Electroactivity Variable Valence NiFe Layered Double Hydroxyde for Cl⁻ Removal through Electrically Switched Ion Exchange

Abstract

NiFe layered double hydroxide (LDH) films with different Ni/Fe molar ratios were successfully prepared on carbon paper (CP) by the potentiostatic method and were used for the removal of chloride ions (Cl−) by electrically switched ion exchange (ESIX) technology. The results showed that the Ni/Fe ratios had a significant effect on the adsorption performance of LDH for Cl−. The prepared NiFe LDH film with Ni/Fe molar ratio of 1 : 1 showed the best Cl− ESIX performance and the maximum adsorption capacity could reach 43.8 mg ⋅ g−1 at 1.4 V (vs. SCE) in 20 ppm Cl− solution. The excellent adsorption performance of LDH for Cl− was mainly due to the coupling of the interlayer anion exchange mechanism and the electroactivity‐variable valence mechanism. In addition, the Cl− regeneration rate remained above 95 % during five repeated adsorption/desorption experiments, and the charging capacity was still about 96 % of the initial capacity even after 1000 CV cycles. Therefore, the NiFe LDH film could be a promising electroactive material for the removal of Cl− from aqueous solution.