Anisotropic growth of Ni3(BO3)2 nanowhiskers on nickel substrates and its application in the fabrication of superhydrophilic surfaces

Abstract

One-dimensional (1D) single-crystalline nickel borate [Ni₃(BO₃)₂] nanowhiskers were successfully grown on Ni substrates using the facile molten-salt method in air with MnO₂ as the agent. The products were characterized via X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The Ni₃(BO₃)₂ nanowhiskers that were synthesized at 950 °C, with diameters ranging from 120 to 250 nm and lengths of up to 50 μm, possessed an ultra-high aspect ratio (more than 100 : 1) and were found to grow along the [021] crystallographic direction. The effects of the growth temperature, holding time and amount of agent on the product morphology were investigated in detail. The products retained a nanowhisker morphology at growth temperatures below 1000 °C but transformed into microtubes when synthesized at 1050 °C. The oxygen liberated by the manganese oxides facilitated the nucleation of Ni₃(BO₃)₂ nanowhiskers. In addition, the surfaces coated with the Ni₃(BO₃)₂ nanowhiskers exhibited good superhydrophilic properties, and the wetting dynamics of such surfaces was investigated.