Three-dimensional (3-D) Nb2O5 nanotube layers with honeycomb structures were successfully synthesized using polystyrene (PS) microsphere templates and NbOx nanocrystals. A densely packed monolayer of monodisperse PS microspheres was deposited onto a silica glass substrate using the LangmuirBlodgett film technique. NbOx nanocrystals were prepared via proton-exchange and exfoliation processes of highly crystalline, layered K4Nb6O17 crystals obtained by flux-growth. The 3-D crystal layers were fabricated by coating the pastes containing NbOx nanosheets onto the PS microsphere templates, followed by a heating treatment in an electric furnace. During the heating process, the PS microsphere templates were thermally decomposed, and the NbOx nanosheets were transformed into Nb2O5 nanotubes. As a result, transparent/colorless, nano-/micro-textured surfaces were formed on the silica glass substrates. The surface structure clearly varied depending on the nanosheet concentration of the pastes. The rough, solid surfaces modified with fluoroalkylsilane were found to be highly hydrophobic (water contact angle=148°). The 3-D nano-/micro-textures of the Nb 2O5-layered surfaces enhanced their hydrophobicity. The highly hydrophobic surfaces were converted to ultrahydrophilic surfaces by photocatalytic oxidation using Nb2O5 nanotube layers.
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