Hydrothermal synthesis of calcium hydroxyapatite nanorods in the presence of PVP

Calcium hydroxyphosphate (Ca₁₀(PO₄)₆(OH)₂, HAP) nanorods have been successfully synthesized by a simple and mild hydrothermal treatment in the presence of polyvinylpyrrolidone (PVP). A complex of calcium nitrate (Ca(NO₃)₂) and Na₂HPO₄ was used to supply the calcium and phosphate ions during the reactions. The synthesis of pure HAP nanorods was under near neutral condition. The morphology and structure of the samples were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy analysis. The nanorods were uniform with diameter of 20–25 nm and length ranging from several hundreds of nanometers to several micrometers. The influence of different experiment conditions, i.e., the PVP concentration, molar ratio of Ca²⁺ to HPO₄ ²⁻, reaction time, and temperature, on the morphology of the nanorods was investigated. The formation mechanism of rod-like HAP and effects of PVP on the crystal nucleation and growth have also been discussed.