Cr(vi) removal performance of activated carbon (CB-AC) and nZVI-modified activated carbon (nZVI@CB-AC) derived from...

This study presents and compares two highly efficient adsorbents derived from waste cigarette butts for the removal of Cr(vi) from aqueous solutions using activated carbon (CB-AC) and nZVI-modified activated carbon (nZVI@CB-AC). Both adsorbents achieved 96-99% Cr(vi) removal at a low amount of 0.03 g under optimal conditions at pH 3. The CB-AC and nZVI@CB-AC adsorbents exhibited adsorption capacities of 101.01 mg g^-1 and 105.26 mg g^-1, respectively. Various characterization analyses revealed the structural properties of the adsorbents and showed a high surface area. The adsorption data of the nZVI@CB-AC fitted best with the Freundlich model, as indicated by a high correlation coefficient (R ² = 0.997). Thermodynamic analyses indicated a spontaneous and endothermic process accompanied by increased randomness at the solid-liquid interface. Selectivity studies showed that CB-AC exhibited a high Cr(vi) removal efficiency even in the presence of competing ions. XPS analysis revealed that the predominant removal mechanism was a redox interaction between Cr(vi) ions and nZVI@CB-AC, which contributed to the adsorbent's higher capacity, faster kinetics, and improved efficiency. Overall, this research emphasized both CB-AC and nZVI@CB-AC as promising and effective adsorbents for Cr(vi) removal from aqueous environments.