Characterization of the Adsorption Mechanism of Cadmium(II) and Methylene Blue upon Corncobs Activated Carbon

Abstract

A promising new activated carbon (AC) was produced from corncobs (CCs) by boric acid-based chemical activation to remove methylene blue (MB) as an organic pollutant and cadmium ions (Cd²⁺) as an inorganic pollutant from aqueous solutions. After the produced activated carbon (CCs-AC) was characterized, the adsorption mechanism of CCs-AC, which is one of the most interesting topics in the literature, was the primarily focus. The possible adsorption mechanisms of Cd²⁺ and MB on CCs-AC from aqueous solutions are discussed with respect to pH, thermodynamic values, and regeneration parameters. The results show that the adsorption of Cd²⁺ on CCs-AC was favorable at pH values higher than 4. In contrast, the adsorption process was almost pH-independent for MB. Variation of pH showed that the adsorption of Cd²⁺ on CCs-AC primarily occurs by electrostatic interaction. However, MB adsorption may also involve π-π dispersion forces and partial hydrogen bonding. The Cd²⁺ adsorbed on CCs-AC was quantitatively desorbed by HCl, whereas MB was not desorbed quantitatively by any solution. While a temperature increase has a positive effect on the adsorption of both methylene blue and Cd²⁺, the thermodynamic results show that MB adsorption is primarily chemisorption (ΔH of 24.28 kJ/mole), while Cd²⁺ adsorption is mostly physisorption (ΔH of 7.20 kJ/mole). Using Langmuir adsorption isotherms, the MB adsorption capacity of CCs-AC, which primarily has a microporous structure, was 0.88 mmol/g, while the Cd²⁺ adsorption capacity was 1.28 mmol/g.

Keywords:

• Adsorption mechanism
• cadmium(II) (Cd²⁺)
• corncob activated carbon
• methylene blue

Acknowledgment

The authors would like to thank Dr. Yunus Onal from İnönü University, Malatya, Turkey, for his contributions.

Disclosure statement

No conflicts of interest are reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.