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

Abstract

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.