Template-free synthesis and photocatalytic activity of {0 0 1}-facets exposed rhombohedral NaNbO3 microcrystals

Abstract

The synthesis and photocatalytic activity of rhombohedral sodium niobate powders by conventional template-free hydrothermal method from NaOH and different polymorphic types of Nb2O5 as starting materials with the presence of KOH as a mineralizer was reported in this work. The results showed that, interestingly, by using freshly-produced amorphous Nb2O5·xH2O, the rhombohedral NaNbO3 plate-like microcrystals with a high c-axis orientation and {0 0 1}-exposed basal facets can be received readily at temperature as low as 180 °C for 24 h. With commercialized monoclinic or orthorhombic Nb2O5 precursors, however, only the pure orthorhombic or a mixture of orthorhombic and rhombohedral NaNbO3 was obtained, respectively. The first-time photodegradation evaluation of methylene blue under UV irradiation for 2 h showed that this polymorphic type can be used as a novel photocatalyst with high photodegradation efficiency for both c-axis oriented, {0 0 1}-facets exposed sample (79%) and random oriented powders (66%). The enhanced photocatalytic activity of the c-axis oriented rhombohedral NaNbO3 microcrystals is ascribed to their {0 0 1}-exposed facets.