Various methods to describe the morphological and textural characteristics of various materials

Abstract

The aim of this study was to compare a variety of methods to describe the textural characteristics of various materials. Several ways could be used to describe the morphological and textural characteristics of various materials in detail such as: (i) adsorption-desorption of low-molecular weight probe compounds (N 2 , CO 2 , Ar, C 6 H 6 , H 2 O, etc.) in the gaseous (vapor) phase with increasing-decreasing pressure; (ii) adsorption of low-or highmolecular weight compounds from liquid solutions with increasing concentration of a solute; (iii) small angle X-ray scattering (SAXS) or small angle neutron scattering (SANS); (iv) quantitative analysis of images recorded using TEM, SEM, AFM, CLSM, etc.; (v) thermoporometry based on DSC or TG measurements with decreasing-increasing temperature; (vi) cryoporometry based on NMR spectroscopy measurements vs. temperature; and (vii) relaxometry based on NMR spectroscopy and thermally stimulated depolarization current measurements. There are several reasons of the use of mentioned above methods in parallel. For example, a material, which is strongly hydrated in native state, can strongly change the texture upon drying; thus, it should be studied in both states. Various adsorbates can penetrate into different pores or differently fill pores of different sizes that should be taken into account upon the analyses of various data. There are accessible and inaccessible pores (such as closed or too narrow for used adsorbate molecules), but SAXS can give information on all pores in contrast to the adsorption methods. Thus, the larger the number of applied methods, the more comprehensive the morphological and textural characterization of the adsorbents, and this is clearly shown below.

Nano/meso/macroporous materials characterization affected by experimental conditions and features of the used methods

“…software can give incorrect results with systematic errors. Better results could be obtained using a complex pore model with slit-shaped (S) and cylindrical (C) pores and voids (V) between spherical nanoparticles (SCV method) with the corresponding parameters for the different phases [17,28]. Additionally, the chemical structure of a solid surface (e.g.…”

“…could be simultaneously used with an appropriate pore model for each component. The use of the SCR procedure gives information on contributions (weight coefficients) of different pore types and different components into the total porosity and specific surface area [17,28]. As a whole, the model errors remain upon the use of the SCV/SCR method because the texture of any adsorbent is not strongly ordered (pores can have very complex shape), there is a surface roughness, etc.…”

“…where E is the interaction energy of an adsorbate molecule with the pore walls and neighboring molecules calculated with the Lennard-Jones potentials. Thus, advantages of the SCV/SCR method are the possibilities to estimate (i) contributions of several phases of complex materials into the textural characteristics; (ii) adequate PSD of complex adsorbents; (iii) both PSD and particle size distribution (PaSD); (iv) errors of the model used that could correspond to a surface roughness of adsorbents [17,28].…”

“…TEM and SEM images ( Fig. 10) could be used to calculate both PSD [16,28] and PaSD (Figs. 2 and 11 a) functions.…”

“…); (iii) nonuniform distribution of components in complex systems; (iv) medium effects (e.g. swelling); and (v) incorrect or inadequate models and methods used in the analyses of the experimental data [1][2][3][4][17][18][19][20][21][22][23][24][25][26][27][28]. As a whole, it is of importance to analyze the differences in the characteristics determined using different indirect methods taking into account the measurement conditions.…”