Hierarchical porous carbon derived from activated biochar as an eco-friendly electrode for the electrosorption of inorganic ions

a Hierarchical porous carbon (HPC) as an eco-friendly electrode material was fabricated from rice husk biochar using the hard template method for electrosorption of ions. The porous structure in HPC materials can be controlled by different activation times to optimize the material physicochemical and electrochemical properties. The HPC sample achieved a high specific surface area (1839 m(2) g(-1)), large pore volume (1.21 cm(3) g(-1)) and 58% mesopore to total pore volume ratio. The HPC electrode exhibited excellent electrochemical properties with a high specific capacitance of 120.5 F g(-1) at 5 mV s(-1) in a 1 M NaCl solution as well as good reversibility for capacitive charge storage. The large ion-accessible specific surface area, interconnected pore structure among micropores and mesopores, and large mesoporosity of the HPC electrode played crucial roles in the enhancement of the electrosorption performance. The HPC electrode exhibited a high electrosorption capacity of 8.11 mg g(-1) and mean deionization rate of 0.92 mg g(-1) min(-1) for 20 mM NaCl in single-pass capacitive deionization. The associated charge efficiency and energy consumption were 48.1% and 0.064 kWh mol(-1), respectively, indicating a low energy requirement of water desalination. Furthermore, the HPC electrode showed good regeneration ability in consecutive cycles for the removal of inorganic pollutants, i.e., NH4+, Mg2+ and Cu2+, with electrosorption capacities of 1.54, 1.53 and 0.52 mg g(-1), respectively. Consequently, HPC from tailored activated rice husk biochar can provide a new opportunity to achieve high-performance electrosorption in various water and wastewater treatment processes.