Immersion Calorimetry Applied to the Study of the Adsorption of Phenolic Derivatives onto Activated Carbon Obtained by Pyrolysis of Potato Peel

摘要

Activated carbons (ACs) were prepared by pyrolysis of potato peel in the presence of zinc chloride (chemical activation). Room-temperature adsorption of phenol, p-cresol, p-chlorophenol and p-nitrophenol from aqueous solutions at room temperature was investigated. Experimental results show that adsorption capacity depends on carbon surface area and porosity, on the solubility of the different phenolic compounds and on the hydrophobicity of the substituent. The relative affinity of the phenolic compounds towards the carbon surface was correlated to the electron donor-acceptor complexes which are formed between the basic sites on the carbon surface and the aromatic ring of the phenol compounds. As a result, the adsorption capacity began to decrease at a pH value that depended on the difference between the external and internal surface charge density, as measured by electrophoresis and the pH of the slurry, respectively. Eventually, immersion enthalpy was determined for each carbon sample. The values always increase with the relative amount adsorbed at equilibrium (Q_e), ranging between 23.5 and 65.4 J/g. Activated carbons with lower total acidity contents show the lowest values, this being related to the different activation treatments carried out by zinc chloride.