Efficient fluoride removal in hybrid capacitive deionization enabled by Ce-Zn-MOF-derived CeO2@C and birnessite electrodes

Efficient removal of fluoride enabled by the CeO 2 @C-δ-MnO 2 cell in HCDI system based on intercalation into the carbon skeleton, coordination with Ce, and electrostatic interaction . • The CeO 2 @C composite was prepared by pyrolysis of a bimetal-organic framework. • A hybrid capacitive deionization system with CeO 2 @C as the anode was constructed. • The CeO 2 @C electrode shows excellent defluorination capacity and cycle performance. • The effect of temperatures on the structure of Ce/Zn-BTC derived carbon was explored. • The multiple defluorination mechanisms in real fluoridated wastewater were explored. Fluorine pollution has become a public health issue of global concern. Capacitive deionization (CDI) presents the benefits of simple operation, high energy efficiency, and good sustainability. The development of high adsorption performance, economical and environmentally friendly defluorination electrodes is the key direction of capacitive deionization. Here, a spherical metal–organic framework (MOF) Ce/Zn-BTC was prepared by solvothermal method utilizing benzene-tricarboxylic (BTC) acid as solvent, and then it was transformed into CeO 2 @C composites through pyrolysis. The spherical structure of the original MOFs is preserved by CeO 2 @C, leading to significant enhancements in specific surface area (275.48 m 2 /g), pore volume (0.3359 cm 3 /g), and electrochemical performance. In this work, the anode material CeO 2 @C was employed for the first time, while birnessite-type MnO 2 (δ-MnO 2 ) was utilized as a cathode material for the fabrication of a hybrid CDI (HCDI) device for the treatment of fluorinated wastewater. The CeO 2 @C/δ-MnO 2 cell shows excellent fluoride removal performance with a removal capacity of 22.03 mg/g for 50 mg/L fluoride solutions under a 1.2 V applied voltage, which is better than most carbon-based materials. Importantly, the CeO 2 @C/δ-MnO 2 cell has favorable fluoride selectivity and regeneration performance (>75 %) even after undergoing ten cycles. Fluoride is mainly removed by intercalation into the carbon skeleton, coordination with Ce, and electrostatic interaction. This study shows that the CeO 2 @C/δ-MnO 2 cell has excellent fluoride removal performance and practical application prospects.