Conventional and photoinduced radioactive ¹³⁷Cs removal by adsorption on FeFe, CoFe, and NiFe Prussian blue analogues

Prussian blue analogues (PBAs) have received much attention as materials for radioactive Cs removal due to their affinity for adsorbing Cs⁺. In this study, we have synthesized PBAs using Ni(II), Co(II), and Fe(II) to prepare NiFe-PBA, CoFe-PBA, and FeFe-PBA and have added different quantities of sodium citrate as a stabilizing agent to adjust particle size and surface area. The PBAs also were composited with TiO₂, and the efficiency of Cs⁺ adsorption was compared in the dark and under UV-light irradiation. Larger surface areas and smaller particle sizes yield better Cs⁺ adsorption with NiFe-PBA, NiFe-TiO₂. FeFe-TiO₂ exhibits enhanced Cs⁺ adsorption under UV irradiation. The adsorption capacity of NiFe-PBA more than doubles from ~0.8 mmol·g⁻¹ in the dark to 1.7 mmol·g⁻¹ under UV light. The adsorption capacity of the NiFe-TiO₂ composite approximately triples from 0.45 mmol·g⁻¹ in the dark to 1.5 mmol·g⁻¹ under UV irradiation. Enhanced photoinduced adsorption on NiFe PBAs also is observed with radioactive ¹³⁷Cs⁺. The enhancement of Cs⁺ adsorption by NiFe PBAs is the result of a photoinduced charge transfer reaction within the NiFe PBA structure. This study is the first report of enhanced photoinduced removal of Cs⁺ using PBAs, which is an attractive strategy for the removal of the radioactive Cs⁺ from contaminated water.