An in Situ Potential-Enhanced Ion Transport System Based on FeHCF–PPy/PSS Membrane for the Removal of Ca2+ and Mg2+ from Dilute Aqueous Solution

Theoretical calculation assisted materials screening of BiOX (X = F, Cl, Br, I) for electrochemical absorption of cesium ions

The electrochemical switching ion exchange (ESIX) technique has been widely used for the separation and recovery of radioactive cesium ions (Cs⁺) from wastewater. In this study, a series of BiOX (X = F, Cl, Br, I) materials were first evaluated for their absorption properties to Cs⁺ through density functional theory (DFT) calculations. The calculations predict that BiOBr has the best absorption performance among the four materials, BiOF, BiOCl, BiOBr, and BiOI, due to its high absorption energy and low ion migration energy barrier to Cs⁺. Simultaneously, the selectivity calculations revealed that BiOBr also showed the best selectivity for Cs⁺ compared with Li⁺ and Na⁺. Subsequently, four materials were prepared using the hydrothermal synthesis method and their electrochemical absorption performance was tested. The results showed that BiOBr has the highest electroactivity, and its absorption capacity was up to 16 mg Cs⁺/g BiOBr in a solution mixture of 50 ppm Li⁺, Na⁺, and Cs⁺. Based on our theoretical calculations and experiments, our findings provide prospective insights for predicting the electrochemical absorption performance of materials using first-principles calculations.

Investigation of a novel high-efficiency ion-permselective membrane module based on the electrochemically switched ion exchange scheme

Electric field-accelerated ion-permselective membrane (EISM) separation has attracted significant attention in recent years. Thus, herein, to further investigate the ion transport mechanism and optimize the separation efficiency, five types of ion-permselective membrane modules (IPMM I–V) based on the electrochemically switched ion exchange (ESIX) scheme were designed. Compared with the traditional ion separation systems, the in situ membrane-based ion separation system was set up with an extra pulse potential applied to the PPy/PSS/SSWM (polypyrrole/polystyrenesulfonate/stainless steel wire mesh) membrane. The continuous permselective separation of K⁺ as target ions was performed from dilute aqueous solution through the IPMM system. The pulse potential combined with the regulated cell voltage was functionalized synergistically to create an “ion-sieving effect” and effectively guide the target cations from the source cell to the receiving cell. Moreover, the formation of an equal potential volume in IPMM-V suppressed the reverse migration of the target ions and the detected ion flux across the membrane was 100 times that of the IPMM-I system. The ion transport mechanism was also analyzed in detail based on the equivalent circuit of the system, and the optimized operation parameters were obtained for the high-efficient ion separation system. These results can provide some beneficial information for the design and practical operation of novel EISM systems.

Novel ion permselective membrane modules based on the ESIX scheme.

Theoretical and experimental investigations of BiOCl for electrochemical adsorption of cesium ions

BiOCl was found to have excellent electrochemical adsorption properties for cesium ions (Cs⁺) in electrochemically switched ion exchange (ESIX). In this work, BiOCl nanosheets were synthesized by a hydrothermal method and used for electrochemical adsorption of Cs⁺. The experimental results showed that BiOCl exhibited higher electrochemical adsorption selectivity for Cs⁺ than Li⁺ and Na⁺. Quantum chemical calculations based on density functional theory (DFT) were first performed to compare the adsorption and migration mechanisms of three ions Li⁺, Na⁺, and Cs⁺ in BiOCl crystals. The calculation results revealed that the excellent electrochemical adsorption performance of BiOCl for Cs⁺ is due to the interaction of embedded Cs with Cl and Bi in BiOCl crystals. This makes it have a higher adsorption energy and a lower ion migration energy barrier due to the balance of interaction forces. In this work experimental and theoretical calculations were used to systematically analyze the adsorption and migration of three ions in BiOCl, which has important guiding significance for the design of highly-efficient electroactive materials for electrochemical adsorption of Cs⁺.