Abstract
We have studied Mg2+ adsorption on hydroxyapatite (HAp) nanocrystals and constructed its isotherm at equilibrium cation concentrations in the range 0–0.35 mol/L. For a number of samples, corresponding to characteristic points in the adsorption isotherm, the composition and the oxidation state of the elements present on the surface of the sorbent have been determined by X-ray photoelectron spectroscopy (XPS). The surface magnesium concentration determined by XPS, which detects only ions in a surface layer a few nanometers in thickness, has been found to be considerably lower than the total amount of cations in the solid phase, evaluated from the experimentally determined adsorption isotherm. We assume that, during the sorption process, some of the magnesium ions substitute for calcium ions in the bulk of the HAp and some adsorb in the form of MgCl2. The results obtained in this study constitute a fundamental basis for practical solutions in designing integrated medications based on HAp with magnesium.
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