Control of one-dimensional hydroxyapatite nanocrystals at mild conditions: organic additive effects

One-dimensional hydroxyapatite (HAp, Ca₁₀(PO4)₆(OH)₂) nanocrystals have been successfully synthesised via the simple precipitation-hydrolysis process on mild solution conditions. At the first precipitation step, the precursor samples of monetite phase CaHPO₄ were prepared with three kinds of organic additives. The results of X-ray diffraction (XRD) patterns show that the structure and crystallinity of CaHPO₄ prepared with the different organic additives are different, which indicates that the organic additives exert influence on the crystal growth of CaHPO₄. During the second process, the HAp nanocrystals with high aspect ratio grew up under a high pH condition. The XRD patterns show that the preference of every nanocrystal growth is the (002) plane. Transmission electron microscopy micrographs indicate that the HAp nanocrystals were affected by the reaction temperature and the pH values of the solution. The organic additives influenced the aspect ratio of HAp nanocrystals, and Fourier transform infrared spectra show that the organic additives were completely dissolved in the aqueous system. This indicates that the organic additives affected the formation of nucleation and growth of HAp nanocrystals, and the influence gradually decreased with the extension of the hydrolysis time, until the organic additives were detached from the HAp crystals.