Effect of doped Sr on catalytic properties of La1‒xSrxMnO3 for RhB degradation

Abstract A series of La1‒xSrxMnO3 were prepared by sol-gel method and used to degrade rhodamine B (RhB) in water. All samples were characterized. The results showed that the degradation of RhB shows a strong dependency on the initial pH value of solution. Sr doping enhances the degradation ability of LaMnO3 for RhB in the 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 appears change. 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 make oxygen diffusion easier compared to the undoped samples.