Fabrication and photocatalytic performance of highly crystalline nanosheets derived from flux-grown KNb3O8 crystals

Potassium triniobate (KNb3O8), which is an oxide semiconductor photocatalyst, has a layered structure consisting of negatively charged sheets of linked NbO6 octahedral units and K+ ions between the sheets. We report the flux growth of KNb3O8 crystals and their application for the photocatalytic decomposition of organic thin films. First, high quality, idiomorphic KNb3O8 crystals were successfully grown by cooling a KCl flux. Transparent-colorless KNb3O8 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 NbOx nanosheets were successfully prepared via a two-step process, that is, proton exchange and subsequent exfoliation of the KNb3O8 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.