Electrochemical Adsorption of Cs⁺ Ions on H-Todorokite Nanorods

In this work, manganese oxide with a 3 × 3 tunnel structure was synthesized. Mg-todorokite was treated with HNO₃ to obtain H-todorokite, which was used as an electrode for adsorption of Cs⁺ from aqueous solution by an electrochemical reaction. H-todorokite was electrochemically reduced to lower oxidation state to enhance its negative charge and simultaneously increase the amount of cations because of the charge compensation. The Cs⁺ adsorption on H-todorokite was completed by a coupled electrochemical reaction (the redox reaction between Mn³⁺ and Mn⁴⁺) and an ion-exchange reaction between Cs⁺ and H⁺ ions. Cyclic voltammetry measurements at different pHs and Cs⁺ concentrations were performed. H-todorokite revealed high electrochemical adsorption capacity for Cs⁺ because of the high crystallinity and stability of the materials, which reached 6.0 mmol g^-1 in 0.1 mol·L^-1 Na₂SO₄ solution.