Photocatalytic degradation of MB on MIn2O4 (M=alkali earth metal) under visible light: effects of crystal and electronic structure on the photocatalytic activity

MIn2O4 (M=alkali earth metal) semiconductors showed a novel photocatalytic activity for Methylene blue (MB) degradation under visible light irradiation. With increasing the ionic radius of M, the catalytic activity decreased monotonously. The possible reason for the activity change was discussed based on the effects of the radius of M ion on the crystal and electronic structure of the materials. XRD and Raman spectroscopic measurements showed that the crystal structure of BaIn2O4 is clearly different from CaIn2O4 and SrIn2O4. The density functional theory (DFT) with plane-wave basis was applied to calculate the density of state and band structure for MIn2O4 (M=Ca, Sr). The calculation revealed that the depth of M ionic core potential affects apparently the band structure. The results indicated that there is a correlation between the photocatalytic activity and the crystal and electronic structure of the photocatalysts.