Environmentally Friendly Growth and Characterization of Photocatalytic K2Nb8O21 Crystals

Idiomorphic and prismatic K2Nb8O21 crystals were successfully grown by the isothermal evaporation of KCl flux. On the basis of their aspect ratio, the crystals were divided into two morphological types, that is, whisker (needle) and prism. Growth was induced by heating mixtures of KCl and Nb2O5 at 1100 °C for 60 h followed by quenching in a furnace with the electric power turned off. The obtained K2Nb8O21 crystals were colorless and transparent. Whiskers having an average size of approximately 160×11.1 µm were grown from high-temperature solutions containing Nb at 1–30 mol %. The grown crystals had roundish or prismatic one-dimensional forms, and their surfaces were very smooth. Their generation and sizes were obviously dependent on the Nb concentration of the starting mixtures. The K2Nb8O21 crystals exhibited high activity for dye adsorption and degradation. The degradation occurred via a photocatalytic process under ultraviolet light irradiation.