Valorization of N-doped biochar into Fe-Cu loaded carbon catalyst from electroplating wastewater: Structure regulation, adsorption performance, and catalytic properties.

The efficient removal and resource recovery of high-concentration heavy metals like Fe3⁺ and Cu2⁺ from electroplating wastewater remains a critical challenge. Herein, a sustainable closed-loop "adsorption-transformation-upcycling" strategy was proposed. Initially, a nitrogen-doped and CaO-activated pinewood biochar (N-aPBC) was synthesized via synergistic modification. Systematic characterization revealed that N-aPBC features a high specific surface area (188.79 m2 g⁻1), a hierarchical porous architecture, and abundant nitrogen-containing functionalities. Adsorption experiments demonstrated superior performance for Fe3⁺ and Cu2⁺, yielding maximum capacities of 287.40 and 61.88 mg g⁻1, respectively. Mechanistic investigations indicated that the adsorption followed the pseudo-second-order kinetic model and Langmuir isotherm, suggesting monolayer chemisorption. The primary removal mechanisms involved surface complexation via N/O-functional groups, coupled with electrostatic attraction and ion exchange. N species and defects tuned surface polarity and electronic structure. Subsequently, the spent adsorbent was calcined to produce a functional material (Fe-Cu-NaB). Electrochemical analyses confirmed that Fe-Cu-NaB exhibited lower charge transfer resistance and enhanced electrocatalytic activity. Notably, Fe-Cu-NaB enhanced the oxidative degradation capacity, achieving high removal rates of 93.64% for ciprofloxacin (CIP) and 65.88% for total organic carbon (TOC) in swine wastewater. This work provides a high-performance adsorbent for heavy metal remediation and establishes a viable pathway for the high-value reutilization of spent adsorbents as efficient catalytic materials.