Alkali-Enhanced Electrochemical Deintercalation of Fluoride Ions on Superlong Lanthanum Metal–Organic Framework Nanowire in Capacitive Deionization

The treatment of fluoride-contaminated drinking water remains a critical environmental challenge. In capacitive deionization (CDI) systems, the strong binding affinity of certain electrode materials toward fluoride ions (F–) often compromises the electrochemical reversibility and limits the regeneration capacity. In this study, superlong lanthanum metal–organic framework (La-BDC) nanowire was synthesized successfully by temperature-modulating crystal nucleation and growth, with a higher specific surface area (293.2 m2 g–1) and an average diameter of ∼20 nm for La-BDC-140 (heated at 140 °C for 20 h). More importantly, La-BDC-140 exhibits exceptional fluoride removal performance in CDI, achieving 28.7 mg g–1 in 50 mL of 10 mg L–1 NaF solution at 1.4 V, significantly higher than values reported in previous studies. In addition, the synergistic effect of alkaline electrolytes and reverse voltage can effectively facilitate the desorption process; hydroxide ions (OH–) compete with F– for binding to the La3+ center, thereby destabilizing the stable La–F bond. Meanwhile, the electrostatic force enhances the migration of fluoride ions away from the electrode surface. This significantly improves the electrodesorption efficiency of electrode materials with high affinity for fluoride ions, achieving a single-cycle desorption rate of approximately 95%. After 20 electrodesorption cycles in alkaline solution, the fluoride removal efficiency was maintained at over 80%, successfully addressing the regeneration challenge commonly associated with high-affinity adsorbents in CDI systems. This work provides a highly efficient and regenerable La-MOF-based electrode for CDI defluoridation, offering a novel approach for the electrodesorption regeneration of electrode materials exhibiting strong binding affinity toward F–.