Modification of activated carbon hydrophobicity by pyrolysis of propene

The chemical nature of the surface of a granular activated carbon has been modified by heat treatment under nitrogen at 1000 °C followed by pyrolysis of propene in the 300–600 °C temperature range. Cracking of propene produces deposits of coke on the more reactive sites of the carbon surface, those produced after the decomposition of the original oxygen surface groups along the previous heat treatment. The process leads to an initial reduction in the number of oxygen surface groups and in the capacity of the carbon to chemisorb oxygen. The further growth of the carbon deposit in the interior of the particle decreases the width of the micropore entrance, which is paralleled by the coating of the external surface of the particle. The reduction in the number of active sites of the carbon leads to a decrease in the enthalpy of immersion into polar liquids such as water and ethylenediamine, the carbon becoming more hydrophobic than the original.