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.

Automated summary

A series of activated carbons were prepared from Datong bituminous coal by steam activation, and the fractal dimensions of pore structures were determined using low-temperature nitrogen adsorption and the Frenkel-Halsey-Hill model. The results showed that both micro- and mesopores were fully developed during steam activation, with activation at 750°C being more conducive to the development of pore structures, especially mesopores. The surface roughness and structure complexity of the activated carbons changed during the activation process, as indicated by the variation of their surface and structure fractal dimensions.