Characterization by Fourier transform infrared spectroscopy of hydroxyapatite co-doped with zinc and fluoride

Pure and Zn²⁺ and/or F⁻ doped hydroxyapatite (HA) were synthesized by the precipitation method and detection of ion incorporations into the HA structure was investigated by a non invasive Fourier transform infrared (FTIR) spectroscopic technique. The synthesized materials were sintered at 1100 °C for 1 h. The Zn²⁺ addition amount was kept constant at 2 mol% whereas F⁻ amount was changed. The weight fractions of the HA and CaO were calculated by Rietveld analysis by using GSAS. Co-doping of Zn²⁺ and F⁻ ions increased the stability of HA. A detailed analysis of FTIR spectroscopy was performed to observe whether HA structure was formed or not. The bands corresponding to the (PO₄³⁻) functional group and (OH⁻) functional group were observed. Moreover, the ion incorporation into the HA structure and the amount of the ions were analyzed by FTIR spectroscopy. The OH…F bands were observed at 711 cm⁻¹ and 3543 cm⁻¹. The Zn–O stretching band was observed at 3403 cm⁻¹ and 433 cm⁻¹. The area calculation under the OH…F bands and (OH⁻) stretching and librational modes of the bands revealed that as the F⁻ amount increased, the area under the bands at 711 cm⁻¹ and 3543 cm⁻¹ increased whereas the area under the (OH⁻) stretching and librational modes of the bands decreased due to the fact that F⁻ ion replaced with (OH⁻) ion in HA structure. All these results showed that Zn²⁺ and F⁻ ions were successfully incorporated into the HA structure. Moreover, the amount of F⁻ ions in the HA structure was successfully confirmed by determination of the area under the F⁻ and (OH⁻) related bands.