Surface Area and Microporosity of Carbon Aerogels from Gas Adsorption and Small- and Wide-Angle X-ray Scattering Measurements

Abstract

A carbon aerogel was obtained by carbonization of an organic aerogel prepared by sol-gel polymerization of resorcinol and formaldehyde in water. The carbon aerogel was then CO 2 activated at 800°C to increase its surface area and widen its microporosity. Evolution of these parameters was followed by gas adsorption and small-and wide-angle X-ray scattering (SAXS and WAXS, respectively) with contrast variation by using dry and wet (immersion in benzene and m-xylene) samples. For the original carbon aerogel, the surface area, S SAXS , obtained by SAXS, is larger than that obtained by gas adsorption (S ads ). The values become nearly the same as the degree of activation of the carbon aerogel increases. This feature is due to the widening of the narrow microporosity in the carbon aerogel as the degree of activation is increased. In addition, WAXS results show that the short-range spatial correlations into the assemblies of hydrocarbon molecules confined inside the micropores are different from those existing in the liquid phase.

Synthesis and structure characterization of polymeric nanoporous microspheres with lignin

“…The beam weakness after passing through the sample was measured, and was corrected taking into account the background observed calculating the absorption factor of each sample. SAXS patterns were analyzed using PANanalytical Easy-SAXS V. 2.0.0.405 program and approaches described in details elsewhere (Brumberger 1965;Dieudonné et al 2000;Fairén-Jiménez et al 2006;Gun'ko et al 2011).…”

“…(4) (since experimental q values are measured between the q min and q max values instead of from 0 and ?). Therefore, the invariant value Q was calculated using equation (Fairén-Jiménez et al 2006)…”

On porosity of archeological bones I — Textural characterization of pathological Spanish medieval human bones

“…It is difficult to understand measurements as they depend not only on bone condition (taphonomy, diagenesis or washing) but also on characterization methods, which see different features. Although experiments with SAXS (Hiller and Wess, 2006;Pijoan et al, 2007) or nuclear magnetic resonance, NMR, have been fruitful (Wang and Ni, 2003), the most direct technique to evaluate texture should be gas adsorption as it happens with other materials (Sing, 2001;Fairén-Jiménez et al, 2006;Smith et al, 2008). Indeed, when a gas or vapor phase is brought into contact with a solid, part of it is taken up and remains on the outside attached to the surface, this phenomenon is known as adsorption.…”

Comparative Characterization of Carbon Adsorbents and Polymer Precursors by Small-Angle X-ray Scattering and Nitrogen Adsorption Methods

“…However, noise contribution increases at q = 2À3 Å À1 at the boundary between SAXS and wide-angle X-ray scattering and outside the Porod range. 12 Therefore, in this q range the PSD calculation becomes questionable, and a smaller boundary value q ≈ 1.25 Å À1 was used ( Figure S2 in SI). The use of the slitshaped/cylindrical pore model with NLDFT gives the PSD peaks of nanopores shifted in comparison with the DFT, QSDFT (slitshaped pore model), and SAXS PSDs (Figure 3b).…”

“…These deviations from the ideal models are due to nonuniformity of pores in ACs that is well seen in high-resolution TEM images. 30 Calculations of the specific surface area using the SAXS data (S SAXS ) can overestimate the S BET values 11,12 (Table 1). However, for some samples, these values are close.…”