FTIR Study on incorporation of CO2 into calcium hydroxyapatite

Calcium hydroxyapatite (CaHAP) particles were prepared by precipitation reactions of Ca(OH)2 and H3PO4 at different pH. Incorporation of CO2 into CaHAP during the preparation was investigated mainly by FTIR spectroscopy. The amount of CO32− ions contained in the formed CaHAP was increased by raising the solution pH. IR bands of the CO32− ions incorporated into CaHAP were assigned by means of CO2 adsorption. The 1414, 1447 and 1500 cm−1 bands were assignable to CO32− ions in OH− sites of the CaHAP crystals and the 1457 and 1550 cm−1 bands to CO32− ions in PO43− sites. This assignment is different from those in the literature. FTIR results demonstrated that the inclusion of CO32− ions in PO43− sites is maximum for CaHAP formed at pH 5.94 and that in OH− sites increases as the solution pH rises.