Synthesis of a novel magnetic biochar composite enhanced with polyaniline for high-performance adsorption of heavy metals: focus on Hg(<scp>ii</scp>) and Cu(<scp>ii</scp>)

This study explores the potential of using magnetic biochar derived from sesame seed cake (PMBS) and enhanced with polyaniline (PANI) for the removal of heavy metals from aqueous solutions. The synthesized PMBS was comprehensively characterized and evaluated as an effective adsorbent for Hg²⁺ and Cu²⁺ removal. This study assessed various physicochemical properties, including surface morphology, porosity, specific surface area, chemical composition, valence states, and magnetic characteristics, of the composite to determine its efficacy in heavy metal removal from wastewater. The adsorption performance of the magnetic biochar was significantly enhanced <i>via</i> PANI doping. Furthermore, the easy magnetic recovery of PMBS from aqueous solutions after adsorption was successfully demonstrated using an external magnetic field. The adsorption kinetics of heavy metal ions on PMBS followed a pseudo-second-order model, while Langmuir isotherm analysis confirmed monolayer adsorption behavior. The maximum adsorption capacities for Hg²⁺ and Cu²⁺ were determined to be 141.89 and 124.78 mg g^-1, respectively. The electrochemical measurements of square wave anodic stripping voltammetry (SWASV) were employed to determine residual metal ion concentrations after adsorption. Calibration curves were constructed by varying the concentration of each ion, both individually (with the other held constant) and simultaneously (with both ions present in the same solution), to evaluate the electrode's performance in mixed-ion systems. The PANI-modified PMBS biochar demonstrates significant potential for wastewater treatment and is suitable for a broader range of separation applications.