Effect of doped strontium on catalytic properties of La1‒xSrxMnO3 for rhodamine B degradation

Abstract

A series of La1‒xSrxMnO3 samples were prepared by sol–gel method and used to degrade rhodamine B (RhB) in water. All samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, temperature-programmed reduction of H2 (H2-TPR) and temperature-programmed desorption of O2 (O2-TPD). The results show that the degradation of RhB is highly dependent on the initial pH value of solution. Sr doping enhances the degradation ability of LaMnO3 for RhB in the time range of 0–40 min under a strong acidic environment, but all samples exhibit similar degradation rate from 40 to 60 min. In La0.7Sr0.3MnO3–RhB reaction system, there are two different degradation pathways, including N-de-ethylation, chromophore cleavage, ring-opening and mineralization. La1‒xSrxMnO3 (x ≤ 0.3) has the perovskite structure of La–Mn oxides, while La0.6Sr0.4MnO3 exhibits a Sr0.4MnLa0.6O2.98 perovskite phase. Sr doping leads to distortion of rhombohedral crystal structure and increases the relative content of Mn4+. The perovskite structure is stable in strong acidic environment during RhB degradation, but the relative content of Mn4+ and Mn3+ on the material surface changes. Sr doped LaMnO3 achieves specific surface area of 58.8 m2/g and total pore volume of 0.152 cm3/g. Furthermore, Sr2+ doping improves redox properties of La–Mn oxides, and the presence of defects makes oxygen diffusion easier compared with the undoped samples.