Study of ²²³Ra uptake mechanism on hydroxyapatite and titanium dioxide nanoparticles as a function of pH

The mechanism of ²²³Ra uptake on hydroxyapatite and titanium dioxide nanoparticles was studied as a function of pH. Both materials are widely used in food industry and medicine. They offer properties suitable for labelling with medicinal radionuclides, particularly for targeted radionuclide therapy. The selected isotope, ²²³Ra, is an alpha emitter widely used in targeted alpha particle therapy due to high-dose delivery in very small tissue volume, nevertheless the results are applicable for any radium isotope including ²²⁶Ra. The study was performed in the pH range 4.5 to 12 for hydroxyapatite nanoparticles and 2 to 12 for titanium dioxide nanoparticles in Britton-Robinson buffer solution. Both nanomaterials at pH 6 and higher showed that over 95% of the radium has been sorbed. According to the applied chemical equilibrium model, the most important species playing a role in sorption on the edge-sites were RaCO₃, RaPO₄ ^-, RaHPO₄ and Ra(Ac^-)₂, and Ra²⁺ and RaH₂PO₄ ⁺ on layer-sites. All experiments were conducted under free air conditions and no negative impact of CO₂ was found. The surface complexation model was found suitable for describing radium uptake by the studied hydroxyapatite and titanium dioxide nanomaterials.