Valorization of lignin-derived carbon nanofibers into Ca-MOF-Based hierarchical electrodes for enhanced fluoride electrosorption

Lignin-derived Ca-MOF carbon nanofibers enabled efficient fluoride CDI. • CMDNF achieved a fluoride electrosorption capacity of 26.81 mg·g −1 . • Fluoride concentration decreased from 10 to 1.15 mg·L −1 . • The electrode retained 91.27% capacitance after 5000 cycles. • CMDNF retained 75.38% adsorption capacity after 15 regeneration cycles. Valorization of renewable lignin into high-performance electrochemical materials offers a sustainable route for advanced water treatment, yet achieving efficient fluoride removal together with long-term electrode stability remains challenging. Herein, we report a hierarchical Ca-MOF/lignin-derived carbon nanofiber (CMDNF) electrode fabricated via in situ solvothermal growth of a Ca-based metal–organic framework on electrospun lignin nanofibers, followed by controlled carbonization. This strategy converts biomass-derived nanofibers into a conductive and hierarchically porous carbon framework integrated with Ca-containing surface environments favorable for fluoride electrosorption. Structural characterization reveals that Ca species are uniformly distributed throughout the carbon architecture, while the lignin-derived framework provides structural robustness, efficient electron transport, and improved ion-accessible pathways. The optimized CMDNF electrode exhibits a specific capacitance of 163F·g −1 at 2 mV·s −1 and retains 91.27% of its initial capacitance after 5000 charge–discharge cycles, demonstrating good electrochemical stability. In fluoride electrosorption experiments, it delivers a maximum adsorption capacity of 26.81 mg·g −1 and reduces the fluoride concentration from 10 mg·L −1 to 1.15 mg·L −1 under model-solution conditions, below the WHO guideline value of 1.5 mg·L −1 . XPS and EPR analyses suggest that the enhanced fluoride removal arises from the combined contribution of Ca-containing oxygen-coordinated surface environments, defect-rich carbon surfaces, and electric double-layer electrosorption. This work demonstrates a feasible strategy for converting lignin into high-performance CDI electrodes and provides useful insight into the rational design of biomass-derived hierarchical materials for fluoride removal at electrode–electrolyte interfaces. Download: Download high-res image (166KB) Download: Download full-size image