Effect of Cu2+ ion on the structural stability of synthetic hydroxyapatite

Abstract

The reaction of synthetic hydroxyapatite, Ca₅(PO₄)₃OH(HAP), with Cu²⁺ ions is investigated by means of pH, pCu and pCa measurements as a function of the time and temperature (30, 40, 45 and 60 °C) and at different Cu²⁺:Ca²⁺ molar ratios in the range 0.01–1.07. The solid phases separated after different times of reaction were investigated with XRD and IR techniques. The Cu²⁺ ions give rise to an acidic solution and promote HAP dissolution; HAP does not incorporate the Cu²⁺ ions and a new phase corresponding to the mineral Cu₂(PO₄)OH (Libethenite) crystallizes quantitatively. In the course of the reaction, with the ratio Cu²⁺:Ca²⁺ in the range 0.1–1, the pH decreases owing to the release of phosphoric acid, whereas it increases for the ratio 0.01. At physiological ionic strength, obtained with NaCl, the solid phase containing Cu is again libethenite, but the process is notably accelerated.