Environmental-friendly modification of porous biochar via K₂FeO₄ as a capacitive deionization electrode material

Capacitive deionization (CDI) is considered a promising technology for desalination, and the preparation of electrode materials with high specific surface area, good hydrophilicity, and porous structure can facilitate the improvement of CDI performance. However, existing research lacks a porous, environmentally friendly biochar electrode and in-depth stability studies. Herein, porous carbon (RSK-x) was fabricated using rice straw as the raw material and K₂FeO₄ as the activator and modifier. The effects of different K₂FeO₄ ratios on the morphology, specific surface area, pore structure, physical phase composition, wettability, and capacitive properties of the porous carbon were investigated via various characterization techniques and electrochemical tests. The results indicated that the overall performance of rice straw carbon was significantly enhanced following modification with K₂FeO₄. The porous carbon (RSK-1.5) exhibited the highest specific surface area (607.53 m² g^-1), superior wettability, and good capacitive properties (150 F g^-1, 0.5 A g^-1) when the mass ratio of K₂FeO₄ to rice straw carbon was 1.5. The RSK-1.5 demonstrated a salt adsorption capacity of 15.44 mg g^-1 in a 500 mg L^-1 NaCl solution at 1.2 V voltage, and the electrode retained 92.81 % of its electrosorption capacity after 10 adsorption/desorption cycles. Furthermore, RSK-1.5 manifested an adsorption capacity of 48.52 mg g^-1 for Cu²⁺ (1.0 V, 200 mg L^-1). This finding underscores the potential of rice straw biochar as a capacitive deionization electrode material.