Effect of the electronegativity on the electrosorption selectivity of anions during capacitive deionization

The effect of electronegativity on the electrosorption selectivity of anions during capacitive deionization was investigated via a combination of experimental and theoretical studies. A model was developed based on chemical thermodynamics and the classic Stern's model to reveal the role of the anode potential and to describe electrosorption selectivity behavior during capacitive deionization. The effects of the anode potential on the adsorption of Cl^- and ReO₄^- were studied and the obtained data were used to validate the model. Using the validated model, the effects of the anode potential and electronegativity of various anions, including Cl^-, ReO₄^-, SO₄^2- and NO₃^- were assessed. The experimental results for the electrosorption of Cl^- and ReO₄^- corresponded well with the developed model. The electrosorption capacity demonstrates a logarithmic relationship with the anode potential. The model showed that the electronegativity significantly affects the selectivity. In a mixed Cl^-, ReO₄^-, SO₄^2- and NO₃^- solution, ReO₄^- was preferentially adsorbed over the other three anions, and the following selectivity was exhibited: ReO₄^- > NO₃^- > Cl^- > SO₄^2-. The results showed that the effect of flow rates on the electrosorption selectivity can be considered negligible when the flow rates are higher than 112 mL min^-1. The anions selectivity can be further enhanced by increasing the anode potential, and electrosorption selectivity is no appreciable decline after 6 experiments.