Titanium (IV) hydroxide-modified biochar electrode for efficient and selective fluorine removal by flow-electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) can be a promising technology for fluorine removal from groundwater. In this study, a new kind of titanium (IV) hydroxide modified biochar (Ti-BC) was prepared by a simple method and used as FCDI electrode materials to selectively remove F^- at the first time. Ti-BC exhibited superior defluorination capabilities due to the its unique mesoporous structure and the introduction of hydroxyl functional groups. The optimal F^- removal performance was obtained by optimizing the operation parameters and the parameter of applied voltage had the greatest impact. Ti-BC electrode performed excellent electrosorption capacity of 9.65 mg/g and electrosorption efficiency of 96.5 %. Besides, the energy consumption was as low as 0.002 kWh/m³. Furthermore, the remarkable selectivity for F^- even in mixed ions systems was confirmed, and the actual fluorine-containing groundwater could be effectively treated to meet the WHO drinking water standard. With the help of characterization techniques and theoretical calculation, the detailed fluorine removal mechanisms were obtained, including physical adsorption, electrostatic attraction, capacitive adsorption and ligand exchange. This work not only proposed new insights into the efficient and selective fluorine removal, but also promoted the development of targeted electrodes for practical application in treating fluorine pollution in groundwater.