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. (c) 2006 Elsevier B.V. All rights reserved.