Effects of substituting Sr2+ and Ba2+ for Ca2+ on the structural properties and photocatalytic behaviors of CaIn2O4

MIn2O4 (M = Ca, Sr, Ba) semiconductors were synthesized by a simple solid-state reaction and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-visible spectrometer. The substitution effects of M2+ ion on the structural and photocatalytic properties for methylene blue (MB) dye degradation were first investigated systematically. It was found that when M goes from Ca to Ba, the crystal structure of these materials changed from orthorhombic to monoclinic structure, resulting in a systematic variation of the photophysical and photocatalytic properties of these materials. Among these semiconductors, CaIn2O4 showed the highest activity in a wide wavelength range of visible light up to 580 nm. The representative product of the MB degradation, SO4, was examined and indicated that MB was partially mineralized on MIn2O4 (M = Ca, Sr, Ba). The pH value of MB solution and the synthesized temperature of the photocatalyst were also found to have a significant effect on the photocatalytic activity of these materials. The possible reaction pathway was suggested.