CO2 Reactivation of Activated Carbon to Improve Its Adsorption Capacity and Rate Toward Chlorpheniramine

The adsorption of chlorpheniramine (CPA) on a series of activated carbon (AC) samples was investigated. Commercial AC Megapol M (MM) samples were reactivated with CO2 at 800 °C for different times. The ACs were designated as MM4, MM8, and MM8A, corresponding to 4, 8, and 8 h cumulative (4 h and 4 h), respectively. The textural properties of MM8A were the highest due to an additional CO2 reactivation process. Quantification of the carboxylic sites showed a decrease in the order MM > MM8A > MM4 > MM8. The Raman spectra of MM, MM4, MM8, and MM8A indicated that for longer CO2 reactivation times, the D to G band intensity ratio (ID/IG) of all ACs increased due to surface defects. The CPA-adsorption capacity of the ACs revealed that MM8A had the highest adsorption capacity, attributed to its low density of carboxylic sites and disordered structure. Increasing the pH solution enhanced the CPA adsorption on MM8A, while temperature had a minor effect. The isosteric heat of adsorption indicated the CPA adsorption on MM8A occurred via physical interactions, with π–π stacking and hydrophobic interactions governing the process at pH = 11. The rate of CPA adsorption on MM8A was studied using diffusional models. The external mass transport model satisfactorily estimated the experimental data. Finally, it was found that CPA adsorbed more rapidly on MM8A than on MM.