Simulation study on the relationship between a high resolution αs-plot and the pore size distribution for activated carbon

The effects of the micropore structure of activated carbons on the high resolution alpha(s)-plot for nitrogen adsorption isotherms were examined with the grand canonical Monte Carlo simulation. Adsorption isotherms of nitrogen were simulated in graphitic slit pores at 77 K as a function of the slit width (w). As no pore effect was observed below P/P-o = 0.6 for w=3.5 nm, alpha(s)-plots for the simulated adsorption isotherms were constructed using the standard isotherm simulated for w=3.5 nm. The simulated alpha(s)-plots had filling and cooperative swings which were experimentally shown in the previous works, and the shape of the simulated alpha(s)-plot varied with the micropore structure. As the subtracting pore effect (SPE) method for the specific surface area (SSA) determination using the ct, plot was proposed in the previous experimental works, the theoretical ground for the SPE method was discussed. The best evaluation method of SSA using the alpha(s)-plot was shown, almost agreeing with the SPE method. This simulation study showed clearly that the SPE method is available for pore systems of w greater than or equal to 0.7 nm, whereas even the SPE method underestimates the SSA of the pores of w less than or equal to 0.6 nm. The observed swings of the a(s)-plot were simulated using the different micropore size distribution. The bimodal micropore size distribution lead to both of filling and cooperative swings, while a single pore size distribution <0.9 MI gave only the filling swing. Thus, four representative types of the alpha(s)-plot for activated carbons were proposed and it was shown how to understand the micropore size distribution through the alpha(s)-plot. (C) 1998 Elsevier Science Ltd. All rights reserved.