Efficient biosorption of cadmium ions from wastewater using iron oxide–maize shell activated bio-carbon nanocomposites

This study presents a novel approach to enhancing the efficiency of cadmium ion (Cd(II)) removal by mixing magnetic behavior into activated carbon (AC) derived from bio-waste. The AC was produced from maize shells and impregnated with iron oxide nanoparticles (Fe₃O₄-MSAC), granting the carbon matrix magnetic characteristics. Characterization techniques such as SEM and FTIR were utilized. Adsorption experiments were conducted under various conditions, including contact times, initial Cd(II) concentrations, various adsorbent dosages (Fe₃O₄-MSAC), and different solutions pH. The results indicated that the adsorption of Cd(II) onto Fe₃O₄-MSAC was attained within 50 min, with a maximum adsorption capacity of 7.95 mg g⁻¹. The adsorption data fitted well with the Langmuir model (R² = 0.998), signifying monolayer adsorption. Additionally, the adsorption kinetics followed a pseudo-second-order model (R² = 0.995), implying chemisorption is the rate-limiting step. The findings also demonstrated that higher temperatures positively affected Cd(II) adsorption, indicating an endothermic process. The regeneration studies demonstrate the adsorbent is used for several adsorption/desorption cycles using HNO₃ as a regenerating agent. The Fe₃O₄-MSAC facilitated easy separation of the material from the treated cadmium ion solution by an external magnetic field, removing the need for filtration.