Effects of hydrothermal temperature and time on hydrothermal synthesis of colloidal hydroxyapatite nanorods in the presence of sodium citrate.

In this paper, colloidal hydrophilic hydroxyapatite nanorods were synthesized in the presence of sodium citrate via thermal-decomplexing method. The influences of hydrothermal temperature and time on the synthesis of HA nanorods were characterized in terms of structure, size, morphology, and colloidal stability through TEM, XRD, zeta potential, DLS and long-term standing test. Results show that increasing hydrothermal temperature and prolonging hydrothermal time would evidently improve crystallinity and enlarge size of HA nanorods but decrease the colloidal stability of nanorods. It is worth noting that the effect of raising the hydrothermal temperature and time on diameter increase is far greater than that on length increase; meanwhile, the colloidal stability would be seriously deteriorated when the hydrothermal temperature is over 180 °C for 24 h or when the hydrothermal temperature is 150 °C for over 48 h, in these cases, dispersion of HA nanorods would apparently settle within 2 months. The origin responding to the results is that although the charge density of HA nanorods is not obviously affected, the dynamic diameters of HA particles increase greatly, which reduces colloidal stability of the dispersion. This work provides new insights into the role of hydrothermal temperature and time on tailoring morphology, crystallinity and colloidal stability of HA nanorods. Moreover, it would be helpful to optimize the experimental procedure both on scientific and industrial applications related to HA. For example, on the premise of satisfying the necessary requirements including crystallinity, size, morphology and colloid stability, it is feasible to compress the consumption of experimental time through raising the hydrothermal temperature, or vice versa.