Kinetic and Mechanistic Analysis of Phenol Adsorption on Activated Carbons from Kenaf

Activated carbons were prepared from kenaf (<i>Hibiscus cannabinus</i> L.). Carbonization was carried out at 600 °C for 2 h, and activation was performed using air at 600 °C and using CO₂ at 750 °C. The activated carbons obtained were treated with HNO₃ and H₂SO₄. The samples were characterized by their chemical and physical structure. The activated carbons obtained were mainly macroporous, and their structure underwent major changes with the activation method and acid treatment. Activated carbons were alkaline and acid-treated carbons were neutral. They were used for phenol adsorption and a kinetic and mechanistic study of adsorption was carried out. The fit to the pseudo-second order and Elovich models was predominant. The rate-limiting step of the process was determined to be diffusion within the pores, as the experimental data fit the Bangham model. DFT simulation showed that the preferred adsorption position involves π-π stacking and that oxidation enhances this interaction. Furthermore, the simulation showed that the interaction of phenol with oxygenated functional groups depends on the type of functional group.