Effects of Substituting Sr²⁺ and Ba²⁺ for Ca²⁺on the Structural Properties and Photocatalytic Behaviors of CaIn₂O₄

MIn 2 O 4 (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 M 2+ 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, CaIn 2 O 4 showed the highest activity in a wide wavelength range of visible light up to 580 nm. The representative product of the MB degradation, SO 4 2 -, was examined and indicated that MB was partially mineralized on MIn 2 O 4 (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.