Abstract
Thin films of cathodically deposited nickel hexacyanoferrate are investigated as electrochemically switched ion-exchange (ESIX) materials for the selective separation of alkali cations in aqueous nitrate solutions at room temperature. Potential cycling in the range −100 to 900 mV vs SCE is used to reversibly load and elute alkali cations. Electrochemical cyclic voltammetry is combined with thin-film energy-dispersive x-ray spectroscopy to nondestructively determine element-specific cation loading in the ion-exchange matrix. Selectivity parameters are reported for the alkali cation pair Cs+/Na+.Separation factors and distribution coefficients for Cs+ in the presence of excess Na+ are determined over the range [Na+]/[Cs+] = 101 − 106 The distribution coefficient for cathodically deposited nickel hexacyanoferrate is greater than 2 × 105 mL/g for [Cs+] = 10minus;6 M and [Na+] ≈ 1 M, which is comparable in magnitude to the bulk metal hexacyanoferrates used in conventional ion exchange. A comparison between cathodically deposited nickel hexacyanoferrate materials and anodically derivatized materials is described. We also show that the Cs-form of the matrix can be electrochemically regenerated to the Na-form with nearly 80% of the intercalated Cs+ removed.
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