Particle size and shape modification of hydroxyapatite nanostructures synthesized via a complexing agent-assisted route

In this work, hydroxyapatite (HAP), Ca₁₀(PO₄)₆(OH)₂, nanostructures including nanorods, nanobundles and nanoparticles have been prepared via a simple precipitation method. In the present method, Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ were used as calcium and phosphorus precursors, respectively. Besides, the Schiff bases derived from 2-hydroxyacetophenone and different diamines were used as complexing agents for the in situ formation of Ca²⁺ complexes. The formation mechanism of 0-D and 1-D nanostructures of HAP was also considered. When the complexing agents could coordinate to the Ca²⁺ ions through N and O atoms to form the [CaN₂O₂]²⁺ complexes, HAP nanoparticles were generated. On the other hand, nanorods and nanobundles of HAP were obtained by forming the [CaN₂]²⁺ as well as [CaO₂]²⁺ complexes in the reaction solution. This work is the first successful synthesis of pure HAP nanostructures in the presence of Schiff bases instead of using the common surfactants. - Highlights: • HAP nanostructures have been prepared by a simple precipitation method. • To control shape and particle size of HAP, different Schiff bases were employed. • 0-D and 1-D HAP nanostructures have been formed by this method