Evaluation of the dispersive component of the surface energy of active carbons as determined by inverse gas chromatography at zero surface coverage

摘要

The methods to obtain the dispersive component of the surface energy (gamma(d)(s)) of active carbons (AC) from inverse gas chromatography (IGC) measurements usually render values much higher than those obtained by other techniques. In this paper this is ascribed to two factors: (i) the high temperatures at that IGC measurements are carried out and (ii) the microporosity of the AC. It is shown that the temperature dependence of the area of the methylene group is an important factor in the high gamma(d)(s) values. Thus, corrections for this dependence should be considered in the calculations. In relation to microporosity, the cooperative effect of the pore walls is also an important factor to be considered in the evaluation of gamma(d)(s). The values gamma(d)(s) obtained after these corrections have their own physical meaning related to ideal flat carbon surfaces. Critical comments are made about some reported relationships between gamma(d)(s), obtained from IGC, and the BET surface area or pore volume of AC as determined from nitrogen adsorption at 77 K. These are based oil the very different experimental conditions at which nitrogen and IGC measurements are carried out.