Selective electrosorption of heavy metal ions from wastewater with S-doped hierarchical porous carbon derived from waste Camellia oleifera shell

Capacitive deionization (CDI) has garnered significant attention in desalination and the removal of heavy metal ions. The quest for cost-effective and high-performance electrode materials is crucial to advance CDI applications. Herein, we report a sulfur-doped hierarchical porous carbon (SPC) derived from waste camellia oleifera shells via a sustainable hydrothermal carbonization process followed by KOH/ammonium salt activation. The optimized SPC-0.2 exhibits exceptional characteristics, featuring a high specific surface area of 1875 m(2) g(-1) and substantial sulfur doping at 8.65 %, leading to enhanced specific capacitance (161.3 F g(-1)) in a 1 M NaCl solution. Under optimal operating conditions (1.2 V, 10 mL min(-1), 500 mg L-1 NaCl), the SPC-0.2 electrode achieves a notable desalination capacity of 26.64 mg g(-1). In particular, the electrode can selectively remove >99 % of Cr3+ and Cu2+ ions (each 10 mg L-1) in a 100 mg L-1 NaCl solution. This high selectivity is attributed to the formation of sulfides via low adsorption energies between the doped sulfur atoms and the targeted heavy metal ions. Furthermore, the SPC-0.2 electrode demonstrates robust reusability and high efficiency in the actual water body. Collectively, our findings underscore the significant potential of the synthesized SPC as an electrode material for CDI, particularly in the selective capacitive removal of heavy metal ions from wastewater. This work not only contributes to the circular economy by using waste biomass, but also offers a viable solution for environmental remediation.