Investigation of radionuclide 60Co(II) binding to TiO2 by batch technique, surface complexation model and DFT calculations

The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment. Herein, the interaction of ⁶⁰Co(II) with TiO₂ in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory (DFT) calculations. The batch experimental results showed that the adsorption of ⁶⁰Co(II) was dependent on pH and independent of ionic strength, indicating the formation of inner-sphere surface complexes on TiO₂ surfaces. The results of surface complexation models and DFT calculations indicated that the surface species of ⁶⁰Co(II) adsorbed on TiO₂ followed the trend: B structure (i.e., ⁶⁰Co(II) was linked to one bridge oxygen site) was the dominant surface species at low pH, and TT structure (i.e., ⁶⁰Co(II) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values. These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed ⁶⁰Co(II) at the molecular level at the TiO₂/water interfaces, as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.