Synthesis, modification and characterisation of K₄Nb₆O₁₇-type nanotubes

Potassium hexaniobate nanotubes have been fabricated from polycrystalline K4Nb6O17 at room temperature using the intercalating and exfoliating methods. These tubular materials were mainly characterized by using electron microscopy. Their structures were found to be multilayer crystalline nanotubes with interlayer spacings from 0.83 to 3.6 nm, depending on the intercalating molecules such as tetra(n-butyl)ammonium hydroxide (TBA(+)OH(-)) and alkylamines (CnH2n+1NH2) with different lengths of the alkyl chains. The number of layers in the wall is in the range of 3 to 8. The outer diameters of the nanotubes are distributed around 20 nm to 90 nm for different products obtained with different alkylamines and the lengths of the nanotubes range from a few hundred nanometers to several micrometers. Comprehensive structural characterization revealed that the majority hexaniobate nanotubes were formed by rolling the monolayer (-Nb6O17-)(n) sheets around the [100] zone axis of K4Nb6O17. Nanotubes with helical angles of larger than 10 degrees were also observed.