Morphological control of synthetic Ni3Si2O5(OH)4 nanotubes in an alkaline hydrothermal environment

Hydrothermal synthesis of nickel silicate nanotubes has been systematically studied in aqueous alkaline environments at 195 degrees C by varying the Ni/Si molar ratio of the solid materials and the concentration of dissolved NaOH in the precursor suspension. A Ni/Si ratio of 1.5 is ideal for the formation of pure multiwalled nanotubes having a characteristic inner diameter of 10 nm and a typical length of 90-300 nm. The nanotubes have straight walls with a high degree of crystallinity. At lower Ni/Si ratios small nanosheets are formed, with a nickel-deficient layered structure, and nanosheets of beta-Ni(OH)(2) are formed in addition to nanotubes at Ni/Si >1.5. Nanotubes are formed over a wide range of NaOH concentration, 2-10 wt%, but the NaOH concentration has a large effect on the aspect ratio, with much longer tubes (almost 300 nm) being formed at 10 wt% NaOH. This result has interesting implications for the design of nickel silicate nanostructures for use in applications such as lithium batteries, mesoporous catalyst supports and reinforced polymer composites.