SYNTHESIS AND CHARACTERIZATION OF Mn-DOPED CALCIUM HYDROXYAPATITE PARTICLES

Abstract

Colloidal manganese (Mn)-doped calcium hydroxyapatites (abbreviated as MnHap) were prepared by the coprecipitation method. The Mn/(Ca+Mn) atomic ratio in the solution (abbreviated as XMn) was varied from 0~0.30. The precipitated particles were characterized by various physicochemical analyses, i.e., TEM, XRD, N2 and H2O adsorptions, TG, FTIR, ICP-AES and XPS measurements. The MnHap particles were produced at 0.01≤XMn≤0.2. The calcium hydroxyapatite produced without Mn ions (XMn=0) was rod-like particles with 23 nm (width) x 55 nm (length). With increase in XMn up to 0.06, the particle width was decreased. The thickness of the rod-like particles produced at XMn≥0.08 was further decreased to ca. 3~5 nm. The spherical nano-particles with ca. 7 nm in diameter precipitated at XMn=0.3 were -TCP and amorphous particles of -MnOOH precursor. The particle color was varied from white to brown, dark-brown and pale-red. The ICP-AES measurement revealed that all the MnHap particles are cation-deficient with XMn values among 1.52~1.63. The lattice constants of c-axis was decreased with increase in XMn at XMn≥0.05 by incorporation of Mn(III) and Mn(IV) ions with smaller atomic radii, 0.072 and 0.053 nm, respectively, instead of Mn(II) ones (0.089 nm). The XPS measurement also revealed that there is no Mn(II) in the MnHap particles but they include both Mn(III) and Mn(IV) ions. The in vacuo IR measurements suggested that the incorporation of Mn ions increased the acidity of surface P-OH groups.