Facile fabrication of nickel phosphate nanotubes via a urea-assisted hydrothermal route

Nickel phosphate nanotubes (NiPO-NTs) were obtained via a simple urea-assisted hydrothermal route in the absence of organic surfactant as the structure-directing agent. The material possessed an urchin-shaped structure, and the one dimensional nanotubes were directed outward around the spheres. SEM and TEM observations indicated that the NiPO-NTs had an outer diameter of about 7.0 nm, inner diameter of 4.0 nm, and length of around 0.75 μm. It is found that the formation of NiPO-NTs was determined by the pH value and its changing rate, which were controlled by urea hydrolysis. Accordingly, a possible mechanism of nanotube formation was proposed. The synthesized NiPO-NTs showed high catalytic performance in the epoxidation of cyclohexene.