Photocatalytic activities of M₂Sb₂O₇ (M = Ca, Sr) for degrading methyl orange

M₂Sb₂O₇ (M = Ca, Sr) photocatalysts were synthesized by a solid state reaction method. The results concerning methyl orange (MO) photodecomposition generally show that the catalytic efficiency of Sr₂Sb₂O₇ is much higher than that of Ca₂Sb₂O₇ under UV light irradiation. The more open structure in Sr₂Sb₂O₇ is suggested to be responsible for its higher photocatalytic activity. In the investigation on pH-dependent photocatalysis over Sr₂Sb₂O₇ catalyst, the pseudo-first reaction rate k was found to be increased by about six times as the pH value decreases from 6.88 to 3.91. We believe that the decolorization of MO in neutral or alkaline conditions is primarily through a photocatalytic process, while the MO photosensitization and photolysis mechanisms play more important roles in acidic conditions.