Hydrogen-treated graphitized carbon blacks

Abstract The isotherms and isosteric heats of adsorption in the region of very low surface coverages have been measured for propylamine and acetic acid on two graphitized carbon blacks, graphitized Sterling FT and MT, before and after hydrogen treatment at 1000°. In order to obtain adsorption isotherms at very low coverages with good precision, a gas chromatographic method has been adopted. The experimental results confirm the effectiveness of the hydrogen treatment in removing trace amounts of surface oxides and the usefulness of an oxygen-free carbon surface in deriving adsorption isotherms of hydrogen-bonding substances. The removal of chemical impurities causes the extent of propylamine adsorption to be sharply reduced and the shape of the isotherm to be altered. On untreated graphitized carbon blacks, the heat of adsorption of propylamine shows an uninterrupted fall as the surface coverage increases, whereas after the hydrogen treatment, a constant value of 7.5 kcal/mole is obtained. In contrast to the behaviour of propylamine, on treated carbon surfaces the adsorption of acetic acid increases and the heat-coverage curve is steeper than for untreated surfaces. This is because the adsorbate can establish strong lateral interactions on a clean surface. The surface density of chemisorbed oxygen on unpurified graphitized Sterling FT is estimated as two oxygen-containing groups per 104 A2.