Surface and structural characterization of Cu-exchanged hydroxyapatites and their application in H2O2 electrocatalytic reduction

• High surface area hydroxyapatite (HA) functionalized with copper at different loadings. • Structural modifications after Cu-exchange investigated combining XRD and ss-NMR. • Surface Ca 2 + substitution by Cu 2 + monitored by IR spectroscopy of adsorbed CO. • Cu-HA tested for the first time in H 2 O 2 electrochemical reduction. • Electrocatalytic activity towards H 2 O 2 increases markedly at higher Cu loadings. We report on the preparation of hydroxyapatite (HA) nanoparticles with high specific surface area, terminated with calcium-rich {0 1 0} facets, and their subsequent surface functionalization with copper by cationic exchange with copper nitrate solutions at different concentrations. Elemental analysis highlighted a progressive increase of the amount of copper incorporated into the HA, reaching a maximum of ∼ 7 wt%. A combined X-ray diffraction and solid-state NMR investigation showed no significant structural differences after the Cu functionalization, confirming that the copper exchange occurs mainly at the surface until saturation and, for the higher Cu concentrations, also in the sub-surface/bulk layers of the material, without altering the HA crystal structure. The gradual substitution of surface Ca 2+ by Cu 2+ was studied also by IR spectroscopy using carbon monoxide as probe molecule. Finally, we assessed the catalytic activity of the materials testing the electrochemical reduction of H 2 O 2 by cyclic voltammetry. We observed a progressive increase in catalytic activity correlated with the amount of Cu, suggesting the possible application of copper-exchanged HA as electrochemical H 2 O 2 sensors.