Abstract
Comparative characterization of the particulate morphology and texture of various silicas (fumed silicas, silica gels, ordered mesoporous silicas) and carbons (chars and activated carbons, AC) is of interest from both theoretical and practical points of view since it allows one better understanding of advantages and disadvantages of various adsorbents upon their interactions with different adsorbates, co-adsorbates, and solutes in various dispersion media. Complete characterization needs application of a certain set of methods that is analyzed in the present paper. It is shown that the main difference in the textural characteristics of silica and carbon adsorbents is due to the absence (silicas) or presence (carbons) of nanopores in nanoparticles (NP). A great contribution of these pores in strongly activated carbons provides the specific surface area values greater by an order of magnitude than that of fumed silicas. Despite a high activation degree of AC, contribution of closed pores or pores inaccessible for nitrogen molecules remains relatively large in contrast to fumed silica A–300 composed of nonporous nanoparticles synthesized in the flame at higher temperature (~80% of melting temperature, Tm, for amorphous silica) than carbon activation temperature (~25%of Tm for carbons). Therefore, the pores inaccessible for nitrogen molecules in fumed silica could be attributed to narrow voids around contact area between neighboring NP in their aggregates, but for AC, there are both closed pores and open nanopores inaccessible for nitrogen molecules. For complete characterization of the morphology and texture of various adsorbents, such methods as transmission and scanning electron microscopies, probe (nitrogen, argon) adsorption, smallangle X-ray scattering (SAXS)and X-ray diffraction (XRD)could be used with appropriate software to analyze the data. The latter is especially important for the analyses of indirect data (e.g., adsorption, SAXS, XRD) characterizing the materials.
Publisher
National Academy of Sciences of Ukraine (Co. LTD Ukrinformnauka) (Publications)
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