Capacitive deionization chloride and fluoride removal by amine and titania-modified biochar electrodes.

This study examines the use of surface-modified biochar as a porous electrode material for the capacitive deionization removal of chloride and fluoride ions. Incorporation of titanium dioxide and amine groups on biochar aims to increase surface-active sites, facilitate salt ion diffusion, and improve charge efficiency and cation/anion selectivity in asymmetric capacitive deionization. Titania, amine, and activated biochar are denoted as TB, AmB, and AcB, respectively. Physical and electrochemical characterizations were performed to investigate the surface properties of fabricated materials. At the optimum TiO₂ loading of 5% (TB-05), the specific capacitance of TB-05 electrode was improved by 35% at scan rate of 1 mV s^–1 in comparison to the AcB electrode, despite a decrease in the specific surface area. Three different asymmetric capacitive deionization cell designs—AmB||TB-05, AcB||TB-05, and AmB||AcB—and two symmetrical cell designs—AcB||AcB and TB-05||TB-05 (anode||cathode)—were tested. A symmetric cell design TB-05||TB-05 had a NaCl removal capacity of 8.51 mg g⁻¹, a 42% improvement in comparison to a symmetric AcB cell (6.01 mg g⁻¹). Further, an asymmetric cell AmB||TB-05 showed 67% charge efficiency improvement over symmetric AcB cell, likely due to a reduced co-ion effect. For fluoride removal, a symmetric TB-05 cell showed a removal capacity of 3.51 mg g⁻¹. This study promotes simple surface-modification methods to make inexpensive commercial biochar into a sustainable, and efficient electrode material available for a scale-up asymmetric capacitive deionization. [ABSTRACT FROM AUTHOR]