Influence of heat treatment on the phase transition of ZrMo2O8 and photocatalytic activity

ZrMo 2 O 7 (OH) 2 ·2H 2 O was obtained from ZrOCl 2 ·2H 2 O and Na 2 MoO 4 ·2H 2 O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo 2 O 7 (OH) 2 ·2H 2 O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo 2 O 7 (OH) 2 ·2H 2 O to orthorhombic LT-ZrMo 2 O 8 up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo 2 O 8 : cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo 2 O 8 above 450°C. The microstructure of the obtained trigonal (α) ZrMo 2 O 8 was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 µm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo 2 O 8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation.