BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 108

multilayer adsorption mechanism in micropores, is that we should have a judi-
cious choice of the reference isotherm. HK model was developed for calculating
micropore size distribution of slit-shaped pore; however, the HK method suffers
from the idealization of the micropore filling process. Extension of this theory
for cylindrical and spherical pores was made by Saito and Foley and Cheng and
Ralph. By applying some modifications on the HK theory, some improved models
for calculating PSD of porous adsorbents have been presented. Many scientists
extended the Nguyen and Do method for the determination of the bimodal PSD
of various carbonaceous materials from a variety of synthetic and experimental
data. The pore range of applicability of this model besides other limitations of ND
method is its main constraint [1, 2, 133].
Many researchers determined the PSD of activated carbons based on liquid
chromatography (LC). Choices of suitable solvent and pore range of applicability
of this method are two main problems that restrict its general applicability. More
sophisticated methods such as molecular dynamics (MD), Monte Carlo simula-
tion, Grand Canonical Monte Carlo simulations (GCMS), and density functional
theory (DFT) are theoretically capable of describing adsorption in the pore sys-
tem. The advantages of these methods are that they can apply on wide range
of pores width. But, they are relatively complicated and provide accurate PSD
estimation based on just some adsorbates with specified shapes. Requiring exten-
sive computation time and significantly different idealized conditions from a real
situation are other drawbacks of such methods. Researchers used a new approach
based on Monte Carlo integration to derive pore size and its volume distribution
for porous solids having known configuration of solid atoms. They applied the
proposed method to a wide range of commonly used porous solids. However,
this method also seems to have limitations of Monte Carlo simulation in addition
to requiring the information of solid atomistic configuration. Recently, some re-
searchers proposed a multiscale approach based on Grand Canonical Monte Carlo
(GCMC) to predict the adsorption isotherms and PSD of porous solids. However,
the proposed methodology needs further improvement to provide high accuracy
predictions besides mass of computations that is needed. Kind of PSD assumes
in DA equation itself, is important in design of PSD modeling. Does this distri-
bution change if the parameters of the DA isotherm change (especially n). Some
researchers studied the simulated nitrogen adsorption isotherms in heterogeneous
carbons and assumed Gaussian distribution of pores. It was shown that the simu-
lated isotherms can be fitted by typical DR, although not in the whole range of
relative pressures. Two groups of low-temperature ( = 77.5 K) N 2 adsorption iso-
therms were generated, and studied the influence of n at constant E 0 and, to the
contrary, the effect of E 0 at constant n. The obtained curves were converted into
high-resolution -plots in order to explain the mechanism of adsorption. Moreover,
the new algorithm (called the adsorption stochastic algorithm (ASA) was used
to solve the problem of fitting the local adsorption isotherms of the Nguyen and