Highly crystalline niobium oxide converted from flux-grown K4Nb6O17 crystals

Abstract

Highly crystalline niobium oxide (Nb 2 O 5 ) nanotubes without defects such as bent and node were successfully prepared by a two-step process. The first step entails making high quality, layered K 4 Nb 6 O 17 crystals as a precursor material. In this study, well-developed, highly crystalline, layered K 4 Nb 6 O 17 crystals were readily grown by the rapid cooling of a KCl flux at a holding temperature of 800 C and a cooling rate of 300 C h À1 . The grown layered crystals of K 4 Nb 6 O 17 were transparentcolorless and had a median diameter of 530 nm. They were plate-like with well-developed faces. The second step is to transform the layered K 4 Nb 6 O 17 crystals into highly crystalline Nb 2 O 5 nanotubes. In order to make the nanotubes, an intercalation-exfoliation process using tetra(n-butyl)ammonium hydroxide (TBA + OH À ) aqueous solution was carried out, and highly crystalline Nb 2 O 5 nanotubes having a uniform diameter were successfully fabricated in this medhod. The crystallinity, uniformity and size (diameter and length) of nanotubes were significantly dependent on those of the precursor crystals. The flux-grown crystals, therefore, played a very important role in the nanotube fabrication. The average length and outer diameter were, respectively, about 100-500 nm and 15-25 nm. The photocatalytic properties of the layered K 4 Nb 6 O 17 crystals and the Nb 2 O 5 nanotubes were basically almost the same, although their Brunauer-Emmett-Teller (BET) surface areas were quite different from each other. The BET surface area of the Nb 2 O 5 nanotubes (108.71 m 2 g À1 ) was ca 20 times larger than that of the layered K 4 Nb 6 O 17 crystals (5.14 m 2 g À1 ). As compared with the flux-grown K 4 Nb 6 O 17 crystals, the Nb 2 O 5 nanotubes exhibited high photocatalytic activity for the photodegradation of trichloroethylene. The grown layered K 4 Nb 6 O 17 crystals and Nb 2 O 5 nanotubes were investigated thoroughly by means of field emission scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction analysis, energy-dispersive X-ray spectrometry, BET surface area and pore size distribution analysis, and spectrophotometry.

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

“…The K 4 Nb 6 O 17 crystals were found to have welldeveloped plate-like forms and relatively uniform size compared with those prepared by a solid-state reaction. In a previous study, the crystal phases were identified as K 4 Nb 6 O 17 based on the XRD pattern, and the diffraction intensity of the (0 4 0) plane was predominant [13]. These highly crystalline K 4 Nb 6 O 17 layers were exfoliated into individual nanosheets via the proton-exchange and exfoliation processes.…”

“…First, high-quality, layered K 4 Nb 6 O 17 crystals were grown by the cooling of a KCl flux. Detailed crystal growth procedures have been reported previously [13]. Next, NbO x nanosheets were prepared by exfoliation of the fluxgrown K 4 Nb 6 O 17 crystals.…”

“…Many researchers have studied various nanomaterials, such as TiO 2 , ZnO, Nb 2 O 5 , SnO 2 and carbon nanotubes [10][11][12][13][14][15]. Various techniques exist for fabricating nanomaterials, including chemical vapor deposition, sol-gel, hydrothermal, solvothermal and chemical treatment of layered materials (exfoliation) [11][12][13][14][15][16][17].…”

“…Various techniques exist for fabricating nanomaterials, including chemical vapor deposition, sol-gel, hydrothermal, solvothermal and chemical treatment of layered materials (exfoliation) [11][12][13][14][15][16][17]. In the exfoliation process, a variety of metal oxides with layered structures can be used as starting materials [13,16]. Among these oxides, potassium hexaniobate (K 4 Nb 6 O 17 ), an oxide semiconductor photocatalyst, has a layered structure consisting of negatively charged sheets based on NbO 6 octahedral units and K + ions between the sheets [18].…”

Highly Crystalline, Idiomorphic Na2Ti6O13 Whiskers Grown from a NaCl Flux at a Relatively Low Temperature

“…[3][4][5][6][7]9] Recently, various 1D metal oxide compounds (such as tungstates, molybdates, niobates, tantalates, and titanates) were synthesized to be high potential photocatalysts. [2][3][4][5][6]9,[11][12][13] Among them, sodium hexatitanate (Na 2 Ti 6 O 13 ) crystal has been studied as a photocatalyst for the degradation of toxic substances and the decomposition of pure water and as oxygen electrodes in potentiometric sensors for O 2 and CO 2 . [14,15] In addition, Na 2 Ti 6 O 13 forms the whisker structure, which is a needle-shaped single crystal with near theoretical strength due to its perfect geometry.…”