Fabrication of highly crystalline NbO _x nanotube/cup-stacked CNT nanocomposites

Carbon nanotubes (CNTs) are promising catalyst supports for fuel cell applications. Metal oxide/CNT nanocomposites are also being studied for dye-sensitized solar-cell, photocatalyst, and sensor applications. The fabrication of nanocomposites consisting of highly crystalline NbO _x nanotubes and cup-stacked carbon nanotubes (CSCNTs) is reported herein. The CSCNTs were selected for the carbon materials because of their distinctive structure. The CSCNTs were photochemically treated with vacuum ultraviolet light, which increased the amount of oxygen-containing functional groups therein. NbO _x nanotubes with no defects were successfully prepared with the chemical treatment of highly crystalline, layered, flux-grown K ₄Nb ₆O ₁₇ crystals. First, K ₄Nb ₆O ₁₇ crystals were grown from a KCl flux at a holding temperature of 800 °C. Next, NbO _x nanosheets were prepared from the layered K ₄Nb ₆O ₁₇ crystals via a two-step exfoliation process, which consists of proton exchange in an acid solution and intercalation of the tetrabutylammonium ions. The NbO _x nanosheets were rolled up into nanotubes with diameters of about 20 nm and lengths of 100-500 nm on the surfaces of the CSCNTs; thus, unique and complex NbO _x/CSCNT nanocomposites were successfully fabricated.