Surface fractal dimension of microporous carbon fibres by nitrogen adsorption

Abstract

The surface fractal dimension of three kinds of microporous carbon fibre has been determined from adsorption data of organic molecules of different molecular sizes (MAI method), by detailed N₂ adsorption isotherms with the aid of the recently proposed Avnir–Jaroniec theory (AJ method) and by small-angle X-ray scattering (SAXS). The application conditions of the AJ theory to the N₂ adsorption isotherm have been examined. The surface fractal dimension by the AJ method depends on the range of the fractional filling. In the fractional filling range ca. 0.8–1.0 the value of the surface fractal dimension is ca. 2.6–2.7 and nearly constant; therefore, this range of adsorption data is suggested for evaluating the fractal dimension by the AJ method. The surface fractal dimension by the MAI method was 2.3–3.0 and that by SAXS was 2.6–2.8 in dry air. Thus the AJ method, which uses a single adsorption isotherm, can give a reasonable value of the surface fractal dimension, similar to those given by MAI and SAXS methods.