Efficient removal of Cu2+ on Medulla Tetrapanacis-based modified biochar: adsorption performance, mechanisms and recycling for fabrication of supercapacitor electrodes

Abstract

Achieving high-capacity removal of Cu²⁺ from effluent remains challenging nowadays. Hence, high-performance calcium chloride modified Medulla Tetrapanacis based biochar (MBC) was prepared by simple impregnation treatment and tube furnace carbonization. The results of sorption experiments confirmed that the MBC obtained at 900 °C (MBC3) possessed the highest sorption under specific conditions (pH = 6 at 0.2 g/L). MBC3 showed the highest fitting to the pseudo-second kinetic model and the Langmuir model (R² = 0.996, 0.947). The fitted MBC3 achieved the maximum adsorption of Cu²⁺ of 945.6 mg/g, being 2.25 times higher than the adsorption of unmodified biochar (BC). Multiple mechanisms including precipitation, ion exchange and surface complexation were evidenced to be associated with the excellent sorption properties of MBC3. Considering the potential hazards of enriched Cu, MBC3 after sorption was reused as ReBC/Cu for preparing supercapacitor electrodes through a facile hydrothermal method (180 °C, 24 h). The adsorbed Cu elements were found to be mainly loaded as oxides in ReBC/Cu. It was calculated that the ReBC/Cu electrode displayed a specific capacitance of 142.5 F/g at 0.5 A/g, which was 49.01 % enhancement compared to that of the unused pristine biochar. This study combines biochar-based adsorption with the preparation of supercapacitor electrodes, which not only achieves efficient copper removal from water, but also provides a promising option for the post-treatment of copper-rich waste adsorbents.