Harnessing porous carbon/iron oxide nanocomposites for arsenic contaminated water remediation and asymmetric supercapacitor

This study presents a sustainable, dual-purpose approach that addresses arsenic remediation and cheap energy storage together. Porous carbon derived from walnut shells was synthesized via two-step carbonization, then composited with α-Fe₂O₃ through hydrothermal treatment to form an efficient As(V) adsorbent. The C/α-Fe₂O₃ hybrid achieved a maximum removal efficiency of 390 mg g⁻¹ at a temperature of 45 °C with 90 % Arsenic removal within the first 40 min. To immobilize the adsorbed arsenic, the spent adsorbent was heat-treated under an inert atmosphere, leading to the formation of stable FeAs and FeAsO₄ phases, alongside γ-Fe₂O₃. The resulting C/Fe–As–O composite as cathode and porous carbon as anode, delivered a specific capacitance of 228 F g⁻¹ and energy density of 81.1 Wh kg⁻¹ at a power density of 800 W kg⁻¹ at 0.5 A g⁻¹ and can maintain C_sp of 59 at ED of 21.1 at PD of 8000 at 5 A g⁻¹. The fabricated device retained nearly 100 % capacitance after 10,000 cycles and successfully powered LEDs in a practical demonstration. This work highlights a scalable and environmentally responsible pathway to convert toxic waste into value-added electrode materials, aligning with circular economy principles and advancing the field of multifunctional energy materials.