Effect of incorporated transition metals on the adsorption mechanisms of radioactive cesium in Prussian blue analogs

Extensive efforts were made to remove radioactive cesium (¹³⁷Cs) from the environment, with Prussian blue analogs (PBAs) emerging as highly selective and efficient materials for ¹³⁷Cs removal. However, limited studies systematically compared Cs⁺ adsorption across different transition metals in PBA. This study investigates the influence of the choice of transition metal ion (Co, Cu, Fe, Mn, Ni, Zn) on Cs⁺ adsorption mechanisms and efficiency. PBAs were synthesized and characterized based on their specific surface area, ion exchange capacity, lattice parameter, and defect sites (as indicated by water molecule content). Cs⁺ adsorption mechanisms varied significantly with transition metals. In CoFe and FeFe PBAs, ion exchange with K⁺ dominated, while CuFe and MnFe PBAs, with more defect sites primarily used ion exchange between H⁺ and Cs⁺. NiFe and ZnFe exhibited enhanced Cs⁺ adsorption under light irradiation, likely due to their light-absorbing properties facilitating a reduction reaction. The Langmuir adsorption isotherm was applied to model the adsorption behavior, confirming that each performance of PBA depends on the transition metal used. These findings suggest that PBAs with various transition metals can efficiently remove ¹³⁷Cs under diverse environmental conditions by using distinct adsorption mechanisms.