From Strong Fluoride Binding to Reversible Electrodesorption: S, N-Regulated La-MOF-Derived Carbon Electrodes for...

La-MOFs exhibit strong affinity toward anions such as F^- and phosphate. However, conventional La-MOFs show limited regeneration performance when used as CDI electrodes, posing a major challenge for practical applications. In this study, a high-performance sulfur and nitrogen co-doped La-BDC-140-derived carbon electrode (La-CNS₃) was fabricated via a coupled carbonization and doping strategy. The optimized La-CNS₃ electrode possessed abundant defects, a mesoporous structure, favorable hydrophilicity, and rapid charge-transfer capability, which collectively enhanced fluoride electrosorption. At 1.4 V, La-CNS₃ achieved a fluoride removal capacity of 31.86 mg·g^-1 for 10 mg·L^-1 F^- solution and up to 195 mg·g^-1 at an initial F^- concentration of 100 mg·L^-1. More importantly, partial fluoride desorption was realized solely under reverse voltage, and the electrode maintained favorable defluoridation performance over 50 adsorption-desorption cycles. In actual groundwater treatment, the effluent fluoride concentration decreased to below 1.0 mg·L^-1 after 120 min. XPS analysis and DFT calculations revealed that fluoride removal was mainly governed by La-F coordination, surface hydroxyl/water ligand exchange, and interfacial charge redistribution. The La₂O₂S/g-C₃N₄ structure provided a favorable balance between fluoride adsorption strength and desorption reversibility. This work offers a promising strategy for designing efficient, selective, and electrically regenerable rare-earth-based CDI electrodes for fluoride-contaminated water treatment.