The effect of pH on the morphological transformation of nanocrystalline hydroxyapatite during wet chemical synthesis

Hydroxyapatite (HAP) is a prominent bioceramic, notably used in the biomedical field. Fundamental properties of the biomaterials are size and shape dependent. High purity, morphology, and size are the main properties to be addressed for clinical application. Therefore, this work reports the effect of pH and annealing temperature on HAP's shape, crystallite, and particle size. Morphologically different hydroxyapatite nanostructures are synthesised by wet chemical precipitation. Furthermore, the pH of the solution varied from 6 to 11, and the calcination temperature was changed from 300 & DEG;C to 900 & DEG;C. Various morphologies of hydroxyapatite nanopowders, such as spherical, distorted boxes, aggregated rods, flakes, and beaded rods-like clusters, have been achieved. Moreover, small crystallite and particle sizes of HAP were observed in an alkaline medium. The spherical-shaped hydroxyapatite with particle size between 21.54 nm to 78.89 nm was obtained at pH 11. In contrast, beaded rods, nanorods, nanoflakes and distorted boxes-like morphology with an average particle size between 28.28 nm and 202.43 nm were successfully synthesised in neutral to moderately basic pH. Moreover, the crystallite size between 8.4 to 77.7 nm was achieved by changing the pH and annealing temperature. The synthesised products were analysed by XRD, FTIR, Raman spectroscopy and SEM to determine the crystallinity, purity, chemical composition, vibrational modes, morphology, and particle size.

Automated summary

This study successfully synthesized hydroxyapatite nanostructures with different morphologies through wet chemical precipitation, and investigated the effects of pH and annealing temperature on their shape, crystallite, and particle size.