Circular Economy‐Driven Cs/Sg/ <scp>MGNPs</scp> / <scp>AC</scp> Composite for Efficient Methylene Blue Removal and Subsequent Valorization as a Urea Oxidation Electrocatalyst

Abstract

ABSTRACT This study demonstrates a circular economy approach by synthesizing a composite adsorbent from slag, slag‐derived magnetic iron nanoparticles, chitosan, and activated carbon (Cs/Sg/MGNPs/AC) for efficient methylene blue (MB) dye removal from aqueous solutions, followed by valorization of the spent adsorbent as an electrocatalyst for urea oxidation reaction (UOR). The composite was fully characterized using FESEM‐EDX, XRD, FTIR, BET nitrogen adsorption, and DLS techniques. It exhibited superior adsorption performance with near‐complete removal (&gt; 98%) at optimal conditions. Adsorption mechanisms were elucidated through isotherm analysis (Freundlich model), kinetic modeling (pseudo‐second‐order and Elovich models), and intraparticle diffusion studies. The process was influenced by pH, adsorbent dosage, contact time, initial dye concentration, and ionic strength. The composite demonstrated selectivity toward cationic dyes over anionic dyes due to electrostatic interactions and functional group characteristics. Following adsorption, the MB‐loaded composite (Cs/Sg/MGNPs/AC/MB) was successfully repurposed as a UOR electrocatalyst, achieving a remarkable current density of 179.90 mA/cm 2 in 1.0 M urea solution, representing a 14.2% enhancement over the pristine composite (157.47 mA/cm 2 ). The MB‐loaded catalyst also exhibits superior electrochemical performance with enhanced double‐layer capacitance (0.5815 mF/cm 2 vs. 0.3265 mF/cm 2 ), lower charge transfer resistance (1.09 Ω vs. 1.47 Ω), and excellent long‐term stability (85.60 mA/cm 2 vs. 69.15 mA/cm 2 over 3600 s). This work establishes a sustainable pathway for converting industrial waste and spent adsorbents into value‐added materials for environmental remediation and energy applications.