Spectroscopic investigation of arsenate and selenate incorporation into hydroxylapatite

Abstract

The mechanism(s) of arsenate and selenate incorporation into hydroxylapatite (HAP) using extended Xray absorption fine structure (EXAFS) spectroscopy was investigated for As- and Se-doped HAP samples with concentrations between 200 and 2500 ppm. EXAFS data on As and Se K-edges have shown similar local coordination environments and are similar to that of P in HAP, suggesting the substitution of arsenate or selenate tetrahedra on the phosphate sites. EXAFS best-fitting for As-doped samples shows that the first shell is fitted with approximately 4 O atoms at similar to 1.68 angstrom, showing As(V) in tetrahedral coordination, and Se K-edge EXAFS data are characterized by the backscattering contributions an oxygen shell at similar to 1.2 angstrom in the Fourier transform, which can be fit with similar to 4 O atoms at similar to 1.65 +/- 0.01 angstrom. This is characteristic of Se-O distances in SeO(4) tetrahedron. These findings suggest that arsenate and selenate substitute for phosphate groups with local distortions during the incorporation of these metals into the structure of HAP. (C) 2009 Elsevier B.V. All rights reserved.