Accessible area and hydrophobicity of activated carbons obtained from the enthalpy characterization

Were determined the immersion enthalpy in benzene and water for 24 carbonaceous materials, granular activated carbon and activated carbon monoliths prepared from African palm stone by chemical activation with H₃PO₄, ZnCl₂ and CaCl₂ solutions. The immersion enthalpies in benzene and water were exothermic, in accordance with a surface process that takes place between the solid and liquid. Benzene enthalpies for this set of solids were ?20.26 and ?181.1 J g^?1 and water enthalpies were between ?7.42 and ?67.01 J g^?1. The textural and chemical surface properties of the activated carbons were related to the immersion enthalpies. Since the evaluation of the porous structure was made with non-polar liquids with which the solid does not have a specific interaction, immersion enthalpy was proportional to the surface area accessible to liquid molecules, which was calculated from the enthalpic determinations based on the assumption of the existence of a direct relationship between the immersion enthalpy and the total area of the solid accessible to liquid molecules. The hydrophobic factor was calculated by dividing the immersion enthalpy in benzene and the immersion enthalpy in water; this is related to the acidity, basicity and hydrophobicity of the activated carbons.