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

HighlightsS, N co-regulated La2O2S/g-C3N4-derived carbon electrodes were successfully fabricated via thiourea-assisted carbonization of La-BDC-140.La-CNS3achieved a high fluoride removal capacity of 195 mg·g−1at an initial fluoride concentration of 100 mg·L−1.Reverse-voltage regeneration enabled reversible fluoride (F−) electrosorption without chemicals.What are the main findings?Under electric-field stimulation, the electrode exhibited excellent reversible adsorption/desorption, with a regeneration efficiency of F−exceeding 70%.Mechanistic analyses revealed that fluoride removal is mainly governed by La-F coordination, surface hydroxyl/water ligand exchange, and interfacial charge redistribution.DFT calculations further confirmed that the La2O2S/g-C3N4structure provides a favorable balance between fluoride adsorption strength and desorption reversibility.What are the implications of the main findings?These findings demonstrate that S, N co-regulation is an effective strategy to address the regeneration limitations of conventional La-based defluoridation materials.The La2O2S/g-C3N4-derived carbon electrode enables high-capacity, selective, and electrically regenerable fluoride removal in capacitive deionization (CDI) systems.This work provides a theoretical basis for designing sustainable rare-earth-based electrodes with balanced fluoride adsorption strength and desorption reversibility.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-CNS3electrode possessed abundant defects, a mesoporous structure, favorable hydrophilicity, and rapid charge-transfer capability, which collectively enhanced fluoride electrosorption. At 1.4 V, La-CNS3achieved a fluoride removal capacity of 31.86 mg·g−1for 10 mg·L−1F−solution and up to 195 mg·g−1at 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−1after 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-C3N4structure 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.