Surface fractal dimension of less-crystalline carbon micropore walls

The texture of pore walls of activated carbon fiber (ACF) treated at a high temperature in Ar was evaluated by surface fractal analysis using two kinds of molecular probe methods. The multiprobe (MP) method using the monolayer capacity of several different probe systems gave evidence for a decrease in the fractal dimension of the micropore walls with an increase in pretreatment temperature. As the BET monolayer gave unrealistic fractal dimension due to an erroneous evaluation of the monolayer in the micropore, this work proposed a new evaluation method of the monolayer in the micropore using the pore volume, average pore width, and molecular radius from the alpha(s) and DR analyses. The single-probe (SP) method developed by Avnir and Jaroniec detects nitrogen and benzene adsorption isotherms. The surface fractal dimension by the MP method was between the surface fractal dimensions determined by the SP method using nitrogen and benzene. The surface fractal dimension sensitive to the probe molecule indicated the presence of irregularities of subnano order in the micropore walls.