Fabrication and photocatalytic performance of highly crystalline nanosheets derived from flux-grown KNb ₃O ₈ crystals

Potassium triniobate (KNb ₃O ₈), which is an oxide semiconductor photocatalyst, has a layered structure consisting of negatively charged sheets of linked NbO ₆ octahedral units and K ⁺ ions between the sheets. We report the flux growth of KNb ₃O ₈ crystals and their application for the photocatalytic decomposition of organic thin films. First, high quality, idiomorphic KNb ₃O ₈ crystals were successfully grown by cooling a KCl flux. Transparent-colorless KNb ₃O ₈ crystals had relatively uniform sizes and shapes. The size, morphology and phase of the grown crystals were dependent on the holding temperature and solute concentration. Next, highly crystalline NbO _x nanosheets were successfully prepared via a two-step process, that is, proton exchange and subsequent exfoliation of the KNb ₃O ₈ crystals. Finally, the nanosheet layer spin-coated on a silica glass was used for photodegradation of hydrophobic organosilane thin films. The fabricated layer was colorless and transparent, and it absorbed ultraviolet (UV) light with a wavelength less than 350 nm. When organosilane thin films were placed in contact with the nanosheet layer and UV light was irradiated to the organosilane thin films through the transparent nanosheet layer, the wettability of organosilane layers was drastically converted from hydrophobic to ultrahydrophilic. The highly crystalline nanosheet layer was found to exhibit excellent photocatalytic properties.