Controllable synthesis of fluorapatite nanocrystals with various morphologies: Effects of pH value and chelating reagent

Fluorapatite (FHAp) nanocrystals with various morphologies were synthesized through a hydrothermal process in the presence of three different chelating reagents: citric acid (CA), ethylenediamine tetraacetate disodium salt (Na2EDTA), and CA/Na2EDTA mixed chelating reagent. The morphology of FHAp nanocrystal is highly dependent on the pH value and nature of chelating reagent. In the case of CA, two main morphologies of FHAp nanocrystals were observed as pH value was varied from 3.6 to 10.0; while one-dimensional (1D) FHAp nanocrystals with hexagonal structure were always produced in the presence of Na2EDTA under different pH values. When the two chelating reagents mentioned above were simultaneously used, tuning the pH value resulted in not only a morphology change but also a structural transformation due to the synergistic effect of the chelating reagents. A possible mechanism for the formation of FHAp nanocrystals with various morphologies was discussed.