From Antibiotic Remediation to Energy Conversion: A Ni–Co–Zn–Al LDH/Activated Carbon Hybrid with Electrocatalytic Activity Toward Urea Oxidation

Colistin sulfate (COL), a critical last-line antibiotic, poses a severe environmental threat due to its persistence and role in spreading mobile resistance genes. This study introduces a novel quaternary Ni-Co-Zn-Al layered double-hydroxide/activated carbon composite (Q-LDH/AC) for highly efficient COL remediation. The composite’s unique architecture, revealed through comprehensive characterization, enables an exceptional adsorption capacity of 952.52 mg·g−1 under optimal conditions (pH 7, 55 °C), a value that significantly surpasses those reported for most previous adsorbents. The process was spontaneous and endothermic, with kinetics and isotherms best described by the pseudo-second-order and Langmuir–Freundlich models, respectively, indicating a complex mechanism dominated by chemisorption on both homogeneous and heterogeneous sites. A key innovative feature is the successful regeneration and reusability of the composite, which retained over 70% efficiency after five cycles, enhancing its potential for practical, cost-effective water treatment applications. The thermodynamic parameters (ΔG° = −8140.68 kJ/mol, ΔH° = +61.22 kJ/mol) indicate that the reaction is spontaneous and endothermic. The interaction mechanism of COL on Q-LDH/AC can be deduced by FT-IR including hydrogen bonding, π-π bonding, electrostatic interactions, and surface complexation. Beyond mere regeneration, this work demonstrates a pioneering circular economy strategy by repurposing the spent COL-laden adsorbent not as waste, but as a high-performance electrocatalyst. In direct urea fuel cell tests, this electrode achieved a superior and stable current density of 45.63 mA/cm2 for Q-LDL/AC, substantially outperforming the pristine Q-LDH/AC/COL (206.63 mA/cm2) and highlighting how the captured pollutant enhances functionality. This dual-purpose approach successfully closes the loop, transforming the environmental liability of antibiotic-laden waste into a valuable resource for energy applications. With a production cost of 2.755 USD/g, this work presents not only a highly effective adsorbent but also a transformative, circular strategy that simultaneously addresses water pollution and energy recovery. These findings offer a promising dual-purpose solution for mitigating the environmental spread of antibiotic resistance through a sustainable cycle that enables efficient antibiotic removal from wastewater while simultaneously converting the captured pollutant into a useful energy resource.