In observation of accurately determining the pore size distribution (PSD) of activated carbons by employing the non-local density functional theory (NLDFT)

the effect of surface roughness resulted from the distribution of carbon atoms on the accuracy was evaluated in terms of comparison of the adsorption equilibrium of argon. The classical NLDFT

which was developed based on the approximation to the smooth distribution of the density near the surface

was modified by taking into account the influence from the uneven distribution of the carbon atoms on the surface. The accuracies of the results from the modified model were firstly evaluated by the adsorption data of argon on adsorbent surfaces which respectively have even and uneven distribution of carbon atoms. Experimental data of argon adsorption on the activated carbon at 87.3 K was then taken as a reference

and comparisons were accordingly made between the adsorption isotherms calculated by the classical and modified NLDFT. The PSD

which covers the range of 0.35-12 nm

was finally determined by employing optimization function. Results show that the modified model can bring about the continuous distribution of PSD

and the relative error between the results determined by calculation via the PSD and those from experiment can be less than 10%. However

the calculation from the classical model has an interrupt at a pore width about 1nm

and the resulted maximum relative error amounts to 45%. It suggests that the modified model can more accurately calculate the PSD of the activated carbon having uneven distribution of carbon atoms around the surface.