Enhancement of cesium adsorption on Prussian blue by TiO₂ photocatalysis: Effect of the TiO₂/PB ratio

The expanding nuclear industry requires the effective elimination of radioactive wastes generated by nuclear power plant operation and nuclear disasters. Herein, we demonstrate that TiO₂ photocatalysis can significantly increase the Cs⁺ adsorption capacity of Prussian blue (PB), revealing that in PB/TiO₂ composites, Cs⁺ ions are adsorbed exclusively on PB. Cs⁺ adsorption capacity equaled 0.09 mmol g_composite⁻¹ (in the dark) and 0.75 mmol g_composite⁻¹ (under UV light irradiation) for the composite with a PB:TiO₂ mass ratio of 5:5, being maximal at a PB:TiO₂ mass ratio of 7:3, and the mechanism of photocatalytic Cs⁺ adsorption enhancement was elucidated and discussed. This enhancement was suppressed by high PB contents (i.e., low TiO₂ contents) because of the concomitant suppression of photogenerated electron transfer from TiO₂ to PB and was also hindered by the presence of K+ and Na+. However, the Cs⁺ adsorption capacity of PB/TiO₂ at high K⁺ concentrations under UV light irradiation was still almost twice as high as that observed in the dark. The increase of Cs⁺ adsorption capacity upon irradiation was ascribed to the concomitant reduction of PB by photogenerated electrons transferred from TiO₂. Thus, the present study provides a new direction for the development of next-generation technologies for radioactive Cs removal from contaminated water.