Fractal Strategy for Improving Characterization of N2 Adsorption-Desorption in Mesopores

The current studies primarily analyze the heterogeneity and complexity of mesopore structures based on low-temperature nitrogen (N-2) adsorption curves and the Frenkel-Halsey-Hill (FHH) fractal model. However, these studies ignore the fact that the low-temperature N-2 desorption curve can also reflect the desorption performance of the mesopore structure. In this research, novel fractal indicators for characterizing the adsorption-desorption performance of mesopores based on the fractal dimension from the N-2 adsorption curves and N-2 desorption curves are proposed. The novel fractal indicators I-1 and I-2 are applied to evaluate the adsorption-desorption performance of mesopores with pore size 2-5 nm and pore size 5-50 nm, respectively. The fractal indicator I-1 shows an increasing trend with coalification, reflecting that the gas adsorption performance of 2-5 nm mesopores is enhanced with coalification. The fractal indicator I-2 exhibits a trend of first increasing and then decreasing with coalification, indicating the gas desorption performance of mesopores with pore size 5-50 nm decreases first and then increases. The proposed indicators provide novel analytical parameters for further understanding the gas adsorption-desorption mechanism of porous coal-based or carbon-based materials.