Assembly of monoclinic ZrO2 nanorods: formation mechanism and crystal phase control

The crystal phase and shape of ZrO2 nanoparticles were finely tuned by mediating the hydrolysis rate of zirconium cations and using sodium oleate as the capping agent under hydrothermal conditions. Pure monoclinic ZrO2 nanorods with a diameter of similar to 3 nm and length of 30-40 nm were obtained at a lower pH value of 9.4; whereas monodispersed ZrO2 particles of similar to 4 nm with mixed monoclinic and tetragonal phases were formed at a higher pH value of 11.4. Their formation mechanism was discussed in terms of the hydrolysis rate of the zirconium cations and the structure-directing role of the oleate species. The monoclinic ZrO2 nanorods showed prominent blue-green fluorescence under excitation by an ultraviolet lamp (365 nm) because of the presence of a large number of oxygen-vacancy defects.