Unique three-dimensional nano-/micro-textured surfaces consisting of highly crystalline Nb2O5 nanotubes

Abstract Three-dimensional (3-D) Nb 2 O 5 nanotube layers with honeycomb structures were successfully synthesized using polystyrene (PS) microsphere templates and NbO x nanocrystals. A densely packed monolayer of monodisperse PS microspheres was deposited onto a silica glass substrate using the Langmuir–Blodgett film technique. NbO x nanocrystals were prepared via proton-exchange and exfoliation processes of highly crystalline, layered K 4 Nb 6 O 17 crystals obtained by flux-growth. The 3-D crystal layers were fabricated by coating the pastes containing NbO x 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 NbO x nanosheets were transformed into Nb 2 O 5 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 2 O 5 -layered surfaces enhanced their hydrophobicity. The highly hydrophobic surfaces were converted to ultrahydrophilic surfaces by photocatalytic oxidation using Nb 2 O 5 nanotube layers.