Substitution of Hydrogen Phosphate (HPO42-) Ions of OCP Hydrated Layers by Dicarboxylate Ions in Hexagonal HAP Nanocrystallites

Abstract

In apatite chemistry, the OCP (octacalcium phosphate) crystals are apatite based and having a hydrated layers which is used in producing of needle or plate-shaped HAP (hydroxyapatite) nanocrystals. Although, the crystals is prepared by a dissolution precipitation reaction. These reaction led to a hexagonal HAP nanocrystals formation under hydrothermal condition from OCP at 180°C for 3 hours with pH of solution adjusted to 5.5 and incorporating dicarboxylate e.g. succinate (OOC.(CH2)2.COO)2- ions having Ca/P molar ratio is expected to be 1.56±0.02, where the morphology of OCP are retained. The hydrogen phosphate (HPO42-) ions in the hydrated layers of OCP are substituted by succinate ions during the incorporation of succinate ions in OCP crystals. Because the HAP crystal system is hexagonal, the crystalline size in the longitudinal direction of various (a,b,c) axes varies depending on the thickness of the laminated plate-shaped HAP crystals. Here, their size as perpendicular to the (100) plane which is calculated by introducing of Scherrer’s equation, D100 = K\(\lambda\)/(\(\beta\) cos\(\theta\)). The organically modified OCP which generated to HAP have unique nanostructure with micrometer thickness are characterized by using of SEM, FTIR and X-ray diffraction analysis.