Green quaternary ammonium nitrogen functionalized mesoporous biochar for sustainable electro-adsorption of perchlorate

In this work, functional mesoporous bean dregs-based biochar electrodes were prepared by electrophoretic deposition for perchlorate (ClO4- ) electro-sorption. We characterized the textural and electrochemical properties of the biochar and determined the kinetics of electro-adsorption. The results show that 15% concentration of ZnO nanoparticle modification is recommended to increase the mesoporous volume, specific surface area, hydrophilicity and conductivity of biochar materials. After betaine functionalization, the obtained biochar (BK-Z15%N) possesses an excellent electrochemical performance with high current density, charging capacity, and low ohmic impedance. As expected, it presents an electro-adsorption capacity of 28.31 mg g-1 toward 20 mg L-1 ClO4at 1 V, which is four times higher than that without voltage and much better than other electrodes in this study and most reported data. The electro-adsorption of ClO4- on BK-Z15%-N electrode fits the fractal model, which is a complex process controlled by the electrical force and independent of solution pH. BrO3- and Cl- are the most competitive anion to ClO4- electro-sorption. Notably, it maintains a sustainable electrochemical regeneration ability due to the reversible redox activity of quaternary amine groups. Therefore, this study offers a remarkable and reliable method for improving the electro-sorption performance of perchlorate.