Electric-field-reversible interfacial activation of a binder-free UiO-66-NH₂/MXene@AC membrane electrode for selective fluoride electroadsorption

Fluoride pollution in industrial and groundwater poses global health risks. Capacitive deionization (CDI) has emerged as a highly promising and energy-efficient electrochemical technology for the removal of ionic contaminants, including fluoride. However, its effectiveness in defluorination is fundamentally limited by the inherent non-selective carbon-based electrode materials and ion exchange membrane for fluorine. In this study, we report a binder-free integrated membrane electrode fabricated by in-situ anchoring a metal organic frame (MOF) material (UiO-66-NH₂) nanochannels and conductive Ti₃C₂ MXene onto activated carbon electrode (UiO-66-NH₂/MXene@AC). In a single-pass mode experiment using a sodium fluoride (NaF) solution, the composite electrode achieved a fluorine remarkable adsorption capacity of 19.26 mg g⁻¹ with 2.68 mg g⁻¹ min⁻¹ of adsorption rate at an applied voltage of 1.4 V and an excellent F⁻/Cl⁻ selectivity of 39.6 (stable at 6.1 over 800 s). Capacity retention after 100 cycles is 83.3%. DFT calculations reveal that sub-nanometer MOF channels preferentially enrich F⁻ via size-sieving and Zr-F Lewis interactions, while MXene terminations modulate surface charge and local acid-base chemistry, synergistically accelerating selective transport. This interface microenvironment regulation strategy offers a general blueprint for designing next-generation, selective membrane capacitive deionization (MCDI) electrodes and brings nanomaterial-enabled defluorination closer to practical deployment.