Surface treatment of calcium hydroxyl and fluoroapatite by (NH4)6[P2W18O62]·14H2O polyoxometalate [P2W18]

The present paper details the surface modification of pure calcium hydroxyl and fluoroapatite (CaHAp and CaFAp) by grafting β-[P2W18O62]6− polyoxometalate (P2W18) with 1:1 and 1:5 mass ratio. The specific surface area (SSA) for pure materials, the X-ray diffraction pattern, the FTIR and the 31P MAS-NMR spectroscopy were used to compare the surface reactivity of CaHAp and CaFAp. These techniques show that the surface of hydroxyapatite is more reactive than that of the fluoroapatite. The reactivity is mainly related to the presence of ≡POH active sites, which are generated by the protonated form of phosphate group (HPO42−).