Synthesis and characterisation of nanocrystalline hydroxyapatite from sea shells

Abstract

Nanocrystalline hydroxyapatite was synthesised by wet chemical reaction between sea shells (CaCO3) which were thermally converted to amorphous calcium oxide (CaO) and then to calcium hydroxide (Ca(OH)2) and reacted with phosphoric acid (H3PO4). Two experiments were conducted using wet chemical synthesis method. Hydroxyapatite (HA) was synthesised by slow addition of phosphoric acid in to calcium hydroxide (Ca(OH)2) without microwave irradiation and in another method; microwave irradiation was carried out after the reactants were combined in a similar manner. In both the experiments, the Ca:P ratio of 1.67 was maintained. pH of the solution was maintained at 9 to avoid the formation of calcium deficient apatites. The synthesised samples show XRD patterns corresponding to hydroxyapatite. The wet chemical process without microwave irradiation resulted in rod shaped HA particles of size 101 nm, whereas microwave irradiation of the solution after reaction also resulted in rod shaped HA but the particle size was only 68 nm as evidenced from XRD analyses. The TEM analyses reveal average aspect ratios of 3.37 ± 1.28 and 5.98 ± 2.28 for methods without and with microwave irradiation respectively.