Cadmium removal from aqueous solutions using olive stone-based carbon materials: a comparative approach

This study presents a comparative investigation of cadmium removal from aqueous solutions using activated carbon and carbon nanosheets derived from olive stones. The aim was to evaluate the adsorption efficiency, capacity, and underlying mechanisms of two adsorbents under varying experimental conditions. Both adsorbents were synthesized via pyrolysis of olive stones to produce activated carbon, followed by ultrasonic treatment to generate carbon nanosheets. The effects of parameters such as contact time, temperature, pH, initial Cd(II) concentration, and adsorbent dosage on Cd(II) removal efficiency and adsorption capacity were systematically investigated. The results showed that all studied parameters significantly influenced adsorption performance, with carbon nanosheets demonstrating superior removal efficiency and a higher adsorption capacity (84.74 mg/g) compared to activated carbon. Thermodynamic studies indicated that the adsorption process was exothermic for activated carbon and endothermic for carbon nanosheets. Kinetic analysis revealed that the pseudo-second-order model best fit the adsorption data for both adsorbents, with higher correlation coefficients for carbon nanosheets. Isotherm modeling showed that Cd(II) adsorption on both adsorbents followed the Langmuir isotherm, suggesting monolayer adsorption on homogeneous surfaces. These findings highlight the potential of carbon nanosheets as an effective alternative to activated carbon for Cd(II) removal, offering valuable insights into the design of more efficient adsorbents for heavy metal remediation in wastewater treatment systems.