Zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon electrode for efficient capacitive deionization defluorination

Excessive fluoride in water is severe harm to human health and has become a global public health problem. However, there is a lack of efficient and affordable defluorination technology, especially for fluoride removal from low concentration F- wastewater. Herein, zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon (ZnO/HPWC) was prepared as electrode for membrane capacitive deionization (MCDI) and used for defluorination. The used activator of ZnCl2 would not only manufacture hierarchical pore structure of wood carbon, but also allow in-situ vertical growth of uniform ZnO nanosheets on HPWC. A high F- removal (94.52%) was achieved at 5 mg L-1 of F− solution by the ZnO/HPWC-based MCDI, as well as its improved electrosorption capacity (31.25 mgF- g-1ZnO/HPWC). Excellent defluorination performance of ZnO/HPWC was also achieved at real wastewater (F-, 6.25 mg L-1), of which the final F- concentration (1.32 mg L-1) can meet the WHO standard of drinking water (<1.5 mg L-1). The defluorination mechanism was studied and discussed, which proved the high defluorination performance of ZnO/HPWC was due to the chemical interaction between F- and ZnO nanosteets, and diffusion capacitance (pseudocapacitance) offered by ZnO nanosheets dominated over the surface capacitance (electric double layer capacitance) by HPWC.