Hydrothermal synthesis and photocatalytic properties of and ( and K)

Alkali tantalates ATaO3 and alkali niobates ANbO3 ( A = Na and K) powders with perovskite structure were synthesized by the hydrothermal method. The band gaps estimated of niobates are smaller than those of tantalates. This factor contributes to red shift in absorbance from tantalates to niobates in diffuse reflection spectra. Their photocatalytic activities were investigated. The order of the activities is NaTaO 3 ⪢ KTaO 3 > NaNbO 3 > KNbO 3 . The cubic crystalline structure of NaTaO3 powder shows the highest photocatalytic activity. The effect of the amount of NaOH in the NaTaO3 preparation upon the photocatalytic activity was studied. Scanning electron microscopy indicates that the appropriate excess alkali in the NaTaO3 preparation can improve the crystallinity of NaTaO3 and suppress formation of defects in NaTaO3 powder, resulting in an increase in the photocatalytic activity.