Synthetic hydroxyapatites doped with Zn(II) studied by X-ray diffraction, infrared, Raman and thermal analysis

• Zn doped hydroxyapatites have been synthesized by precipitation methods (pH 9, T=95 °C) in air.
• CaHap crystallizes in P21/b, while (Ca, Zn)Hap samples (showing Ca deficiency) were hexagonal, P63/m.
• Zn(II) could be introduced in the hexagonal apatite structure up to 9.1% in wt in the Ca2 site.
• Synthetic path allowed to obtain (Ca, Zn)Hap samples with small carbonate contain, closer to human bone composition.

Calcium hydroxyapatite (CaHap) formation when different amounts of Zn(II) are present in the mother solution has been investigated by atomic absorption, infrared and Raman spectroscopies, X-ray diffraction and thermal analysis (DTA and TG). The studied samples have been synthesized at T=95 °C and pH 9 in air. The analysis of the results have shown that the pure CaHap sample crystallizes in the monoclinic form P21/b. Concentrations up to 20% of Zn(II) in the mother solution, equivalent to smaller concentrations in solid (up to 9.1% in wt), favor the formation of the hexagonal apatite, P63/m, while Zn(II) concentrations higher than 20% in solution help an amorphous phase development where vibrational spectra indicated coexistence of two phases: an apatite and ZnNH4PO4·H2O. Infrared data of thermal treated samples endorse that HPO42− ion had not been incorporated in Zn(II) doped samples during the synthesis process. Present results also allow to conclude that Zn(II) cation exhibits a preference to occupy the Ca2 site of the apatite structure and induces water adsorption and a small quantity of CO32− cation incorporation, leading to formation of a less crystalline Ca deficient apatite.

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