Publication: Variability of the surface properties of sepiolite
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Publication Date
2012
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Elsevier
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Abstract
A comparative study of a wide collection of sepiolites (22 samples from different locations, including samples
coming from the greatest deposits of sepiolite in the world) was made with the aim of understanding the real
variability of the surface properties in sepiolite. The samples have been studied by XRD, Electron Microscopy
(TEM and SEM) and the adsorption–desorption of N2. The influence of possible impurities, crystallinity and
crystalline defects, and the textural variations, is taken into account to explain the high differences found
in the specific surface area of sepiolites. The studied samples display a high variability in crystallinity, fibre
length and texture. The BET surface varies between 77 and 399 m2 g−1, demonstrating the significant variation
in the surface properties in natural sepiolites. Both the external and the microporous area vary between
very wide extreme values, from 52 m2 g−1 to 246 m2 g−1 for the microporous area and 6 m2 g−1 to
178 m2 g−1 for the external area. The exceptionally low values of these properties found in some samples
cannot be related to the presence of impurities, but rather to their structural and textural features. Two
types of microporosity that can be described are structural microporosity and interfibre microporosity. The
SSA and the porosity of each sepiolite is the result of the sum of the intracrystalline or structural microporosity
and the textural porosity (interfibre microporosity and mesoporosity). As a consequence, there is a hierarchical
distribution of pore sizes, which is different for each sepiolite. The lowest values of microporosity are
related to the presence of very open pores and the sepiolites with higher SSA are those having a smaller
length and a more closed porosity.