Fourier-transform infrared study of CO2 adsorption on non-stoichiometric strontium hydroxyapatites

Abstract

The surface of colloidal strontium hydroxyapatite (SrHAP) particles with different Sr : P molar ratios from 1.51 to 1.71 has been characterized by means of an FTNIR spectrometer. The IR spectra of the Sr-deficient SrHAP gave rise to 3684, 3662 and 3640 cm^–1 bands, which are assigned to surface P—OH groups. The Sr-rich SrHAP exhibited a band at 3710 cm^–1 in addition to the three surface P—OH bands. The amount of irreversible adsorption of CO₂ on the Sr-rich SrHAP was larger than that on the Sr-deficient samples. The change in the spectra after CO₂ adsorption by the sample proved that the irreversible adsorption sites of CO₂ on the Sr-deficient SrHAP are the less-acidic surface P—OH groups giving the 3640 cm^–1 band and those on the Sr-rich SrHAP are surface OH^– ions. The mechanism of irreversible adsorption of CO₂ is discussed.