A Step toward Control of the Surface Structure of Biomimetic Hydroxyapatite Nanoparticles: Effect of Carboxylates on the {010} P-Rich/Ca-Rich Facets Ratio

Two types of biomimetic hydroxyapatite (HA) nanoparticles were prepared by acid-base neutralization reactions, using Ca(OH)(2) or Ca(CH3COO)(2) as a calcium source, to evaluate the effect of acetate anions on particle formation. High-resolution transmission electron microscopy observations provided evidence that in both cases nanoparticles are elongated along the c-axis, but to a more limited extent when prepared in the presence of acetates, and are mainly limited by {010} facets. IR spectra of nanoparticles containing adsorbed CO revealed that the actual termination of these are both of the {010}_Ca-rich and {010}_P-rich type, the latter being significantly more abundant for HA nanoparticles grown in the medium containing CH3COO species. Moreover, these nanoparticles appeared to be more sensitive toward aggregative stacking by thermal treatment, resulting in a significant decrease in specific surface area, while retaining the size of primary particles.