxide radical anion (˙O₂⁻), hole (h⁺), and hydroxyl radical (˙OH), and the sequence of the contributions of the ROS to the photocatalytic activity of the composite is ˙O₂⁻ > h⁺ > ˙OH. Furthermore, the photocatalytic mechanism of Y-La_0.7Sr_0.3MnO₃/TiO₂ is proposed in this work.