Mechanism adsorption analysis during the removal of Cd²⁺ and Cu²⁺ onto cedar sawdust via experiment coupled with theoretical calculation: Mono- and multicomponent systems

In this work, a deeper comprehension of the adsorption phenomena for Cd²⁺ and Cu²⁺ occurring in mono- and multicomponent systems on an adsorbent material obtained from cedar sawdust was accomplished by using spectroscopic characterization, and computational tools. The adsorbents were prepared by a simple calcination process at 300, 400, and 500 °C or pyrolysis at 300 °C. The experimental results showed that the adsorption capacity of the CS-C-400 adsorbent is higher for Cd²⁺ (36 mg g⁻¹) than Cu²⁺ (15 mg g⁻¹) ions in monocomponent systems (50 mg of adsorbent, 50 mL of solution, pH = 5, 25 °C, 200 rpm, and 72 h). In contrast, the trend for the adsorption capacity was Cu²⁺ > Cd²⁺ in most of the concentrations for multicomponent systems, due to that Cu²⁺ showed greater antagonism to Cd²⁺ during the competitive adsorption (qCd²⁺ was 96 % reduced). Computational results correlated well with the experimental ones and evidenced the occurrence of complexation interactions between metal ions and the surface oxygenated functional groups (hydroxyl, carboxyl, ester, and ether) onto the adsorbent surface, as was also proposed through spectroscopy results. Computational and experimental results indicate that Cd²⁺ and Cu²⁺ adsorption on the adsorbent surface is governed by the occurrence of complexation, and π-cation interaction for both ions, while ionic exchange plays a significant role in Cd²⁺ adsorption.