Environmental Engineering Reference
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Do method to experimental data. The obtained results show that the DA equation
generates isotherms describing almost a homogeneous structure of pores and/or
a bimodal heterogeneous structure. Corresponding PSDs indicate the presence
of homogeneous porosity, primary and/or secondary micropore filling, or both.
The parameter of the DA equation is responsible not only for the homogeneity of
pores (the deviation of pores from average size) but for the adsorption mechanism
in micropores. In other words, lowering n leads to the change in this mechanism
from primary to simultaneous primary and secondary micropore filling. Taking all
obtained results into account suggests that the DA equation is probably the most
universal description of adsorption in micropores. All theoretical models (as, for
example, considered in the current study: HK, ND, and DFT, etc.) are connected
with their own specific assumptions of the description of the porous structure and/
or mechanism of adsorption. Of course, those postulations can significantly influ-
ence obtained results, PSD curves. The modeling of local and/or global adsorption
isotherms for different pore widths using DFT theory, Monte Carlo simulations,
and the ND model leads to results that should be, for some cases, treated with
caution. The main simplifications of those theories are, for example, the neglect
of the pore connectivity, ignoring of different thickness of carbon microcystal-
lites forming micropores, or existence of various surface groups on the surface
of activated carbons. Moreover, it is very difficult to find papers where authors
obtained satisfactory results (using the abovementioned theories) describing si-
multaneously the experimental adsorption isotherm, adsorption enthalpy, and
entropy (or heat capacity) for adsorption in microporous carbons around room
temperature. Although all simulation and modeling of carbons is very interesting
and sometimes spectacular, it should be remembered that small changes in the
values of fundamental parameters taken as constants in calculations can lead to
drastic changes in the results obtained. In this review, the results of this type of
the calculation are speculative as long as a satisfactory model of the structure of
carbons is not evaluated. It should be pointed out that very complicated models of
the structure of a microporous activated carbon are sometimes considered in some
advanced numerical and simulation calculations (for example, the RMC method,
where the surface sites have been added at random points on the edges of the
graphene microcrystals characterizing by differing size and shape) in order to de-
scribe the “real” structure of activated carbons. However, taking into account this
complex structure is connected with considerable extension of the time of calcula-
tions. On the other hand, very puzzling results are obtained from the description
of the micropore structure of various carbonaceous materials (the different origin
and thermal or chemical treatment)) for the reason that the differences between
the micropore size distribution plots are insignificant. For example, Ismadji and
Bhatia published the results of microporosity determination from DFT method
for three carbons, that the number of peaks on PSD curves and the ranges of their
location, as well as the shapes, are very similar. In our opinion this behavior of
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