Experiments and physical Investigation on the adsorption of methylene on activated carbon

In this study, activated carbon (AC) derived from olive waste was employed as an alternative adsorbent for the removal of methylene blue (MB) from aqueous solutions. The AC was characterized using FTIR, SEM, XRD and N₂ adsorption-desorption analyses. The pseudo-second-order kinetic model and the Langmuir adsorption isotherm provided a good fit to the experimental data at 298, 303, and 313 K. A multilayer adsorption model was applied to elucidate the adsorption mechanisms between the dye molecules and the adsorbent. The number of MB active sites (n) was greater than unity at all temperatures, indicating a vertical orientation of the adsorbed molecules. The number of active sites (D_m) showed only slight variation with temperature. The decrease in MB adsorption capacities (Q_m) from 235.21 to 198.62 mg·g⁻¹ over the temperature range of 298-313 K was primarily influenced by the n parameter. Adsorption energy analysis revealed that MB adsorption was exothermic and occurred via a physisorption process. This study provides valuable insights into the interactions between MB molecules and AC active sites.