Evolution of pore structures and fractal characteristics of coal-based activated carbon in steam activation based on nitrogen adsorption method

To investigate the structures and fractal characteristics of micro- and mesopores during steam activation, a series activated carbons were prepared from Datong bituminous coal by physical activation at 750 and 850 degrees C. Lowtemperature nitrogen adsorption and Frenkel-Halsey-Hill model were employed to determine the fractal dimensions of pore structures. The results demonstrate that micro- and mesopore structures were fully developed during steam activation, and activation at 750 degrees C was conducive to the development of pore structures, especially mesopores. The samples had similar pore size distributions that the micropore diameters mainly centered at 0.4-0.8 nm and 1.2-1.8 nm, and the mesopores mainly distributed in the range of 2-9 nm. The variation of surface and structure fractal dimensions for activated carbons with different burn-offs indicated that the surface roughness and structure complexity changed during activation process. The fractal dimensions of micropore surface (D1) and micropore structure (D2) had positively linear correlation with Smic/SBET and Vmic/Vtot, respectively. While the mesopore surface fractal dimensions (D1') have a negative association with Sext/SBET, and the structure fractal dimensions (D2') have a negative but weak association with Vmes/Vtot.